Characteristics of earthquake sequence in northern Himalayan region of South Central Tibet – Precursor search and location of potential area of future earthquake

Abstract

This paper reports that three earthquake sequence occurred in 1996 ( m b 5.9), 1998 ( m b 5.8) and 2004–2005 ( m b 6.2, 6.3) were observed preceding the anomalous seismic activity. The nature of anomalous seismicity associated with these earthquakes have been investigated considering earthquakes with m b ⩾ 4.1 (cut off magnitude for this region) in four seismic episodes (NAGM): normal/background (N); anomalous/swarm (A); precursory gap (G) and mainshock sequence (M), respectively. It is established here that the anomalous seismicity/swarm patterns follow episodes of relatively very low seismic activity and it is an important finding to visualize that an area might be preparing for the occurrence of a forthcoming mainshock. Such anomalous seismic patterns were observed prior to medium size mainshocks that occurred from 1963 to 2006 in South Central Tibet (SCT) region to the north of Central Himalaya. From these observations it may be inferred here that the patterns of anomalous seismicity/earthquake swarms may be considered as an important parameter (precursor) for the forecasting of long-range earthquake hazards in the SCT region. In consideration of spatial and the temporal clustering of swarm events that are prominent and confined in a vertical column of 10–45 km, enabled to locate potential area enclosed by 29.6–30.1°N and 87.8–88.1°E where future earthquake of magnitude 6.0 and above in the depth range 25 ± 15 km may be seated. In view of this multi-parameter short term precursory signals monitoring is suggested for the delineated preparatory area to make earthquake prediction/forecasting programs more meaningful.