ArticlePDF Available

Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland

Authors:

Abstract

A novel high-resolution (2–4 m source and receiver spacing) reflection and refraction seismic survey was carried out for aquifer characterization and to confirm the existing depositional model of the interlobate esker of Virttaankangas, which is part of the Säkylänharju-Virttaankangas glaciofluvial esker-chain complex in southwest Finland. The interlobate esker complex hosting the managed aquifer recharge (MAR) plant is the source of the entire water supply for the city of Turku and its surrounding municipalities. An accurate delineation of the aquifer is therefore critical for long-term MAR planning and sustainable use of the esker resources. Moreover, an additional target was to resolve the poorly known stratigraphy of the 70–100-m-thick glacial deposits overlying a zone of fractured bedrock. Bedrock surface as well as fracture zones were confirmed through combined reflection seismic and refraction tomography results and further validated against existing borehole information. The high-resolution seismic data proved successful in accurately delineating the esker cores and revealing complex stratigraphy from fan lobes to kettle holes, providing valuable information for potential new pumping wells. This study illustrates the potential of geophysical methods for fast and cost-effective esker studies, in particular the digital-based landstreamer and its combination with geophone-based wireless recorders, where the cover sediments are reasonably thick.
PAPER
Interlobate esker architecture and related hydrogeological features
derived from a combination of high-resolution reflection seismics
and refraction tomography, Virttaankangas, southwest Finland
Georgiana Maries
1
&Elina Ahokangas
2
&Joni Mäkinen
2
&Antti Pasanen
3
&
Alireza Malehmir
1
Received: 25 April 2016 /Accepted: 4 December 2016
#The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract A novel high-resolution (24 m source and receiver
spacing) reflection and refraction seismic survey was carried out
for aquifer characterization and to confirm the existing deposi-
tional model of the interlobate esker of Virttaankangas, which is
part of the Säkylänharju-Virttaankangas glaciofluvial esker-chain
complex in southwest Finland. The interlobate esker complex
hosting the managed aquifer recharge (MAR) plant is the source
of the entire water supply for the city of Turku and its surround-
ing municipalities. An accurate delineation of the aquifer is there-
fore critical for long-term MAR planning and sustainable use of
the esker resources. Moreover, an additional target was to resolve
the poorly known stratigraphy of the 70100-m-thick glacial
deposits overlying a zone of fractured bedrock. Bedrock surface
as well as fracture zones were confirmed through combined re-
flection seismic and refraction tomography results and further
validated against existing borehole information. The high-
resolution seismic data proved successful in accurately delineat-
ing the esker cores and revealing complex stratigraphy from fan
lobes to kettle holes, providing valuable information for potential
new pumping wells. This study illustrates the potential of geo-
physical methods for fast and cost-effective esker studies, in
particular the digital-based landstreamer and its combination with
geophone-based wireless recorders, where the cover sediments
are reasonably thick.
Keywords Esker architecture .Landstreamer .
Unconsolidated sediments .Geophysical methods .Finland
Introduction
Eskers, defined as stratified sediments of gravel and sand de-
posited by glacial melt-water streams (Banerjee and
McDonald 1975; Shreve 1985; Hebrand and Åmark 1989;
Gorrell and Shaw 1991; Warren and Ashley 1994;Huddart
et al. 1999; Brennand 2000), are hydrogeological settings of
great significance in areas that have undergone glaciation such
as in Finland, Sweden, the British Isles, USA and Canada.
They are remarkable aquifers that are often used also for con-
struction aggregates, thus an accurate understanding and sub-
surface delineation of the large-scale structures as well as
hydrogeological units within these precious groundwater res-
ervoirs is essential for their environmental and economic us-
age (Boucher et al. 2015;Nadeauetal.2015). Eskers host
marked groundwater aquifers and sites for managed aquifer
recharge (MAR) plants for groundwater production (Artimo
et al. 2010; Jokela and Kallio 2015).
Eskers are also associated with tunnel channels (or tunnel
valleys) which are the erosive expression of channelized sub-
glacial water flows and often truncate subglacial bedforms
and/or till (Burke et al. 2012). A few exceptionally large es-
kers, like the Säkylänharju-Virttaankangas complex in south-
west Finland, are attributed to time-transgressive deposition
within an interlobate joint between two differently behaving
ice streams (Punkari 1980; Kujansuu et al. 1995; Mäkinen
2003a). Interlobate esker complexes are extensive and are
Electronic supplementary material The online version of this article
(doi:10.1007/s10040-016-1513-9) contains supplementary material,
which is available to authorized users.
*Georgiana Maries
georgiana.maries@geo.uu.se
1
Department of Earth Sciences, Uppsala University, Uppsala, Sweden
2
Department of Geography and Geology, University of Turku,
Turku, Finland
3
Unit of Industrial Environments and Recycling,Geological Survey of
Finland (GTK), Kuopio, Finland
Hydrogeol J
DOI 10.1007/s10040-016-1513-9
characterized by up to 100-m-thick glacial sediments compris-
ing of large-scale depositional units with a wide range of in-
ternal structures. Therefore, these complexes demand deep
penetrating investigation methods that can provide a link be-
tween bedrock surface topography and large-scale esker ele-
ments in order to reliably model hydrogeological units as well
as the related groundwater flow.
An efficient way to recharge aquifers for environmental or
economic benefits such as providing fresh water supplies for
entire communities (Bouwer 2002; Dillon 2005), MAR appli-
cations benefit from increasing multidisciplinary studies that
combine geophysical methods and hydrogeology aspects
(Rossi et al. 2014;Ulusoyetal.2015). Near-surface geophys-
ical methods have routinely been used for engineering, geo-
technical, environmental or hydrogeological applications
(Telford et al. 1990; Sheriff and Geldart 1995), but in the last
30 years the high-resolution reflection seismic method, the
primary choice for hydrocarbon exploration, has also been
employed for near-surface investigations (Steeples and
Miller 1988); several case studies attest their effectiveness
(Miller et al. 1989; Baker et al. 2000; Juhlin et al. 2002;
Pugin et al. 2004a; Schmelzbach et al. 2005; Sloan et al.
2007;Malehmiretal.2013a,b). Seismic methods (refraction
and reflection), like other geophysical methods, are non-
invasive and provide an efficient tool for delineating shallow
(<150 m) yet heterogeneous, geologically complex targets
such as groundwater reservoirs, aquifers and structures
hosting or controlling their locations (Pullan et al. 1994;
Bradford 2002;Sharpeetal.2003;Huuseetal.2003;
Francese et al. 2005; Giustiniani et al. 2008; Burke et al.
2008;Pasanen2009; Comas et al. 2011). There is a gradual
shift towards acquiring high-resolution seismic data, in partic-
ular within unconsolidated or normally consolidated sedi-
ments, by employing fast and cost-effective methods such as
seismic landstreamers (van der Veen and Green 1998; van der
Veen et al. 2001; Huuse et al. 2003; Pugin et al. 2004a,b,
2009a,b; Almholt et al. 2013).
Continuous developments in the acquisition systems
and sensor types have led to landstreamers being employed
for numerous near surface investigations, including
groundwater and glacial landform studies, proving their
time- and cost-effective acquisition with high data quality.
By definition, a landstreamer is an array of seismic sensors
that can be towed behind a vehicle without the need for
planting the sensors (Kruppenbach and Bedenbender
1975). While most landstreamers use geophones (analogue
systems) for data acquisition, a newly developed advanced
MEMs-based (micro-electro mechanical) broadband seis-
mic landstreamer (Brodic et al. 2015; Malehmir et al.
2015a,2015b,2016a,2016b) was employed in this study
for delineating subsurface structures of a major interlobate
esker system and a MAR aquifer in Virttaankangas, in the
southwest of Finland.
Prior to this study, in 2011, a pilot test of employing a
seismic landstreamer was conducted at Virttaankangas using
geophones (Pugin et al. 2014) indicating the applicability of
the method, but with some uncertainties in separation of boul-
dery esker deposits, diamictons and bedrock facies. The main
objective of this study is to test the applicability of the newly
developed MEMs-based landstreamer (Brodic et al. 2015)as
an advanced seismic method for aquifer characterization with-
in complex glaciofluvial deposits with thick (1040 m) dry
sediments above the water table. The present study focuses on
the coarse-grained glaciofluvial hydrogeological unit that
forms the main Virttaankangas esker aquifer (Artimo et al.
2003) within the MAR plant area. The main aquifer includes
the boulder-rich esker core (50150 m wide) that has a high
hydraulic conductivity10
4
to 10
0
m/s for the whole coarse-
grained unit (Artimo et al. 2003) and is the target for pumping
station locations.
The seismic data were expected: (1) to help locate the high
hydraulic conductivity esker core and its stratigraphic position
within the fractured bedrock zone, including bedrock overlay-
ing diamictons, (2) to delineate large-scale architectural esker
elements (esker core, fan lobe channels) within the coarse-
grained hydrogeological unit of the MAR plant, (3) to define
large-scale deformation structures (morphologically undetect-
able kettle holes, MUKHs) and their bedrock contact (influ-
ence on MAR residence times and groundwater flow paths),
and (4) to characterize the lateral relationships of the esker
elements and the underlying bedrock surface. In addition,
one of the two seismic profiles, profile 2, was designed to
accurately delineate the esker core for locating new pumping
stations within the widest and structurally most complicated
part of the coarse-grained unit. This is the first case study
where an advanced high-resolution seismic landstreamer sur-
vey has been utilized for aquifer characterization and valida-
tion of the hydrogeological properties within an interlobate
esker system. Results illustrate the potential of the combined
refraction and reflection methods for these purposes.
Study area
Field area
The Säkylänharju-Virttaankangas (S-V) glaciofluvial com-
plex forms a part of the 150-km-long Koski-Pori esker chain
in southwest Finland (Fig. 1). The Virttaankangas plain hosts
an operational MAR plant that provides a potable water re-
source for over 300,000 inhabitants within the Turku city re-
gion (Artimo et al. 2003,2008). The MAR plant consists of
several infiltration ponds and pumping stations as well as nu-
merous observation wells at strategic locations within the es-
kers elements (e.g. Fig. 2) that provide groundwater levels and
lithological characterization with bedrock information at
Hydrogeol J
scattered locations. A finite-difference (grid-type) groundwa-
ter flow model within an area of 80 km
2
includes the descrip-
tion of the geometry of the hydrogeological units (Fig. 3). The
flow parameters of the coarse-grainedunit studied herein have
been described in more detail than within the rest of the model
(A. Artimo, Turku Region Water Ltd, personal communica-
tion, 2016).The flow modelincorporatesa depositional model
of the esker verified with infiltration and pumping tests as well
as tracer tests including oxygen isotopes of infiltrated water.
The depositional model is based on extensive ground penetrat-
ing radar (GPR) surveys (21 km) supported by reference data
from boreholes and exposed gravel/sand pits (Artimo et al.
2010). Bedrock topography is provided by a rough modeling
of a network of gravity data points (Valjus 2006). The
Fig. 1 Virttaankangas study area near the city of Turku and the location
of the seismic profiles (profiles 1 and 2), main esker core, Löytäne
tributary esker, Myllylähde spring and fractured bedrock zone. The
extent of the MAR plant area with infrastructure (observation wells and
infiltration pools) and the coarse-grained unit provided by Turku Region
Water Ltd. The index map groundwater areas © Finnish Environment
Institute (2016), coastline and water bodies © NLS (2016).The map of
superficial deposits of Finland © Geological Survey of Finland and the
base map and LiDAR © NLS (2010)
Hydrogeol J
depositional environments and related depositional stages dur-
ing the last deglaciation as well as related main hydrogeological
units have been studied earlier by several authors (Artimo et al.
2003;Mäkinen2003a,b; Mäkinen and Räsänen 2003). The
two survey profiles in this study were targeted to delineate the
most complex parts of the coarse-grained hydrogeological unit
(Fig. 1).
Geological setting and three-dimensional geologic model
The Säkylänharju-Virttaankangas (S-V) glaciofluvial com-
plex is situated on the Precambrian Svecofennian basement
of igneous and metamorphic rocks (1,7501,900 Ma) located
1015 km southeast of the basement contact with the younger
Jotnian Satakunta sandstones (1,2001,500 Ma; Korsman
et al. 1997). The Säkylänharju main ridge is about 12km
wide with a summit (Porsaanharju) rising close to the ancient
highest shoreline. The main ridge gradually decreases in
Fig. 2 Main esker architecture
elements and MAR plant
infrastructure in relation to the
main bedrock fracture in the
vicinity of seismic profile 1 in the
eastern part of Virttaankangas.
The hydraulic importance of the
large-scale cross-bedded fan lobes
is depicted by their impact on
flow direction of the infiltrated
water and related residence times
due to the dip of the cross beds as
seen in one of the infiltration
areas. Bedrock elevation contours
modified from Valjus (2006)
Bedrock
Till
Glaciofluvial coarse-grained unit
Glaciofluvial fine-grained unit
Silt and clay
Littoral sand
Fig. 3 The main 3-D hydrogeological units of the Virttaankangas aquifer
(From: Artimo et al. 2010). The esker core is contained within the
glaciofluvial coarse-grained unit. MUKH structures are treated as a sep-
arate unit. Red dashed line in the bottom unit represents fractured bedrock
Hydrogeol J
height into Virttaankangas, a 5 km fan-like plain in the south-
east (Fig. 1.) The core of the main esker is connected to the
smaller 1015-m-thick core of the Löytäne tributary esker
(aquifer) in the northwestern end of the MAR plant area.
The tributary esker sediments route the groundwater flow to-
wards the Myllylähde spring (discharge ca. 2,500 m
3
/day) in
the southwest side of the glaciofluvial complex. The
glaciofluvial sediments have a thickness of 1040 m, reaching
over 70 m in some places. A major fractured bedrock zone of
about 200300 m wide and 4580 m deep has been inferred at
Virttaankangas in NNWSSE orientation (Fig. 1). The esker
core and fan sediments turn to follow the fracture zone to-
wards the south, but the stratigraphy of the zone is not ade-
quately described. A few deep boreholes (e.g. VI596) within
the fracture zone display poorly hydraulically conductive
diamicton below the esker core.
The Säkylänharju main ridge formed in a large
interlobate ice-marginal embayment (as subaqueous cre-
vasse deposits) of the deglacial Yoldia Sea Phase and
was altered by intense shoreline erosion during the rapid
glacio-isostatic land uplift (Mäkinen 2003a,b). The
coarse-grained parts of the main esker ridge have been
levelled less by the shore erosion, leading to only 13-
m-thick littoral sand and gravel deposits in contrast to
the surrounding plain. The wide eastern part of the
plain, that covers sandy and fine-grained glaciofluvial
sediments, is composed of postglacial shore deposits
(520 m thick) formed during a spit-platform develop-
ment in the Ancylus Lake phase of the ancient Baltic
Sea (Mäkinen and Räsänen 2003).
The internal architecture of the Virttaankangas area in-
cludes the coarse-grained and continuous subglacially formed
esker core covered by ice-marginally deposited overlapping,
successive esker fans (Mäkinen 2003b). These fans show
large cross-bedded fan lobe structures, laterally fining and
upward coarsening sequences, as well as large-scale deforma-
tion often related to MUKH structures (Mäkinen 2003b)that
well delineate the path of the esker core (see Fig. 2). Figure 4
shows a conceptual 3D model of the area with simplified
geology and internal architecture of the esker elements based
on earlier GPR surveys supported with borehole data, sedi-
ment exposures and hydrogeological data. However, the GPR
data are restricted to the topmost 20 m. Some of the deposi-
tional features (fan lobe channels, a MUKH structure and the
bouldery esker core) are illustrated through field photos
(Fig. 5) from an aggregate pit in the vicinity of the main esker
core.MUKHstructureswereformedwhenburiedblocksof
ice melt and subsequently the holes were filled with collapsing
esker fan sediments and shore deposits. Especially large
MUKH structures beside the esker core have been interpreted
to extend down to bedrock (Artimo et al. 2010). Finally, the
fan and kettle hole morphology have been levelled by intense
erosion (1020 m) due to shoreline processes. The large
MUKH structures with often fine-grained margins have
marked influence on groundwater flow properties and are thus
treated as separate sedimentological units in the groundwater
flow model (Artimo et al. 2003,2010). Moreover, MUKH
structures have been used to create reverse gradients between
infiltration ponds and pumping stations. The connection of the
Säkylänharju main esker core and Löytäne tributary esker
Esker core
MUKH Pit
Surface
Fan lobe channel
Esker fan (from GPR)
Esker fan
Esker sediment
Coarse-grained esker core
Shore deposit
Deformed sediment (from GPR)
Deformed sediment
Water table
Depositional unit boundary
Esker core trend and groundwater flow direction
MUKH/fan lobe extent
Fan lobe trend
Infiltration pond
Flow direction of infiltrated water
Reverse groundwater flow gradient along MUKH
Pumping well
Pit
Fine-grained sediment (bottom fan)
Bedrock
Legend
Fig. 4 Schematic model of the
successive esker fans and the
main depositional and
hydrogeological units. Green
color represents overlapping
esker fans with distinct fan lobe
channels, while yellow color
refers to fan bottom fine-grained
sediments. MUKH refers to
morphologically undetectable
kettle hole. The model is based on
GPR surveys with reference data
from pit exposures and boreholes.
The main components of the
MAR plant (pumping wells and
infiltration ponds) are included
with the directions of infiltrated
water flow in relation to the main
esker elements. Bedrock (in
black) is based on gravity
modelling and boreholes
Hydrogeol J
cores is still poorly known, but it forms a marked widening of
the coarse-grained hydrogeological unit. This widening is also
associated with a secondary esker enlargement on the eastern
side of the main core. The proximal part of the enlargement is
situated on the main Säkylänharju ridge (ice-marginal cre-
vasse deposits), whereas the distal part is composed of mostly
fine-grained sediments below the shore deposits of the
Virttaankangas plain (Mäkinen 2003b).
Methods
Seismic data acquisition
The seismic survey consisted of two seismic profiles (profiles
1 and 2), each about 1 km long, in the proximity of the water
company infiltration pools (Figs. 1and 2). Profile 1 was set up
along a sandy road, roughly in NWSE direction (Fig. 2).
With a similar set-up, orientated in SWNE, profile 2 was
surveyed on a sandy road, 200 m away from profile 1, next
to an old open pit, but continued on a trail in the forest on
loose sandy sediments. Figure 6shows two photos illustrating
the data acquisition and field conditions along profile 2. The
profile locations were designed to intersect the estimated esker
core positions (profiles 1 and 2), to reveal the esker stratigra-
phy in the fractured bedrock (profile 1), and to illustrate the
cross-sectional structure of the main esker aquifer (profile 2).
Sercel Lite 428 data acquisition system and a newly devel-
oped 200 m-long landstreamer comprising of 80-3C (three
component) MEMs sensors (Brodic et al. 2015) were used
for the data acquisition. 3C sensors record the wave motion
along three axes, one vertical and two horizontal, where the
horizontal components are in-line relative to the sensor array,
and cross-line (perpendicular) to the sensor array, respective-
ly; the sensor array is set up in the in-line direction. The array
consisted of, at the time of the survey, four segments each
containing 20 sensors; in one segment sensors were spaced
4 m apart and in the other three they were spacedat 2 m. Easily
towed by a 4 WD vehicle (Fig. 6), the landstreamer array was
moved until the desired survey length was covered. In order to
account for the low fold at the end points of each segment, 51
single component wireless sensors connected to 10-Hz geo-
phones were deployed along the profiles, spaced at about ev-
ery 20 m. The landstreamer system and the acquisition unit
used to acquire the data use GPS time for time sampling and
time stamping; hence, it allows them to be merged at later
times with wireless recorders that operate in a passive mode
(continuous recording).
The same geometry spread was used for both seismic re-
fraction and reflection data. Seismic energy was generated
using a Bobcat-mounted 500-kg drop-hammer (Place et al.
2015), with three shot records per location in order to provide
high signal-to-noise ratio after the vertical stacking of the re-
peated shot records. Given the nature of the source, only the
vertical component data were used in the present study. The
shot spacing was kept 4 m for both profiles and the energy
source proved to be a good choice despite the dry and uncon-
solidated glacial sediments that can highly attenuate the seis-
mic response. Shallow reflections are identifiable in most shot
gathers, implying that the source was optimal for this survey.
Fan lobe channels MUKH structure Bouldery esker core
Fan lobe channels MUKH structur Be ouldery esker core
a) b) c)
Fig. 5 Field photos from an aggregatepit in the vicinity of the main esker
core that show typical elements found in the internal architecture of an
esker system; similar landforms to the ones interpreted and discussed later
in the paper: afan lobe channels; btypical MUKH structure; cbouldery
esker core. Photos by Elina Ahokangas and Joni Mäkinen
Wireless sensors
connected to
10 Hz geophones
Landstreamer array
Drophammer
source
2 m 20 m
Fig. 6 Field conditions during the seismic survey (July 2014). Bobcat
mounted drop-hammer (500 kg) was used to generate seismic energy at
every shot location (only fired close to the streamer sensors). Inset shows
a photo of the streamer while moving to a new position in a forest track
with uneven and loose sediments along part of profile 2. The wireless
recorders (1020 m apart) connected to 10 Hz geophones were spaced
along the landstreamer array and fixed for the whole profile. Photos by
Alireza Malehmir
Hydrogeol J
The key acquisition parameters are summarized in Table S1 of
the electronic supplementary material (ESM). Figure 7shows
two examples of shot gathers, after vertical stacking of the
repeated shot records, from each profile. Most shot gathers
have excellent data quality, except at a few places along pro-
file 2 in the forest track (likely due to bad sensor coupling);
water pumps along the forest tracks also generated noise at
times during the acquisition.
Refraction and reflection data imaging
Data processing started with refraction seismic tomography
given the quality of the first breaks particularly at far offsets.
First breaks were picked automatically and manually corrected
where needed. Refraction tomography was carried out using a
diving-wave (or turning-ray) first break tomographic inversion
method (Tryggvason et al. 2002)usingcellsof2and1min
horizontal and vertical directions; in the lateral direction cells
were kept large to force the model to look 2D although the
modeling uses a 3D algorithm for travel time calculations. For
details about the tomographic velocity models, readers are re-
ferred to Table S1 and Fig. S1 of the ESM. The wireless sensors
spaced along the entire length of each profile allowed the
energy from the refracted waves to be recorded as far as
1 km notably improving both the investigation depth for the
refraction tomography and the fold coverage at depth for the
reflection data.
For the reflection data processing, a simple and conven-
tional algorithm was chosen to avoid generating processing
artefacts (Black et al. 1994; Steeples and Miller 1998). The
algorithm is based on signal enhancement in the pre-stack data
and CMP (common midpoint; 2-m spacing) stacking after
normal moveout corrections. The most crucial processing step
was the velocity analysis given the deep underground water
table (about 2050 m below ground level in some places),
subsurface heterogeneity (subaqueous channels, kettle holes)
and dipping bedrock in the study area. Indications of water-
table reflections were noticeable in some shot gathers like the
ones shown in Fig. 7(the top red arrow). The seismic reflec-
tion processing flow is detailed in Table S2 in the ESM.In
conjunction with the seismic survey a test was also conducted
where planted MEMs sensors were placed next to the streamer
sensors in order to check whether the landstreamer sensors
had reliable and consistent travel time phases with the planted
ones (Brodic et al. 2015). Checking the phase and amplitude
of data was crucial for both reflection and refraction imaging
but also for future studies using the landstreamer.
The heterogeneity within the sediments and bedrock undu-
lations made the reflection imaging quite challenging particu-
larly with the velocity analysis. It appeared that one set of
reflections was very shallow (i.e. above water table) and an-
other one was focused on the bedrock surface and the struc-
tures in its immediate vicinity. An approach tested before
(Miller and Xia 1998; Juhlin et al. 2010; Malehmir et al.
2013a; Place et al. 2015) was to combine two different sets
of reflections, by generating a stack focusing on very shallow
reflections and another one focusing on bedrock reflections or
below the water table. This gave the best results for profile 1
where 1020 m deep shallow structures could be identified.
Data interpretation procedure
The interpretation of seismic reflections and their scale is guided
by the hydrogeological units and more specifically the reference
depositional model for the coarse-grained unit, which is based on
previous studies (Fig. 3). This reference model forms also the
base for the understanding of the groundwater environment and
related flow model. The reference model shows three basic large-
scale esker elements: esker core (glaciofluvial coarse-grained
unit), MUKH structures (separate unit) and large-scale cross-bed-
ded fan lobe channels (Baker 1973; Theakstone 1976) deposited
towards the esker margins (glaciofluvial fine-grained unit). In
addition to these, the remaining stratified esker sediments form
the main bodies of the esker fans. These elements are the major
0.00
0.05
0.10
0.15
0.20
0.25
Time (s)
Offset (m)
0.00
0.05
0.10
0.15
0.20
Time (s)
Offset (m)
End traces
from wireless
sensors
End traces
from wireless
sensors
End traces
from wireless
sensors
End traces
from wireless
sensors
End traces from wireless
sensors
End traces from wireless
sensors
a) b)
-534 -435 -335 -239 -144 -128 -112 -96 -76 -64 -56 -46 -37 -28 -18 -10 0 8 18 26 36 43 63 163 264 465 -125 -91 -75 -59 -43 -25 -18 -8 0 10 18 28 36 46 56 64 74 82 92 279 382 484 586 686 787 880
5 101520253035404550556065707580859095100105110115120125130
Channel
5 101520253035404550556065707580859095100105110115120125130
Channel
0.25
2200 m/s
1870 m/s
510 m/s
441 m/s
485 m/s
4820 m/s
615 m/s
1264 m/s
2950 m/s
4890 m/s
Profile 1 Profile 2
Fig. 7 Example raw shot gathers (after vertical stacking of the repeated
shot records) and apparent velocities from aprofile 1 and bprofile 2. The
red arrows indicate distinct reflections identifiable already in the raw
data. The wireless sensors are noticeable at far offsets and tend to be in
general noisier and have lower frequency content; however, the first
breaks are identifiable almost on all traces. Note that for display
purposes the offset distance between receivers is not scaled
Hydrogeol J
hydrogeological features that affect the artificial recharge and
groundwater flow within the MAR plant. The main reflection
patterns identified from the 2 km of seismic reflection data can
be interpreted as large-scale seismic facies (Fig. 8). The more
detailed interpretation of the stratified esker fan sediments is
inhibited by the resolution of the seismic data in relation to the
small-scale complexity of the sediments. The interpretation of the
elements or the seismic facies forms the basis for the zonation of
the coarse-grained unit, which is relevant for the more detailed
hydrogeological model.
Results and interpretations
Water table and bedrock surface
The results of seismic refraction tomography along the two
lines are shown in Fig. 9. Available boreholes near (ca. 5
10 m) the profiles are projected into the tomography sections
for comparison. The subsurface is characterized by rapid verti-
cal velocity gradients where the water table is remarkably deep.
Soft and dry unconsolidated sediments, like sand-dominated
littoral deposits (110 m thick), are characterized by a low
velocity (ca. 500 m/s) in the first few meters below the land
surface. When the sediments become saturated (below water
table or its vicinity) the seismic velocity makes a large increase
to 1,5001,800 m/s, which is typical for sandy or silty sedi-
ments (e.g., Malehmir et al. 2013a; Salas-Romero et al. 2016).
During the preparation of the seismic data, a clear reflection
of about 500 m/s consistently appeared at shallow depths on
most shot gathers after direct arrivals (see for example the top
red arrow in Fig. 7a,b). This was judged to be from the tran-
sition zone where the unconsolidated sediments change from a
dry state to a partially or completely water-saturated state. It is
in general a sharp surface, clearly depicted in the velocity
models being gently dipping towards the low land areas
(Fig. 9). The water table at the time of the seismic survey (S.
Saraperä, Turku Region Water Ltd, personal communication,
2014) is shown as a blue-white dashed line onthe tomography
sections and in most places matches well the tomography
results; however, near surface velocities are expected to be
extremely sensitive to the dry/saturated sediments interface
found in the vicinity of the water table, therefore the velocity
model does not follow the water-table boundary in some
areas. This seems to be the case at the NW part of profile 1,
especially at distance 200300 m where the coarse-grained
and conductive esker fan apex (borehole VI485) is expected
to rise above the water table (Fig. 9a). The fan apex consists of
40 m-thick gravel with a 20-mintervening bed of sandy gravel
(7393 m a.s.l.) that holds the water table. Low velocity areas
observed below the water table may be explained by
dislocated sediments and MUKH structures, as for example
in profile 1 (Fig. 9a)at400500 m distance or at 300400 m
distance along profile 2 (Fig. 9b), as deformed sediments do
not have similar seismic velocity compared with undisturbed
materials. Coarsest sediments are concentrated on the NE end
of the profile 2 where the corresponding low-velocity zone
due to unsaturated sediments is thicker from the contribution
of surface topography (higher elevation). The water table was
observed at 2040 m depth in this part of the profile.
The bedrock surface is identified in the distinctly high
(>5,000 m/s) velocity regions. For profile 1 (Fig. 9a), three bore-
holes intersect the bedrock (VI485, VI596, V566). Borehole
VI596 hits fractured bedrock, and VI7 ends in gravel-
dominated boulder-rich sediments (Fig. 9a). V566 hits the bed-
rock at 62.8 m a.s.l., while V550 ends in a silty bed at about
62 m a.s.l. The two distinct zones of high seismic velocities (>
5,000 m/s) match well with the bedrock as indicated by bore-
holes VI485 and VI566 near both ends of profile 1 (Fig. 9a).
Bedrock surface can be reliably picked from the tomographic
velocity model. The central part of profile 1 (300600 m dis-
tance), where still relatively high velocities (> 3,000 m/s) are
observed, represents a major fractured bedrock zone, manifested
itself as a zone of bedrock depression. Velocities around 3,000 m/
s indicate fractured/weathered bedrock (Barton 2007). This de-
pression was also suggested by gravity surveys in the study area
(Valjus 2006). For profile 2, boreholes VI282, VI285 and VI252
are drilled down to bedrock, while VI250 and VI6 end in boul-
dery sand and gravel, respectively (Fig. 9b). VI251 indicates a
layer of till at 73 m a.s.l. A major depression in the bedrock is
observed in the central part of the profile, around 300400 m
distance (Fig. 9b).
Description and interpretation of seismic profile 1
Profile 1 is divided into 4 zones based on the reflection
patterns or large-scale seismic facies (Fig. 10b, c). The
bedrock level in the NW end of the profile (zone 1) is
roughly at 5060 m a.s.l. The sediments here show cha-
otic and dislocated (deformed) reflections in association
with concave large-scale geometry and comprise a large-
scale seismic facies unit (small MUKH structures) that is
partly in contact with the arched stratified facies and the
bedrock. Seismic facies (Fig. 8) with arched geometry in
contact with the bedrock (ca. 50 m thick at the 200300 m
distance) indicates the architecture of the esker core as
supported by the borehole data (VI485).
Zone 2 exhibits a steep drop in the bedrock level associated
with vertically dislocated strong reflections at 300350 m dis-
tance from the line beginning that are related to the highly
fractured margin of the wider fractured bedrock zone. The
reflections within zone 2 indicate coarse-grained materials
but are difficult to interpret; however, the zone can be divided
roughly in two parts. The lower part below 70 m a.s.l. contains
sediments filling the fractured zone, whereas the upper part on
the SE side of the esker core contains mainly horizontal
Hydrogeol J
Seismic facies Lithology S
and hydrogeological implic
Arched geometry, convex
refle ons; st igh amplitude
or non-s low amplitude
refle ons and di
nature, lower boundary with
bedrock contact.
Bouldery
gravel
Esker core of typical dimensions
formed by meltwater flow in subglacial
tunnel
main aquifer, groundwater
Concave large-scale geometry,
various amplitude reflec
refle ons, margi
and bedrock contact.
Mixed
sediments
with fine-
grained beds
MUKH –structure with large-scale
e
Restricts and guides groundwater
flow with longer residenc
reverse gradients
from
Large trough-shaped geometry,
weakly str fied, low amplitude to
transparent ates
sediments below.
ely
homogeneous
sand to gravel
sediments
Major channels of subaqueous fan
n with large-scale cross
bedded fill.
ponds, they direct the water flow
.
Large concave geometry, thick and
with the arched esker core facies,
truncates sediments below.
Gravel and
sand
sediments
Proximal channelized subaqueous fan
sediments adjacent to the esker core
High hydraulic condu vity
Mainly horizontal or low angle
moderate to low amplitude
refle ons, mainly co nuous
refle ons, som trough-
below.
Silt to sand
and gravel
sediments
Subaqueous fan (body) sediments with
small channels (cut and fill) or mass
flow deposits, fine-grained lower fan
sediments.
infil and
im .
Stra , low to moderate
to
uppermost horizontal sediments.
Lower part non-str fied with poor
refle ons. Erosional unconformity
to fan body sediments. Poor facies
coverage by the survey.
Sand to gravel
and diamicton
below
Crevasse deposits (subaqueous) of the
main interlobate ridge in glacial bay
superimposed on the esker fan
sediments. Possible large-scale cross
bedded sets underlain by mass-flow
diamicton
They affect groundwater flow
s as revealed by water
chemistry.
Strong, high amplitude refle ons,
thick unit, lower boundary with
bedrock contact
Diamicton S
core)
Poor hydraulic conduc ity, fills
the major fracture zone below the
esker deposits
Strong, high amplitude reflec
ma ulated
Bedrock
contact
Bedrock surface
Boundary for groundwater flow
models
(top)
Concave geometry in bedrock and
especially below esker core facies,
intermediate amplitude reflec .
Dislocated/faulted high amplitude
refle ons in bedrock.
(top)
Basement
rocks
)
Possible
remnant of
Jothnian
sandstone
within the
fracture valley
(top)
Fractured bedrock with only horizontal
fracturing reflected
It assists to high hydraulic
ity below the esker
core/main aquifer.
Faulted fracture valley margin
and importance not known.
Fig. 8 Seismic facies and their interpretation
Hydrogeol J
reflections from stratified sediments with trough-shaped struc-
tures. The seismic facies in the upper part is interpreted as
subaqueous esker fan sediments (Fig. 8).
Zone 3 includes the ca. 200-m-wide bedrock fracture zone,
the bottom of which is at 1015 m a.s.l. The seismic facies with
strong horizontal reflections varying in thickness (up to 30 m)
above the bedrock extends across the fractured zone (Fig. 8)and
is interpreted as diamicton, probably till, as supported by stratig-
raphy and boreholes VI568 and VI596 within the fractured zone.
This facies is overlain by the esker core (slightly arched geometry
0080070060050040030020010
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Distance along profile (m)
120
100
80
60
40
20
0
-20
Elevation (m)
VI485 VI V7 I550VI596
Approx. elevation (m)
0 100 200 300 400 500 600 700 800 900 1000
100
80
60
40
20
-20
0
a)
b)
c)
Zone 1 Zone 2 Zone 3 Zone 4
MUKH + def Esker core + proximal fan Steep bedrock Upper fan + troughs Upper fan + distal sediments
Esker core + lower fan
Approx. elevation (m)
0080070060050040030020010
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Time (s)
Distance along profile (m)
120
100
80
60
40
20
0
-20
CDP
Zone1 Zone 2 Zone 3 Zone 4
MUKH + def Esker core + proximal fan Steep bedrock Upper fan + troughs Upper fan + distal sediments
Esker core + lower fan
GW
GW
Br
Br
Br
Br
Distance along profile (m)
Time (s)
Br Br Br Br
Br
Br Br
Br
Br Br Br
Profile 1
GW
GW
VI566
Sand
Fine sand
Silty sand
Coarse sand
Gravelly sand
Bouldery sand
Gravel
Sandy gravel
Bouldery gravel
Till
Gravelly till
Bouldery till
Bouldery silt
Clay silt
Silty clay
Boulders
Bedrock
Br
Water table (GW)
Unconformity
Trough and
fan lobe channel
MUKH - structure
Dislocated margin
Gravel bed
Esker core
Diamicton
Bedrock (Br)
Fractured bedrock
(m/s)
1000
2000
3000
4000
5000
6000
330
SESE
SESENWNW
NWNW
SESENWNW
120
Fig. 10 a Seismic reflection (unmigrated but time to depth converted
using a constant velocity of 1,000 m/s) section along profile 1 with the
projected tomography section on top, including existing borehole data
(indicated with red bars); bthe seismic reflection section with
interpreted depositional zones, borehole stratigraphy and indication of
bedrock from the boreholes; cthe interpretation of depositional units
and indication of bedrock from boreholes along profile 1
Elevation (m)
0 100 200 300 400 500 600 700 800 900 1000
a)
115
90
65
40
15
0
0 100 200 300 400 500 600 700 800 900 1000
Distance alon
g
profile
(
m
)
Elevation (m)
130
110
90
70
50
30
20
b)
SW NE
NW SE
VI485 VI7
VI6
VI250VI282
VI550VI596
VI285 VI252
GW
GWGW
Distance along profile (m)
GW
GW
GWGW
(m/s)
1000
2000
3000
4000
5000
6000
330
Profile 2
Profile 1
Br
Br Br
Br
Br
VI251
VI566
Br
Fig. 9 Seismic refraction tomography sections along a profile 1 and b
profile 2. Boreholes near the profiles are indicated using red bars. Awide
bedrock fracture zone is estimated from 300 to 600 m distance along
profile 1. The depth to bedrock indicated by the boreholes matches well
the increased seismic velocity (> 5,000 m/s). The blue dashed line
represents the water table at the time of the seismic acquisition (July
2014), matching well the velocity transition from 400500 to 1,500
1,800 m/s
Hydrogeol J
facies) consisting of bouldery gravel (VI596) and two esker fan
lobe channels (large trough-shaped weakly stratified facies on its
NW side). The weak boundary separating the facies indicates
similar coarse-grained materials; however, the discontinuous re-
flection between the troughs and partly below the esker core
might indicate the existence of two different diamictons. The
esker fan lobe channels were formed within the bedrock fracture
valleyandlatercoveredbysubsequenteskerfansediments.The
esker core is about 20 m thick, but the shape of the core is not
distinctly arched due to the diagonal position relative to profile 1.
The shallowest part of zone 3 includes a continuous hori-
zontal reflection at ca. 6070 m a.s.l. above the esker core and
the large trough-shaped facies, and is partly truncated by the
narrow troughs of zone 2 (subaqueous fan body sediments,
Fig. 8) and overlain by other horizontal reflections in zone 4. It
extends across the fractured bedrock until the unconformity at the
SE-end of the zone, it indicates a change from sandy to bouldery
gravel as observed in borehole VI596 (at 6873 m a.s.l.) and is
characterized as esker fan sediments (Fig. 10c). An indication of
the water table at 86 m a.s.l. is seen within the fan sediments.
Zone 4 is located outside the fractured bedrock and com-
prises mainly horizontal reflections that are truncated in the
upper part by the about 100-m-wide trough-shaped facies sim-
ilar to those in zone 3. Boreholes indicate sand-dominated
sediments with intercalation of fine-grained sediments close
to the bedrock surface (VI550). The seismic facies of zone 4
are interpreted as esker fan sediments. The trough-shaped fa-
cies represent fan lobe channels.
Description and interpretation of reflection seismic
profile 2
Profile 2 is perpendicular to the esker system and lies across
the coarse-grained hydrogeological unit (main aquifer) at its
widest point in zone 3 (Fig. 1). Based on the bedrock level
interpretation, the thickness of the deposits varies between 40
and 70 m (Fig. 11c). The shallow strong reflection just below
90 m a.s.l. at the SW-end of the profile is indicative of the water
table (ca. 88 m a.s.l.) The profile is divided into 5 zones based
on the different reflection characteristics (Fig. 11b, c). The up-
permost part of the profile 2 first shows an erosional unconfor-
mity that is overlain by the topmost shore deposits as observed
from the nearby pit exposures. Starting with zone 2 towards the
northeast, the uppermost part is characterized by a continuous,
moderate-amplitude reflection that is slightly distorted by a
concave unconformity between 800 and 850 m, extending to
the bedrock. This continuous moderate-amplitude reflection
and the overlying homogeneous unit lacking reflectivity are
associated with the last depositional stages of the interlobate
complex covered by the shore deposits.
Zone 1 runs along the tributary esker core (Fig. 1) towards
the northeast following the margin of the bedrock deepening
0 100 200 300 400 500 600 700 800 900 1000
Elevation (m)
130
110
90
70
50
30
10
VI6
VI250
VI282 VI285 VI252
Approx. elevation (m)
Distance along profile (m)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Time (s)
0 100 200 300 400 500 600 700 800 900
130
110
90
70
50
30
10
Zone 1
Distal fan / fan lobes
Zone 2
MUKH / fan
Zone 3
esker cores + proximal fan
Zone 4
MUKH / fan
Zone 5
secondary
esker
enlargement
(tunnel exit)
Approx. elevation (m)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Time (s)
0 100 200 300 400 500 600 700 800 900
130
110
90
70
50
30
10
Distance along profile (m)
Distance along profile (m)
GW GW
GW GW
?
(m/s)
1000
2000
3000
4000
5000
6000
330
Water table (GW)
Unconformity
Fine-grained
sediments
Trough and
fan lobe channel
MUKH - structure
Dislocated margin
Esker core
Fractured bedrock
Bedrock (Br)
Profile 2
Br
Br
Br
Br Br
Br Br
Zone 1
Distal fan / fan lobes
Zone 2
MUKH / fan
Zone 3
esker cores + proximal fan
Zone 4
MUKH / fan
Zone 5
secondary
esker
enlargement
(tunnel exit)
a)
b)
c)
GWGW
VI251
Br
Br
?
Sand
Fine sand
Silty sand
Coarse sand
Gravelly sand
Bouldery sand
Gravel
Sandy gravel
Bouldery gravel
Till
Gravelly till
Bouldery till
Sandy silt
Bouldery till
Clay tilt
Silty clay
Boulders
Bedrock
SWSW NENE
SWSW NENE
SWSW NENE
Fig. 11 a Seismic reflection (unmigrated but time to depth converted
using a constant velocity of 800 m/s) section along profile 2 with the
projected tomography section on top, including existing borehole data
near the profile; bthe seismic reflection section with interpreted
depositional zones, borehole stratigraphy and indication of bedrock
from the boreholes; cthe interpretation of depositional units and
indication of bedrock from boreholes along profile 2
Hydrogeol J
at 4550 m level (Mäkinen (2003b). Gravel-dominated mate-
rials in borehole VI275 (ca. 50 m northwest of the profile)
support the presence of the tributary esker. The reflections
below the water table are mainly horizontal with stronger re-
flections at ca. 6070 m a.s.l., which correspond to silty sand
(borehole VI282). The silty-sand unit is underlain by a vague-
ly convex package, up to 20 m thick, at 250350 m distance
along the profile. According to borehole VI282, this reflection
corresponds to sand and stony (bouldery) gravel that is known
to scatter the seismic signal, and thus the underlying bedrock
is not observed as a clear continuous reflection. The upper-
most sediments above the water table consist of horizontal
reflections truncated by 1015-m-thick and over 100-m-
wide trough-shaped facies (Fig. 8). Zone 1 is interpreted to
represent esker fan sediments. Beds of bouldery gravel at 43
50 m a.s.l. and sand at 5059 m level a.s.l. (VI282) correspond
to lower proximal tributary fan sediments, whereas the upper-
most trough-shaped reflections show cross-bedded fan lobe
channels from the main esker as indicated by the previous
observations from the nearby aggregate pits (Figs. 5a and 8).
However, the detailed understanding of the contact between
the tributary esker fans and the main esker fans remains poor.
Zone 2 is characterized by a major ca. 200-m-wide and
up to 70 m-thick concave feature extending down to bed-
rock (Fig. 8). Comparison with the tomography results
supports the presence of a major low-velocity depression
in this part of the profile (Fig. 11a). The bottom part ap-
pears as a zone lacking reflectivity while the middle part
shows complex and discontinuous/dislocated reflectivity.
The reflections associated with the bedrock geometry form
a seismic facies interpreted as a large MUKH structure
with collapsed/deformed esker fan sediments (illustrated
also in Fig. 5b). These large MUKH structures typically
occur on both sides of the esker core and in many places along
the esker at the margins of the coarse-grained hydrogeological
unit. The reflection seismic section along profile 2 provides
the first reliable evidence for the hypothesized bedrock con-
tact of the large MUKH-structures, which is encouraging.
On the northeast side of the large MUKH-structure, zone 3
shows two arched structures with vague inner reflections sepa-
rated by a large concave geometry seismic facies with reflec-
tions indicating thick stratified beds (Fig. 8). The arched geom-
etry facies at 700 m distance is mainly composed of stony and
sandy gravel as indicated by boreholes VI6 and VI285. This
gravel facies is underlain by a concave geometry with horizon-
tal reflections in the bedrock (Fig. 8). The arched facies are
interpreted as bouldery esker core sediments, where the core
at 700 m represents the known position of the main esker core,
while the core at 550 m is associated with the previously unde-
tected tributary esker core., suggesting that the two esker cores
join a bit further towards the southeast. Based on the deposi-
tional model, the trough-shaped structure between the cores
might be interpreted as a proximal fan structure. Zone 3 forms
the main aquifer of the glaciofluvial complex. The thick con-
cave geometry facies between the esker cores is interpreted as a
proximal fan structure. Horizontal reflections below the main
esker core indicate intense fracturing due to pressurized melt-
water flow in the subglacial tunnel. This is an important inter-
pretation, because it suggests that the aquifer extends down to
bedrock, typical for an esker environment.
Zone 4 is characterized by a large concave geometry seis-
mic facies with vaguely dislocated reflections below the up-
permost continuous intermediate reflection. The eastern side
of the facies shows an unconformity that extends down to
bedrock. The reflections below the unconformity show low-
angle reflections dipping to the NE. The sediments bordered
by the esker core and the concave unconformity are
interpreted to represent the SE-end of a second large MUKH
structure as supported by the previous studies (Mäkinen
2003b). The low-angle sediments on the NE side of the
MUKH structure exhibit undeformed esker fan sediments.
The strong reflector roughly at 90 m a.s.l. indicates the water
table. Bedrock surface is picked up again as a strong reflection
similar to that observed below the esker core within zone 3.
Profile 2 ends close to the highest part of the Säkylänharju
ridge, where zone 5 reveals a marked change in seismic facies
with a set of toplap reflections (Fig. 8) in sandy deposits un-
derlain by diamicton (VI251). The toplap reflections stop at
the uppermost continuous intermediate reflection and resem-
ble large-scale cross-bedding that dip parallel to the main
ridge. These deposits are related to the meltwater flows along
the interlobate crevasse forming the widening of the coarse-
grained hydrological unit (Artimo et al. 2003). The diamicton
below the crevasse deposits might represent mass-flow de-
posits lateral to the esker fan sediments.
Discussion
Due to the complex and heterogeneous subsurface, the depo-
sitional structures at Virttaankangas are characterized by large
vertical velocity gradients over short depths, which is further
complicated when the unconsolidated sediments make the
transition to the water-saturated zone. As the water-table zone
is approached, velocities are especially sensitive and can vary
from just a few hundreds of meter per second to an increase of
four times or more (Bachrach and Nur 1998). Additionally,
the complex depositional environment such as esker cores,
MUKH structures and fan lobe channels as well as the frac-
tured bedrock lead to lateral velocity variations. Even though
in shallow seismic surveys reflections from the water table are
not always common (Steeples and Miller 1998), one can no-
tice these reflections here distinctly in the shot gathers (e.g.
Fig. 7) and with some interruption in the stacked sections as
well. Given the shallow depth of investigation and the char-
acteristic challenges associated with near-surface structures in
Hydrogeol J
seismic reflection data (Frei et al. 2015), the processing fo-
cused on imaging the rapidly lateral/vertical variations in the
shallow structures above the bedrock. After an extensive ve-
locity analysis during data processing, constant velocities
were used for the final time todepth conversion of the seismic
sections (1,000 m/s for profile 1 and 800 m/s for profile 2).
Some errors are expected (on the order of a few meters) in the
depth position of the reflections given the rapid velocity
change with depth in the study area; however, the refraction
section together with a good knowledge of the depositional
environment from existingdata help limit this uncertainty. The
bedrock surface is interpreted from the high amplitude contin-
uous deep reflections even though at places the bedrock re-
flection is lost underneath gravel and sand beds, as the seismic
signal can easily be scattered in such an environment.
The seismic results of the Virttaankangas area confirm the
location and dimensions of the esker core that is the main aqui-
fer and the target for the pumping stations of the MAR plant.
The esker core facies has a distinct arched shape due to esker
deposition in an R-channel (Röthlisberger 1972)restingonhard
crystalline bedrock. The character of the reflections, high am-
plitudes and discontinuous nature, can characterize coarse-
grained sediments that are likely indicative of esker cores
(Pugin et al. 2009a). The results confirm that continuous and
thick till beds below the esker core within the fractured bedrock
zone form poorly conductive sediments that are important for
the groundwater flow model, but it was revealed that the till
beds were partly eroded during the esker deposition lateral to
the main core. This indicates a proximal fan deposition and
wide high conductivity zone within a constrained environment
of the fractured bedrock (Fig. 12a). The position of the tributary
esker along profile 2 is a new finding in this study (Fig. 12b)
and will improve the high hydraulic conductivity close to the
main core. Its position is also supported by very short residence
times for infiltrated water in that area (Aki Artimo, Turku
Region Water Ltd, personal communication, 2016). The new
seismic data also suggest high conductivity in fractured bedrock
structure below the esker core.
Earlier studies indicated the presence of large MUKH
structures on the sides of the esker core with suggested
bedrock contact (Mäkinen 2003b). This study now con-
firms the large dimensions of the MUKH structures and
their contact to bedrock (Fig. 12). The results also show
their complex deformed internal structure restricting the
groundwater flow with increased residence times of the
infiltrated water. These MUKH structures are described in
Fig. 12 The interpreted main esker elements (esker core, fans, MUKH
structures; shown in color) and bedrock characteristics based on profile 1
compared to the earlier research (Mäkinen 2003b;showningrayscale)
for aprofile 1 and bprofile 2. Bedrock elevationcontours modified from
Valjus ( 2006)
Hydrogeol J
the groundwater flow model with specific parameters and
have been used for the artificial infiltration and the creation
of inverse gradients. The fan lobe channels, their lateral
extents and relationship to the highly conductive esker core
were shown with adequate detail in this study. Two previ-
ously unknown fan lobes lateral to the main esker core were
identified within the bedrock fracture zone. The contact
between the secondary esker enlargement deposits and the
esker fans was better identified near the top of the main
ridge, which strengthens the delineation of the wider
coarse-grained hydrogeological unit (Fig 12b).
The novel high-resolution landstreamer seismic survey of-
fered valuable and continuous depth information down to bed-
rock and was capable of detecting main structures associated
with the stratigraphically and hydrogeological relevant units
in complex interlobate esker deposits. Thus, the method is
highly cost-effective over wide study areas with enough
paths/roads, where inadequate sedimentological and litholog-
ical data hinder reliable correlation; furthermore, if the thick-
ness of the deposits exceeds about 40 m or if the surficial
sediments are not suitable for GPR survey (e.g., clay rich
and saturated), the high-resolution seismic method can stand
alone. However, if a more detailed sedimentological under-
standing or local depositional model is needed (e.g. for de-
tailed groundwater flow modeling) the method should still be
combined with GPR surveys if possible. Given that there is
enough space for maneuvering the source, and coupling con-
ditions are fulfilled, a survey could be carried out in a sparse
layout in forests as well, particularly by using wireless re-
corders. Peat bogs or peatlands, and generally thick layers of
soft vegetation, would greatly attenuate the seismic signal and
are known to be challenging environmentsfor seismic surveys
(Miller et al. 1992). They are, however, part of the esker en-
vironments, and studies on MAR require surveys that image
the whole aquifers area (Rossi et al. 2014). GPR measure-
ments are known to successfully image peatlands (Comas
et al. 2004; Lowry et al. 2009) but keeping in mind GPRs
limited penetration depth, a high-resolution seismic survey
will allow a reliable delineation of the esker systems with
the surrounding wetlands.
As esker cores, esker fans included, can reach up to 500 m
width, and accounting for the surroundings plains, landstreamer
surveys are suitable for efficiently covering long distances.
Streams or springs that require an interruption in the seismic line
are accounted for with wireless recorders that assure continuity in
the survey line. Defining the hydrogeological units of the aqui-
fers from boreholes only and open pits is risky due to uncertainty
in these sparse data that assume continuous units. An entire aqui-
fer can be sampled in one seismic campaign (in 1 week for
example) and a combined geophysical-hydrogeological model-
lingstrategywillyieldanimprovedimagecomparedtoanyof
the approaches taken separately (Rubin et al. 1992). Seismic
sections display continuous profiles of one (or several) km where
complementary data can be overlaid and provide control for the
interpretation.
Conclusions
Two ca. 1-km-long seismic profiles were successfully
acquired over a relatively thick complex and heteroge-
neous glacial environment, at Virttaankangas, Finland.
The 200-m-long prototype landstreamer system was test-
ed for its suitability for hydrogeological characterization
of the complex interlobate esker deposits down to bed-
rock. High quality refraction and reflection seismic data
were acquired in an efficient survey combining the
landstreamer and wireless recorders that proved crucial
in providing information from more than 100 m-thick
bedrock glacial cover. Data processing had to account
for a challenging setting in terms of a deep water table
at certain locations (ca. 40 m) and rapid changes in the
depositional environment. The aquifer features were
identified from a combination of reflection imaging
and refraction tomography results allowing a good con-
trol and complementary interpretation of the results.
Besides the bedrock surface, the refraction seismic
results confirm a zone of fractured bedrock where the
velocities are around 3,000 m/s. The correlation between
the tomography and the reflection seismic sections pro-
vides a good overview of the sedimentary structures
along each profile. Further, the sections are rich in re-
flectivity and hence they allow comparison to the
existing depositional model with a delineation of the
main architectural elements relevant for the
hydrogeological model as well as for groundwater flow
modellingdowntothebedrocklevel.
The main findings of this study are valuable for the
future sustainable use of the aquifer and are summarized
as following:
&The cost- and time-effective seismic survey enabled the
characterization of the hydrogeologically relevant large-
scale esker architectural elements that impact the ground-
water infiltration and flow.
&Seismic facies were used to improve the determination of
hydraulic conductivity distribution in the groundwater flow
model down to bedrock level. This also promoted the inte-
gration of scattered geological data for modelling purposes.
&Deep fractured bedrock with complex overlying stratigra-
phy was delineated and the hydraulic connection between
the hydraulically conductive unit and bedrock was shown.
&New data enable accurate planning for future pumping wells
and infiltration areas in the most complex and widest part of
the coarse-grained unit (within the esker core sediments).
Hydrogeol J
&The combination of seismic and GPR surveys together
with neighboring borehole information within thick and
widespread glaciofluvial deposits provides the best ap-
proach for accurate depositional models with minimized
need for borehole reference.
Acknowledgements The authors would like to thank Trust 2.2
(http://www.trust-geoinfra.se) Formas project (252-2012-1907) under
which this test survey was initiated. Turku Region Water Ltd, the
Geological Survey of Finland (GTK) and University of Turku/Dept. of
Geography and Geology sponsored the data acquisition and collaborated
in this project. Graduate students from Uppsala University participated in
the fieldwork for which the authors are grateful. A. Tryggvason (Uppsala
University) is thanked for providing the PStomo_eq available to use for
travel time tomography. GLOBE Claritasunder license from the Institute
of Geological and Nuclear Sciences Limited, Lower Hutt, New Zealand,
was used to process the seismic data. We are thankful for valuable and
critical comments provided by Dr. David Sharpe and two anonymous re-
viewers that together with the editor helped improve the quality of the
paper.
Open Access This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a link
to the Creative Commons license, and indicate if changes were made.
References
Almholt A, Wisén R, Jorgensen R, Ringgaard J, Nielsen U (2013) High
resolution 2D reflection seismic land streamer survey forgroundwa-
ter mapping: case study from southeast Denmark. In: SEG Technical
Program Expanded Abstracts 2013. Society of Exploration
Geophysicists, Tulsa, OK, pp 18941898
Artimo A, Mäkinen J, Berg RC, Abert CC, Salonen VP (2003) Three-
dimensional geologic modeling and visualization of the
Virttaankangas aquifer, southwestern Finland. Hydrogeol J 11:
378386. doi:10.1007/s10040-003-0256-6
Artimo A, Saraperä S, Ylander I (2008) Methods for integrating an extensive
geodatabase with 3D modeling and data management tools for the
Virttaankangas Artificial Recharge Project, southwestern Finland.
Water Resour Manag 22:17231739. doi:10.1007/s11269-008-9250-z
Artimo A, Saraperä S, Puurunen O, Mäkinen J (2010) The Turku Region
Artificial Infiltration Project, Finland: tools for enhanced aquifer
characterization. ISMAR, Abu Dhabi, United Arab Emirates, pp
93100
Bachrach R, Nur A (1998) Highresolution shallowseismic experiments
in sand, partI: water table, fluid flow, and saturation. Geophysics 63:
12251233. doi:10.1190/1.1444423
Baker G, Steeples D, Schmeissner C, Spikes K (2000) Collecting
seismic-reflection data from depths shallower than three meters.
In: Symposium on the application of geophysics to engineering
and environmental problems 2000. Environment and Engineering
Geophysical Society, Denver, CO, pp 12071214
Baker VR (1973) Paleohydrology and sedimentology of Lake Missoula
flooding in Eastern Washington. In: Geological society of America
special papers. Geological Society of America, Boulder, CO, pp 173
Banerjee I, McDonald B (1975) Nature of esker sedimentation. In:
Jopling AV, McDonald BC (eds) Glaciofluvial and glaciolacustrine
sedimentation. Society of Economic Paleontologists and
Mineralogists, Tulsa, OK
Barton N (2007) Rock quality, seismic velocity, attenuation and anisotro-
py. CRC, Auckland, New Zealand
Black RA, Steeples DW, Miller RD (1994) Migration of shallow seismic
reflection data. Geophysics 59:402410. doi:10.1190/1.1443602
Boucher C, Pinti DL, Roy M, Castro MC, Cloutier V, Blanchette D,
Larocque M, Hall CM, Wen T, Sano Y (2015) Groundwater age
investigation of eskers in the Amos region, Quebec, Canada. J
Hydrol 524:114. doi:10.1016/j.jhydrol.2015.01.072
Bouwer H (2002) Artificial recharge of groundwater: hydrogeology and en-
gineering. Hydrogeol J 10:121142. doi:10.1007/s10040-001-0182-4
Bradford JH (2002) Depth characterization of shallow aquifers with seismic
reflection, part I: the failure of NMO velocity analysis and quantitative
error prediction. Geophysics 67:8997. doi:10.1190/1.1451362
Brennand TA (2000) Deglacial meltwater drainage and glaciodynamics:
inferences from Laurentide eskers, Canada. Geomorphology 32:
263293. doi:10.1016/S0169-555X(99)00100-2
Brodic B, Malehmir A, Juhlin C, Dynesius L, Bastani M, Palm H (2015)
Multicomponent broadband digital-based seismic landstreamer for
near-surface applications. J Appl Geophys 123:227241.
doi:10.1016/j.jappgeo.2015.10.009
Burke MJ, Brennand TA, Perkins AJ (2012) Evolution of the subglacial
hydrologic system beneath the rapidly decaying Cordilleran Ice
Sheet caused by ice-dammed lake drainage: implications for
meltwater-induced ice acceleration. Quat Sci Rev 50:125140.
doi:10.1016/j.quascirev.2012.07.005
Burke MJ, Woodward J, Russell AJ, Fleisher PJ, Bailey PK (2008)
Controls on the sedimentary architecture of a single event englacial
esker: Skeiðarárjökull, Iceland. Quat Sci Rev 27:18291847.
doi:10.1016/j.quascirev.2008.06.012
Comas X, Slater L, Reeve AS (2004) Geophysical evidence for peat basin
morphology and stratigraphic controls on vegetation observed in a
Northern Peatland. J Hydrol 295:173184. doi:10.1016/j.
jhydrol.2004.03.008
Comas X, Slater L, Reeve AS (2011) Pool patterning in a northern
peatland: geophysical evidence for the role of postglacial landforms.
J Hydrol 399:173184. doi:10.1016/j.jhydrol.2010.12.031
Dillon P (2005) Future management of aquifer recharge. Hydrogeol J 13:
313316. doi:10.1007/s10040-004-0413-6
Finnish Environment Institute (2016) Ground water areas 1: 20 000.
Spatial datasets. http://www.syke.fi/openinformation
Francese R, Giudici M, Schmitt DR, Zaja A (2005) Mapping the geom-
etry of an aquifer system with a high-resolution reflection seismic
profile. Geophys Prospect 53:817828
Frei W, Bauer R, Corboz P, Martin D (2015) Pitfalls in processing near-
surface reflection-seismic data: beware of static corrections and mi-
gration. Lead Edge 34:13821385. doi:10.1190/tle34111382.1
Giustiniani M, Accaino F, Picotti S, Tinivella U (2008) Characterization
of the shallow aquifers by high-resolution seismic data. Geophys
Prospect 56:655666. doi:10.1111/j.1365-2478.2008.00705.x
Gorrell G, Shaw J (1991) Deposition in an esker, bead and fan
complex, Lanark, Ontario, Canada. Sediment Geol 72:285
314. doi:10.1016/0037-0738(91)90016-7
Hebrand M, Åmark M (1989) Esker formation and glacier dynamics in
eastern Skane and adjacent areas, southern Sweden. Boreas 18:67
81. doi:10.1111/j.1502-3885.1989.tb00372.x
Huddart D, Bennett MR, Glasser NF (1999) Morphology and sedimen-
tology of a high-arctic esker system: Vegbreen, Svalbard. Boreas 28:
253273. doi:10.1111/j.1502-3885.1999.tb00219.x
Huuse M, Lykke-Andersen H, Piotrowski JA (2003) Geophysical inves-
tigations of buried Quaternary valleys in the formerly glaciated NW
European lowland: significance for groundwater exploration. J Appl
Geophys 53:153157. doi:10.1016/j.jappgeo.2003.08.003
Hydrogeol J
Jokela P, Kallio E (2015) Sprinkling and well infiltration in managed aquifer
recharge for drinking water quality improvement in Finland. J Hydrol
Eng 20, B4014002. doi:10.1061/(ASCE)HE.1943-5584.0000975
Juhlin C, Dehghannejad M, Lund B, Malehmir A, Pratt G (2010)
Reflection seismic imaging of the end-glacial Pärvie Fault system,
northern Sweden. J Appl Geophys 70:307316. doi:10.1016/j.
jappgeo.2009.06.004
Juhlin C, Palm H, Müllern C-F, Wållberg B (2002) Imaging of ground-
water resources in glacial deposits using high-resolution reflection
seismics, Sweden. J Appl Geophys 51:107120
Korsman K, Koistinen T, Kohonen G, Wennerström M, Ekdahl H,
Honkamo M, Idman H, Pekkala Y (eds) (1997) Bedrock map of
Finland 1: 1 000 000. Geological Survey of Finland, Espoo, Finland
Kruppenbach JA, Bedenbender JW (1975) United States patent:
3923121towed land cable. US Patent and Trademark Office,
Alexandria, VA
Kujansuu R, Kurkinen I, Niemelä J (1995) Glaciofluvial deposits in Finland.
In: Ehlers J, Kozarski S, Gibbard PL (eds) Glacial deposits in North-
East Europe. Balkema, Rotterdam, The Netherlands, pp 7784
Lowry CS, Fratta D, Anderson MP (2009) Ground penetrating radar and
spring formation in a groundwater dominated peat wetland. J Hydrol
373:6879. doi:10.1016/j.jhydrol.2009.04.023
Mäkinen J (2003a) Timetransgressive deposits of repeated depositional se-
quences within interlobate glaciofluvial (esker) sediments in Köyliö,
SW Finland. Sedimentology 50:327360. doi:10.1046/j.1365-
3091.2003.00557.x
Mäkinen J (2003b) The development of depositional environments with-
in the interlobate Säkylänharju-Virttaankangas Glaciofluvial
Complex in SW Finland. Suomalainen Tiedeakatemia, Helsinki,
Finland
Mäkinen J, Räsänen M (2003) Early Holocene regressive spit-platform and
nearshore sedimentation on a glaciofluvial complex during the Yoldia
Sea and the Ancylus Lake phases of the Baltic Basin, SW Finland.
Sediment Geol 158:2556. doi:10.1016/S0037-0738(02)00240-3
Malehmir A, Bastani M, Krawczyk C, Gurk M, Ismail N, Polom U,
Persson L (2013a) Geophysical assessment and geotechnical inves-
tigation of quick-clay landslides: a Swedish case study. Surf
Geophys. doi:10.3997/1873-0604.2013010
Malehmir A, Saleem MU, Bastani M (2013b) High-resolution reflection
seismic investigations of quick-clay and associated formations at a
landslide scar in southwest Sweden. J Appl Geophys 92:84102.
doi:10.1016/j.jappgeo.2013.02.013
Malehmir A, Wang S, Lamminen J, Bastani M, Vaittinen K, Juhlin C, Place J
(2015a) Delineating structures controlling sandstone-hosted base-metal
deposits using high-resolution multicomponent seismic and radio-
magnetotelluric methods: a case study from northern Sweden.
Geophys Prospect 63:774797. doi:10.1111/1365-2478.12238
Malehmir A,Zhang F, Dehghannejad M, Lundberg E, Döse C, Friberg O,
Brodic B, Place J, Svensson M, Svensson M (2015b) Planning of
urban underground infrastructure using a broadband seismic
landstreamer: tomography results and uncertainty quantifications
from a case study in southwestern Sweden. Geophysics 80:B177
B192. doi:10.1190/geo2015-0052.1
Malehmir A, Socco LV, Bastani M, Krawczyk CM, Pfaffhuber AA,
Miller RD, Maurer H, Frauenfelder R, Suto K, Bazin S, Merz K,
Dahlin T (2016a) Near-surface geophysical characterization of areas
prone to natural hazards: a review of the current and perspective on
the future. Adv Geophys 57:229312. doi:10.1016/bs.agph
Malehmir A, Andersson M, Mehta S, Brodic B, Munier R, Place J,
Maries G, Smith C, Kamm J, Bastani M, Mikko H, Lund B
(2016b) Post-glacial reactivation of the Bollnäs fault, central
Sweden: a multidisciplinary geophysical investigation. Solid Earth
7:509527. doi:10.5194/se-7-509-2016
Miller P, Shaw GH, Glaser P, Siegel D (1992) Bedrock topography be-
neath the Red Lake peatlands. Geol Soc Am Abstracts with
Programs 24:7
Miller R, Steeples D, Brannan M (1989) Mapping a bedrock surface
under dry alluvium with shallow seismic reflections. Geophysics
54:15281534. doi:10.1190/1.1442620
Miller RD, Xia J (1998) Large nearsurface velocity gradients on
shallow seismic reflection data. Geophysics 63:13481356.
doi:10.1190/1.1444436
Nadeau S, Rosa E, Cloutier V, Daigneault R-A, Veillette J (2015) A GIS-
based approach for supporting groundwater protection in eskers:
application to sand and gravel extraction activities in Abitibi-
Témiscamingue, Quebec, Canada. J Hydrol Reg Stud 4(Part B):
535549. doi:10.1016/j.ejrh.2015.05.015
National Land Survey of Finland (2010) Base map 1: 20 000. Sheet
M3331L. NLS File service of open data. https://tiedostopalvelu.
maanmittauslaitos.fi/tp/kartta?lang=en. Accessed December 2016
National Land Survey of Finland (2016) General map 1: 1000 000. NLS
File service of open data. http://tiedostopalvelu.maanmittauslaitos.
fi/tp/kartta?lang=en
Pasanen A (2009) The application of ground penetrating radar to the study of
Quaternary depositional environments. Res Terrae Ser A 27:145
Place J, Malehmir A, Högdahl K, Juhlin C, Nilsson KP (2015) Seismic
characterization of the Grängesberg iron deposit and its mining-
induced structures, central Sweden. Interpretation 3:SY41SY56.
doi:10.1190/INT-2014-0212.1
Pugin AJM, Larson T, Bergler S, McBride J, Bexfield C (2004a) Near-
surface mapping using SH-wave and P-wave seismic land-streamer
data acquisition in Illinois, U.S. Lead Edge 23:677682.
doi:10.1190/1.1776740
Pugin AJM, Larson T, Sargent S (2004b) 3.5 Km/Day of high resolution
seismic reflection data using a landstreamer. In: Symposium on the
application of geophysics to engineering and environmental prob-
lems 2004. Environment and Engineering Geophysical Society,
Denver, CO, pp 13801388
Pugin AJM, Pullan S, Hunter J, Oldenborger G (2009a) Hydrogeological
prospecting using P- and S-wave landstreamer seismic reflection
methods. Surf Geophys. doi:10.3997/1873-0604.2009033
Pugin AJ-M, Pullan SE, Hunter JA (2009b) Multicomponent high-
resolution seismic reflection profiling. Lead Edge 28:12481261
Pugin AJ, Mäkinen J, Ahokangas E, Artimo A, Vanhala H, Pasanen A,
Moisio K, Virtasalo J, Tuusjärvi M (2014) High-resolution seismic
reflection survey with landstreamer on the characterization of the
Virttaankangas aquifer, SW Finland. In: Virtasalo J, Tuusjärvi M
(eds) Abstract book. Guide 58, 1st Finnish National Colloqvium
of Geosciences, Espoo, 1920 March 2014, Geological Survey of
Finland, Espoo, pp 6364
Pullan SE, Pugin AJM, Dyke LD, Hunter JA, Pilon JA, Todd BJ, Allen
VS, Barnett PJ (1994) Shallow geophysics in a hydrogeological
investigation of the Oak Ridges Moraine, Ontario. In: Proceedings
of the Symposium on the Application of Geophysics to Engineering
and Environmental Problems: SAGEEP94, Boston, MA,
March 1994, pp 2731
Punkari M (1980) The ice lobes of the Scandinavian ice sheet during the
deglaciation in Finland. Boreas 9:307310. doi:10.1111/j.1502-
3885.1980.tb00710.x
Rossi PM, Ala-aho P, Doherty J, Kløve B (2014) Impact of peatland
drainage and restoration on esker groundwater resources: modeling
future scenarios for management. Hydrogeol J 22:11311145.
doi:10.1007/s10040-014-1127-z
Röthlisberger H (1972) Water pressure in intra- andsubglacial channels. J
Glaciol 11:177203
Rubin Y, Mavko G, Harris J (1992) Mapping permeability in heteroge-
neous aquifers using hydrologic and seismic data.Water Resour Res
28:18091816. doi:10.1029/92WR00154
Salas-Romero S, Malehmir A, Snowball I, Lougheed BC, Hellqvist M
(2016) Identifying landslide preconditions in Swedish quick clays:
insights from integration of surface geophysical, core sample- and
Hydrogeol J
downhole property measurements. Landslides 13:905923.
doi:10.1007/s10346-015-0633-y
Schmelzbach C, Green AG, Horstmeyer H (2005) Ultra-shallow seismic
reflection imaging in a region characterized by high source-generated
noise. Surf Geophys 3:3346. doi:10.3997/1873-0604.2004027
Sharpe DR, Pugin A, Pullan SE, GorrellG (2003) Application of seismic
stratigraphy and sedimentology to regional hydrogeological investi-
gations: an example from Oak Ridges Moraine, southern Ontario,
Canada. Can Geotech J 40:711730. doi:10.1139/t03-020
Sheriff RE, Geldart LP (1995) Exploration seismology. Cambridge
University Press, New York
Shreve RL (1985) Esker characteristics in terms of glacier physics,
Katahdin esker system, Maine. Geol Soc Am Bull 96:639.
doi:10.1130/0016-7606(1985)96<639:ECITOG>2.0.CO;2
Sloan SD, Tsoflias GP, Steeples DW, Vincent PD (2007) High-resolution
ultra-shallow subsurface imaging by integrating near-surface seismic
reflection and ground-penetrating radar data in the depth domain. J
Appl Geophys 62:281286. doi:10.1016/j.jappgeo.2007.01.001
Steeples D, Miller R (1998) Avoiding pitfalls in shallow seismic reflec-
tion surveys. Geophysics 63:12131224. doi:10.1190/1.1444422
Steeples DW, Miller RD (1988) Seismic reflection methods applied to
engineering, environmental, and groundwater problems. In: Proc.
(1st) Symp. on the application of geophysics to engineering and
environmental problems, Soc. Eng. and Mineral Exploration
Geophysicists, Golden, CO, pp 409461
Telford WM, Geldart LP, Sheriff RE (1990) Applied geophysics.
Cambridge University Press, Cambridge, UK
Theakstone WH (1976) Glacial lake sedimentation, Austerdalsisen, Norway.
Sedimentology 23:671688. doi:10.1111/j.1365-3091.1976.tb00101.x
Tryggvason A, Rögnvaldsson S ður T, Flóvenz ÓG (2002) Three-
dimensional imaging of the P- and S-wave velocity structure and
earthquake locations beneath southwest Iceland. Geophys J Int 151:
848866. doi:10.1046/j.1365-246X.2002.01812.x
Ulusoy İ, Dahlin T, Bergman B (2015) Time-lapse electrical resistivity
tomography of a water infiltration test on Johannishus Esker,
Sweden. Hydrogeol J 23:551566. doi:10.1007/s10040-014-1221-2
Valjus T (2006) Turun Seudun Vesi. Pohjavesialueen kallionpinnan tason
1073 määritys painovoimamittausten avulla [Turku Region Water
Ltd. The determination of the groundwater areas bedrock surface
level by gravity measurements]. Geological Survey of Finland,
Espoo, pp 41
van der Veen M, Spitzer R, Green A, Wild P (2001) Design and applica-
tion of a towed landstreamer system for costeffective 2-D and
pseudo-3-D shallow seismic data acquisition. Geophysics 66:482
500. doi:10.1190/1.1444939
van der Veen M, Green AG (1998) Land streamer for shallow seismic
data acquisition: evaluation of gimbal-mounted geophones.
Geophysics 63:14081413. doi:10.1190/1.1444442
Warren WP, Ashley GM (1994) Originsof the ice-contact stratified ridges
(eskers) of Ireland. SEPM J Sediment Res. doi:10.1306/D4267
DD9-2B26-11D7-8648000102C1865D
Hydrogeol J
... Glaciofluvial deposits, especially eskers, are important aquifer types in the Fennoscandian Shield and in northern regions formed during the last deglaciation, e.g., in Finland, Sweden, and North America (e.g., [1][2][3][4][5]). In Finland, there are over 5000 classified groundwater areas, covering a surface area of approximately 7059 km 2 (Figure 1, index map), which are mainly unconfined esker aquifers. ...
... µS/cm), pH (5.60-6.80), and alkalinity (0.11-0.92 mmol/L) (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) are presented as red dots along the top of (c), where w, sp, s, and a denote winter, spring, summer, and autumn, respectively. ...
... The atmosphere could be another source of CO 2 [20]. From both sources, CO 2 gas dissolves into the solution and generates carbonic acid (H 2 CO 3 ) and consequently HCO 3 − and H + in the solution. H + is consumed in silicate weathering, which produces silicic acid (H 4 SiO 4 ), clay minerals, Fe, Mn, and other elements (e.g., Ca, Na, Mg, K, and Al) from the silicate mineral compounds. ...
Article
Full-text available
Article link: https://www.mdpi.com/2073-4441/16/22/3301 This study investigated the hydrogeochemistry of a shallow Quaternary sedimentary aquifer in an esker deposition in western Finland, where distinct spatial and temporal variability in groundwater hydrogeochemistry has been observed. Field investigation and hydrogeochemical data were obtained from autumn 2010 to autumn 2013. The data were analyzed using the multivariate statistical methods principal component analysis (PCA) and hierarchical cluster analysis (HCA), in conjunction with groundwater classification based on the main ionic composition. The stable isotope ratios of δ18O and δD were used to determine the origin of the groundwater and its connection to surface water bodies. The groundwater geochemistry is characterized by distinct redox zones caused by the influence of organic matter, pyrite oxidation, and preferential flow pathways due to different hydrogeological conditions. The groundwater is of the Ca-HCO3 type and locally of the Ca-HCO3-SO4 type, with low TDS, alkalinity, and pH, but elevated Fe and Mn concentrations, KMnO4 consumption, and, occasionally, Ni concentrations. The decomposition of organic matter adds CO2 to the groundwater, and in this study, the dissolution of CO2 was found to increase the pH and enhance the buffering capacity of the groundwater. The mobility of redox-sensitive elements and trace metals is controlled by pH and redox conditions, which are affected by the pumping rate, precipitation, and temperature. With the expected future increases in precipitation and temperature, the buffering capacity of the aquifer system will enhance the balance between alkalinity from bioactivity and acidity from recharge and pyrite oxidation.
... Finland (Maries et al. 2017), Sweden (DE GEER 1968, Norway (Kløve et al. 2017), ...
Thesis
Full-text available
Eskers are complex geological formations in northern countries that provide crucial resources such as drinking water, sand/gravel, outdoor recreational sites, and productive forests. The sustainable management of these resources requires baseline ecological knowledge of the ecosystems associated with eskers. However, very little information exists about the ecology of freshwater ecosystems on eskers. This study uses a food web approach to identify the environmental variables, biological diversity, and indicator species associated with esker lakes to better understand their ecological functioning and biodiversity patterns to benefit their sustainable management and conservation. Fifty lakes were sampled in the Abitibi- Témiscamingue region (Canada), half on eskers and half on the surrounding boreal clay belt to include the most abundant lake ecosystems of the region. Physicochemical, environmental, and anthropogenic variables measured in the two lake types showed that esker lakes differed markedly from clay lakes. Nutrient concentrations, conductivity, and macrophyte cover were significantly lower in esker lakes than in clay lakes, whereas dissolved oxygen saturation and concentration showed the opposite trend. Three interconnected trophic levels of the esker lake food webs—waterbird, fish, and macroinvertebrate communities—were characterized for biological diversity and the associated species. We found a lower Shannon diversity index for waterbirds (mean ± standard deviation; 0.7 ± 0.2), fish (0.4 ± 0.3), and macroinvertebrates (0.9 ± 0.3) in esker lakes than the clay lakes (1.1 ± 0.4, 0.9 ± 0.3, and 1.3 ± 0.5, respectively). Common goldeneye (Bucephala clangula) and Canada goose (Bucephala clangula) were associated significantly with esker lakes. In contrast, Ring-necked duck (Aythya collaris) and Hooded merganser (Lophodytes cucullatus) were associated significantly with clay lakes. Perlidae was similarly associated with esker lakes as an indicator for macroinvertebrates. Anthropogenic activities such as forest harvesting have altered the waterbird community, and recreational activities around the lakes have modified the fish and macroinvertebrate communities. We conclude that esker lakes differ from other regional lakes and are associated with specific environmental and biological variables and indicator species. The biological diversity in esker lakes is lower than that of clay lakes for all studied trophic levels of the food web, but these waterbodies provide preferential habitats for some species. This research provides the first baseline ecological information necessary to establish sustainable management and conservation strategies for this vulnerable ecosystem.
... Shear wave velocity (Vs) is an important geo-mechanical property in engineering construction, seismic response studies, earthquake hazards, soil amplification, liquefaction, and modeling the subsurface environment (Imai and Tonouchi 1982;Anderson et al. 1996;Xia et al. 2002;Lin et al. 2004;Ismail and Sargent 2006;Ismail and Anderson 2007;Lee and Trifunac 2010;Wong et al. 2011;Rehman et al. 2016;Maries et al. 2017;Al-Amri et al. 2022;Abdullatif et al. 2022). Vs is measured using a variety of geophysical and engineering techniques, including seismic cone penetrometer test (SCPT), suspension PS logger, borehole survey, spectral analysis of surface waves (SASW), and multichannel analysis of surface waves (MASW), (Nazarian 1984;Song et al. 1989;Hunter and Woeller 1990;Joh 1996;Nigbor and Imai 1994;Brown 1998;Park et al. 1999;Xia et al. 1999;Jarvis and Knight 2000;Tunçel et al. 2021;Al-Amri et al. 2022). ...
Article
We compared shear wave velocity (Vs) profiles from multichannel analysis of surface waves (MASW) to downhole Vs profiles measured in 10 boreholes in central Illinois to evaluate the reliability of the MASW Vs profiles measured in glacial deposits. The Vs profiles from the two methods were compared by calculating multiple statistical parameters, including average difference, average relative difference, relative standard deviation, and correlation coefficient resulting in overall average values of 71 m/s, 17%, 17%, and 79%, respectively. Such comparisons showed that the MASW-derived Vs profiles compare fairly well with Vs profiles acquired by downhole logging and that the MASW method provides reliable Vs measurements for mapping subsurface geology in the glacial deposits. We also used the data to investigate the effect of the rapid change in lithology with depth and the number of layers of the initial model input to MASW inversion on the reliability of the measured MASW Vs measurements. The lithologic heterogeneity did not have a significant effect on the MASW-derived Vs measurements. However, using an initial model input to MASW inversion with fewer number of layers has generally improved the accuracy of the MASW Vs measurements.
... In particular, by recording both P-and S-wave data, it is very efficient in determining the properties of subsurface [25-27, 34, 36, 50, 65, 66]. The seismic method has been used in several geological contexts, such as on Quaternary deposits and on various hydrogeological studies of tunnel valley aquifers in USA and Canada (i.e., [4,45,46,50,63]) and Northern Europe [33,35,42] as well as in esker characterization in Canada [8,19,20,50,51,56], in Finland [5,14,41] and in the Alpine range [15]. In addition, the seismic method has been applied in urban environments [13,[25][26][27]36] and in the shallow subsurface imaging of transport routes [40,48]. ...
Chapter
In the last decades, many efforts have been dedicated to improve direct and indirect methodologies to study and monitor the aquifers. In particular, seismic method was successfully applied for this purpose. In this work a case study in the North East of Italy is described, for which seismic data were acquired and analyzed to characterize an aquifer system. All the phases of the experiment are illustrated, from the choice of the acquisition parameters to the final interpretation. Both 2D and 3D data were acquired in different seasons in order to define any possible seasonal variation. In order to obtain detailed petrophysical information, amplitude preserving processing, advanced tomographic imaging and Amplitude Versus Offset procedures were used. This analysis enabled to estimate the petro-physical properties of the subsoil and to locate a deeper aquifer not yet identified, as confirmed by a subsequent new well. The discovered aquifer, at 480 m depth, has been proved to be suitable for capturing for domestic purposes.
... Sediments deposited by water currents can constitute a significant potential for geomaterials (Kurjanski et al. 2021). They are particularly important and are most exploited in the construction industry (Mossa and James 2013;Bendixen et al. 2019) or as an aquifer for agricultural needs (Marie et al. 2017;Erikson et al. 2019). Their well-sorted deposition depends on the hydrodynamics and geomorphology of the river valley (Dietrich et al. 2017). ...
Article
The sedimentary architecture of the Middle Sanaga deposits in the Central Cameroon Region was studied by combining sedimentological and surface geoelectrical techniques. Lithologic columns from hand augers and pits were correlated to geoelectrical profiles. All of these data were analysed to determine the volumes of lithological units that constitute significant potential geomaterial deposits (gravels, sands, and clays). From surface to depth, geoelectrical results show four main units: conductive GU1 (100 Ωm), semi-resistive GU2 (800 Ωm), resistive UG3 (1000–2000 Ωm), and highly resistive GU4 (over 2000 Ωm). The calibration results identify three lithological units: LU1 composed of poorly sorted pebbles and gravels; LU2 consisting of well-classified medium to coarse sands, asymmetry towards fine to coarse elements; and LU3 consisting of silty clays and clayey sands. Correlation of results assigns GU1 and LU3 to low hydrodynamics, GU2 and LU2 to medium hydrodynamics, and GU3 with LU1 to high hydrodynamics. A 3D filling model has been developed. This model shows that the volume of GU1-LU3 is estimated of 33,549,496 m3, for GU2-LU2 is estimated of 18,352,728 m3, and of GU3-LU1 of 7,687,875m3. This study has important implications for the knowledge and characterization of lithological units, especially geomaterials.
... Therefore, shallow Vs reflection methods are highly useful for earthquake hazard studies (e.g., Woolery et al. 1993;Harris and Street 1997;Benjumea et al. 2003;Motazedian and Hunter 2008;Harris 2009Harris , 2010Hunter et al. 2010b;Odum et al. 2010). Shallow multicomponent reflection surveying recently is showing great potential (Pugin et al. 2009(Pugin et al. , 2010Pugin and Yilmaz 2019) and is now being adopted into numerous projects with complex near-surface stratigraphy (e.g., Maries et al. 2017;. ...
Article
Full-text available
Reflection and critically refracted seismic methods use traveltime measurements of body waves propagating between a source and a series of receivers on the ground surface to calculate subsurface velocities. Body wave energy is refracted or reflected at boundaries where there is a change in seismic impedance, defined as the product of material density and seismic velocity. This article provides practical guidance on the use of horizontally propagating shear wave (SH-wave) refraction and reflection methods to determine shear wave velocity as a function of depth for near-surface seismic site characterizations. Method principles and the current state of engineering practice are reviewed, along with discussions of limitations and uncertainty assessments. Typical data collection procedures are described using basic survey equipment, along with information on more advanced applications and emerging technologies. Eight case studies provide examples of the techniques in real-world seismic site characterizations performed in a variety of geological settings.
Book
Instrumentation and measurement technologies are currently playing a vital role in the monitoring, assessment, and protection of water resources. The whole water sector involves multiple technological contexts for monitoring the resource, given the broad multidisciplinary context, which covers water from its natural domains up to the various man-made infrastructures. Water cycle management refers to a very complex framework, which requires reliable technological responses to the questions raised in meteorology, hydrology, water resources management, hydraulic engineering, and, more in general, environmental management, with the related societal implications. Measurement techniques and sensing methods for observing water systems are rapidly evolving, requiring a continuous update in measurement technologies and methods. Effective and sustainable planning of the water cycle management requires the design and implementation of a systematic monitoring approach. In particular, instrumentation and measurement technologies are pervasive in all the necessary aspects of assessing, monitoring, and controlling water systems. Thus, assessing the water resource and its relationship with the various environmental stressors, including the anthropic pressures on it, requires adequate knowledge, technologies, and infrastructures to deal with the challenges of today. It is also important to underline that this aspect applies to both quantitative and qualitative monitoring activities, being the threats to the quality of the resource also indirectly affecting its availability and quantity. This book provides an updated framework of observational techniques, sensing technologies, and water management and protection data processing. In data analytics, attention is given to the synergy between different sensing systems and between measurements and modeling approaches. The coexistence in this book of measurement techniques, sensing methods, and data science implications for observing water systems emphasize the strong link between measurement aspects and computational and modeling. The present volume provides a portrait of current measurement technologies and data analysis approaches for water systems monitoring and management, also offering insights into the enabling technologies that are today fostering the concept of smart water systems. The 23 chapters of this book are organized to survey current technologies and available methods for assessing and monitoring water resources in multiple domains. In particular, the selected contributions are intended to cover the following thematic areas: (i) remote sensing methods; (ii) instrumentation for direct water sensing; (iii) water sensor networks and ICT infrastructures; (iv) geophysical techniques; (v) synergy between measurements and modeling. For more details, please visit the Springer website: https://link.springer.com/book/10.1007/978-3-031-08262-7
Article
Seismic ray tomography is a popular tool for reconstructing seismic velocity models from traveltime data. Here we study how the model parametrization affects the resolution and accuracy of the tomographic inversion for the near-surface model building. In particular, we consider the weighting of the elements of the model perturbation vector based on the values of the initial velocity model. When the model parameters are defined in terms of velocities then tomographic-inversion resolution is better for shallow part but degrades for deeper part of the model. The opposite is true when the model parameters are defined in terms of slowness values. This effect is associated with the method of forming the tomographic matrix. When linearizing the tomography problem for different model parameters, the matrix elements have different weight coefficients. This affects the inversion results and can lead to large errors. We suggest a new parametrization (in-between the velocity and the slowness) that provides better quality of the tomographic inversion and balanced resolution between shallow and deeper part of the model. Good performance of this new parametrization is confirmed by a series of synthetic tests and one real-data example. This article is protected by copyright. All rights reserved
Article
Groundwater is a nearly exclusive water resource, specifically for the communities which are part of the Chicago metropolitan area. However, water shortage is predicted for many communities in this region, and demand for locating and delineating groundwater is increasing to fulfill the water supply. Shallow sand and gravel aquifers within the glacial deposits of the area specifically are high volume aquifer and less stressed compare to deeper bedrock aquifer. Yet, these aquifers are poorly understood in terms of their extent and lateral variability. This study applied the shear-wave seismic reflection method to delineate the thickness, lateral extent, and internal variability of these aquifers. We acquired horizontally polarized shear-wave (SH-waves) reflection data along five profiles of a total length of 11 km using the land streamer technology in McHenry County in northern Illinois to delineate sand and gravel aquifers. As shear waves propagate through the rock matrix and less sensitive to the presence of water, information from nearby borings and water wells aided the interpretation of the acquired SH-wave seismic profiles. We delineated multiple sand and gravel units of potential aquifers of different thicknesses and lateral extent along with the seismic profiles. The relatively higher vertical and lateral resolution of the shear-waves reflection method and its insensitivity to water saturation or chemistry made it an ideal method to resolve sand and gravel units of potential aquifers within the complex geological environment if aided by water-well information.
Book
Full-text available
ROCK QUALITY, SEISMIC VELOCITY, ATTENUATION AND ANISOTROPY Summary Seismic measurements take many forms and appear to have a universal role in the Earth Sciences. They are the means for most easily and economically interpreting what lies beneath the visible surface. There are huge economic rewards and losses to be made when interpreting the shallow crust or subsurface more, or less accurately, as the case may be. This book describes seismic behaviour at many scales and from numerous fields in geophysics, tectonophysics and rock physics, and from civil, mining and petroleum engineering. Addressing key items for improved understanding of seismic behaviour, it often interprets seismic measurements in rock mechanics terms, with particular attention to the cause of attenuation, its inverse seismic quality, and the anisotropy of fracture compliances and stiffnesses. Reviewed behaviour stretches over ten orders of magnitude, from micro-crack compliance in laboratory tests to cross-continent attenuation. Between these extremes lie seismic investigation of rock joints, boreholes, block tests, dam and bridge foundations, quarry blasting, canal excavations, hydropower and transportation tunnels, machine bored TBM tunnels, sub-sea sediment and mid-ocean ridge measurements, where the emphasis is on velocity-depth-age models. Attenuation of earthquake coda-waves is also treated, including in-well measurements. In the later chapters, there is a general emphasis on deeper, higher stress, larger scale applications of seismic, such as shear-wave splitting for interpreting the attenuation, anisotropy and orientation of permeable 'open' fracture sets in petroleum reservoirs, and the 4D seismic effects of water-flood, oil production and compaction. The dispersive or frequency dependence of most seismic measurements and their dependence on fracture dimensions and fracture density is emphasized. The possibility that shear displacement may be required to explain permeability at depth is quantified. This book is cross-disciplinary, non-mathematical and phenomenological in nature, containing a wealth of figures and a wide review of the literature from many fields in the Earth Sciences. Including a chapter of conclusions and an extensive subject index, it is a unique reference work for professionals, researchers, university teachers and students working in the fields of geophysics, civil, mining and petroleum engineering. It will be particularly relevant to geophysicists, engineering geologists and geologists who are engaged in the interpretation of seismic measurements in rock and petroleum engineering.
Article
Full-text available
Glacially induced intraplate faults are conspicuous in Fennoscandia where they reach trace lengths of up to 155 km with estimated magnitudes up to 8 for the associated earthquakes. While they are typically found in northern parts of Fennoscandia, there are a number of published accounts claiming their existence further south and even in northern central Europe. This study focuses on a prominent scarp discovered recently in lidar (light detection and ranging) imagery hypothesized to be from a post-glacial fault and located about 250 km north of Stockholm near the town of Bollnäs. The Bollnäs scarp strikes approximately north–south for about 12 km. The maximum vertical offset in the sediments across the scarp is 4–5 m with the western block being elevated relative to the eastern block. To investigate potential displacement in the bedrock and identify structures in it that are related to the scarp, we conducted a multidisciplinary geophysical investigation that included gravity and magnetic measurements, high-resolution seismics, radio-magnetotellurics (RMT), electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). Results of the investigations suggest a zone of low-velocity and high-conductivity in the bedrock associated with a magnetic lineament that is offset horizontally about 50 m to the west of the scarp. The top of the bedrock is found ∼ 10 m below the surface on the eastern side of the scarp and about ∼ 20 m below on its western side. This difference is due to the different thicknesses of the overlying sediments accounting for the surface topography, while the bedrock surface is likely to be more or less at the same topographic level on both sides of the scarp; else the difference is not resolvable by the methods used. To explain the difference in the sediment covers, we suggest that the Bollnäs scarp is associated with an earlier deformation zone, within a wide (> 150 m), highly fractured, water-bearing zone that became active as a reverse fault after the latest Weichselian deglaciation.
Article
Water flowing in tubular channels inside a glacier produces frictional heat, which causes melting of the ice walls. However the channels also have a tendency to close under the overburden pressure. Using the equilibrium equation that at every cross-section as much ice is melted as flows in, differential equations are given for steady flow in horizontal, inclined and vertical channels at variable depth and for variable discharge, ice properties and channel roughness. It is shown that the pressure decreases with increasing discharge, which proves that water must flow in main arteries. The same argument is used to show that certain glacier lakes above long flat valley glaciers must form in times of low discharge and empty when the discharge is high, i.e. when the water head in the subglacial drainage system drops below the lake level. Under the conditions of the model an ice mass of uniform thickness does not float, i.e. there is no water layer at the bottom, when the bed is inclined in the down-hill direction, but it can float on a horizontal bed if the exponent n of the law for the ice creep is small. It is further shown that basal streams (bottom conduits) and lateral streams at the hydraulic grade line (gradient conduits) can coexist. Time-dependent flow, local topography, ice motion, and sediment load are not accounted for in the theory, although they may strongly influence the actual course of the water. Computations have been carried out for the Gornergletscher where the bed topography is known and where some data are available on subglacial water pressure.
Article
Water flowing in tubular channels inside a glacier produces frictional heat, which causes melting of the ice walls. However the channels also have a tendency to close under the overburden pressure. Using the equilibrium equation that at every cross-section as much ice is melted as flows in, differential equations are given for steady flow in horizontal, inclined and vertical channels at variable depth and for variable discharge, ice properties and channel roughness. It is shown that the pressure decreases with increasing discharge, which proves that water must flow in main arteries. The same argument is used to show that certain glacier lakes above long flat valley glaciers must form in times of low discharge and empty when the discharge is high, i.e. when the water head in the subglacial drainage system drops below the lake level. Under the conditions of the model an ice mass of uniform thickness does not float, i.e. there is no water layer at the bottom, when the bed is inclined in the down-hill direction, but it can float on a horizontal bed if the exponent n of the law for the ice creep is small. It is further shown that basal streams (bottom conduits) and lateral streams at the hydraulic grade line (gradient conduits) can coexist. Time-dependent flow, local topography, ice motion, and sediment load are not accounted for in the theory, although they may strongly influence the actual course of the water. Computations have been carried out for the Gornergletscher where the bed topography is known and where some data are available on subglacial water pressure.
Article
Near-surface seismic data are a challenge to the processing geophysicist who is familiar only with handling seismic data for target depths larger than 200 to 400 m. Residual static-correction techniques and migration procedures are used routinely for processing deeper data and can destroy data quality in the near surface. Near-surface seismic presents unique problems in processing because it usually is of suboptimal quality and often is recorded in an environment characterized by complex geologic structures. In a presentation of three case histories, one shows less severe consequences, and the other two portray disastrous consequences caused by static corrections and migration not being applied correctly. Graphical examples document the limitations of the residual statics and migration procedures. However, the method of hybrid seismic surveying is a positive and generally applicable solution when dealing with data from the shallow subsurface.