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Back-arc extension in the Andaman Sea: Tectonic and magmatic processes imaged by high-precision teleseismic double-difference earthquake relocation

DRS at CSIR-National Institute of Oceanography

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Title Back-arc extension in the Andaman Sea: Tectonic and magmatic processes imaged by high-precision teleseismic double-difference earthquake relocation
 
Creator Diehl, T.
Waldhauser, F.
Cochran, J. R.
KameshRaju, K.A.
Seeber, L.
Schaff, D.
Engdahl, E.R.
 
Subject seismic activity
tectonics
volcanism
mid-ocean ridges
 
Description The geometry, kinematics, and mode of back-arc extension along the Andaman Sea plate boundary are refined using a new set of significantly improved hypocenters, global centroid moment tensor (CMT) solutions, and high-resolution bathymetry. By applying cross-correlation and double-difference (DD) algorithms to regional and teleseismic waveforms and arrival times from International Seismological Centre and National Earthquake Information Center bulletins (1964-2009), we resolve the fine-scale structure and spatiotemporal behavior of active faults in the Andaman Sea. The new data reveal that back-arc extension is primarily accommodated at the Andaman Back-Arc Spreading Center (ABSC) at approx. 10 degrees, which hosted three major earthquake swarms in 1984, 2006, and 2009. Short-term spreading rates estimated from extensional moment tensors account for less than 10 percent of the long-term 3.0-3.8 cm/yr spreading rate, indicating that spreading by intrusion and the formation of new crust make up for the difference. A spatiotemporal analysis of the swarms and Coulomb-stress modeling show that dike intrusions are the primary driver for brittle failure in the ABSC. While spreading direction is close to ridge normal, it is oblique to the adjacent transforms. The resulting component of E-W extension across the transforms is expressed by deep basins on either side of the rift and a change to extensional faulting along the West Andaman fault system after the Mw=9.2 Sumatra-Andaman earthquake of 2004. A possible skew in slip vectors of earthquakes in the eastern part of the ABSC indicates an en-echelon arrangement of extensional structures, suggesting that the present segment geometry is not in equilibrium with current plate-motion demands, and thus the ridge experiences ongoing re-adjustment.
 
Date 2013-07-10T07:09:22Z
2013-07-10T07:09:22Z
2013
 
Type Journal Article
 
Identifier Journal of Geophysical Research (B: Solid Earth), vol.118; 2013; 2206–2224
http://drs.nio.org/drs/handle/2264/4332
 
Language en
 
Rights An edited version of this paper was published by AGU. Copyright [2013] AGU. To view the published open abstract, go to http://dx.doi.org/10.1002/jgrb.50192
 
Publisher American Geophysical Union