DEVELOPING A PALEOSEISMIC AGE MODEL FOR LARGE-MAGNITUDE EARTHQUAKES ON FAULT SEGMENTS OF THE HIMALAYAN FRONTAL THRUST IN INDIA

Crustal collision at the boundary between Eurasia and the Indian subcontinent has produced a system of transverse, thrust faults which accommodate a share of the strain associated with convergence and the concomitant uplift of the Himalayan mountain range. The foremost of these faults is the Himalayan Frontal Thrust (HFT), which impels depositional units of an earlier foreland basin over those of the Indo-Gangetic Plain. Throughout the last two centuries, the HFT has produced numerous, large-magnitude earthquakes along discrete segments of the fault that are constrained through instrumental and historical records. Paleoseismic studies have aimed to establish comparable constraint for pre-instrumental ruptures of the fault. Of particular interest is the segment of the fault that lies between the areas affected by the 1905 A.D. Kangra and 1934 A.D. Nepal-Bihar earthquakes, due to an apparent long-term quiescence that suggests the potential for impending large-scale rupture. Establishing the timing of earthquakes along this segment of the HFT, known as the Central Seismic Gap (CSG), is critical in assessing seismic risks for highly populated areas proximal to the fault. While several paleoseismic trenching studies have been conducted across the HFT along and adjacent to the CSG, a comprehensive analysis of the radiocarbon ages associated with these studies has not previously been completed. Accordingly, the object of this study is to provide improved temporal constraint for large-magnitude ruptures on the CSG by compiling recent, paleoseismic findings from seven published trench sites along this segment of the fault. Age models were developed for each of the sites based on published radiocarbon results, with consideration given to the stratigraphic context of each trench, using the OxCal software program. The results are presented here alongside published trench logs in a panoptic illustration that offers a coherent chronology for large-scale ruptures of the CSG, indicating that the western section likely ruptured in the event corresponding to historical accounts of an earthquake in 1344 A.D.