Vineet K. Gahalaut

Aseismic plate boundary in the Indo-Burmese wedge, northwest Sunda Arc

Plate motion, crustal deformation, and earthquake occurrence processes in the northwest Sunda Arc, which includes the Indo-Burmese wedge (IBW) in the forearc and the Sagaing fault in the backarc, are very poorly constrained. Plate reconstruction models and geological structures in the region suggest that subduction in the IBW occurred in the geological past, but whether it is still active and how the plate motion between the India and Sunda plates is partitioned between motion in the IBW and Sagaing fault is largely unknown. Recent GPS measurements of crustal deformation and available long-term rates of motion across the Sagaing fault suggest that ∼20 ± 3 mm/yr of the relative plate motion of ∼36 mm/yr between the India and Sunda plates is accommodated at the Sagaing fault through dextral strike-slip motion. We report results from a dense GPS network in the IBW that has operated since 2004. Our analysis of these measurements and the seismicity of the IBW suggest that the steeply dipping Churachandpur-Mao fault in the IBW accommodates the remaining motion of ∼18 ± 2 mm/yr between the India and Sunda plates through dextral strike-slip motion, and this motion occurs predominantly through velocity strengthening frictional behavior, i.e., aseismic slip. The aseismic motion on this plate boundary fault significantly lowers the seismic hazard due to major and great interplate earthquakes along this plate boundary.

Oblique convergence and slip partitioning in the NW Himalaya: Implications from GPS measurements

We report GPS measurements of crustal deformation across the Kashmir Himalaya. We combined these results with the published results of GPS measurements from the Karakoram fault system and suggest that in the Kashmir Himalaya, the motion between the southern Tibet and India plate is oblique with respect to the structural trend. We estimated this almost north-south oblique motion to be 17 ± 2 mm/yr, which is partitioned between dextral motion of 5 ± 2 mm/yr on the Karakoram fault system and oblique motion of 13.6 ± 1 mm/yr with an azimuth of N198°E in the northwest-southeast trending Kashmir Himalayan frontal arc. Thus, the partitioning of the India-Southern Tibet oblique motion is partial in the Kashmir Himalayan frontal arc. However, in the neighboring Nepal Himalaya, there is no partitioning; the entire India-Southern Tibet motion of 19–20 mm/yr is arc normal and is accommodated entirely in the Himalayan frontal arc. The convergence rate in the Kashmir frontal Himalaya is about 25% less than that in the Nepal Himalayan region. However, here the Karakoram fault system accommodates about 20% of the southern Tibet and Indian plate convergence and marks the northern extent of the NW Himalayan arc sliver. The Kaurik Chango rift, a north-south oriented seismically active cross-wedge transtensional fault appears to divide the sliver in two parts causing varying translatory motion on the Karakoram fault on either side of the Kaurik Chango rift.

The fury of the floods in the north-west Himalayan region: the Kedarnath tragedy

The floods in the parts of the north-west Himalayan region caused severe damage in the Uttarakhand state of India and in some parts of western Nepal. The severity of the floods and damage was maximum in the Kedarnath region, home of a very famous Hindu pilgrimage. It caused the death of about 4000 people and almost a similar number are still missing. The flash floods were mainly caused by the heavy rainfall, triggering landslides in some places, damaging buildings and infrastructures. The extensive damage and large death toll expose the vulnerability of the mountainous region and lack of coordinated relief and rescue operation.

Constraints on the Source Parameters of the 26 January 2001 Bhuj, India, Earthquake from Satellite Images

The Bhuj earthquake of 26 January 2001 (M w 7.6) was the largest in- tracontinental earthquake of the modern era of seismology. Field investigations did not provide any evidence of coseismic surface rupture or ground deformation due to primary faulting. We analyze pre- and postearthquake satellite images of the epicen- tral region to suggest that there was a significant change in the flooding pattern of the seasonal Rann of Kachchh lagoon after the 2001 and 2002 monsoons in the region of coseismic uplift. The maximum uplift is located about 15 km north of the reported epicenter and acted as a barrier against the northward draining rainwater runoff. Furthermore, the earthquake caused a northward shift in the southern limit of the Rann of Kachchh. We use this information to place constraints on the location and geometry of the earthquake rupture and suggest that the depth of the updip edge of the rupture is about 10 km.

The 4 January 2016 Manipur earthquake in the Indo-Burmese wedge, an intra-slab event

ABSTRACT Earthquakes in the Indo-Burmese wedge occur due to India-Sunda plate motion. These earthquakes generally occur at depth between 25 and 150 km and define an eastward gently dipping seismicity trend surface that coincides with the Indian slab. Although this feature mimics the subduction zone, the relative motion of Indian plate predominantly towards north, earthquake focal mechanisms suggest that these earthquakes are of intra-slab type which occur on steep plane within the Indian plate. The relative motion between the India and Sunda plates is accommodated at the Churachandpur-Mao fault (CMF) and Sagaing Fault. The 4 January 2016 Manipur earthquake (M 6.7) is one such earthquake which occurred 20 km west of the CMF at ∼60 km depth. Fortunately, this earthquake occurred in a very sparse population region with very traditional wooden frame houses and hence, the damage caused by the earthquake in the source region was very minimal. However, in the neighbouring Imphal valley, it caused some damage to the buildings and loss of eight lives. The damage in Imphal valley due to this and historical earthquakes in the region emphasizes the role of local site effect in the Imphal valley.

Coulomb stress change due to 2005 Kashmir earthquake and implications for future seismic hazards

We calculate static stress change due to the 2005 Kashmir earthquake (M = 7.6). We suggest that the earthquake caused significant increase in stress in the Indo-Kohistan seismic zone (IKSZ) region, lying to the NW of the rupture and moderate increase in the adjacent Himalayan region, lying to the SE of rupture. Thus, these regions have been brought closer to the failure. On the other hand, the Salt Range region lies in the stress shadow of the earthquake, implying that future earthquakes in this region will be inhibited. We find that this earthquake may not be compared with typical Himalayan earthquake, and hence, rupture features of this earthquake may not be directly applicable to the earthquakes of the Himalayan region.

No evidence of unusually large postseismic deformation in Andaman region immediately after 2004 Sumatra-Andaman earthquake

[1] Static offsets due to the 26 December 2004 Sumatra-Andaman earthquake have been reported from the campaign mode GPS measurements in the Andaman-Nicobar region. However, these measurements contain contributions from postseismic deformation that must have occurred in the 16-25 days period between the earthquake and the measurements. We analyse these and tide gauge measurements of coseismic deformation, a longer time series of postseismic deformation from GPS measurements at Port Blair in the South Andaman and aftershocks, to suggest that postseismic displacement not larger than 7 cm occurred in the 16-25 days following the earthquake in the South Andaman and probably elsewhere in the Andaman Nicobar region. Earlier, this contribution was estimated to be as large as 1 m in the Andaman region, which implied that the magnitude of the earthquake based on these campaign mode measurements should be decreased. We suggest an Mw for this earthquake as 9.23.

Rupture mechanism of the 1993 Killari earthquake, India: constraints from aftershocks and static stress change

The Killari earthquake of September 29, 1993 (Mw=6.2) in peninsular India triggered several aftershocks that were recorded by a network of 21 stations. We computed the change in regional static stress caused by coseismic slip on the earthquake rupture and correlated it with the aftershocks with a view to constrain some of the rupture parameters of this earthquake. We evaluated the six available estimates of fault plane solutions for this earthquake and concluded that reverse slip on a 42j dipping, N112j trending fault, which extends up to the surface from a depth of 7 km, produces maximum correlation between the increased static stress and aftershock distribution. Our analysis suggests that the majority of coseismic slip occurred on the part of the rupture that lies in the depth range of 3–6.5 km. D 2003 Elsevier B.V. All rights reserved.

M 6.9 September 18, 2011 Sikkim earthquake

A strong earthquake (6.9 M w) occurred in the Sikkim–Nepal region of the Himalayan arc which caused the death of about 100 people. The earthquake involved predominantly strike-slip motion on a steep fault, which is transverse to the Himalaya. It implies that the rupture of this earthquake did not occur on the Himalayan detachment, which slips in a stick-and-slip manner to accommodate 2cm/year of convergence within the Himalaya. Although there is uncertainty about the depth estimates and ambiguity in the fault plane, amongst many other rupture models of the earthquake it is suggested that this, and a similar such earthquake on 20 August 1988 in the Himalayan foothills, occurred in response to the subduction of the Munger-Saharsa ridge on the Indian plate. The occurrence of this earthquake highlights the role of transverse features in the Himalayan tectonics.

Three great tsunamis : Lisbon (1755), Sumatra-Andaman (2004) and Japan (2011)

1. Fundamentals of Tsunami.- 1755 Lisbon Earthquake and Tsunami.- 2004 Sumatra-Andaman Earthquake and Tsunami.- 2011 Tohoku-Oki Earthquake and Tsunami.- Global Effort to Forecast and Mitigate Tsunami Hazard.- Looking into the Future.