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The seismic activities and hazards in People’s Democratic Republic Laos were analyzed using the most up-to-date seismicity data. Both the a- and b-values of the frequency-magnitude distribution model, including the return period of earthquake magnitude in the range of 5.0 - 6.0 Mw, were evaluated spatially in a region that ex­tends 300 km from Laos. Six seismic source zones with different seismic activities were found. Based on these seismic source zones and a suitable attenuation model, seismic hazards were then analyzed in both deterministic and probabilistic scenarios. The deterministic map showed a possible maximum ground shaking up to 0.4 g in Northern Laos, whereas the ground shaking calculated from the probabilistic ap­proach was < 0.32 g for 2% probability of exceedance in the next 50 yr. The prob­ability of exceedance of an earthquake with a Modified Mercalli intensity scale of level IV - V, VI and VII in Laos in the next 50 yr was > 90, 70 - 90, and 20 - 40%, respectively, and was higher in the northern part. From these seismic activities and hazard analyses, Laos can be clearly separated into the three hazard zones of north­western, northeastern and southern Laos with a high, medium and low earthquake hazard, respectively. Therefore, effective mitigation plans to reduce the impact of seismic hazards should be formulated and in particular for a number of major prov­inces located in the northern part of Laos.
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doi: 10.3319/TAO.2017.03.23.01
* Corresponding author
E-mail: Pailoplee.S@gmail.com
Analyses of seismic activities and hazards in Laos: A seismicity approach
Santi Pailoplee * and Punya Charusiri
Morphology of Earth Surface and Advanced Geohazards in Southeast Asia Research Unit (MESA RU), Department of Geology,
Faculty of Science, Chulalongkorn University, Bangkok, Thailand
ABSTRACT
The seismic activities and hazards in People’s Democratic Republic Laos were
analyzed using the most up-to-date seismicity data. Both the a- and b-values of the
frequency-magnitude distribution model, including the return period of earthquake
magnitude in the range of 5.0 - 6.0 Mw, were evaluated spatially in a region that ex-
tends 300 km from Laos. Six seismic source zones with different seismic activities
were found. Based on these seismic source zones and a suitable attenuation model,
seismic hazards were then analyzed in both deterministic and probabilistic scenarios.
The deterministic map showed a possible maximum ground shaking up to 0.4 g in
Northern Laos, whereas the ground shaking calculated from the probabilistic ap-
proach was < 0.32 g for 2% probability of exceedance in the next 50 yr. The prob-
ability of exceedance of an earthquake with a Modified Mercalli intensity scale of
level IV - V, VI and VII in Laos in the next 50 yr was > 90, 70 - 90, and 20 - 40%,
respectively, and was higher in the northern part. From these seismic activities and
hazard analyses, Laos can be clearly separated into the three hazard zones of north-
western, northeastern and southern Laos with a high, medium and low earthquake
hazard, respectively. Therefore, effective mitigation plans to reduce the impact of
seismic hazards should be formulated and in particular for a number of major prov-
inces located in the northern part of Laos.
Article history:
Received 31 August 2016
Revised 23 March 2017
Accepted 23 March 2017
Keywords:
Seismicity, Frequency-magnitude
distribution model, Seismic hazard
analysis, Laos
Citation:
Pailoplee, S. and P. Charusiri,
2017: Analyses of seismic activities
and hazards in Laos: A seismic-
ity approach. Terr. Atmos. Ocean.
Sci., 28, 843-853, doi: 10.3319/
TAO.2017.03.23.01
1. INTRODUCTION
Although People’s Democratic Republic Laos (hereaf-
ter called Laos) is far away from the major tectonic plate
boundary (the Sumatra-Andaman Subduction Zone), the
tectonic stress caused by the present-day Indian-Eurasian
plate collision influences areas within the plate (Vergnolle
et al. 2007). As a result, Laos and the adjacent areas are
dominated by some inland seismogenic fault zones, such as
the Dien Bien Phu (Zuchiewicz et al. 2004), Mae Ing (Fen-
ton et al. 2003), Nam Ma (Morley et al. 2007), and the Red
River (Duong and Feigl 1999) fault zones. Based mainly on
instrumental earthquake records, a number of shallow crust-
al earthquakes have been recorded in the vicinity of Laos,
and in particular in the northern part, during the last three
decades of 1980 - 2015 (Fig. 1). Among these earthquake
records, at least 17 large earthquakes with a Mw ≥ 6.0, plus
the three major earthquakes of the Mw-7.0 and Mw-7.7 in
1988 and the latest Mw-7.1 earthquake posed in 2011, have
been reported. Accordingly, Laos has experienced recent
hazardous earthquake ground shaking.
Up to the present, the only seismic hazard map of Laos
was a preliminary one developed by the United Nations
Office for Coordination of Humanitarian Affairs (OCHA;
http://ochaonline.un.org). This map, however, depicts the
severity of earthquakes in terms of the Modified Mercalli
Intensity (MMI) scale for a 250-yr return period. In order
to serve the infrastructure and utility advancements in Laos
according to the upcoming ASEAN Economics Community
(AEC), seismic hazard maps showing the ground shaking
distribution should be proposed, and so this was the main
aim of this study.
2. SEISMICITY DATA AND COMPLETENESS
Within seismic hazard analysis (SHA), seismogenic
faults are recognized as the major sources of earthquakes
and local paleoseismological evidence is required for the
determination of earthquake activities and in particular for
Terr. Atmos. Ocean. Sci., Vol. 28, No. 6, 843-853, December 2017
Santi Pailoplee & Punya Charusiri
844
the major-to-great earthquakes (Mw ≥ 7.0). However, ac-
cording to the lack of paleoseismological investigations in
Laos and the neighborhood areas, this SHA of Laos was
focused on the accessible seismicity data.
In order to consider effectively the seismicity affecting
to Laos, the earthquake data were collected in a region that
extends 300 km from Laos (Gupta 2002). In the vicinity of
Laos (latitude 10.8 - 25.7°N and longitude 96.7 - 111.0°E),
7540 earthquakes with a magnitude range of 1.0 - 7.7 have
been reported during 1964 - 2015 by (1) the International
Seismological Centre and (2) the US National Earthquake
Information Center. For this study, all the earthquakes re-
ported in the mb or Ms scales were converted directly to the
Mw scale using the relationships contributed empirically by
the available earthquake data (Figs. 2a and b). Meanwhile,
ML scale was converted to mb according to the relationship
in Fig. 2c. After that, the obtained mb was re-converted to
Mw scale using the relationship as shown in Fig. 2a. Thereaf-
ter, the dependent foreshocks and aftershocks were screened
for using the Gardner and Knopoff (1974)’s assumption and
deleted. As a result, 1906 main shocks, representing the
seismotectonic activities remained. The GENAS algorithm
(Habermann 1987) was used to check for man-made arti-
facts in the earthquake records, as reported previously (Wyss
1991; Zuniga and Wiemer 1999). According to the GENAS
algorithm, 1216 events of mainshocks with a Mw 3.3 re-
corded during 1980 - 2014 conformed to a linear cumulative
pattern (Fig. 2d), which implied that these data are complete
and meaningful for seismicity investigations, and so were
used as the complete dataset in this study.
3. SEISMMIC ACTIVITIES
Characterization of the seismic activities at a particular
region is commonly expressed in seismic hazard parameters.
Based on Kramer (1996), the three parameters that represent
the seismic activity and are considered in SHA are the maxi-
mum credible earthquake (MCE) and the frequency-magni-
tude distribution model (FMD) a- and b-coefficient values
(Gutenberg and Richter 1944), as expressed in Eq. (1);
()log NabM=-
(1)
where N is the number of earthquakes with magnitude M
generated per year. The a- and b-values are positive con-
stants that vary in both time and space windows.
From Eq. (1) and the plot of the complete earth-
quake data as the magnitude versus the cumulative number
(Fig. 2e), based on the entire-magnitude-range technique
(Woessner and Wiemer 2005), the straight line showing the
best regression fit indicated FMD a- and b-values of 4.38
and 0.75 ± 0.03, respectively. The magnitude of complete-
ness (Mc), which represents the recording capability of the
seismic network, was limited at Mw ≥ 4.2.
For spatial investigation of the FMD, the study area
was divided into 0.25° × 0.25° cells and earthquakes located
within a 200-km radius from each cell were plotted using the
Fig. 1. Map of mainland Southeast Asia showing the epicentral distributions of the completeness earthquake data (grey circles). Earthquakes with a
Mw6.0 and ≥ 7.0 are illustrated as blue circles and red stars, respectively. The red lines delineated in the maps are the seismogenic faults previously
proposed by Pailoplee et al. (2009). (1) Red River, (2) Nam Ma, (3) Mae Ing, and (4) Dien Bien Phu fault zones. (Color online only)
Seismic Activities and Hazards in Laos 845
ZMAP program (Wiemer 2001) as applied successfully by
a number of seismicity analysis (i.e., Gambino et al. 2014;
Meng and Peng 2014; Özmen et al. 2014). The FMD a- and
b-values were then estimated and mapped (Figs. 3a and b).
Due to the lack of earthquake data, the FMD plot at North-
eastern Thailand, Southern Laos, Vietnam and Cambodia
were not available.
Two regions showing prominent high a-values (3.0 -
5.0), were found at Northern Laos and the Vietnam-South-
ern China border (Fig. 3a), whereas the areas surrounding
Western Thailand and the Thailand-Laos border revealed
comparatively low a-values (0.5 - 1.0). Since the FMD
a-value implies seismically the entire rate of seismicity,
Northern Laos and the Vietnam-Southern China border area
was interpreted as a high seismic activity region (Fig. 3a).
The calculated FMD b-values ranged from 0.4 - 1.4
and showed a spatial distribution that was quite similar to
that for the FMD a-value (Fig. 3a). In contrast to the FMD
a-value, higher FMD b-values imply seismically a lower
chance of generating a large earthquake. Thus, the areas
conforming to high or low FMD a- and b-values are not
congruent and prevent a more exact determination of their
seismic hazard status. In order to clarify the earthquake ac-
tivities, the return period of Mw-5.0 and Mw-6.0 earthquakes
were estimated after weighting of both the a- and b-values
(Yadav et al. 2011; Figs. 3c and d).
For the return period of a Mw-5.0 earthquake, most of
the areas had a short recurrence interval of 0 - 10 yr, although
the northeastern part of the study area had a return period of
a Mw-5.0 earthquake in the range of 10 - 25 yr and up to 50 yr
in the eastern part of the Southern China (Fig. 3c).
For the return period of a Mw-6.0 earthquake, the differ-
ent hazardous zones were more clearly illustrated. The first
zone, with regionally high seismic activities, was the Myan-
mar-Southern China border with an estimated return period
of < 10 yr. The second area is a small stripe of moderate
seismic activity that delineates NE-SW along the northern
parts of Vietnam, Laos and Thailand and has a return period
of around 10 - 30 yr. The third area, with a low seismic ac-
tivity, was the eastern part of the Vietnam-Southern China
(a) (b)
(d)
(c)
(e)
Fig. 2. Relationship of the magnitude scales between (a) Mw-mb, (b) Mw-MS, and (c) mb-ML (d) Cumulative number of earthquakes with Mw ≥ 3.3 re-
corded during 1980 - 2014. (e) The FMD plot of the completeness earthquake data, where the straight line depicts the best fit of the earthquake data.
Santi Pailoplee & Punya Charusiri
846
(a) (b)
(c) (d)
(e)
Fig. 3. Maps showing the spatial distributions of the FMD (a) a-value and (b) b-value, and the return periods of earthquak es of (c) 5.0 Mw and (d)
6.0 Mw, respectively. (e) six potential seismic source zones (A - F) defined in this study. (Color online only)
Seismic Activities and Hazards in Laos 847
border with a return period of a Mw-6.0 earthquake of up to
40 yr (Fig. 3d).
4. SEISMIC SOURCE ZONATION AND
PARAMETERIZATION
In SHA, the theoretical identification of seismic source
zones needs a complete integration of the geological back-
ground, tectonic setting and paleoseismological evidence,
including the historical and instrumental earthquake records.
However, in practice this data cannot always be perfectly
compiled and this is the case here for Laos. Some models
of the seismic source zones within the study area have been
proposed previously (Nutalaya et al. 1985; Charusiri et al.
2005; Pailoplee and Choowong 2013), but these models
suggested that Laos and the adjacent areas were the same
seismic source. In order to gain more details in the SHA, in
this study the seismic source in Laos and the adjacent areas
were newly defined from the return period map of the Mw-
6.0 earthquake (Fig. 3d). As a result, six potential seismic
source zones (A - F) that represent different return periods
of 0 - 10, 10 - 20, 20 - 30, 30 - 40, 40 - 50, and > 50 yr, re-
spectively, were proposed (Fig. 3e and Table 1).
In order to provide the earthquake parameters needed
for the SHA, the completeness earthquake data located
within each defined seismic source zone were collected.
The bulk FMD was plotted and the a- and b-values were
evaluated for each seismic source (Fig. 4). Due to the lack of
paleoseismological data mentioned above, the MCE in each
source zone was alternatively estimated based on the maxi-
mum earthquake reported in the completeness earthquake
(a) (b) (c)
(d) (e) (f)
Fig. 4. The FMD plots of the six seismic source zones as illustrated in Fig. 3e.
Zone MCE FMD a-value FMD b-value Mc
A 7.7 3.91 0.71 4.2
B 7.1 3.96 0.73 4.3
C 6.5 3.58 0.75 4.0
D 6.8 2.46 0.55 3.4
E 6.8 2.94 0.75 3.8
F 6.8 3.34 0.74 3.8
Table 1. Seismic parameters representing the earth-
quake potential in each of six defined seismic source
zones (A - F).
Santi Pailoplee & Punya Charusiri
848
catalogue. The details of the seismic parameters evaluated
for the six seismic source zones are expressed in Table 1.
5. SEISMIC HAZARD ANALYSIS
In the SHA computation, the six areal seismic source
zones (section 4) and the territory of Laos were converted
equally to 0.25° × 0.25° grid points. The seismic param-
eters expressed in Table 1 were then utilized to evaluate the
earthquake potential of each seismic source zone. The strong
ground-motion attenuation models of Sadigh et al. (1997)
[Eq. (2)] were applied as suggested by Chintanapakdee et
al. (2008) for Thailand, including the neighborhood areas.
Accordingly, the SHA was based on two well-known sce-
narios of the deterministic and probabilistic seismic hazard
analyses, as detailed in sections 5.1 and 5.2, respectively.
() (8.5 )
()
()
ln
ln exp
ln
CCMC M
CR CCM
CR 2
PGA .
rup
rup
12 3
25
456
7
=+ +-
+++
++
6
@
(2)
According to Eq. (2), the peak horizontal ground accel-
eration is in (g) for the rock site condition, M means the mo-
ment magnitude, Rrup denotes the distance measured from
the earthquake source to the site of interest (km), and C1 - C7
are constants of the relationship (Sadigh et al. 1997). In case
of rock site condition, C3 = 0, C4 = -2.1, and C7 = 0. For M
6.5, C1 = -0.624, C2 = 1.0, C5 = 1.297, and C6 = 0.250 mean-
while for M > 6.5, C1 = -1.274, C2 = 1.1, C5 = -0.485, and C6
= 0.524. The standard deviation (σ) = 1.39 - 0.14 M.
5.1 Deterministic Seismic Hazard Analysis (DSHA)
Conceptually, the DSHA aims at finding the maximum
ground shaking as possible at a given site. This assumption
ensures that a structure can withstand the MCE, it will au-
tomatically withstand all other (i.e., smaller earthquakes)
as well. As a result, according to Krinitzsky (2003), each
obtained MCE (Table 1) was assumed to occur within the
seismic source zone at the shortest distance from the source
to the investigation site. Utilizing the applied attenuation
model as expressed in Eq. (2), the seismic hazards were es-
timated in terms of peak ground acceleration (PGA) without
regard to the likelihood of earthquake occurrence.
The obtained DSHA maps of Laos illustrate that the
distribution of PGA ranged from 0 - 0.4 g (Fig. 5). Usu-
ally, the high hazard levels are found in the northern part
where a number of seismogenic faults have been defined
(Pailoplee et al. 2009). Among the significant provinces of
Laos, Louang Namtha province was the most earthquake-
prone area with a calculated PGA of up to 0.4 g from the
DSHA. Meanwhile, for Sam Neua, Luang Prabang, Vang
Vieng, and Paklay provinces, including the capital city of
Laos (Vientiane), the DSHA revealed a PGA in the range
of 0.27 - 0.32 g. In Southern Laos, the seismic hazard was
Fig. 5. Possible PGA map of Laos, as evaluated by DSHA. (Color online only)
Seismic Activities and Hazards in Laos 849
quite low and mostly less than 0.04 g. The low-hazard areas
were occupied by Thakhek, Savannakhet, Champasak, and
Khong provinces (Fig. 5).
5.2 Probabilistic Seismic Hazard Analysis (PSHA)
In contrast to the DSHA, PSHA (Cornell 1968) esti-
mates the likelihood (λ) that a specific ground-shaking level
(A) of interest is equal to or exceeds the ground-shaking
level (A0), as expressed in Eq. (3);
() () () (,),AA vfmf rPAmrAmrdmdr
0iMiRi
i
Ns
0
1
$$m=
=
6
@
/##
(3)
where fMi(m) is the probability density function of mag-
nitude (Youngs and Coppersmith 1985); fRi(r) is the
probability density function for source-to-site distance;
P[A(m, r) ≥ A0 | m, r] is the probability of exceedance (POE)
of a threshold value A0 depending on m, r, and the utilized
attenuation model. The term vi is the average rate of earth-
quake occurrence for an individual seismic source zone r
from the total Ns recognizing seismic source zones.
Utilizing the CU-PSHA software (Pailoplee and Palasri
2014), the fMi(m) was evaluated for each of the 10 magnitude
ranges subdivided between MCE (in Mw unit)-3.0 Mw. The
fRi(r) was estimated in each of the 50 case studies from the
longest to shortest distance from the source to site. From
each pair of fMi(m) and fRi(r) supplemented by the attenua-
tion model, 200 cases of POE were calculated for a PGA of
between 0.005 and 1.995. Then at each investigated site, the
hazard curve showing the relationship between the POE and
the PGA in the Y- and X-axis, respectively, was formed.
The hazard curves of some of the major provinces (11
in total) in Laos are shown in Fig. 6, where it is noticeable
that Luang Prabang, Louang Namtha, and Paklay provinces
are located in a high earthquake hazard region. Meanwhile,
Vientiane, and Sam Neua provinces are in a comparatively
low seismic hazard area.
With respect to the PSHA map, Kramer (1996) pro-
posed two useful methods for mapping the PSHA based on
the hazard curve of the ground shaking map and the prob-
ability map, and these are analyzed in turn in sections 5.2.1
and 5.2.2, respectively.
5.2.1 Ground Shaking Maps
A ground shaking map illustrates spatially the PGA
level (in units of g) that corresponds to a particular POE in
the time span of interest (Kramer 1996). In this PSHA, the
ground shaking maps for a 2 and 10% POE in 50 yr were
derived (Fig. 7), and were found to be roughly analogous
to that obtained from the DSHA (Fig. 5), except that the
hazard level was lower in the PSHA than in DSHA. For
instance, taking a 2% POE (Fig. 7a), a high hazard level of
0.24 - 0.27 g was found in the northwestern part of Laos,
where Louang Namtha, Luang Prabang, Vang Vieng, Pak-
lay, and Sam Neua provinces are located. Meanwhile, the
PGA in the northeastern part of Xieng Khouang and Vien-
tiane provinces was around 0.12 - 0.21 g, which is defined
as a comparatively moderate seismic hazard zone in Laos.
The lowest seismic hazard in Laos was in the southern part
at Thakhek, Savannakhet, Champasak, and Khong provinc-
es, where the calculated PGA was less than 0.04 g which
conforms to the result obtained from the DSHA (Fig. 5).
With regards to the PSHA map of the 10% POE in the
next 50 yr (Fig. 7b), two zones of a different seismic hazard
could be classified. The high hazard of PGA (0.12 - 0.20 g)
dominated the northern part of Laos, whereas the southern
part was less than 0.04 g (Fig. 7b).
5.2.2 Probability Maps
Although the ground shaking maps of the PGA levels
are more precise, they are not user friendly for informing the
public, but rather are typically used more for science and en-
gineering purposes. Therefore, based on Kramer (1996), the
probability maps representing simply the POE (%) of each
severity of earthquake hazard were formed. In this study ac-
cording to the hazard curve of each grid point, the PGA val-
ues were converted to the MMI levels based on the empiri-
cal PGA-MMI relationship proposed by Pailoplee (2012)
for Myanmar and the adjacent areas as shown in Eq. (4);
()..logPGA MMI025310=-
(4)
where PGA is in (cm s-2). Thereafter, the POE of MMI lev-
els IV to VII in the next 50 yr were evaluated and mapped
(Fig. 8). Two zones could clearly be separated in the proba-
bility maps of MMI levels IV and V (Figs. 8a and b), where a
high probability was found in the northern part, followed by
negligible hazard zones in the southern parts, respectively.
For MMI levels VI (Fig. 8c), the northwestern part still
had a POE of more than 70% in the next 50 yr, highlighting
the severe seismic hazard in this region. Meanwhile, for the
moderate hazard areas of the northeastern part, the POE in
the next 50 yr was 40 - 60%. For the rest of Southern Laos,
there was less than a 10% POE of a MMI level VI in the
next 50 yr (Fig. 8c). In addition, for the MMI level VII, the
whole country of Laos showed a POE of less than 40%, and
in the southern part this was < 10% (Fig. 8d).
6. CONCLUSION
In this study, the seismic activities and hazards were
analyzed for Laos. In order to clarify the earthquake sources
impacting upon Laos, the available seismicity data were
Santi Pailoplee & Punya Charusiri
850
analyzed statistically. The earthquake parameters (FMD a-
and b-values and the MCE), including the recurrence inter-
vals of 5.0-Mw and 6.0-Mw earthquakes were estimated spa-
tially. From this, six seismic source zones were defined for
Laos based on the different earthquake recurrence intervals.
Utilizing these seismic source zones and suitable at-
tenuation models, the seismic hazard in this area was ana-
lyzed using both deterministic and probabilistic scenarios,
and the obtained maps classified Laos into three seismic
hazard zones (Table 2).
Although this study is an important step in the earth-
quake hazard evaluation in Laos, more work is still neces-
sary. In order to constrain both the seismic activities and
hazards analyzed here, further studies on the paleoseismol-
ogy at sites specific to the active faults within and surround-
ing Laos should be performed.
Acknowledgements This research was supported by the
National Research Council of Thailand (NRCT) Fund 2017.
Thanks are also extended to T. Pailoplee for the preparation
of the draft manuscript. I thank the Publication Counseling
Unit (PCU), Faculty of Science, Chulalongkorn University,
for a critical review and improved English. I acknowledge
thoughtful comments and suggestions by the editors and
anonymous reviewers that enhanced the quality of this man-
uscript significantly.
Fig. 6. Hazard curves (PGA vs. POE plots) for the 11 major provinces in Laos, as evaluated by PSHA. (Color online only)
(a) (b)
Fig. 7. Probabilistic seismic hazard maps of Laos showing a ground shaking of (a) 2% and (b) 10% POE in the next 50 yr. (Color online only)
Seismic Activities and Hazards in Laos 851
(a) (b)
(c) (d)
Fig. 8. Probabilistic seismic hazard maps of Laos showing the probabilities (%) that ground shaking will be equal to or greater than MMI levels of
(a) IV, (b) V, (c) VI, and (d) VII in the next 50 yr. (Color online only)
Northwestern Northeastern Southern
Province
Louang Namtha
Luang Prabang Vang Vieng
Paklay
Sam Neua
Xieng Khouang
Vientiane
Thakhek
Savannakhet
Champasak Khong
DSHA 0.32 - 0.4 g 0.12 - 0.32 g < 0.12 g
PSHA
PGA of 2% POE in 50 yr 0.24 - 0.32 g 0.12 - 0.20 g < 0.12 g
PGA of 10% POE in 50 yr 0.12 - 0.20 g 0.12 - 0.20 g < 0.08 g
POE of MMI IV in 50 yr > 90% > 80% < 10%
POE of MMI V in 50 yr > 90% > 80% < 10%
POE of MMI VI in 50 yr 70 - 90% 40 - 60% < 10%
POE of MMI VII in 50 yr 20 - 40% 10 - 20% < 10%
Table 2. Summarized SHA in Laos based on various conditions of interest.
Santi Pailoplee & Punya Charusiri
852
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... However, in recent years, several lines of evidence support the concept that both Thai and Laos are also earthquakeprone areas. Tectonically, previous and recent paleoseismological investigations show that the two countries are, to some extent, controlled by inland active faults [1,2,3,4,5,6,7,8] as shown in Fig. 1. Pailoplee and Choowong [9] reported that several seismic source zones in mainland Southeast Asia are tectonically and seismically active. ...
... Therefore, Laos has also experienced hazardous ground shaking. Up to now, only two seismic hazard maps have been documented: one is the map developed by the United Nation Office for Human Affairs [43], and the other by Pailoplee and Charusiri [6]. The former is a preliminary map which illustrates the earthquake severity with modified Mercalli Intensity (MMI) scale for 50-yr return period, and the latter is much more sophisticated, however both do not contain the new data on recent earthquake activities. ...
... Due to the appearance of 3 new active faults reported in this study area, both DHSA and PSHA maps are different from the previous maps reported by Pailoplee and Charusiri [6] for Thailand and these two kinds of SHA maps are almost similar to those of Pailoplee and Charusiri [6] for Laos. For instance, the high PGA from the DSHA map in western and northwestern Laos varies from 0.32 to 0.4g [6]. ...
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In both Thailand and Laos seismic hazards have been classified as the low-lying region of mainland Southeast Asia. Nevertheless in recent times few intermediate and large earthquakes have taken place until recently. Therefore our prime objective is to characterize seismic hazards in Thailand and Lao PDR (or Laos) by utilizing geologic fault and most update seismic data. We identified more than 60 active faults using remote sensing, morpho-tectonic, paleoseismic trenching, and quaternary dating information from the current and previous studies. At least six seismic source zones have been utilized based upon the most recent geologic, tectonic, and seismicity data. Earthquake catalogues from various sources have been determined, registered, and filtered. Strong ground motion attenuation model have been selected by comparing several well-accepted published models with strong ground motion recorded in both Thailand and Laos. Seismic hazard analysis (SHA) can be performeded by using 2 methods: deterministic seismic hazard analysis (DSHA) and probabilistic seismic hazard analysis (PSHA). DHSA has been adopted for the designs of critical construction and PSHA has been acquired for the noncritical construction. The established SHA maps by this two methods can be carried out by applying past earthquake events and new active fault data.. The DSHA map displays possible ground shaking up to 0.35 g in northern and western Thailand and up to 0.4 g in northwestern Laos, whereas the ground shaking computed from the PSHA approach is <0.3 g in northern Thailand and <0.32 g in Laos for 2 % probability of exceedance in the next 50 yrs and roughly become higher in the northern part of both countries. The DSHA map reveals relatively high hazard level in areas of central and northwestern Laos as well as northern and western Thailand, medium hazard level in northeastern Laos and southern Thailand, and low hazard level in southern Laos as well as central and eastern Thailand. The PSHA map generally displays seismic hazard distribution almost similar to that of the DSHA map but with comparatively lower hazard levels. Paleoseismic investigations are quite essential for defining seismotectonic faults, new seismic source zones, and hazard level. It is also believed that several fault lines may have occurred within the weak and major crustal structures. Effective mitigation plan to reduce impact of seismic hazard is, therefore, formulated urgently and in many major cities located in northern and western Thailand as well as in northwestern and central Laos.
... The location of the post-impact scoria cones on the BVF, hence the area with the highest probability of future vent opening, seems related to the impact crater structure rather than to the local tectonic stress. From a regional tectonic perspective, several works report the current state of stress field for northern Southeast Asia, including Laos (Pailoplee et al. 2009;Pailoplee and Charusiri 2017;Meyers et al. 2018). Particularly, these works report seismogenic faults in central and northern Laos, which can be divided into two groups, SW-NE and SE-NW oriented faults (Pailoplee and Charusiri, 2017), mostly in a strike-slip regime driven by the Sagaing Fault and Red River Fault (Meyers et al. 2018). ...
... From a regional tectonic perspective, several works report the current state of stress field for northern Southeast Asia, including Laos (Pailoplee et al. 2009;Pailoplee and Charusiri 2017;Meyers et al. 2018). Particularly, these works report seismogenic faults in central and northern Laos, which can be divided into two groups, SW-NE and SE-NW oriented faults (Pailoplee and Charusiri, 2017), mostly in a strike-slip regime driven by the Sagaing Fault and Red River Fault (Meyers et al. 2018). None of this work shows local faults and their orientation in southern Laos, where the BVF is located. ...
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Chapter
The c. 500-km-long Mae Ping fault zone trends NW–SE across Thailand into eastern Myanmar and has probably undergone in excess of 150 km sinistral motion during the Cenozoic. A large, c. 150-km-long, restraining bend in this fault zone lies on the western margin of the Chainat duplex. The duplex is a low-lying region dominated by north–south-trending ridges of Mesozoic and Palaeozoic sedimentary, metamorphic and igneous rocks, flanked by flat, post-rift basins of Pliocene–Recent age to the north and south. A review of published cooling-age data, plus new apatite and zircon fission-track results indicates that significant changes in patterns of exhumation occurred along the fault zone with time. Oldest uplift and erosion (Eocene) occurred in the Umphang Gneiss region, west of an inferred thrust-dominated restraining-bend setting. From 36 Ma to 30 Ma, exhumation was strongest north of the duplex, along the NW–SE-trending segment of the fault zone at the (northern) exiting bend of the Chainat duplex. This region of the fault zone is characterized by a mid-crustal level shear zone 5–6 km wide (Lan Sang Gneisses), that passes to the NW into an apparent strike-slip duplex geometry. The deformation is interpreted to have occurred during passage around the northern restraining bend, which resulted in vertical thickening, uplift, erosion and extensional collapse of the northern side of the shear zone. This concentration of deformation at the bends at the ends of the restraining bend is thought to be a characteristic of strike-slip-dominated restraining bends. Following Late Oligocene–Early Miocene extension, there is apatite fission-track evidence for 22–18 Ma exhumation in the Chainat duplex, that coincides with a phase of inversion in the Phitsanulok Basin to the north. The Miocene–Recent history of the Chainat duplex is one of minor sinistral and dextral displacements, related to a rapidly evolving stress field, influenced by the numerous tectonic reorganizations that affected SE Asia during that time.
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