Numerical modeling of seismicity and geodynamics of the Kachchh rift zone, Gujarat, India Inessa Vorobieva a,b , Prantik Mandal c, ⁎, Alexander Gorshkov a,b a Institute of Earthquake Prediction Theory and Mathematical Geophysics, Federal Agency for Scientific Organizations, 84/32 Profsouznaya, Moscow 117997, Russia b Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris, Cedex 05, France c CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500007, A.P., India abstract article info Article history: Received 24 January 2014 Received in revised form 10 July 2014 Accepted 16 July 2014 Available online xxxx Keywords: Block-and-fault structure Rift basin Numerical modeling Geodynamics Post-seismic deformations Focal mechanisms The numerical block-and-fault model of lithosphere dynamics and seismicity (BAFD) is used to understand crust- al motion and features of the observed seismicity in the Kachchh rift zone, Gujarat, Western India. The block- model allows simulating seismicity and geodynamics simultaneously unlike other modeling approaches for studying seismicity or geodynamics. The model structure of Kachchh rift zone is composed of seven major crustal blocks separated by fault planes. Based on the orientation of boundary crustal block movements, we develop a set of numerical experiments to analyze the spatial distribution of earthquakes, frequency-to-magnitude relation- ships, earthquake focal mechanisms, velocity field, and fault slip rates in the model. The main results of our modeling suggest that an NNW–SSE trending compression is a principal driving force in the Kachchh rift zone that explains basic features of the regional seismicity, direction of block motions, and the presence of an exten- sional stress regime associated with the Cambay rift zone. Large synthetic events occur on the fault segments as- sociated with the Allah-Bund fault, Katrol hill fault and north Wagad fault which have been causative faults for the 1819 Mw7.7 Allah-Bund, 1956 Mw6.0 Anjar and 2001 Mw7.7 Bhuj earthquakes. The frequency–magnitude distribution for both synthetic seismicity and observed seismicity shows a similar slope. The focal mechanisms of the synthetic events are found to be consistent with those of earthquakes in the region. A special attention has been paid to study long-term and post-seismic deformations. Our results are in a qualitative agreement with the GPS post-seismic observations in the Kachchh rift zone. We infer that the observed seismicity and crustal block motions are a consequence of the dynamics of the entire regional fault and block system rather than that of a single causative fault only. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In this paper, we study the Kachchh rift zone (KRZ), which is pres- ently seismically most active intraplate region in the Indian subconti- nent, in general, and in the Gujarat state, in particular. Two large continental earthquakes, the 1819 Allah-Bund, Mw7.7, and the 2001 Bhuj, Mw7.7 have occurred in the region within a span of 182 years, which killed 22,000 people (Chung and Gao, 1995; Gupta et al., 2001; Rajendran and Rajendran, 2001). We focus on the BAFD modeling of the KRZ with an objective to explain: • the patterns of earthquake occurrences along the existing faults in terms of the regional driving forces • the long-term crustal block motion and post-seismic deformation. The concept of numerical BAFD modeling was introduced by Gabrielov et al. (1990), and described in detail by Soloviev and Ismail- Zadeh (2003). The block model simulates both fast (synthetic seismici- ty) and slow (tectonic motions) movements of blocks, and therefore permits to study seismicity and its connection with the geodynamics of a given region. Thus, it provides a straightforward tool for a broad range of problems, like the study of the dependence of seismicity on the general properties of the fault networks and rheology, and the for- mulation and testing of different hypothesis about driving tectonic forces controlling the seismicity and geodynamics in a studied region. The method allows us to use a realistic geometry of the blocks, based on any relevant information, in particularly maps of morphostructural zoning. In BAFD modeling, driving tectonic forces (velocities of the boundary blocks and underlying medium) are prescribed using geodet- ic data (GPS) and geodynamic models. While the rheology of fault zones can also be incorporated using the existing knowledge of lithospheric structure (in terms of crust–mantle structure and velocities of seismic wave propagation) and heat flow data. The model provides an effective capability to include the set of docu- mented constraints supplied by widely available earthquake catalogs. This is done by means of the comparison of the frequency-to- magnitude relation, of the focal mechanisms, of earthquake productivity, Tectonophysics xxx (2014) xxx–xxx ⁎ Corresponding author. Tel.: +91 40 27012888. E-mail address: prantik@ngri.res.in (P. Mandal). TECTO-126395; No of Pages 13 http://dx.doi.org/10.1016/j.tecto.2014.07.020 0040-1951/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Please cite this article as: Vorobieva, I., et al., Numerical modeling of seismicity and geodynamics of the Kachchh rift zone, Gujarat, India, Tectonophysics (2014), http://dx.doi.org/10.1016/j.tecto.2014.07.020