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Aftershock tectonics of the 1978 Tabas-e-Golshan (Iran) earthquake sequence: a documented active 'thin-and thick-skinned tectonic' case |
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| Authors: | Manuel Berberian |
| Institution: | Department of Earth Sciences, Bullard Laboratories, University of Cambridge, Madingley Rise, Madingley Road, Cambridge CB3 OEZ |
| Abstract: | Summary. In this study a locally recorded aftershock sequence of the 1978 Tabas-e-Golshan earthquake ( M Almost all aftershocks follow very closely the pattern of the earthquake faults at the surface and lie in the hanging-wall block of the active fault. The hypocentres occurred mainly at depths less than 23 km with a high concentration of seismic activity between 8–14 km depth. The aftershocks clearly demonstrate an active imbricate listric thrust system with fault planes flattening into a basement decollement zone, and the reactivation of different basement reverse faults in response to a considerable amount of shortening of the top sedimentary cover. The sense of motion was almost universally thrusting and the aftershocks shared the same tectonic causes as the main shock. The study indicates that the development of the young fold-thrust mountain belts necessarily involves basement shortening (thin-and thick-skinned tectonics) and that the 'frontal reverse faults' in young active fold-thrust mountain belts are the most seismically active faults. Geological and seismic data propose that the active frontal reverse fault systems are possibly reactivated old normal faults and may add support to the contention of reversal of fault motion during re thickening of continental crust. The active 'thin-and thick-skinned tectonics' documented in this study may prevail in other young and active fold-thrust mountain belts which are characterized by a thick sequence of telescoped top sedimentary cover over a decollement detachment zone. |
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