Publications

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2016
Melgar, D, Allen RM, Riquelme S, Geng JH, Bravo F, Baez JC, Parra H, Barrientos S, Fang P, Bock Y, Bevis M, Caccamise DJ, Vigny C, Moreno M, Smalley R.  2016.  Local tsunami warnings: Perspectives from recent large events. Geophysical Research Letters. 43:1109-1117.   10.1002/2015gl067100   AbstractWebsite

We demonstrate a flexible strategy for local tsunami warning that relies on regional geodetic and seismic stations. Through retrospective analysis of four recent tsunamigenic events in Japan and Chile, we show that rapid earthquake source information, provided by methodologies developed for earthquake early warning, can be used to generate timely estimates of maximum expected tsunami amplitude with enough accuracy for tsunami warning. We validate the technique by comparing to detailed models of earthquake source and tsunami propagation as well as field surveys of tsunami inundation. Our approach does not require deployment of new geodetic and seismic instrumentation in many subduction zones and could be implemented rapidly by national monitoring and warning agencies. We illustrate the potential impact of our method with a detailed comparison to the actual timeline of events during the recent 2015 M(w)8.3 Illapel, Chile, earthquake and tsunami that prompted the evacuation of 1 million people.

2009
Barbot, S, Fialko Y, Bock Y.  2009.  Postseismic deformation due to the M(w) 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault with spatially variable rate-and-state friction parameters. Journal of Geophysical Research-Solid Earth. 114   10.1029/2008jb005748   AbstractWebsite

We investigate the coseismic and postseismic deformation due to the M(w) 6.0 2004 Parkfield, California, earthquake. We produce coseismic and postseismic slip models by inverting data from an array of 14 continuous GPS stations from the SCIGN network. Kinematic inversions of postseismic GPS data over a time period of 3 years show that afterslip occurred in areas of low seismicity and low coseismic slip, predominantly at a depth of similar to 5 km. Inversions suggest that coseismic stress increases were relaxed by predominantly aseismic afterslip on a fault plane. The kinetics of afterslip is consistent with a velocity-strengthening friction generalized to include the case of infinitesimal velocities. We performed simulations of stress-driven creep using a numerical model that evaluates the time-dependent deformation due to coseismic stress changes in a viscoelastoplastic half-space. Starting with a coseismic slip distribution, we compute the time-dependent evolution of afterslip on a fault plane and the associated displacements at the GPS stations. Data are best explained by a rate-strengthening model with frictional parameter (a - b) = 7 x 10(-3), at a high end of values observed in laboratory experiments. We also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks. The rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip, suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep. The San Andreas fault around Parkfield is deduced to have large along-strike variations in rate-and-state frictional properties. Velocity strengthening areas may be responsible for the separation of the coseismic slip in two distinct asperities and for the ongoing aseismic creep occurring between the velocity-weakening patches after the 2004 rupture.