image: Evolution of earthquake-induced tsunami in a bay traversed by a strike-slip fault. Colors indicate sea-surface height relative to undisturbed water level; wave height may exceed 2 m in some places. Top: Instantaneous tsunami generation phase coincident with earthquake propagation; Middle: postseismic tsunami generation phase, in which gravity-driven tsunami waves dominate; Bottom: backward propagation of large wave fronts reflected from bay tip. view more
Credit: Ares J. Rosakis
A study suggests that earthquakes on strike-slip faults can cause tsunamis in shallow bays even without an undersea landslide. Large tsunamis are generally attributed to earthquakes on normal and thrust faults that produce substantial vertical seafloor displacements, such as the magnitude 9.0 2011 Tohoku-Oki event. Through modeling, Ahmed Elbanna and colleagues found that earthquakes on strike-slip faults, which occur when two sides of a fault scrape along each other, can cause tsunamis in shallow bays even in the absence of vertical displacement from an undersea landslide. The authors developed a computational framework combining earthquake rupture dynamics with models of tsunami generation and propagation. The framework revealed that large horizontal displacements associated with strike-slip faulting can deform the depth contours of the bay by horizontally pulling and pushing the coastal slopes. The deformation leads to the displacement of water in the vertical direction and initiation of tsunami waves. The authors hypothesized that faults nearest to the shore and either traversing the bay or angling toward the coastline present the biggest hazard. Additionally, an apex at the bay's tip also increased the tsunami hazard. According to the authors, this tsunami generation mechanism may be a previously unrecognized hazard for coastal cities worldwide, and tsunami risk in areas near bays traversed by faults, such as San Francisco Bay and Tomales Bay in northern California, should be revisited.
Article #20-25632: "Anatomy of strike-slip fault tsunami genesis," by Ahmed Elbanna et al
MEDIA CONTACT: Ares J. Rosakis, California Institute of Technology, Pasadena, CA; tel: 626-200-9298; email: arosakis@caltech.edu; Ahmed E. Elbanna, University of Illinois Urbana-Champaign, IL; tel: 217-751-2117; email: elbanna2@illinois.edu
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Journal
Proceedings of the National Academy of Sciences