Seismotectonic Study of the Two Recent SCR Earthquakes in Central India

Seismotectonics of the two recent earthquakes, 1993 Killari, m_h 6.3 and 1997 Jabalpur, m_h 6.0, are examined to understand the nature of seismicity and generating process of the Stable Continental Region (SCR) earthquakes in central India. The Killari earthquake and its aftershocks are confined to a shallower depth (0 - 15 km), a common type of SCR events, whereas the Jabdpur earthquake and its aftershocks occurred at a deeper depth (35-40 km), uncommon in SCR seismicity. The frequency-magnitude relation (b-value) estimated for the two aftershock sequences is compatible (0.46 and 0.49), and is typical for a SCR. The attenuation rates (p-value) of the aftershocks are, however, very much different; it is low (0.27) for the Killari aftershock sequence and high (1.30) for the Jabalpur sequence; the aftershocks continued for about six months in the Killari area, whereas it died down within one and a half months in Jabalpur area for almost a similar magnitude of the main shock. The maximum intensity reached VII for both the main shocks.

Fault-plane solutions of the Killari earthquakes reveal reverse faulting for the main shock and the deeper aftershocks (depth 6-15 km) and strike-slip faulting for the shallower aftershocks (0-5 km). It is inferred that interaction of two faults generated the main shock and the aftershocks at shallower depth. These two faults are correlatable with the E-W Tirna river and NW-SE Tirna tributary. The Jabalpur earthquake and its aftershocks, on the other hand, reveal a consistent reverse-fault mechanism with a left-lateral strike-slip motion. The deep ischolar_mained Narmada South Fault has been activated at the crust-mantle boundary and generated the main shock and the aftershocks at deeper depth. The consistent NNE-SSW compressional stress, revealed by the fault-plane solutions, suggests that the SCR earthquakes in Peninsular India are generated by the relative movement of various crustal blocks along pre-existing faults/weak zones at different depth levels due to post collisional movement of the Indian plate in the NNE direction.