J. K. Catherine

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.

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.

A preliminary assessment of internal deformation in the Indian Plate from GPS measurements

Abstract The rate of convergence of the Indian Plate with respect to Eurasia has been obtained using IGS GPS stations at Hyderabad (HYDE) and Bangalore (IISC), in conjunction with a select set of other IGS stations. The rates obtained for HYDE and IISC are 37.09±1.4 and 35.68±1.7 mm/yr, respectively. The difference in the velocities of these two peninsular Indian stations with respect to Eurasia necessitated a fresh investigation into possible deformation between HYDE and IISC. Separate processing of the baseline with ambiguity resolution suggests a differential motion of 5.01±0.6 mm/yr between the two GPS sites, with HYDE moving S68°E relative to IISC. The available geological and geophysical data also suggest that this part of peninsular India is undergoing internal deformation.

Dichotomy in mode propagation of coseismic ionospheric disturbance: Observations from 11 April 2012 Indian Ocean earthquake

The ionosphere response to the great intraplate Indian Ocean earthquake of 11 April 2012 (Mw 8.6) and its largest aftershock (Mw 8.2) is analyzed using GPS-aided total electron content (TEC) measurements. Data from the dense GPS networks, SuGAr (Sumatran GPS Array) and the permanent Andaman-Nicobar array, formed the near-field observations at distances 250–1200 km from the epicenter. Stations such as IISC, DGAR, and few others provided measurements over 2000 km from the epicenter. The coseismic ionospheric disturbances (CIDs) with a propagation velocity of 930–1262 m/s, equals the speeds of the shock acoustic waves, arrive within 10–18 min after the earthquake occurrence. The observed phenomenon of CID splitting into two modes, north and south of the epicenter, is akin to the well-documented effects of anisotropy on wave propagation. Closer to the epicenter, to its south, the propagation velocity of CID is ~1 km/s, and farther southeast of the network the velocity reduces to 500–600 m/s. In contrast, toward Andaman in the north, the CID propagation velocity increases to 2–3.5 km/s. The zenith angle of the line of sight between the GPS receiver and satellite appears to influence the amplitude of the TEC fluctuations. The anomalous azimuthal variation of the Rayleigh wave radiation pattern best explains the observed N-S asymmetry of CID.

Seamount subduction and rupture characteristics of the March 11, 2011, Tohoku earthquake

We suggest that the spatial location of the 2011 Tohoku earthquake rupture and slip distribution on it was strongly influenced by the subduction of seamount chains. Subduction of seamounts across the Japan trench caused weak coupling on the plate interface which acted as barriers to the 2011 Tohoku earthquake rupture and thus delimited it.

First estimate of plate motion at Maitri GPS site, Indian base station at Antarctica

We analyse GPS data from the Indian permanent GPS station at Maitri for measuring the plate motion at this site.We find that this site moves at a velocity of 4.6 mm/year predominantly towards north, which is consistent with the expected plate motion of Antarctic plate at this site.