Earthquake Geology of Jammu, Kashmir & NW Himalaya

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THE MOMENT Magnitude (Mw) 7.8 earthquake that occurred on 25th April 2015 in Nepal is ranked among the largest ever recorded instrumental earthquakes in Nepal since 1934, Bihar-Nepal earthquake of Mw 8.4, which killed about 15000 people. This earthquake was expected, and was hosted on one of the segments of Main Frontal Thrust (MFT), the megathrust structure that accommodates on an average some ~2 cm/year of the regional convergence between India and Eurasia plates. The total length of this fault is more than 2000 kilometer, and it marks the present day active plate boundary along which accumulated stress is occasionally released through medium to large magnitude earthquakes. Thus, it is not surprising that the ongoing collision has resulted in more than seven major earthquakes along the Himalayan arc in the past ~100 years.

Jammu and Kashmir lies on the west of the active plate boundary, and it passed through Jammu city; however, no trace of this fault has been mapped on surface in this region, and thus it is assumed that it runs under as a blind structure (have not ruptured the surface) that controls the frontal-fold thrust belt in Jammu region. The latest research demonstrates that there is a possibility of a major earthquake on this fault, which could happen anytime because currently in Jammu, and Kashmir region the tectonic stress is ripe to host such an earthquake. However, the presence of another major fault, the Riasi fault system, south of the Kashmir basin, has also been seismically quite for some time, and thus there is a possibility that this fault could host a major earthquake anytime soon. Importantly this fault merges at depth with the frontal blind thrust, and thus there is possibility that major earthquake could either occur on the Riasi fault system or the frontal fold-thrust belt, or both. Such an earthquake is estimated to be of (Mw > 8) or even bigger, a much bigger event than the Mw 7.6 earthquake that occurred on the Balakot- Bagh fault in Pakistan Azad Kashmir in 2005.

A well-documented major fault system cuts through Kashmir basin, and has the potential to host Mw 7.6 or greater earthquake. This fault system has not been studied in detail, thus there are greater uncertainties in understanding of this very fault. Although geomorphic studies clearly suggest that the fault is active, and has recently moved however, only a detailed work in the future will shed more light on its activity, and how much energy has been released through the fault.

With our current understanding of all the three (03) major active earthquake sources mapped in Jammu and Kashmir region (from north these are: Kashmir basin fault/Balapor fault, Raisi fault, frontal fold-thrust belt) it is clear that a major or mega earthquake is bound to happen on either the Raisi fault or the frontal fold-thrust belt or both. This can occur anytime. We understand the limitations of a few studies that have been done in Jammu, and Kashmir region to map, and understand the seismic risk, however, the major disaster cannot be overlooked. With many uncertainties that remain to understand the nucleation, propagation, behavior, and stress accumulation on faults, unknown active faults, it is safe to conclude that major/mega earthquake disaster is Kashmir is unavoidable. And for a reliable seismic hazard and risk evaluation some detailed paleoseismological studies are extremely necessary to determine the current status of strain accumulation on faults/folds or fault-segments.

Further, our current knowledge about major earthquakes suggests that they generally do not follow a pattern, and occur randomly anytime, thus the time since the last great historical earthquake is of no real significance. This means that the concept of a rather regular return time between catastrophic earthquakes is probably not relevant for the Himalaya.

Please understand that the earthquake threat in Jammu and Kashmir is real and, it should not be taken lightly. However the earthquake science is at a stage where scientists more or less understand the cause of earthquakes but are not very confident about the prediction of an incoming event. This means that there is a need to understand how to live with earthquakes without a successful prediction in sight. This can be achieved if we strictly abide by the strict construction standards, careful geological evaluation of building sites, and public education. This should be done now.

And in Jammu, and Kashmir there is a greater need to start a state of the art earthquake research facility for the security, and safety of the people.

 

 

 

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