Structural Control on Downdip Locking Extent of the Himalayan Megathrust. Issue 6 (19th June 2018)

• Record Type: Journal Article
• Authors: Lindsey, Eric O.; Almeida, Rafael; Mallick, Rishav; Hubbard, Judith; Bradley, Kyle; Tsang, Louisa L. H.; Liu, Yixiang; Burgmann, Roland; Hill, Emma M.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 6(2018)
• Page Start: 5265
• Page End: 5278
• Publication Date: 2018-06-19
• Subjects: interseismic deformation -- fault geometry -- Nepal -- Main Himalayan Thrust -- fault structure -- duplex; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2018JB015868
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Geologic reconstructions of the Main Himalayan Thrust in Nepal show a laterally extensive midcrustal ramp, hypothesized to form the downdip boundary of interseismic locking. Using a recent compilation of interseismic GPS velocities and a simplified model of fault coupling, we estimate the width of coupling across Nepal using a series of two‐dimensional transects. We find that the downdip width of fault coupling increases smoothly from 70 to 90 km in eastern Nepal to 100–110 km in central Nepal, then narrows again in western Nepal. The inferred coupling transition is closely aligned with geologic reconstructions of the base of the midcrustal ramp in central and eastern Nepal, but in western Nepal, the data suggest that the location is intermediate between two proposed ramp locations. The result for western Nepal implies either an anomalous coupling transition that occurs along a shallowly dipping portion of the fault or that both ramps may be partially coupled and that a proposed crustal‐scale duplexing process may be active during the interseismic period. We also find that the models require a convergence rate of 15.5 ± 2 mm/year throughout Nepal, reducing the geodetic moment accumulation rate by up to 30% compared with earlier models, partially resolving an inferred discrepancy between geodetic and paleoseismic estimates of moment release across the Himalaya. Key Points: The limit of fault coupling on the Main Himalayan Thrust agrees with geologic models of the midcrustal ramp in central and eastern Nepal In western Nepal, the fault coupling transition falls between two proposed ramp locations, and we suggest that both may be active The moment accumulation rate in our model is 30% smaller than previous results, partially resolving an apparent seismic moment deficit