Publication Date:
2014-08-08
Description:
ABSTRACT The return times of large Himalayan earthquakes are poorly constrained. Despite historical devastation of cities along the mountain range, definitive links between events and specific segments of the Main Frontal Thrust (MFT) are not established, and paleo-seismological records have not documented the occurrence of several similar events at the same location. In east-central Nepal, however, recently discovered primary surface ruptures of that mega-thrust in the AD 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces. We present here a refined, longer slip history of the MFT's two overlapping strands (Patu and Bardibas Thrusts) in that region, based on updated geomorphic/neo-tectonic mapping of active faulting, two 1.3 km-long shallow seismic profiles, and logging of 2 rivercut cliffs, 3 paleo-seismological trenches and several pits, with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages. The amount of hanging-wall uplift on the Patu thrust since 3650 ± 450 years requires 3 more events than the two aforementioned. The uplift rate (8.5 ± 1.5 mm/yr), thrust dip (25° ± 5 °N) and apparent characteristic behavior imply 12–17.5 m of slip per event. On the Bardibas thrust, discrete pulses of colluvial deposition resulting from the co-seismic growth of a flexural fold scarp suggest the occurrence of 6 or 7 paleo-earthquakes in the last 4500 ± 50 years. The coeval rupture of both strands during great Himalayan earthquakes implies that, in Eastern Nepal, the Late Holocene return times of such earthquakes probably ranged between 750 ± 140 and 870 ± 350 years.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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