- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
The Himalaya is one of the most seismically active regions of the world. The occurrence of several large magnitude earthquakes viz. 1905 Kangra earthquake (Mw 7.8), 1934 Bihar–Nepal earthquake (Mw 8.2), 1950 Assam earthquake (Mw 8.4), 2005 Kashmir (Mw 7.6), and 2015 Gorkha (Mw 7.8) are the testimony to ongoing tectonic activity. In the last few decades, tremendous eforts 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 identifed 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.
One of the most robust conclusions that can be drawn from this work is that there were multiple events with overlapping surface ruptures along the HFT in the western, central, and eastern Himalaya. Interpreting that whole of the Himalayan front ruptured in two or three earthquakes is ambiguous and needs more extensive research work to verify this postulation. From our analysis, it can be ascertained that Himalayan front was ruptured by multiple events in small patches with an average rupture length of ~300 km, limiting earthquakes with a magnitude of Mw 7.9–8.0. Te 1255 AD medieval earthquake reported in Kathmandu Valley ruptured at least 350 km of the Himalayan frontal arc from Koliabas to Bardibas in eastern Nepal. For 1555 AD, Kashmir earthquake more work is required to precisely comment on the extent of surface rupture. For 1408/1344 AD earthquake, there could be two scenarios, either it ruptured the entire ~1000 km of the Himalayan arc from Kathmandu to Hajipur or there were two separate events with a range of 1450 ± 50 AD in the 15th century. Te northwest Himalaya, except one hinterland 1905 AD Kangra earthquake, has not experienced any recent large magnitude earthquake after 1344, 1505, and 1555 AD events. Since then, around 600 years have passed, and thus, a possibility of occurrence of a large or great magnitude earthquake in this region cannot be ruled out.