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Published October 1999 | public
Journal Article

Seismotectonics of the Nepal Himalaya from a local seismic network

Abstract

The National Seismological Network of Nepal consists of 17 short period seismic stations operated since 1994. It provides an exceptional view of the microseismic activity over nearly one third of the Himalayan arc, including the only segment, between longitudes 78°E and 85°E, that has not produced any M>8 earthquakes over the last century. It shows a belt of seismicity that follows approximately the front of the Higher Himalaya with most of the seismic moment being released at depths between 10 and 20 km. This belt of seismicity is interpreted to reflect interseismic stress accumulation in the upper crust associated with creep in the lower crust beneath the Higher Himalaya. The seismic activity is more intense around 82°E in Far-Western Nepal and around 87°E in Eastern Nepal. Western Nepal, between 82.5 and 85°E, is characterized by a particularly low level of seismic activity. We propose that these lateral variations are related to segmentation of the Main Himalayan Thrust Fault. The major junctions between the different segments would thus lie at about 87°E and 82°E with possibly an intermediate one at about 85°E. These junctions seem to coincide with some of the active normal faults in Southern Tibet. Lateral variation of seismic activity is also found to correlate with lateral variations of geological structures suggesting that segmentation is a long-lived feature. We infer four 250–400 km long segments that could produce earthquakes comparable to the M=8.4 Bihar–Nepal earthquake that struck eastern Nepal in 1934. Assuming the model of the characteristic earthquake, the recurrence interval between two such earthquakes on a given segment is between 130 and 260 years.

Additional Information

© 1999 Elsevier Science Ltd. The authors are most grateful to all the staff of the National Seismological Centre (NSC), DMG and LDG who have contributed to the installation and maintenance of the permanent and mobile stations and routine processing of the seismic data. G.R. Chitrakar and B. Kafle of NSC are acknowledged for editing the routine processing of seismic data. Figures were drafted by F. Guillois and E. Thauvin. We benefited from reviews by N. Seeber and Anne Paul. K. Burke and Dr Upreti provided helpful comments for the preparation of the final version of the manuscript.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023