Crustal heterogeneities beneath the 2011 Talala, Saurashtra earthquake, Gujarat, India source zone: Seismological evidence for neo-tectonics A.P. Singh a,⇑ , O.P. Mishra b,c , B.K. Rastogi a , Santosh Kumar a a Institute of Seismological Research (ISR), Raisan, Gandhinagar 382 009, Gujarat, India b Geo-Seismology Division, Geological Survey of India (GSI), 27, J.L. Nehru Road, Kolkata 700 016, West Bengal, India c Geological Disaster Division, SAARC Disaster Management Centre, New Delhi 110 002, India article info Article history: Received 20 July 2012 Received in revised form 20 October 2012 Accepted 4 November 2012 Available online xxxx Keywords: Seismic tomography The 2011 Talala earthquake Seismic velocity Poisson’s ratio Neo-tectonics Crustal heterogeneities abstract During the 1st decade of the 21st century, the study area of Talala, Saurashtra of western India witnessed three damaging earthquakes of moderate magnitude, year 2007 [Mw 5.0; Mw 4.8] and in the year 2011 [Mw 5.1] that generated public panic in the region. The last damaging moderate earthquake of the 20th October 2011 in Talala region (21.09°N;70.45°E), located at about 200 km south to the devastating 2001 Bhuj (23.412°N, 70.232°E) mainshock (Mw 7.6), jolted the entire Saurashtra region of Gujarat. A long ser- ies of aftershocks followed hereafter, recorded at nine seismograph/accelerograph stations. Hypocenters of aftershocks were relocated accurately using absolute and relative travel time (double-difference) method. In this study, we, for the first time, determined 3-D tomographic images of the upper crust beneath the 2011 Talala earthquake source zone by inverting about 1135 P and 1125 S wave arrival time data. Estimates of seismic velocities (Vp, Vs) and Poisson’s ratio (r) structures offer a reliable interpreta- tion of crustal heterogeneities and their bearing on geneses of moderate earthquakes and their aftershock sequences beneath the source zone. It is found that the 2011 Talala mainshock hypocenter depth (6 km) is located near the boundary of the low and high velocity (Vp, Vs) and the source zone is associated with low-r anomalies guarded by the prominent high-r anomalies along the active fault zone having strike- slip motion beneath the earthquake source zone. The pattern of distribution of (Vp, Vs, r) and its associ- ation with occurrences of aftershocks provide seismological evidence for the neo-tectonics in the region having left lateral strike-slip motion of the fault. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Gujarat, a provincial state of federal India is the most seismi- cally active regions of India after the Himalayan seismic belt, which witnessed the two most damaging earthquakes [e.g., the 1819 Kachchh earthquake (Mw 8.0); the 2001 Bhuj earthquake (M7.6)] along with several moderate earthquakes of magnitude M P 6.0 in the annals of western Indian seismology (Gaur, 2001; Singh et al., 2001a,b; Mishra and Zhao, 2003; Singh et al., 2011, 2012a,b; Rastogi et al., 2011). The 2001 Bhuj earthquake has been considered as the largest intraplate earthquake occurred in modern seismology era. The intense shaking due to 2001 Bhuj earthquake bought out changes in the ocean and land surface parameters (Singh et al., 2001a,b). Various seismological and geophysical stud- ies suggest that the Bhuj earthquake was associated due to fluid filled fractured rock matrix at the depth of 20–25 km (Kayal et al., 2002; Negishi et al., 2002; Mishra and Zhao, 2003; Sastry et al., 2008; Naganjaneyulu et al., 2010; Singh et al., 2011, 2012a,b). The intense aftershock activity of the 2001 Bhuj earthquake is still continuing. The Talala, Saurashtra region in the Gujarat is also experiencing tremors since 2001 every year during September to November after heavy rainfall (Rastogi et al., 2008, 2012). The entire Gujarat and adjoining region have been divided into three geographical regions namely, Saurashtra, Mainland, and Kachchh. The Saurashtra region of Gujarat consti- tutes a crucial component of the geodynamical system of the wes- tern continental margin of India. It falls under two seismic zones IV and III of the seismic zoning map of India (BIS, 2002) with likely magnitudes of 7.0 and 6.0, respectively. The Saurashtra region has been experiencing stray tremors once in a while in the last two centuries at several places (Fig. 1a) such as Junagadh, Jamnagar, Dwarka, Paliyad, Rajkot, Ghogha, and Bhavnagar (Srivastava and Rao, 1997; Yadav et al., 2011; Rastogi et al., 2012). During the 1st decade of the 21st century, the study area Talala in Saurashtra was rocked by three damaging earthquakes of moderate magnitudes, among which are: the two earthquakes of the year 2007 of magnitudes (Mw 5.0; Mw 4.8), and an earthquake of magnitude (Mw 5.1) of the year 2011 that generated severe 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2012.11.017 ⇑ Corresponding author. Tel.: +91 79 66739020, mobile: +91 9099034461; fax: +91 79 66739015. E-mail address: apsingh07@gmail.com (A.P. Singh). Journal of Asian Earth Sciences xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Please cite this article in press as: Singh, A.P., et al. Crustal heterogeneities beneath the 2011 Talala, Saurashtra earthquake, Gujarat, India source zone: Seismological evidence for neo-tectonics. Journal of Asian Earth Sciences (2012), http://dx.doi.org/10.1016/j.jseaes.2012.11.017