
Application of realtime GPS to earthquake early warning
in subduction and strikeslip environments

Simona Colombelli
UC Berkeley and Università di Napoli Federico II
Richard M. Allen
University of California, Berkeley
Aldo Zollo
Università di Napoli Federico II
J. Geophys. Res., 118, 3448–3461, doi: 10.1002/jgrb.50242, 2013.
Download a preprint:
ColombelliAllenZolloGPS4EEWJGR2013.pdf
 
Application of the realtime GPS methodology to the M9 TohokuOki earthquake. More videos below.

Abstract
We explore the application of GPS data to earthquake early warning and investigate whether the coseismic ground deformation can be used to provide fast and reliable magnitude estimations and ground shaking predictions. We use an algorithm to extract the permanent static offset from GPS displacement time series and invert for the slip distribution on the fault plane, which is discretized into a small number of rectangular patches. We developed a completely “selfadapting” strategy in which the initial fault plane model is built based on a quick, approximate magnitude estimation and is then allowed to increase in size based on the evolutionary magnitude estimation resulting from the slip inversion. Two main early warning outputs are delivered in realtime: magnitude and the alongstrike extent of the rupture area. These are finally used to predict the expected ground shaking due to the finite source. We tested the proposed strategy by simulating realtime environments for three earthquakes. For the Mw 9.0, 2011 TohokuOki earthquake, our algorithm provides the first magnitude estimate of 8.2 at 39 s after the origin time and then gradually increases to 8.9 at 120 s. The estimated rupture length remains constant from the outset at ~360 km. For the Mw 8.3, 2003 TokachiOki earthquake, the initial magnitude estimate is 8.5 at 24 s and drops to 8.2 at 40 s with a rupture length of 290 km. Finally, for the Mw 7.2, 2010
El MayorCucapah earthquake, the magnitude estimate is 7.0 from the outset with a rupture length of 140 km. The accuracy of the ground shaking prediction using the GPSbased magnitude and finite extent is significantly better than existing seismologybased point source approaches. This approach would also facilitate more rapid tsunami warnings.
Supplementary materials  animations
The Auxiliary Material contains the complete simulated realtime processing output for our GPS strategy for the three analyzed earthquakes (animated MPEG files).
The following videos/files show the results of the GPS processing every second for the three selected events: the Mw 9.0, 2011 TohokuOki earthquake, the Mw 8.3, 2003 TokachiOki earthquake, and the Mw 7.2, 2010 El MayorCucapah earthquake. The animations show the time evolution of the slip distribution and the corresponding magnitude value. The background color represents the predicted intensity distribution using the current magnitude value and the distance from the finite fault (L10). Black vectors represent the true horizontal offset while white vectors show the static displacement resulting from the inversion algorithm. The length estimations L10 and L90 are also plotted as vectors on the fault plane with a narrow gray vector, and a thick black vector, respectively. The small circles on L90 represent the centroid position. The current time, magnitude value and L10 estimate from the inversion are also displayed in the gray box. For each event, the simulation starts as soon as the first static offset estimation is available and its then run every second, each time considering all the available data. For the three analyzed events, the realtime estimated length (from magnitude updates) does not exceed the length of starting model, thus the increase in size of the fault plane is thus never triggered.
Simulation of the GPS strategy for the Mw 9.0 2011 TohokuOki earthquake.
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Simulation of the GPS strategy for the Mw 8.3, 2003 TokachiOki earthquake.
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Simulation of the GPS strategy for the Mw 7.2, 2010 El MayorCucapah earthquake.
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