ArticlePublisher preview available

Tomographic Images of Magma Chambers Beneath the Avacha and Koryaksky Volcanoes in Kamchatka

DOI:10.1029/2019JB017952
Authors:
N. A. Bushenkova at A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS
N. A. Bushenkova
Ivan Koulakov
Ivan Koulakov
Ivan Koulakov
  • This person is not on ResearchGate, or hasn't claimed this research yet.
Sergey L. Senyukov at Kamchatka branch of the Geophysical Service of Russian Academy of Sciences
Sergey L. Senyukov
E. I. Gordeev at Institute Of Volcanology And Seismology
E. I. Gordeev
Show all 7 authorsHide
Read publisher preview
Download citation
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

A new tomographic model (Vp, Vs and Vp/Vs ratio) was built for two neighboring active volcanoes, Avacha and Koryaksky, which represent a serious hazard to the population and infrastructure of Petropavlovsk‐Kamchatsky, the main city of Kamchatka, Russia. Arrival times of seismic P‐ and S‐waves from almost 5,000 local events, recorded by a permanent network of seismic stations during 2009–2018, were used for tomography. The resolution of the derived models was carefully tested by a series of synthetic simulations. Prominent anomalies with extremely high Vp/Vs ratios (up to 2.4) were retrieved directly beneath both volcanoes and interpreted as magma reservoirs containing high degrees of partial melt and/or fluids. Beneath Avacha, the upper limit of the anomaly is located at the depth of ~2 km below the surface. The reservoir appears to be connected to the surface by a neck‐shaped anomaly of high Vp/Vs ratio associated with active seismicity, which is interpreted as a magma and fluid conduit. Beneath Koryaksky, the magma related anomaly is deeper: its upper limit is located at a depth of ~ 7 km below the surface. This anomaly is connected with the volcanic cone, and is associated with a vertical seismicity cluster, which possibly marks the pathway of fluid ascent and degassing. Between the volcanoes, a 2–3 km thick layer of very low Vp and Vs is interpreted as deposits of volcanoclastic sediments. Generally low Vp/Vs ratios in the area between the volcanoes show that the magma reservoirs in the upper crust are not interconnected.
Topography in the area of the Avacha group. Triangles indicate the stations of the permanent seismic network. Dotted lines highlight the major patterns discussed in the text. Inset shows the Kamchatka Peninsula; brown rectangle indicates the location of the study area. Red dots mark the Holocene volcanoes.
Topography in the area of the Avacha group. Triangles indicate the stations of the permanent seismic network. Dotted lines highlight the major patterns discussed in the text. Inset shows the Kamchatka Peninsula; brown rectangle indicates the location of the study area. Red dots mark the Holocene volcanoes.
… 
Locations of seismic events in the area of the Avacha group in map view (upper plot) and in three vertical sections (lower plots). In the map, the colors of dots represent focal depths (H).
Locations of seismic events in the area of the Avacha group in map view (upper plot) and in three vertical sections (lower plots). In the map, the colors of dots represent focal depths (H).
… 
Results of the dVp, dVs, and Vp/Vs ratio recovery for the checkerboard model with alternating anomalies of 4‐km lateral size, without changes in depth. Dotted lines indicate the contours of the synthetic anomalies. Thin lines depict relief contours with a step of 500 m.
Results of the dVp, dVs, and Vp/Vs ratio recovery for the checkerboard model with alternating anomalies of 4‐km lateral size, without changes in depth. Dotted lines indicate the contours of the synthetic anomalies. Thin lines depict relief contours with a step of 500 m.
… 
Source locations in the same synthetic checkerboard model as shown in Figure 3. Red dots depict modeled locations, and the ends of the black lines indicate the true locations. The locations are shown in map view (left column) and vertical section 1, as shown in Figure 2 (right column). The location results correspond to the initial 1‐D model, and the final 3‐D velocity distributions are presented in the upper and lower rows, respectively. The corresponding source misfits are 1.49 and 0.60 km. Thin lines depict relief contours with a step of 500 m. Yellow triangles depict the seismic stations. Insets in vertical sections show the histograms of source mislocations after the first and third iterations.
Source locations in the same synthetic checkerboard model as shown in Figure 3. Red dots depict modeled locations, and the ends of the black lines indicate the true locations. The locations are shown in map view (left column) and vertical section 1, as shown in Figure 2 (right column). The location results correspond to the initial 1‐D model, and the final 3‐D velocity distributions are presented in the upper and lower rows, respectively. The corresponding source misfits are 1.49 and 0.60 km. Thin lines depict relief contours with a step of 500 m. Yellow triangles depict the seismic stations. Insets in vertical sections show the histograms of source mislocations after the first and third iterations.
… 
Synthetic test with free‐shaped anomalies defined in the horizontal projection. The left two columns show the initial synthetic anomalies of dVp and dVs at 0 and 4 km bsl. The right two columns are the recovery results for dVp, dVs, and Vp/Vs ratio at the same depths. Dotted lines indicate the contours of the synthetic anomalies. Thin lines depict relief contours with a step of 500 m.
+7
Synthetic test with free‐shaped anomalies defined in the horizontal projection. The left two columns show the initial synthetic anomalies of dVp and dVs at 0 and 4 km bsl. The right two columns are the recovery results for dVp, dVs, and Vp/Vs ratio at the same depths. Dotted lines indicate the contours of the synthetic anomalies. Thin lines depict relief contours with a step of 500 m.
… 
Figures - available from: Journal of Geophysical Research: Solid Earth
This content is subject to copyright. Terms and conditions apply.
  • A preview of this full-text is provided by Wiley.
  • Learn more
Preview content only
Content available from Journal of Geophysical Research: Solid Earth
This content is subject to copyright. Terms and conditions apply.
Tomographic Images of Magma Chambers Beneath
the Avacha and Koryaksky Volcanoes in Kamchatka
Natalia Bushenkova
1,2
, Ivan Koulakov
1,2
, Sergey Senyukov
3
, Evgeny I. Gordeev
4
,
Hsin‐Hua Huang
5
, Sami El Khrepy
6,7
, and Nassir Al Arifi
6
1
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia,
2
Novosibirsk State University,
Novosibirsk, Russia,
3
Kamchatkan Branch of Geophysical Survey RAS, Petropavlovsk‐Kamchatsky, Russia,
4
Institute of
Volcanology and Seismology FEB RAS, Petropavlovsk‐Kamchatsky, Russia,
5
Institute of Earth Sciences, Academia Sinica,
Taipei, Taiwan,
6
King Saud University, Riyadh, Saudi Arabia,
7
National Research Institute of Astronomy and Geophysics,
Helwan, Egypt
Abstract A new tomographic model (Vp, Vs, and Vp/Vs ratio) was built for two neighboring active
volcanoes, Avacha and Koryaksky, which represent a serious hazard to the population and infrastructure
of Petropavlovsk‐Kamchatsky, the main city of Kamchatka, Russia. Arrival times of seismic Pand Swaves
from almost 5,000 local events, recorded by a permanent network of seismic stations during 2009–2018,
were used for tomography. The resolution of the derived models was carefully tested by a series of synthetic
simulations. Prominent anomalies with extremely high Vp/Vs ratios (up to 2.4) were retrieved directly
beneath both volcanoes and interpreted as magma reservoirs containing high degrees of partial melt and/or
fluids. Beneath Avacha, the upper limit of the anomaly is located at the depth of ~2 km below the surface.
The reservoir appears to be connected to the surface by a neck‐shaped anomaly of high Vp/Vs ratio
associated with active seismicity, which is interpreted as a magma and fluid conduit. Beneath Koryaksky,
the magma related anomaly is deeper: Its upper limit is located at a depth of ~7 km below the surface. This
anomaly is connected with the volcanic cone and is associated with a vertical seismicity cluster, which
possibly marks the pathway of fluid ascent and degassing. Between the volcanoes, a 2‐to 3‐km thick layer of
very low Vp and Vs is interpreted as deposits of volcanoclastic sediments. Generally low Vp/Vs ratios in
the area between the volcanoes show that the magma reservoirs in the upper crust are not interconnected.
1. Introduction
Avacha and Koryaksky are called “home volcanoes”for Petropavlovsk‐Kamchatsky, the main city of
Kamchatka (~200,000 inhabitants) and are the main attraction for the local population and numerous tour-
ists. However, being located at a distance of 25–30 km from populated areas, these volcanoes represent a ser-
ious potential hazard for the city. Petropavlovsk‐Kamchatsky was built on pyroclastic flows ejected by a
catastrophic explosion, which occurred approximately 30,000 years ago (Melekestsev et al., 1992). A repeat
eruption of similar magnitude may be devastating for the city. More information about the geological evolu-
tion and eruption activity of volcanoes of the Avacha group is given in section 2.
The Avacha volcano is relatively well studied compared to the other volcanoes of Kamchatka, thanks to its
close location to the city and relatively simple access, as well as the high motivation of the local authorities to
forecast possible volcanic catastrophes that may affect Petropavlovsk‐Kamchatsky. For example, in the
library depositary of the Institute of Volcanology and Seismology in Kamchatka, there are more than 200
scientific papers (mostly in Russian) containing multidisciplinary scientific investigations on the Avacha
and Koryaksky volcanoes. Geophysical studies have been actively performed in the Avacha group area for
more than 50 years. The first geophysical evidence for the presence of a magma chamber beneath Avacha
was obtained by detailed on‐land gravity measurements in 1960–1962 (Steinberg & Zubin, 1963). That study
estimated the upper boundary of the chamber to be at a depth of 1.5–2 km below sea level (bsl). Later,
Masurenkov (1970) took into account realistic density values of Avacha's magmatic rocks and corrected
the parameters of the magma source. Gravity measurements for a larger area around the Avacha group were
merged by Zubin and Kozyrev (1988) and used to construct a density model of the upper crust in this region.
The summits of the Avacha and Koryaksky volcanoes were associated with a gravity high. To the southwest
of the Avacha volcano, they identified a prominent low‐gravity anomaly that was interpreted as a trace of a
magma reservoir shifted with respect to the main cone. More than 1,000 data points from magnetotelluric
©2019. American Geophysical Union.
All Rights Reserved.
RESEARCH ARTICLE
10.1029/2019JB017952
Key Points:
•The 3‐D seismic modeling shows the
structure of the plumbing systems
beneath the Avacha and Koryaksky
volcanoes
•Beneath Avacha, a high Vp/Vs
conduit connects a 2‐km‐deep
magma chamber to the crater
•Beneath Koryaksky, the top of the
magma chamber is visible at a depth
of 7 km below the surface
Correspondence to:
I. Koulakov,
koulakoviy@ipgg.sbras.ru
Received 30 APR 2019
Accepted 16 AUG 2019
Accepted article online 23 AUG 2019
BUSHENKOVA ET AL. 9694
Published online 10 SEP 2019
Citation:
Bushenkova, N., Koulakov, I.,
Senyukov, S., Gordeev, E. I., Huang,
H.‐H., El Khrepy, S., & Al Arifi, N.
(2019). Tomographic images of magma
chambers beneath the Avacha and
Koryaksky volcanoes in Kamchatka.
Journal of Geophysical Research: Solid
Earth,124, 9694–9713. https://doi.org/
10.1029/2019JB017952
... These condensates may form brines that migrate towards the surface along fracture networks, explaining extensive fumarolic activity at the surface (Hudson et al., 2022;MacQueen et al., 2021). Alternatively, high V P /V S anomalies have been attributed to the penetration of meteoric water into the volcanic cone through existing fractures (Bushenkova et al., 2019;Koulakov et al., 2021). ...
... Many seismic tomography studies have been undertaken at a wide variety of volcanoes (e.g. Lees, 1992;Aloisi et al., 2002;Patane et al., 2002;Londoño & Sudo, 2003;Molina et al., 2005;Vanorio et al., 2005;Lin et al., 2014;Greenfield et al., 2016;Vargas et al., 2017;Bushenkova et al., 2019;Koulakov et al., 2020;Ulberg et al., 2020;Wilks et al., 2020). The seismic tomography images produced by these studies show some similarities but often the crustal substructure and its interpretation varies considerably from volcano to volcano. ...
... Koryaksky volcano in Kamchatka erupted months before the seismic events used in the tomographic study of Bushenkova et al. (2019) were recorded. Despite the different tectonic setting, the tomographic images show a similar structure to Nabro. ...
View
... In this study, we construct a new seismic velocity model based on a considerably enlarged data set and using another tomography code LOTOS (Koulakov, 2009a), which previously demonstrated its efficiency for studying different volcanic systems in the world (Bushenkova et al., 2019;Kasatkina et al., 2014;Koulakov et al., 2013). Here, we will pay special attention to showing the distributions of the Vp/Vs ratio, which is presumed the most sensitive seismic attribute to the presence of partially molten and fluid saturated magma. ...
... Below the cones A and D, we observe locally high P-wave velocity patterns (indicated by "1" and "2"), which give the inverse correlation of dVp and dVs and high values of Vp/Vs ratio. Such a relationship is a clear attribute of the presence of the magma with some content of partial melts and fluid saturation (Takei, 2002), which is normally observed in tomography models for most active volcanoes (Bushenkova et al., 2019;Kasatkina et al., 2014;Koulakov et al., 2013). ...
... The P-wave velocity is primarily sensitive to the composition, whereas the variation of the S-wave veloc-ity is mostly controlled by the presence of a liquid phase. The coexistence of higher P-and lower S-wave velocity, and the corresponding very high values of Vp/Vs ratio is a rather typical feature observed beneath many active volcanoes and interpreted as magma reservoirs or conduits (Bushenkova et al., 2019;Koulakov et al., 2013Koulakov et al., , 2020Koulakov et al., , 2021. Indeed, the intruded magma has a different composition compared to the host crustal rocks, which determines the higher Vp. ...
Multiple Magma Sources Beneath the Okmok Caldera as Inferred From Local Earthquake Tomography
Article
Full-text available
  • Oct 2022
Okmok volcano located on the northeastern part of the Umnak Island is one of the most active volcanoes in the Aleutian Arc. It was initially built as a large shield volcano, but 12,000 and 2,050 years ago, it experienced two caldera‐forming eruptions that destroyed the central part of the volcano. The post‐caldera eruptions have occurred mostly along the inner perimeter of the caldera from cinder and tuff cones. Here, we use the local earthquake data of the Alaska Volcano Observatory (AVO) in the time period from 2003 to 2017 to build a model with the 3D distributions of the P and S wave velocities and Vp/Vs ratio. At depths of more than 10 km, we observe a vertically aligned anomaly of high Vp/Vs ratio interpreted as a long‐lived conduit likely responsible for the volcano evolution since its origin. Above this conduit, we reveal a large anomaly of high Vp/Vs ratio representing the main magma reservoir that is connected with several shallow anomalies located below the centers of recent eruptions in the caldera. One of such anomalies represents a large shallow reservoir below the Cone A, which was the source of most of Okmok's historical eruptions. The most recent eruption occurred in 2008 and was fed by a magma diapir that was initially formed in the central magma reservoir and then slowly ascended through a ductile silica rich layer at depths from 6 to 2 km. This interpretation is consistent with the petrology studies and modeling of ground deformations.
View
... These tests have shown that the uncertainties related to the damping definition and the trade-off between the source and velocity parameter determinations do not allow us to provide exact numerical values for the seismic parameters; therefore, we cannot uniquely convert our model into petrological properties. Nevertheless, our resulting images look similar to those of a number of models that were constructed for a variety of onshore active volcanoes, where the magmas and geothermal sources were investigated independently by using different approaches [24][25][26] . Based on these resemblances, our tomographic model reveals some structures that are likely associated with the volcano plumbing system and tectonic processes that are present along the spreading center. ...
... The striking feature of the Vp and Vs anomaly distributions is their nearly perfect inverse correlation, which is a typical relationship that is observed in many active magmatic systems 24,25 . Indeed, P-wave velocities are more sensitive to rock compositions and are normally higher in magmas arriving from the mantle than in crustal rocks 25 . ...
... The striking feature of the Vp and Vs anomaly distributions is their nearly perfect inverse correlation, which is a typical relationship that is observed in many active magmatic systems 24,25 . Indeed, P-wave velocities are more sensitive to rock compositions and are normally higher in magmas arriving from the mantle than in crustal rocks 25 . On the other hand, the S-wave velocities are mostly affected by the presence of liquid phases (e.g., melts and fluids) and are usually lower in active magma sources that contain partially molten materials and dissolved fluids. ...
Low-degree mantle melting controls the deep seismicity and explosive volcanism of the Gakkel Ridge
Article
Full-text available
  • Jun 2022
The world’s strongest known spreading-related seismicity swarm occurred in 1999 in a segment of the Gakkel Ridge located at 85°E as a consequence of an effusive-explosive submarine volcanic eruption. The data of a seismic network deployed on ice floes were used to locate hundreds of local earthquakes down to ∼25 km depth and to build a seismic tomography model under the volcanic area. Here we show the seismicity and the distribution of seismic velocities together with the 3D magmatic-thermomechanical numerical model, which demonstrate how a magma reservoir under the Gakkel Ridge may form, rise and trigger volcanic eruptions in the rift valley. The ultraslow spreading rates with low mantle potential temperatures appear to be a critical factor in the production of volatile-rich, low-degree mantle melts that are focused toward the magma reservoirs within narrow magmatic sections. The degassing of these melts is the main cause of the explosive submarine eruptions.
View
... Furthermore, the active-source survey could only provide P-wave data. As shown by many seismic studies of volcanoes (e.g., Bushenkova et al., 2019;Koulakov et al., 2021;Vargas et al., 2017), joint interpretation of P-and S-wave velocities can give much richer information to interpret tomography results in terms of melt and fluid distributions. ...
... The tomographic inversion was performed using the LOTOS code for passive-source body-wave tomography (Koulakov, 2009). This code has been implemented in a large number of studies and is particularly suitable for studying volcanoes (e.g., Bushenkova et al., 2019;García-Yeguas et al., 2014;Koulakov et al., 2020Koulakov et al., , 2021. One of the most recent examples is La Palma, another island of the Canary Islands archipelago, for which the tomography model inferred the structure of the magma source during an ongoing eruption in 2021 (D'Auria et al., 2022). ...
Local Earthquake Seismic Tomography Reveals the Link Between Crustal Structure and Volcanism in Tenerife (Canary Islands)
Article
Full-text available
  • Mar 2023
Volcanic activity on Tenerife Island is extremely diverse. Three radial rift zones are characterized by cinder cones from basaltic fissure eruptions. A triple junction in central Tenerife exhibits a complex of merged, predominantly phonolitic, stratovolcanoes. The Las Cañadas caldera and widespread ignimbrite deposits reveal high explosive potential. We investigated the crustal and upper mantle structure beneath Tenerife using local earthquake data recorded by two dense seismic networks on the island. For our tomographic inversion, we selected >130,000 P‐ and S‐wave arrivals from ∼6,300 events that occurred during seismic unrests in 2004–2005 and 2017–2021. Synthetic tests confirmed that we could robustly resolve seismic velocity structures to ∼20 km depth. In the upper crust (down to ∼7 km) beneath central Tenerife, a prominent high‐velocity anomaly represents the rigid core of the volcanic complex; at greater depths, a strong low‐velocity anomaly reveals abrupt crustal thickening. Vp and Vs contour lines of 5.2 and 2.85 km/s, respectively, reveal Moho depth variation; crustal thickness beneath Las Cañadas reaches ∼17 km, whereas that beneath other parts of Tenerife is ∼10 km. An anomaly at ∼5 km beneath the caldera with low Vp, low Vs, and high Vp/Vs might be associated with a major phonolitic magma reservoir. Similar anomalies at ∼ sea level may represent shallow magma sources responsible for recent eruptions. Seismicity occurs in a columnar area of high Vp, high Vs, and low Vp/Vs, and may represent hydrothermal fluid migration through brittle media. Based on our results, we constructed a conceptual model of volcanic activity on Tenerife.
View
... The derived dVp, dVs, and, especially, Vp/Vs-ratio anomalies provided important information about the magma plumbing processes beneath the Semisopochnoi Island volcanoes. Based on experimental studies 29 and several previous tomographic studies of other volcanoes [8][9][10][11]25,30,31 , some common relationships between seismic parameters and rock properties can be proposed. For example, P-wave velocity is mostly sensitive to rock composition, whereas S-wave velocity is mostly affected by the presence of a liquid phase (e.g., melt and volatiles). ...
... Here, the Vp and Vs anomalies generally look inversely correlated. The positive Vp anomaly inside the caldera coexists with the strong negative Vs anomaly, which causes a very high Vp/Vs ratio, exceeding 2. These patterns are typical attributes of magma storage areas observed below many active volcanoes 25,30,31 . In all the vertical sections shown in Fig. 7, this anomaly is located between 3 and 5 km www.nature.com/scientificreports/ ...
Structure of the magma plumbing system beneath Semisopochnoi Island (Aleutian Arc) inferred from seismic tomography
Article
Full-text available
  • Jun 2022
Semisopochnoi Island is a remote and little-studied volcanic island in the western part of the Aleutian Arc. The existence of several active volcanic centers and a 5000–7000-year-old large caldera makes this island an important site for volcanic hazard assessment in the Northern Pacific. Based on local seismicity data recorded by six permanent seismic stations, we created the seismic tomography model, including the 3D distributions of Vp, Vs, and Vp/Vs ratios to a depth of 10 km. This model provides the first geophysical insight into the interior structure of Semisopochnoi Island and sheds light on the processes in the magma plumbing system beneath all volcanic centers on the island. At depths of 5–10 km, we observed a columnar-shaped high Vp/Vs-ratio anomaly below the caldera in the central part of the island, which likely represents the steady magma conduit. This conduit is headed by a prominent high Vp/Vs-ratio anomaly located 3–5 km directly below the caldera, which represents the magma reservoir feeding Cerberus and other Holocene-aged volcanic centers on Semisopochnoi Island.
View
... The low number of stations used in the current study compared to most other tomography studies may have resulted in the poor source locations and the low quality of the tomographic images. However, other studies with similar station con gurations have provided fair-quality results, such as eight stations on Avacha volcano [25] , eight stations on Nevado del Huila [26] , and four stations on Udina [27] . All of these studies underwent subsequent extensive testing that proved the reliability of the models. ...
... Here, the Vp and Vs anomalies generally look inversely correlated. The positive Vp anomaly inside the caldera coexists with the strong negative Vs anomaly, which causes a very high Vp/Vs ratio, exceeding 2. These patterns are typical attributes of magma storage areas observed below many active volcanoes [25,33,34] . In all the vertical sections shown in Fig. 7, this anomaly is located between 3 and 5 km deep. ...
Structure of the magma plumbing system beneath Semisopochnoi Island (Aleutian Arc) inferred from seismic tomography
Preprint
Full-text available
  • Apr 2022
Semisopochnoi Island is a remote and little-studied volcanic island in the western part of the Aleutian Arc. The existence of several active volcanic centers and a 5,000–6,900-year-old large caldera makes this island an important site for volcanic hazard assessment in the Northern Pacific. Based on local seismicity data recorded by six permanent seismic stations, we created the seismic tomography model, including the 3D distributions of Vp , Vs , and Vp/Vs ratios to a depth of 10 km. This model provides the first geophysical insight into the interior structure of Semisopochnoi Island and sheds light on the processes in the magma plumbing system beneath all volcanic centers on the island. At depths of 5–10 km, we observed a columnar-shaped high Vp/Vs -ratio anomaly below the caldera in the central part of the island, which likely represents the steady magma conduit. This conduit is headed by a prominent high Vp/Vs -ratio anomaly located 3–5 km directly below the caldera, which represents the magma reservoir feeding Cerberus and other Holocene-aged volcanic centers on Semisopochnoi Island.
View
... Numerous seismic tomography studies of volcanic regions have identified shallow low-velocity structures that are interpreted as highly fractured, unconsolidated, and/or hydrothermally altered volcanic materials, including those for Deception Island volcano [11][12][13] , Avacha group volcanoes 14 and Mt. Etna 15,16 . ...
Rapid magma ascent beneath La Palma revealed by seismic tomography
Article
Full-text available
  • Oct 2022
For the first time, we obtained high-resolution images of Earth's interior of the La Palma volcanic eruption that occurred in 2021 derived during the eruptive process. We present evidence of a rapid magmatic rise from the base of the oceanic crust under the island to produce an eruption that was active for 85 days. This eruption is interpreted as a very accelerated and energetic process. We used data from 11,349 earthquakes to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to 10 km depth and; (3) a large sub-crustal magma-filled rock volume intrusion extending from 7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously. Prior to eruption onset, magma ascended from 10 km depth to the surface in less than 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material.
View
View
View
View
Local Earthquake Tomography of the Nevado del Huila Volcanic Complex (Colombia): Magmatic and Tectonic Interactions in a Volcanic-Glacier Complex System
Article
Full-text available
  • Feb 2019
Nevado del Huila is an active volcano in Colombia having high explosive potential and serious hazard for surrounding population. Here we present the first 3‐D seismic velocity model of the Nevado del Huila Volcanic Complex based on local earthquake tomography. We used 13,790 events with the corresponding 49,412 P wave and 47,972 S wave arrival times recorded by the Volcanological and Seismological Observatory of Popayán (Colombia). The period of observations from 2007 to 2016 covers stages of eruptions (first registered to date) and repose of the volcano. The seismic structure reveals two prominent nearly vertical anomalies with high Vp/Vs ratio that are interpreted as conduits connecting the volcano structures with a deeper seated magma reservoir. The anomaly beneath the southern flank of the volcano is limited by the Calambayú Fault and coincides with the dense seismicity cluster. We interpret this anomaly as the pathway of fluids following the weakened rocks along the fault zone. Another anomaly located beneath the main summit of Nevado del Huila probably represents the magma conduit that fed the previous eruption of this volcano. The seismicity here is not as intensive as that beneath the southern flank, which is possibly caused by higher temperature and ductile properties of rocks in the conduit. At depths from 2 to 4 km below surface, we observe the limit between higher Vp/Vs below and lower Vp/Vs above that possibly represents the level of fluid degassing due to decompression.
View
Causes of volcanic unrest at Mt. Spurr in 2004–2005 inferred from repeated tomography
Article
Full-text available
  • Nov 2018
Abstract Mt. Spurr is the largest active volcano in Alaska of high explosive potential. The most recent activity, including two recent magmatic eruptions in 1953 and 1992, has occurred via the flanking Crater Peak. From 2004 to 2006, strong seismicity, gas flux, and heating were observed in the summit area, which had remained inactive for more than 5 Ka. To understand the cause of this reactivation, we performed repeated tomography inversions that clearly imaged the magma reservoir beneath Mt. Spurr and showed temporal changes in its shape and intensity. During the two years preceding the unrest, we observed ascension of the upper limit of the reservoir-related anomaly from a depth of 5 to 3 km below the surface, accompanied by strong seismicity. During the following years, the shape of the anomaly remained unchanged, but its intensity weakened. These observations may indicate the release of fluids from the ductile reservoir and fast upward ascent through the brittle cover that caused intensive seismicity and gas flux during the unrest from 2004 to 2006. The origin of this zone will possibly cause a resumption of explosive eruptions in the summit area of Mt. Spurr.
View
Collisional Processes in the Crust of the Northern Tien Shan Inferred From Velocity and Attenuation Tomography Studies
Article
Full-text available
  • Feb 2018
Based on seismic data from existing seismic networks in Kyrgyzstan, we have constructed new crustal models of seismic velocity and attenuation for P- and S-waves beneath the Kyrgyz Tien Shan. With data from more than 6,000 events recorded by the international KNET network, the most detailed structures were detected in the central-northern part of the study region, where the Kazakh Shield collides with the northern Tien Shan. The independently computed 3D distributions of P- and S-wave attenuation show features that are consistent with the main structural elements. The high-attenuation areas correspond to folded areas of the northern Tien Shan, whereas the partitions of the stable Kazakh Shield and the Issyk Kul block match with the low-attenuation areas. The velocity model reveals some structures that help to determine the details of the collision processes in the northern Tien Shan. In the upper crust, we observe the alternation of several higher- and lower-velocity anomalies that likely represent the interaction of brittle and ductile crustal layers of the collided Kazakh and Tien Shan plates. In deeper sections, both P- and S-wave velocity models show a prominent low-velocity anomaly just beneath the northern boundary of Tien Shan. We propose that this anomaly represents an anomalous crustal thickening at the point of underthrusting of the Kazakh Plate beneath Tien Shan.
View
Structure of Volatile Conduits beneath Gorely Volcano (Kamchatka) Revealed by Local Earthquake Tomography
Article
Full-text available
  • Nov 2017
Gorely is an active volcano located 75 km from Petropavlovsk-Kamchatsky, Kamchatka. In 2010–2015, it exhibited strong activity expressed by anomalously high gas emission. In 2013–2014, we deployed a temporary network consisting of 20 temporary seismic stations that operated for one year. We selected 333 events with 1613 P-wave and 2421 S-wave arrival times to build the first tomographic model of this volcano. The seismic model was carefully verified using a series of synthetic tests. Our tomographic model provides a mechanism for volatile feeding of Gorely. An unexpected feature of the model was low Vp/Vs ratios; below 1.4 in some parts. One reason for such low Vp/Vs ratios is gas contamination due to magma degassing. In the central part of the model, directly underneath the Gorely crater, we observe a 2.5 km wide and 1.5 km thick seismic anomaly with a very high Vp/Vs ratio of up to 2. This may represent a magma reservoir with a high melt and/or volatile content. The upper limit of this anomaly, 2.5 km below the surface, may indicate the degassing level, which coincides with the most intense seismicity. Below this reservoir, we observe another columnar high Vp/Vs ratio anomaly. This can be interpreted as a conduit bringing magma and fluids from deeper sources.
View
TEMPERATURE AND GAS COMPOSITION OF THE AVACHINSKY VOLCANO FUMAROLES (KAMCHATKA) IN 2013−2016
Article
Full-text available
  • Jan 2017
The article presents data on Avachinsky Volcano fumaroles' temperature and gas composition obtained during the 2013-2016 observations and shows temperature dynamics over this period of the high-temperature Western fumarole and Eastern fumarolic field assigned to the fissure appeared in lava «plug» as a result of the weak explosive eruption in autumn 2001. Temperature of 818°С was registered in the Western fumarole to be the highest ever measured at Avachinsky Volcano. Gas composition of the monitored fumarole on Eastern field and its variation in time were studied. We compared the obtained data with the previous data on gas observations from Avachinsky Volcano and other active volcanoes in Kamchatka and the data on the average values from the volcanoes of the subduction zones.
View
Three different types of plumbing system beneath the neighboring active volcanoes of Tolbachik, Bezymianny, and Klyuchevskoy in Kamchatka: KLYUCHEVSKOY VOLCANO GROUP TOMOGRAPHY
Article
Full-text available
  • Apr 2017
The Klyuchevskoy group of volcanoes (KGV) in Kamchatka includes three presently active volcanoes (Klyuchevskoy, Bezymianny and Tolbachik) located close together in an area of approximately 50 × 80 km. These three volcanoes have completely different compositions and eruption styles from each other. We have analyzed new data recorded by a temporary seismic network consisting of 22 seismic stations operated within the area of Tolbachik in 2014–2015 in conjunction with the data from the permanent network and the temporary PIRE network deployed at the Bezymianny volcano in 2009. The arrival times of the P and S waves were inverted using a local earthquake tomography algorithm to derive 3D seismic models of the crust beneath the KGV as well as accurate seismicity locations. High-resolution structures beneath the Tolbachik volcanic complex were identified for the first time in this study. The tomography results reveal three different types of feeding systems for the main KGV volcanoes. The basaltic lavas of the Klyuchevskoy volcano are supplied directly from a reservoir at a depth of 25–30 km through a nearly vertical pipe-shaped conduit. The explosive Bezymianny volcano is fed through a dispersed system of crustal reservoirs where lighter felsic material separates from the mafic component and ascends to the upper crust to form andesitic magma sources. For Tolbachik, low-viscosity volatile-saturated basalts ascend from two deep reservoirs following a system of fractures in the crust associated with the intersections of regional faults.
View
Unrest of the Udina volcano in Kamchatka inferred from the analysis of seismicity and seismic tomography
Article
The Udina complex, consisting of two stratovolcanoes—Bolshaya and Malaya Udinas—is located at the southeastern edge of the Klyuchevskoy volcano group (KGV) in Kamchatka. Prior to 2017, it was considered to be extinct; however, since late 2017, continuing seismic activity beneath Bolshaya Udina has been recorded, which may indicate the possible awakening of this volcano complex. To perform a detailed investigation of this seismic process, we installed four temporary seismic stations in the vicinity of the Udinas0 volcanoes and operated them for two months—from May to July 2018. Using the data obtained from this network, we detected and localized 559 local events in the area of the Udina volcanoes. Furthermore, we performed a tomographic inversion to improve the locations of the sources. The tomography unexpectedly resulted in a stable model, which was carefully verified via a series of different tests. We found that the seismicity formed an elliptical cluster oriented in the north-northeast–south-southwest direction. Beneath the volcano, the seismicity occurred at depths of greater than 5 km from the surface. In the tomography model, we observed an anomaly of a high Vp, low Vs, and high Vp/Vs ratio located directly beneath Bolshaya Udina. These seismic properties may indicate the presence of magma intrusions with a high content of melts and fluids, which may justify changing the current status of this volcano from “extinct” to “active.” We also observed that the seismicity cluster connects Bolshaya Udina with the Tolud zone, where continuous seismicity has been observed at depths of approximately 10–20 km in previous years. This zone is considered to be a magma storage in the lower crust that contributed to feeding the fissure eruptions in the Tolbachinsky Dol. Based on the results of this study, we conclude that during 2018, the Tolud magma source appeared to have built another pathway to Bolshaya Udina.
View
Evolution of the Magma Conduit Beneath the Galeras Volcano Inferred From Repeated Seismic Tomography
Article
  • Jul 2018
The Colombian volcano Galeras is one of the most active volcanoes in the world, and it has an andesitic composition and high explosive potential. We consider the period of 1989–2015, in which the volcano manifested frequent eruptions and high seismic activity. To study the temporal variations in the seismic structure beneath Galeras, we implemented an algorithm of repeated tomography using selected data sets with similar geometries. We obtained the variations in the seismic velocity structures beneath Galeras during the three time episodes of 1989–2000, 2001–2007, and 2008–2015. In the second episode, we observe a columnar anomaly with a high V p/V s ratio that possibly represents a conduit transporting a new portion of magma material from below. This result may indicate that in this period, which culminated with dome emplacement and collapse, the volcano was directly fed from deeper magma sources. In other episodes, the conduit is less visible in the tomography models, and we propose that the volcanic activity was merely controlled by shallow magma reservoirs at 2–4 km below the surface.
View
View
Ages of active volcanoes in the Kuril-Kamchatka region
Article
  • Jan 1995
The births (ages) of most of the active volcanoes, calderas, and large craters produced by caldera-resembling eruptions (subcaldera craters) were dated as a result of geological, geomorphological, tephrochronological, and isotopic studies. The dated active volcanoes were found to be fairly young formations, the age of the oldest being 40-50 thousand years. Most of the presently highly active volcanoes had been born at the very end of the late Pleistocene or during the Holocene. Carbon-14 ages were determined for the majority of the Holocene volcanoes. The periods of time when Holocene volcanoes had been synchronously active were 7500-7800 and 1300-1800 years ago. -from Journal summary
View