Slow rupture in Andaman during 2004 Sumatra-Andaman earthquake: a probable consequence of subduction of 90°E ridge

One of the most enigmatic features of the 2004 Sumatra–Andaman earthquake was the slow rupture speed and low slip on the northern part of the rupture under the Andaman region. We propose that the aseismic 90°E Ridge (NER) on the Indian Plate obliquely subducts under the Andaman frontal arc region. Though other possibilities also exist, we hypothesized that this ridge probably acted as a structural barrier influencing rupture characteristics of the earthquake. Here we present several features of the Andaman region that favour NER subduction under the region, which include (i) comparatively shallow bathymetry and trench depth, (ii) low seismicity, (iii) significant variation in the azimuths of coseismic horizontal offsets due to the 2004 Sumatra–Andaman earthquake, (iv) lack of post-seismic afterslip on the coseismic rupture in the Andaman frontal arc region, (v) low P wave with only small decrease in S wave speed from tomographic studies, (vi) gravity anomalies on the Indian Plate indicating continuation of the ridge under the Andaman frontal arc and (vii) lack of back arc volcanoes in the Andaman region

The 2007 Bengkulu earthquake, its rupture model and implications for seismic hazard

The 12 September 2007 great Bengkulu earthquake (Mw 8.4) occurred on the west coast of Sumatra about 130 km SW of Bengkulu. The earthquake was followed by two strong aftershocks of Mw 7.9 and 7.0. We estimate coseismic offsets due to the mainshock, derived from near-field Global Positioning System (GPS) measurements from nine continuous SuGAr sites operated by the California Institute of Technology (Caltech) group. Using a forward modelling approach, we estimated slip distribution on the causative rupture of the 2007 Bengkulu earthquake and found two patches of large slip, one located north of the mainshock epicenter and the other, under the Pagai Islands. Both patches of large slip on the rupture occurred under the island belt and shallow water. Thus, despite its great magnitude, this earthquake did not generate a major tsunami. Further, we suggest that the occurrence of great earthquakes in the subduction zone on either side of the Siberut Island region, might have led to the increase in static stress in the region, where the last great earthquake occurred in 1797 and where there is evidence of strain accumulation

Localized crustal deformation in the Godavari failed rift, India

Six years of GPS measurements of crustal deformation in the Godavari failed rift (GFR) of stable India plate suggest very localized deformation. Elsewhere, all along the GFR the deformation is very low (<1.5 mm/yr). Localized deformation (up to 3.3±0.5 mm/yr) at least at two sites, implying compression on steep faults located on the southern margin of the GFR, is coincident with the region characterized by high level low-magnitude seismicity of past six years and implies strain accumulation for future moderate to strong magnitude earthquake in the region. The localized deformation is consistent with the view about deformation in such regions where seismicity migrates and deformation rate changes with time

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

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

Low deformation rate in the Koyna–Warna region, a reservoir triggered earthquake site in west-central stable India

We analyse nine years of GPS measurements of crustal deformation from the Koyna–Warna region within the stable India plate. The Koyna–Warna region experienced a strong earthquake on 10 December 1967 (M 6.3) that is considered to have been induced by the impoundment of the Koyna reservoir and the continuing earthquake activity in the region is considered to be associated with the Koyna and Warna reservoirs. The earthquakes occur in a very small region of 30 × 10 km² in two well defined seismic zones, the NNE–SSW trending Koyna Seismic zone, and the NNW–SSE trending Warna Seismic Zone. These zones are characterised by predominantly left-lateral strike slip motion and normal motion, respectively. In 2003, we initiated campaign-mode GPS measurements in the region. Analysis of the GPS data collected over nine years indicate low to moderate deformation rate (<2 ± 0.5 mm/year) at a few sites within and close to the fault zones and no resolvable deformation elsewhere. This has been seen in many intra-plate seismic regions of the world with varying causative mechanism for the deformation. In the Koyna Warna region, the observed surface displacement rates of up to 2 mm/year near the fault zones are consistent with a fault slip rate of about 7 mm/year, and with the inferred sense of motion on the faults. The inferred fault slip rate is consistent with the total moment release during earthquakes of past six years in the Koyna Warna region which may imply that the ongoing earthquake activity causes the deformation in the region

2008 Little Andaman aftershock: genetic linkages with the subducting 90°E ridge and 2004 Sumatra–Andaman earthquake

We analyse the June 27, 2008 Little Andaman aftershock (Mw 6.6) of December 26, 2004 Sumatra–Andaman earthquake (Mw 9.2) that occurred near the trench in the subducting India plate beneath the Sunda Plate. Unlike majority of the other aftershocks in the frontal arc, the Little Andaman aftershock and its own aftershocks occurred through normal slip on the north–south oriented steep planes. We use the coseismic and ongoing postseismic deformation due to the 2004 Sumatra–Andaman earthquake at a GPS site nearest to the Little Andaman aftershock and compute changes in the Coulomb stresses due to the coseismic slip and postseismic afterslip. The Coulomb stress on the Little Andaman aftershock fault plane progressively increased since the 2004 Sumatra–Andaman earthquake which probably led to the occurrence of the Little Andaman aftershock on the pre-existing N–S oriented strike-slip steep planes of the subducting 90°E ridge that were reactivated through normal slip

Facial emotion processing in criminal psychopathy - Preliminary functional magnetic resonance imaging study

BACKGROUND: It has been suggested that people with psychopathic disorders lack empathy because they have deficits in processing distress cues (e.g. fearful facial expressions). AIMS: To investigate brain function when individuals with psychopathy and a control group process facial emotion. METHOD: Using event-related functional magnetic resonance imaging we compared six people scoring > or =25 on the Hare Psychopathy Checklist-Revised and nine non-psychopathic healthy volunteers during an implicit emotion processing task using fearful, happy and neutral faces. RESULTS: The psychopathy group showed significantly less activation than the control group in fusiform and extrastriate cortices when processing both facial emotions. However, emotion type affected response pattern. Both groups increased fusiform and extrastriate cortex activation when processing happy faces compared with neutral faces, but this increase was significantly smaller in the psychopathy group. In contrast, when processing fearful faces compared with neutral faces, the control group showed increased activation but the psychopathy group decreased activation in the fusiform gyrus. CONCLUSIONS: People with psychopathy have biological differences from controls when processing facial emotion, and the pattern of response differs according to emotion type