Crustal Strain Patterns in the Satpura Mountain Belt, Central India: Implications for Tectonics and Seismicity in Stable Continental Regions S. MOHANTY 1 Abstract—The Satpura Mountains of central India represents an ancient orogenic belt of the Mesoproterozoic time. It has a distinct sygmoidal (S-shaped) geometry with long EW and short NE–SW alignments. The mountain belt has been affected by tec- tonic activities throughout the geological past. The association of high seismicity, high heat flow and high Bouguer gravity anomaly with high topography of the region is a very distinct feature of the mountain range. Present analysis demonstrates that the average velocity for central India has a value of *54 mm/year towards N050°. The velocity field vector can be partitioned into an eastward component parallel to the Satpura Mountain Belt and a northward component across the belt. The partitioned components provide evidence for sinistral strike–slip deformation of anomalously high shear strain rate of *3 9 10 -9 /year in the region. Similar high shear strain rates are also found from the strain determined by GPS data. An extremely high rate of extensional strain (*600 9 10 -9 / year), which is comparable to that of the continental rift systems, is recorded from geodetic data of the Satpura Mountain Belt and the adjacent regions. Regional sinistral shape of the Satpura Mountains involved in a sinistral-slip transtension regime is interpreted to be the cause of high extensional and shear strain regime of the area. The occurrence of normal faulting detected in several deep seismic sounding profiles, the Moho upwarp, crustal thinning, high heat flow and high seismicity of the Satpura region are explained by this tectonic model. Key words: Seismicity, heatflow, gravity, topography, trans- tension, Satpura Mountains. 1. Introduction Seismicity of stable continental regions (conti- nental interiors) takes place in the upper part of a single rigid plate (JOHNSTON and KANTER, 1990). Two models (regional stress and local stress) have been proposed to explain the intraplate earthquakes that occur in these regions. In the first model, broad-scale uniform regio- nal stresses are considered to be responsible for the occurrence of intraplate earthquakes on low-strength zones around pre-existing faults of the upper crust (SYKES, 1978;HINZE et al., 1988;JOHNSTON and KANTER, 1990;ZOBACK, 1992). In the second model, concen- trations of local stresses in the regions of low viscosity zones in the crust and/or mantle have been explained by several processes (mantle convection plume, high temperature, fault intersections, and high water con- tent) (CAMPBELL, 1978;TALWANI, 1988, 1999;LIU and ZOBACK, 1997;STUART et al., 1997;KENNER and SEGALL, 2000;IIO and KOBAYASHI, 2002). Peninsular India was considered to be a stable shield free from earthquake activities. The recent occurrences of earthquakes greater than 5 in magni- tude in many places (e.g. at Bharuch in 1970; Anjar in 1956; Latur in 1993; Jabalpur in 1997 and Bhuj in 2001) have prompted many investigations into understanding seismic mechanisms in the apparently stable continental region. Historical records (BANSAL and GUPTA, 1998) show that earthquakes of low to moderate intensity have occurred in an *EW trending zone (the Satpura Mountain Belt) in the central part of India (Figs. 1, 2). The belt forms a distinct morphotectonic unit, which has been active from the Proterozoic to the present (WEST, 1962). The region has also been a zone of high heat flow (Fig. 3), high topography, high gravity anomaly (Fig. 4), and high seismicity (Fig. 2) in comparison to the sur- rounding areas (VARMA and BANERJEE, 1992;RAVI SHANKER, 1997;MISHRA and GUPTA, 1997;MOHANTY, 2004). The objective of the present analysis is to determine the causal links between these features and to develop a tectonic model for the seismicity of the Satpura region. 1 Department of Applied Geology, Indian School of Mines, Dhanbad 826004, India. E-mail: mohantysp@yahoo.com Pure Appl. Geophys. 168 (2011), 781–795 Ó 2010 Springer Basel AG DOI 10.1007/s00024-010-0152-7 Pure and Applied Geophysics