Medieval seismicity on the Himalayan Frontal Thrust Fault at Lal Dhang, Uttarakhand, India
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Abstract
The Himalayan Frontal Thrust Fault (HFT) lies at the active, tectonic boundary between Eurasia and the Indian subcontinent. Continuous convergence between the landmasses causes strain to accumulate on the fault, which is intermittently released during seismic events. Throughout the last two centuries, several large-magnitude earthquakes have occurred on the HFT without producing measurable vertical offsets at the ground surface, leading many to refer to these events as blind-thrust earthquakes. However, large fault scarps along the HFT indicate that past ruptures of the fault were not blind and may have been much greater in magnitude. Recent paleoseismological studies have aimed to characterize the earthquakes that generated these features. One of these studies focused on defining the seismic parameters of a specific segment of the fault by comparing findings across several sites, including the site of Lal Dhang in Uttarakhand, India. The results of this study point to lingering uncertainties specific to the site of Lal Dhang that warrant additional research, including poor temporal constraint of past fault ruptures, disparities in deformational structures when compared to surrounding sites, discrepancies in fault scarp height as compared to apparent net slip measurements, and questions surrounding local interactions between fluvial terrace development and fault scarp generation. The goal of this research was to conduct a comprehensive and detailed analysis of the seismic history at the site of Lal Dhang. The work was distributed across three intersecting objectives: 1) development of an age model for previous earthquakes on the segment of the HFT that includes Lal Dhang, 2) determination of the faulting sequence, timing, and seismic parameters of previous earthquakes at the site, and 3) investigation of the interaction between local tectonic and fluvial landscape development. Data produced through this study have narrowed the constraint on rupture timing at the site of Lal Dhang and along the western section of the CSG. Results presented here include improved estimates for coseismic slip and vertical separation at the site of Lal Dhang, which are comparable to surrounding sites, and a model for local fault scarp generation and associated landscape development. Implications for future research are considered and discussed.
Table of Contents
Introduction -- A paleoseismic age model for large-magnitude earthquakes on fault segments of the Himalayan Frontal Thrust in the central seismic gap of northern India -- Late Medieval seismicity on the Himalayan Frontal Thrust at Lal Dhang, Uttarakhand, India -- Tectonic influences on landscape development along the Himalayan Frontal Thrust Fault at Lal Dhang, Uttarakhand, India
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Ph.D. (Doctor of Philosophy)