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Using Heterogeneous 3D Earth Models to Constrain Interseismic and Postseismic Deformation in Southern California and Nepal


Rollins, John Christopher (2018) Using Heterogeneous 3D Earth Models to Constrain Interseismic and Postseismic Deformation in Southern California and Nepal. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9X06572.


We characterize interseismic strain accumulation across the Los Angeles basin and postseismic deformation following the 2010 Mw=7.2 El Mayor-Cucapah and 2015 Mw=7.8 Nepal earthquakes using geodetic data. These settings are all characterized by strong 3D heterogeneities of elastic structure, ductile properties, fault geometries, and fault slip behavior, and we use constaints from seismology, long-term tectonic modeling, geology, and other sources to construct detailed models of these heterogeneities. Postseismic surface displacements following the 2010 El Mayor-Cucapah earthquake indicate viscoelastic relaxation in the shallow Salton Trough mantle and possibly the lower crust, a process that would have been enhanced by high heat flow induced by crustal extension at the tip of the Gulf of California. We find that a dense and prolonged aftershock sequence in the Yuha Desert may have been driven by aseismic afterslip coupled with fluid flow. Our study of interseismic strain accumulation across the Los Angeles basin shows that the soft sedimentary basin has a first-order effect on the elastostatic Green’s functions mapping fault creep and locking at depth to surface deformation, and therefore on the estimation of interseismic fault creep rates and strain accumulation at depth. We infer modest interseismic coupling on the three major thrust faults underlying the Los Angeles basin, corresponding to an annual seismic moment deficit buildup rate (to be presumably released in earthquakes) of 1.7 +1.2/-0.5 x 1017 Nm/yr. We estimate the long-term seismicity model needed to balance the rate of moment deficit accumulation assuming a truncated Gutenberg-Richter magnitude-frequency distribution of earthquakes. The long-term catalog is consistent with the instrumental rates of small and moderate earthquakes and tops out at a M~6.9 earthquake every ~430 years. Finally, we characterize the postseismic deformation following the 2015 Nepal earthquake using models of the thermal structure, state of stress, and rheology that are based on the long-term evolution and topography of the Himalaya. The rheological structure based on these models predicts negligible postseismic viscoelastic deformation. Afterslip on the downdip extension of the rupture cannot realistically explain the observed displacements either. We find that the postseismic deformation is well explained by a combination of afterslip on the downdip edge of the coseismic rupture (as well as a narrow zone in between the mainshock and a large aftershock) and, more prominently, transient viscoelastic relaxation in the hot Tibetan crust. These processes contribute to the stress loading of the Main Himalayan Thrust.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Interseismic strain accumulation; postseismic deformation; geodesy
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Avouac, Jean-Philippe
Thesis Committee:
  • Gurnis, Michael C. (chair)
  • Avouac, Jean-Philippe
  • Lapusta, Nadia
  • Clayton, Robert W.
Defense Date:9 November 2017
Non-Caltech Author Email:john.c.rollins (AT)
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX09AP08H
Record Number:CaltechTHESIS:11202017-145930076
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Ch. 2. adapted for Appendix.
Rollins, John Christopher0000-0002-5291-6956
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10563
Deposited By: John Rollins
Deposited On:21 Nov 2017 22:02
Last Modified:04 Oct 2019 00:18

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