Abstract
The inversion seismic tomography algorithm (ITS) was used to calculate 3D seismic anomalies models for velocities of P- and S-waves in the zone of the Sunda arc, Indonesia. In the area under study, strong earthquakes (M>4.8) are clustered in the zone of high P-wave velocities. Earthquake hypocenters are located in zones of both high and low velocity anomalies of S-waves. The giant Sumatra earthquake (December 26, 2004, Mw=9.0) ruptured the greatest fault length of any recorded earthquake, and the rupture started in the area wherein the sign of P-wave velocity anomalies is abruptly changed. We calculated seismotectonic deformations (STD) from data on mechanisms of 2227 earthquakes recorded from 1977 to 2013, and our calculations show that the STD component, that controls vertical extension of rocks, is most stable through all the depth levels. In the marginal regions at the western and eastern sides of the Sunda arc, the crustal areas (depths from 0 to 35 km) are subject to deformations which sign is opposite to that of deformations in the central part. Besides, at depths from 70 to 150 km beneath the Sumatra earthquake epicentre area, the zone is subject to deformations which sign is opposite to that of deformations in the studied part of the Sunda arc. For earthquakes that may occur in the crust in the Sunda arc in the contact zone of the plates, maximum magnitudes depend on the direction of pressure imposed by the actively subducting plate, which is an additional criteria for determining the limit magnitude for the region under study.
Highlights
The giant Sumatra earthquake (December 26, 2004, Mw=9.0) has become a subject of many interesting publications both abroad [Cheng Zong-yi, Zhu Wen-yao, 2001; Chlieh et al, 2007; Dewey et al, 2007; Engdahl et al, 2007; Vallee, 2007] and in Russia [Rebetskii, Marinin, 2006; Shevchenko et al, 2006]
With account of the fact that it was followed by several strong seismic events near the Sumatra Island, our idea was to conduct a detailed study of seismotectonic deformations (STD) and recent earthquakes
By analyzing of the distribution of earthquake epicentres in the maps of increasing and decreasing velocity of compressional and shear waves, we found that the majority of seismic events (M> 4.8) in the study region are clustered within the zone of high velocity of P-waves
Summary
The giant Sumatra earthquake (December 26, 2004, Mw=9.0) has become a subject of many interesting publications both abroad [Cheng Zong-yi, Zhu Wen-yao, 2001; Chlieh et al, 2007; Dewey et al, 2007; Engdahl et al, 2007; Vallee, 2007] and in Russia [Rebetskii, Marinin, 2006; Shevchenko et al, 2006]. With account of the fact that it was followed by several strong seismic events near the Sumatra Island, our idea was to conduct a detailed study of seismotectonic deformations (STD) and recent earthquakes. The Sunda arc represents a convergent margin and reflects processes of interaction between the IndoAustralian and Eurasian lithospheric plates that are approaching each other This movement takes place along the Andaman, Nicobar, Sumatra and Java islands. In the focal area of the giant Sumatra earthquake of December 2004, thrusting took place along the gently sloping plane in the west–south-western direction [The Global Centroid-Moment-Tensor..., 2015]. Similar focal mechanisms are typical of the strongest aftershocks and earthquakes recorded both before and after the Sumatra earthquake, except seismic events of the shear type near Andaman and Nicobar islands. It is logical to suggest that deep processes and the structure of the crust and the lithospheric mantle play an important role in the distribution of deformation and the occurrence of the earthquake foci
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