Astha Singh Chauhan

Geneva Academy of International Humanitarian Law and Human Rights · La w

1] Over the last 20 years, the Great Sumatran Fault (GSF) has been studied on land, but we have very little information about its offshore extension NW of Sumatra and its link with the West Andaman Fault to the north. The problem is further complicated by its vicinity to the volcanic arc. Here we present detailed analyses of the offshore extension...

Over the last 20 years, the Great Sumatran Fault (GSF) has been studied on land, but we have very little information about its offshore extension NW of Sumatra and its link with the West Andaman Fault to the north. The problem is further complicated by its vicinity to the volcanic arc. Here we present detailed analyses of the offshore extension of...

In subduction zones the plate interface (megathrust) is typically poorly imaged at depths > 12 km, however its precise geometry and nature as well as the positions of updip and downdip limits of the seismogenic zone are important elements to understand the generation of megathrust earthquakes. Using deep marine seismic reflection and refraction dat...

We present images from a deep multi-channel seismic reflection survey acquired in 2006 over the oceanic lithosphere of the Wharton Basin offshore northern Sumatra, NW of Simeulue island. The main ~230-km long seismic profile is roughly parallel to the trench at ~32-66 km distance from the subduction front and crosses (at oblique angles to both flow...

The subduction of large topographic features such as seamounts has been linked to plate locking, earthquake generation and segmentation, as well as crustal erosion at subduction zones. However, the role of subducted features in the generation of megathrust earthquakes has been difficult to discern because traditional imaging techniques are limited...

In the last five years, there have been three great megathrust earthquakes in the Sumatra subduction zone, and a part of the zone is still locked. We have carried out deep seismic reflection surveys along the SW Sumatran margin and have imaged backthrusts along four profiles down to 15-20 km depth. We find that the seismic images of the backthrusts...

The thickness of the crust created at ocean spreading centres depends on the spreading rate and melt production in the mantle. It is ˜5-8 km for a crust formed at slow and fast spreading centres and 2-4 km at ultra-slow spreading centres away from hotspots and mantle anomalies. The crust is generally thin at the fracture zones and thick beneath hot...

Subducted bathymetric highs and lows provide important controls on the locking mechanism, earthquake generation and segmentation, and on crustal erosion at subduction zones. However, until now, it has been only possible to image subducted features down ~10 km depth due to a combination of poor penetration of seismic energy, reverberation of seismic...

The great earthquakes occur on megathrusts, the interface between the subducting downgoing plate and the overriding plate, rupturing the seismogenic zone that generally lies between 10 and 30 km depths beneath the forearc. The overriding plate beneath the forarc region consists of accreted sediments and crystalline crust, also referred to as backst...

Sumatra megathrust earthquake on 26 December 2004 (Mw = 9.1) was initiated around 30 km depth and ruptured a zone of approximately 150 km wide and 1500 km along Indo-Australian plate from Simeuleu to the Andaman Island. Two active marine seismic experiments were carried out to acquire seismic wide-angle refraction/reflection using 56 OBS' (Sumatra...

Recent studies suggests that tsunami risk along the SW coast of Sumatra could be due to co-seismic slip along a backthrust at the NE Margin of the Mentawai Island and associated landslides (Singh et al., 2010). Using a combination of high-resolution seismic reflection and bathymetry data, they observed deposits of large submarine landslides at the...

The 26 December 2004 Sumatra earthquake (Mw = 9.1) initiated around 30 km depth and ruptured 1300 km of the Indo-Australian Sunda plate boundary. During the Sumatra OBS (ocean bottom seismometer) survey, a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography...

The Indo-Australian plate subducts obliquely beneath the Sunda plate leading to a slip partitioning into pure thrust and strike-slip motion. Just in the last 5 yr, three pure thrust earthquakes of Mw > 8.4 have occurred along this subduction interface. The Great Sumatra Fault, traversing the Sumatra continental block, takes up a significant part of...

In July-August 2005 during the MD-149 Sumatra aftershocks survey, 20 Ocean Bottom Seismometers (OBSs) were deployed offshore Northern Sumatra, to study the regional seismicity and aftershock patterns following the Giant 26 December 2004 event. The aftershocks have been relocated based on generic seismic velocity models of the subsurface, so-far. He...

The Sumatra subduction zone is seismically most active region on the Earth, and has been the site of three great earthquakes only in the last four years. The first of the series, the 2004 Boxing Day earthquake, broke 1300 km of the plate boundary and produced the devastating tsunami around the Indian Ocean. The second great earthquake occurred thre...

Forearc tectonics at accretionary convergent margins has variously been studied using analogue and numerical modelling techniques. Numerous geophysical investigations have targeted the subsurface structure of active forearc settings at convergent margins. However, several critical details of the structure, mode of tectonic evolution and the role fo...

Passive seismic experiments to study seismicity require a long term deployment of ocean-bottom seismometers (OBSs). These instruments also record a large amount of non-seismogenic signals such as movement of large ships, air-gun shots, and marine mammal vocalizations. We report a bi-product of our passive seismic experiment (BBMOMAR) conducted arou...

The Sumatra subduction system is a classic example of an oblique subduction where the slip is portioned into pure thrust along the Sumatra-Andaman megathrust and strike-slip along the Great Sumatra Fault (GSF). Only in the last five years there have been three great pure thrust earthquakes along the Sumatran subduction zone. However, the 1900 km lo...

The 26th December 2004 Sumatra earthquake (Mw=9.1) initiated around 30 km depth and ruptured 1300 km of the IndoAustralian/Sunda plate boundary. During the Sumatra-OBS survey a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography and forward modeling. Togeth...

Joint interpretation of deep seismic reflection and wide angle seismic data reveals detailed structure and deformation of the subduction zone across the epicentral region of the 26 December 2004 Great Sumatra earthquake. This seismic line starts from the oceanic plate through the accretionary prism, outer-arc high (Simeulue plateau) and Simeuleu fo...

The Indo-Australian plate subducts obliquely beneath the Sunda plate leading to a slip partitioning into pure thrust and strike-slip motion. Just in the last three and half years, three pure thrust earthquakes of Mw>8.4 have occurred along this subduction interface. The great Sumatra Fault, traversing the Sumatra continental block along the volcani...

Sumatra megathrust system is an obliquely convergent boundary where slip-partitioning has been variously inferred from slip-vectors of recorded earthquakes and geodetic models. The submarine West Andaman fault (WAF) has been variously interpreted as the dextral twin of the on-land great Sumatra fault, accommodating the strike parallel convergence....

The massive tsunami generated during the Great Sumatra-Andaman earthquake of 26 December 2004 killed over 250000 around the coastlines of Southeast Asia, with the biggest loss in northern Sumatra of about 150000 lives where runup heights reached up to 30 metres. The source of the 26 December 2004 tsunami has been related to vertical coseismic uplif...

The thickness of the crust created at ocean spreading centers depends on the spreading rate and melt production in the mantle, and is ~6-7 km for a crust formed at a fast spreading centre. The presence of a plume in the vicinity of a spreading center enhances the melt production and leads to a thicker crust. On the other hand, thin crusts are assoc...

Continental backstop is described as basement structure below the arc-ward end of the fore-arc. This backstop not only influences the development of the overlying sedimentary structure, but also affects seismicity along the megathrust. Our study is based on high quality seismic reflection data acquired perpendicular to the trench near the epicenter...

The Indo-Australian plate subducts obliquely beneath the Sunda plate leading to the slip-partitioning into pure thrust and strike-slip motion. Just in the last three and half years, three pure thrust great earthquakes (Mw>8.4) have occurred along the subduction interface. The great Sumatra Fault, traversing the Sumatra continental block, takes up a...

We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysi...

The great Sumatra earthquake of 26 December 2004 was the third largest event to occur in a subduction zone in the past 50years. The rupture initiated at 30-40km depth northwest of Simeulue Island and propagated for ~1,300km to the northern Andaman Islands. The earthquake was caused by sudden slip along the plate interface between the subducting Ind...

The new bathymetry and seismic data were acquired during the PreTI-Gap marine survey (February 15 to March 6, 2008). The survey was carried out along the NE margin of Mentawai Island using multi-beam swath bathymetry equipment, and 28-channels seismic streamer and four-airgun source. The first target was the Mega Island region near the epicenter of...

Results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2) are presented. These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient anal...

We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysi...

The 26th December 2004 great Sumatra earthquake (Mw=9.1) is among the 4 largest earthquakes ever recorded and the largest of the last 40 years. It initiated at a depth of 20-30 km and ruptured about 1300 km of the Indo-Australian/Sunda plate boundary, from the vicinity of Simeulue Island up to the north of Andaman Islands. During the SAGER-OBS crui...

Two deep penetrating wide angle seismic refraction profiles were acquired during the SUMATRA-OBS cruise offshore Sumatra, to image the subsurface in the zone of maximum co-seismic slip for the great Sumatra- Andaman earthquake of December 2004. Here we present the 2-D velocity image of the subsurface obtained by traveltime tomographic inversion of...

The great (M = 9.3) Sumatra-Andaman earthquake of 26 December 2004 was the third largest subduction event in the last 50 years. The rupture initiated at 30-40 km depth northwest of Simeulue Island and propagated as far as the northern Andaman Islands, breaking a total area of about 1300 x 150 km2. The earthquake was caused by a sudden slip -up to 3...

Recently, we acquired deep seismic reflection data using a state-of-the-art technology of Schlumberger having a powerful source (10,000 cubic inch) and a 12 km long streamer along a 250 km long trench parallel line offshore Sumatra in the Indian Ocean deformation zone that provides seismic reflection image down to 40 km depth over the old oceanic l...

The Great Andaman-Sumatra earthquake rupture initiated at about 30 km below seafloor along a megathrust at the interface of the downgoing Indian plate and overriding Sunda plate. The rupture propagated to the seafloor and produced a slip on the scale of 15-20 m, which produced the disastrous tsunami that took over 280,000 lives and unaccountable lo...

The 26th December 2004 Great Sumatra Earthquake is the second largest earthquake (Mw=9.1) recorded during the past century. In order to investigate the sea-floor morphology and potentially recent fault activity related to the seismic activity, swath bathymetric mapping was conducted by the French vessel R/V Marion Dufresne during Sumatra-Aftershock...

The 26th December 2004 great Sumatra earthquake (Mw=9.1) is among the 4 largest earthquakes ever recorded and the largest of the last 40~years. It initiated at a depth of 20-30~km and ruptured about 1300~km of the Indo-Australian/Sunda plate boundary, from the vicinity of Simeulue Island up to the north of Andaman Islands. The SAGER program is part...

The 26 December 2004 Sumatra-Andaman earthquake (Mw~9.3) rupture initiated northwest of Simeulue Island with an initial speed of 0.5-1.0 km/s for about first 100 km then accelerated to over 2.5-3.0 km/s and propagated northwards up to Andaman Islands, rupturing over 1300 km of the plate boundary uni-directionally and causing a disastrous tsunami in...

From July 13 to 27, 2006, we carried out a deep seismic reflection survey along two lines on board the WesternGeco seismic vessel Geco Searcher. The vessel was equipped with one 12 km and one 5.5 km Q- Marine streamers. The long streamer was towed at 15 m depth, providing low frequency signal for deep targets, and the short streamer was towed at 7....

The Great Sumatra-Andaman Earthquake of December 26, 2004 initiated around 3 N near Simeulue and the rupture propagated for about 1250 km up to Andaman Islands. These results were further confirmed by the aftershocks that are located in the same region between 3 N and 12 N. The epicenter of second large mega-thrust earthquake of March 28, 2005 was...

The Sumatra earthquake of 26 December 2004 ( M w = 9.3) was one of the largest megathrust earthquakes ever recorded using a modern seismic network. The rupture initiated around 3°N near Simeulue Island and propagated northward for about 1250 kilometers up to the Andaman Islands. Nearly three months later, on 28 March 2005, a second large earthquake...

The Sumatra earthquake of 26 December 2004 (Mw = 9.3) was one of the largest megathrust earthquakes ever recorded using a modern seismic network. The rupture initiated around 3°N near Simeulue Island and propagated northward for about 1250 kilometers up to the Andaman Islands. Nearly three months later, on 28 March 2005, a second large earthquake o...