Experimental investigation of strong ground motion due to thrust-fault earthquakes

Vahe Gabuchian, Ares J. Rosakis, Nadia Lapusta, & David D. Oglesby

Published 2014, SCEC Contribution #1767

Thrust-fault earthquakes are studied in the laboratory earthquake setup previously used to investigate analog strike-slip seismic events. Dynamic mode II ruptures are generated along pre-existing faults in an analog material, Homalite H-100, and their interaction with the free surface is studied for both sub-Rayleigh and supershear rupture speeds. High-speed digital photography and laser velocimeter diagnostics are used synergistically to identify and study the ground velocity signatures caused by the various features of the generated ruptures. The obtained surface-normal motions of both sub-Rayleigh and supershear ruptures show substantial asymmetry between the hanging and foot-wall, with the hanging-wall experiencing much larger velocity amplitudes. The main features of the surface velocity traces at various stations can be explained by the calculated arrivals of various waves and fronts - Mach cones, P and S waves, and sub-Rayleigh features. In both the sub-Rayleigh and supershear cases, the arrival of the rupture tip generates a prominent Rayleigh wave traveling along the simulated earth's surface. Supershear events feature larger amplitudes of ground shaking profiles but exhibit less hanging-to-foot-wall asymmetry than sub-Rayleigh events. All signatures in the surface motion records attenuate and broaden with increasing distance from the fault trace. The signatures corresponding to the arrival of the Mach fronts attenuate with distance at a slower rate than those from sub-Rayleigh ruptures. The arrival of the up-dip rupture at the free surface creates a “reflected”, down-dip propagating rupture that generates its own Mach cone. These additional Mach fronts further amplify ground shaking on the hanging and foot walls.

Citation
Gabuchian, V., Rosakis, A. J., Lapusta, N., & Oglesby, D. D. (2014). Experimental investigation of strong ground motion due to thrust-fault earthquakes. Journal of Geophysical Research: Solid Earth, 119(2), 1316-1336. doi: 10.1002/2013JB010409.