Seismotectonics of the Nepal Himalaya from a local seismic network

The National Seismological Network of Nepal consists of 17 short period sei smic stations operated since 1994. It provides an exceptional view of the m icroseismic activity over nearly one third of the Himalayan are, including the only segment, between longitudes 78 degrees E and 85 degrees E, that ha s 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 a ccumulation in the upper crust associated with creep in the lower crust ben eath the Higher Himalaya. The seismic activity is more intense around 82 de grees E in Far-Western Nepal and around 87 degrees E in Eastern Nepal. West ern Nepal, between 82.5 and 85 degrees E, is characterized by a particularl y low level of seismic activity. We propose that these lateral variations a re related to segmentation of the Main Himalayan Thrust Fault. The major ju nctions between the different segments would thus lie at about 87 degrees E and 82 degrees E with possibly an intermediate one at about 85 degrees E. These junctions seem to coincide with some of the active normal faults in S outhern Tibet. Lateral variation of seismic activity is also found to corre late with lateral Variations of geological structures suggesting that segme ntation is a long-lived feature. We infer four 250-400 km long segments tha t could produce earthquakes comparable to the M = 8.4 Bihar-Nepal earthquak e that struck eastern Nepal in 1934. Assuming the model of the characterist ic earthquake, the recurrence interval between two such earthquakes on a gi ven reserved.