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Experimental Investigation of Thrust Fault Rupture Mechanics

Citation

Gabuchian, Vahe (2015) Experimental Investigation of Thrust Fault Rupture Mechanics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9J96497. http://resolver.caltech.edu/CaltechTHESIS:04222014-195027916

Abstract

Thrust fault earthquakes are investigated in the laboratory by generating dynamic shear ruptures along pre-existing frictional faults in rectangular plates. A considerable body of evidence suggests that dip-slip earthquakes exhibit enhanced ground motions in the acute hanging wall wedge as an outcome of broken symmetry between hanging and foot wall plates with respect to the earth surface. To understand the physical behavior of thrust fault earthquakes, particularly ground motions near the earth surface, ruptures are nucleated in analog laboratory experiments and guided up-dip towards the simulated earth surface. The transient slip event and emitted radiation mimic a natural thrust earthquake. High-speed photography and laser velocimeters capture the rupture evolution, outputting a full-field view of photo-elastic fringe contours proportional to maximum shearing stresses as well as continuous ground motion velocity records at discrete points on the specimen. Earth surface-normal measurements validate selective enhancement of hanging wall ground motions for both sub-Rayleigh and super-shear rupture speeds. The earth surface breaks upon rupture tip arrival to the fault trace, generating prominent Rayleigh surface waves. A rupture wave is sensed in the hanging wall but is, however, absent from the foot wall plate: a direct consequence of proximity from fault to seismometer. Signatures in earth surface-normal records attenuate with distance from the fault trace. Super-shear earthquakes feature greater amplitudes of ground shaking profiles, as expected from the increased tectonic pressures required to induce super-shear transition. Paired stations measure fault parallel and fault normal ground motions at various depths, which yield slip and opening rates through direct subtraction of like components. Peak fault slip and opening rates associated with the rupture tip increase with proximity to the fault trace, a result of selective ground motion amplification in the hanging wall. Fault opening rates indicate that the hanging and foot walls detach near the earth surface, a phenomenon promoted by a decrease in magnitude of far-field tectonic loads. Subsequent shutting of the fault sends an opening pulse back down-dip. In case of a sub-Rayleigh earthquake, feedback from the reflected S wave re-ruptures the locked fault at super-shear speeds, providing another mechanism of super-shear transition.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:thrust fault; earthquake; experiment; hanging wall; foot wall; ground motion; asymmetry; fault opening; slip; supershear; rupture; mechanics
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Rosakis, Ares J.
Group:Graduate Aerospace Laboratories
Thesis Committee:
  • Ravichandran, Guruswami (chair)
  • Rosakis, Ares J.
  • Lapusta, Nadia
  • Bhat, Harsha S.
Defense Date:23 April 2015
Non-Caltech Author Email:vahegabuchian (AT) gmail.com
Funders:
Funding AgencyGrant Number
National Science FoundationEAR-1142183
Southern California Earthquake CenterEAR-0529922
Department of Energy National Nuclear Security AdministrationDE-FC52-08NA28613
Record Number:CaltechTHESIS:04222014-195027916
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:04222014-195027916
DOI:10.7907/Z9J96497
ORCID:
AuthorORCID
Gabuchian, Vahe0000-0001-7457-5921
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8199
Collection:CaltechTHESIS
Deposited By: Vahe Gabuchian
Deposited On:11 May 2016 16:54
Last Modified:11 May 2016 16:54

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