Overestimation of the earthquake hazard along the Himalaya: constraints in bracketing of medieval earthquakes from paleoseismic studies

Abstract

The Himalaya is one of the most seismically active regions of the world. (Mw 7.8) are the testimony to ongoing tectonic activity. In the last few decades, tremendous efforts have been made along the Himalayan arc to understand the patterns of earthquake occurrences, size, extent, and return periods. Some of the large magnitude earthquakes produced surface rupture, while some remained blind. Furthermore, due to the incompleteness of the earthquake catalogue, a very few events can be correlated with medieval earthquakes. Based on the existing paleoseismic data certainly, there exists a complexity to precisely determine the extent of surface rupture of these earthquakes and also for those events, which occurred during historic times. In this paper, we have compiled the paleo-seismological data and recalibrated the radiocarbon ages from the trenches excavated by previous workers along the entire Himalaya and compared earthquake scenario with the past. Our studies suggest that there were multiple earthquake events with overlapping surface ruptures in small patches with an average rupture length of ~300 km limiting Mw 7.8-8.0 for the Himalayan arc, rather than two or three giant earthquakes rupturing the whole front. It has been identified that the large magnitude Himalayan earthquakes, such as 1905 Kangra, 1934 Bihar-Nepal, and 1950 Assam, that have occurred within a time frame of 45 years. Now, if these events are dated, there is a high possibility that within the range of ±50 years, they may be considered as the remnant of one giant earthquake rupturing the entire Himalayan arc. Therefore, leading to an overestimation of seismic hazard scenario in Himalaya.

Himalayan earthquakes: a review of historical seismicity and early 21st century slip potential

“…Grey dashed bars indicate synchronous slip in single earthquakes with surface ruptures exceeding 200 km proposed variously by Mugnier et al (2013), Rajendran et al (2018b) and Wesnousky et al (2019). A, Arora & Malik (2017), ; Malik et al ( , 2008Malik et al ( , 2010a; B, Kumahara & Jayangondaperumal (2013); C, Kumar et al (2006) strain. For example, if the region of preseismic strain accumulation is only 20 km wide, the maximum slip that can be stored and released, no matter how long the interval since the previous earthquake, is only 2 m (20 km × 10 −4 strain).…”

“…They invoke arguments ranging from the observation that such a large earthquake is unknown in India's history, that creep processes absorb India's convergence, or that physical segmentation of the Himalaya prevents through-going propagation of ruptures longer than a few hundred kilometres (e.g. Srivastava et al 2013;Gupta & Gahalaut 2015;Arora & Malik 2017). However, support for each of the above constraints is subjective or weak, and in some cases, demonstrably wrong.…”

Hazards and disasters in the Anthropocene: some critical reflections for the future

“…Earth hazard geosciences span the interface of the earth and human and social sciences. The former is generally concerned with an analysis of potentially hazardous events and processes such as earthquakes, tsunamis, droughts, bushfires, and so on, seeking to understand their causes, processes, distributions, frequencies, magnitudes, intensities, past histories, likely future occurrence, impacts, and effects (Arora and Malik 2017;Hyndman and Hyndman 2014;Nott 2016;Somerville 2014). Experts are interested in observing, measuring, monitoring, modelling, and forecasting these potentially hazardous events.…”

Introduction to thematic collection “Historical and geological studies of earthquakes”

“…By conducting trenching surveys across active faults, occurrence of past surface ruptures or earthquakes can be examined. Arora and Malik (2017) compiled the paleoseismological data from numerous trenches excavated by previous workers along the entire Himalaya arc and recalibrated the radiocarbon ages. They showed that the pattern of past earthquake scenarios consists of overlapping multiple earthquakes with an average rupture length of ~ 300 km (Mw 7.8-8.0), rather than two or three giant earthquakes rupturing the entire Himalayan arc.…”