Preliminary Coseismic Displacement Field M 8.8 Maule Earthquake, Chile, Feb 27 2010

This is the preliminary solution obtained by Project CAP (Central and Southern Andes GPS Project) for the coseismic displacement field associated with the recent M 8.8 Maule earthquake in south-central Chile. Peak measured displacement is 3.04 m near the city of Concepcion, Chile. Significant displacements are evident as far east as Buenos Aires, Argentina (2-4 cm) and as far north as the Chilean border with Peru.

The areas with the largest expected displacements are not yet re-surveyed, but surveyors are already occupying several marks in that and surrounding areas, so this initial result will soon be updated to show the movements at additional locations. Continuous GPS stations are also being set up as equipment becomes available.

The CAP team led by Mike Bevis (Ohio State University, University of Mempis, University of Hawaii, the Instituto Geografico Militar (IGM) de Chile, Universidad de Concepcion (Ch.), the Centro de Estudios Cientificos (CECS, Ch.), IGM de Argentina, Universidad Nacional de Cuyo, Argentina and Universidad Nacional de Buenos Aires, Argentina) are actively collaborating with Caltech geodesists (Jeff Genrich and Mark Simons), and are coordinating with the Sergio Barrientos (Universidad de Chile) and their French partners (ENS/IRD), so as to maximize the amount of geodetic data being collected. The American team is being supported by UNAVCO, who are sending GPS equipment to supplement that which CAP and Caltech already had in Chile and Argentina. All these data will be placed in open archives at Universidad de Chile and at UNAVCO, as soon as the data are recovered.

IGM Chile and Mike Bevis (OSU) are leading field activities in Chile including Geodesists Dana Caccamise and Eric Kendrick, Bob Smalley (UM) is leading the work in Argentina, and Ben Brooks (U Hawaii) and Mark Simons (Cal Tech) are coordinating processing and logistical support stateside.

This preliminary geodetic solution was computed by James Foster and Ben Brooks at the University of Hawaii.

Processing Description

All available data for continuous GPS in South America from Jan 30 through Mar 5 were processed using GAMIT (King et al., 2009) with additional IGS sites included to provide reference frame stability. Data through Feb 28 were processed using the MIT precise orbits. More recent data used the IGS rapid orbit solutions. Orbits were held tightly constrained and standard EOP and earth and ocean tides were applied. Due to the number of stations, two separate subnets were formed with common fiducial sites. The subnets were merged, and, through Feb 28, combined with MIT's global solution using GLOBK. Displacements for the Maule earthquake were calculated by performing daily Helmert transformations for the network solutions prior to the earthquake to define the best pre-quake position for each site, in an ITRF2005 reference frame. This process was repeated for the post-earthquake solutions (data from the day of the earthquake had the first 8 hours (earthquake was at 06:34 UTC). The displacements were calculated by taking the difference between the pre- and post- earthquake positions and performing a Helmert transformation that minimized the displacements for a subset of sites distant from the earthquake. Errors for the positions were calculated based on the scatter of the solutions about the mean position, while the displacement errors were calculated by assuming that the errors in the pre- and post-earthquake positions were independent.

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