Evidence on triggered seismicity associated with the  October 20, 1991 Uttarkashi earthquake (Garhwal Himalaya)

Shanker, D. and Kapur, Nipun and Singh, V. P. (2003) Evidence on triggered seismicity associated with the  October 20, 1991 Uttarkashi earthquake (Garhwal Himalaya). Acta Geodaetica et Geophysica Hungarica, 38 (3). pp. 363-374. ISSN 1217-8977

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Abstract

Two swarms of small earthquakes occurred on 22-24 October, 1995 and 13-18 September, 1996 about 15 km to the West-South-West (WSW) of the 1991 Uttarkashi earthquake (mb = 6.6) in Himalayas. The later swarm has migrated 5 km to the WSW of the former. Analyses of their seismicity rates, width of apertures and migration rates show that these swarms are triggered by a disturbance caused by the occurrence of the Uttarkashi earthquake thus triggered by this event. The disturbance, having slow propagation, rate represents evidence of creep of the earth material transferring stresses to the WSW direction. Occurrence  of creep (stable-slip) motion is supported by the inferred south-west (SW) orientation of compressive stresses in  Uttarkashi earthquake and presence of the north-west (NW) trending shear zones in the region. Ongoing convergence between India and Tibet would have provided the necessary tectonic forces transverse to the NW-SE trend of the Garhwal Himalayas indicating the future seismic activity of the region.

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