Potential source zones for Himalayan earthquakes: constraints from spatial–temporal clusters

Abstract

The Himalayan fold-thrust belt has been visited by many disastrous earthquakes (magnitude [ 6) time and again. This active collisional orogen bordering Indian subcontinent in the north remains a potential seismic threat of similar magnitude in the adjoining countries like India, Pakistan, Nepal, Bhutan and China. Though earthquake forecasting is riddled with all conjectures and still not a proven presumption, identifying likely source zones of such disastrous earthquakes would be an important contribution to seismic hazard assessment. In this study, we have worked out spatio-temporal clustering of earthquakes (Mb C 4.5; 1964 in the Himalayas. 'Point density' spatial statistics has helped in detecting 22 spatial seismicity clusters. Earthquake catalog is then treated with a moving time-distance window technique (inter-event time 35 days and distance 100 ± 20 km) to bring out temporal clusters by recognizing several foreshock-main shock-aftershock (FMA) sequences. A total of 53 such temporal sequences identified in the process are confined within the 22 spatial clusters. Though each of these spatio-temporal clusters deserves in-depth analysis, we short-listed only eight such clusters that are dissected by active tectonic discontinuities like MBT/MCT for detail study. Spatio-temporal clusters have been used to constrain the potential source zones. These eight well-defined spatio-temporal clusters demonstrate recurrent moderate to large earthquakes. We assumed that the length of these clusters are indicating the possible maximum rupture lengths and thus empirically estimated the maximum possible magnitudes of eight clusters that can be generated from them (from west to east) as 8. 0, 8.3, 8.2, 8.3, 8.2, 8.4, 8.0 and 7.7. Based on comparative study of the eight cluster zones contemplating with their temporal recurrences, historical seismic records, presence of intersecting faults and estimated magnitudes, we have guessed the possibility that Kangra, East Nepal, Garhwal and Kumaun-West Nepal clusters, in decreasing order of earthquake threat, are potential source zones for large earthquakes (C7.7 M) in future.

Clusters of Moderate Size Earthquakes along Main Central Thrust (MCT) in Himalaya

“…But these hypotheses need to be backed by experimental data. These inferences hold good for clustering of earthquakes in the Himalaya, especially in the lesser Himalaya where a characteristic earthquake model is apparent [10].…”

“…in the frontal belt of Himalaya. Though Lesser Himalayan earthquakes and related seismic hazards have been studied in details [10], the seismogenesis due to MCT and clustering of earthquakes related to this are somewhat neglected or oversimplified. At the same time, the seismic potentiality of the MCT to generate moderate size events (1980( Gangtok, 1991 Uttarkashi, 1999 Chamoli, 2009 Bomdila etc.)…”

Evaluation of seismogenesis behavior in Himalayan belt using data mining tools for forecasting

“…contained seismically monitored earthquake data recorded during the years 1900 -2010 by various agencies of the entire South Asia, which are statistically analyzed in this study to understand the nature and extent of seismogenesis in the Himalayan basin. We have correlated our results with other available published inferences to understand the nature of earthquake swarms and clusters [47]. In Figure 2, we attempted to show the completeness of the earthquake data which has been used in this study.…”

Identification of seismically susceptible areas in western Himalaya using pattern recognition

“…Compared to the regions already discussed, seismicity was found to be sparse in three regions, viz., south of the MBT, along the Jhelum Fault, and in the region along ISZ, roughly defined between MCT, Shyok Suture, Kishtwar Fault and Tso Morari Fault. Mukhopadhyay et al (2011) observed five spatial clusters in the vicinity of MCT in the entire Himalayan arc, and put forward the hypothesis that MCT is seismically active in segments. This aspect was used for segmentation of MCT (Mridula et al 2016, communicated).…”