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摘要
Precursory swarms associated with major earthquakes in the Western Nepal Himalaya and its adjoining region (bounded by 28.0A degrees-31.0A degrees N and 79.5A degrees-82.2A degrees E) have been studied using seismicity data from 1963 to 2006. The delineation of preparation zones for future seismic disturbances is carried out using the temporal and the spatial distribution of earthquakes, considering the events with cutoff magnitude m (b) a parts per thousand yen 4.3 in four anomalous episodes: normal/background (N); anomalous/swarm (A); precursory gap (G) and main shock sequence (M), respectively. Five cases of anomalous seismicity have been identified, including two cases for which quiescence episodes still continue. Three moderate earthquakes of 1980 (m (b) 6.1, Bajhang), 1984 (m (b) 5.6, Bajura) and 1999 (m (b) 6.6, Chamoli) in Western Nepal and its adjoining Indian region were preceded by well-defined patterns of anomalous seismicity/precursory swarm. Two additional cases of anomalous seismicity patterns were observed: (1) 1999-2006, and (2) 2003-2006. In these two cases no main shock has yet occurred. However, the seismicity from 1999 onwards has fluctuated from low to high to low, as in the precursory sequences for previous earthquakes. The occurrence of the swarm sequence followed by a quiescence phase, which is still continuing, is an indication of a precursory seismicity gap in the region. From the predictive equations developed for the Himalayan frontal arc, it is estimated that an earthquake of M 6.5 +/- A 0.5 may occur at any time up to 2011 in an area bounded by 29.3A degrees-30.5A degrees N and 81.2A degrees-81.9A degrees E, in the focal depth range 10-30 km.
- 出版日期2010-6
