Abstract

Three microearthquake surveys were carried out in Shillong Plateau, Mikir Hills, and Assam valley areas during 1984 to 1986. Some 422 events are relocated by the Homogeneous Station Method. The microseismicity map reveals intense crustal (10 to 40 km) activity beneath the Tura area of Shillong Plateau. The areas to the west of Shillong and the area around Mikir Hills also show high activity. The microseismicity map further shows major tectonic lineaments that are compatible with the Landsat Imagery lineaments and the major faults. Composite focal mechanisms of the microearthquakes show spatial variation of the tectonic stresses in the region. An ENE-WSW horizontal compressive stress is dominant in the Tura area, whereas a SE-NW horizontal compressive stress is dominant in the Shillong and Mikir Hills areas.

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