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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, B04409, doi:10.1029/2003JB002843, 2004

Crustal deformation measurements in Guerrero, Mexico

Kristine M. Larson

Department of Aerospace Engineering Sciences, University of Colorado, Colorado, USA


A. R. Lowry

Department of Physics, University of Colorado, Boulder, Colorado, USA


Vladimir Kostoglodov

Instituto de Geofísica, National Autonomous University of Mexico, Mexico City, Mexico


Wallis Hutton

Hutton Consulting, Seattle, Washington, USA


Osvaldo Sánchez

Instituto de Geofísica, National Autonomous University of Mexico, Mexico City, Mexico


Ken Hudnut

U.S. Geological Survey, Pasadena, California, USA


Gerardo Suárez

Instituto de Geofísica, National Autonomous University of Mexico, Mexico City, Mexico


Abstract

GPS measurements of crustal deformation in Guerrero, southern Mexico, include surveys collected between 1992 and 2001 as well as continuous GPS measurements at a few sites. These geodetic observations are used to calculate interseismic deformation rates and assess the presence and possible location of transient deformation during the period encompassing 1992.25 to 2001.75. The data are used to examine transient deformation in 1998 previously described from data at a single site by Lowry et al. [2001] . Survey measurements and continuous data from a site near Popocatépetl volcano confirm the 1998 transient, and survey data also suggest another transient occurred following the 14 September 1995 (M w = 7.3) Copala earthquake. All of the available GPS position estimates have been inverted for a combined model of slip during each event plus the steady state slip on the plate interface. Modeling of the steady state deformation rates confirms that the Guerrero seismic gap is partially frictionally locked at depths shallower than about 25 km and accumulating strain that may eventually be released in a great earthquake. The data also suggest that there is frictional coupling to much greater (>40 km) depths, which releases more frequently in aseismic slip events. The locations and sizes of the transient events are only partially constrained by the available data. However, the transient models which best fit the GPS coordinate time series suggest that aseismic slip was centered downdip of the seismogenic portion of the plate-bounding thrust in both events, and the moment release had equivalent magnitudes M w = 7.1 + 1.3/−1.0 in 1995–1996 and 7.1 + 0.4/−0.1 in 1998.

Received 13 October 2003; accepted 19 March 2004; published 28 April 2004.

Index Terms: 1208 Geodesy and Gravity: Crustal movements—intraplate (8110); 1243 Geodesy and Gravity: Space geodetic surveys.

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Citation: Larson, K. M., A. R. Lowry, V. Kostoglodov, W. Hutton, O. Sánchez, K. Hudnut, and G. Suárez (2004), Crustal deformation measurements in Guerrero, Mexico, J. Geophys. Res., 109, B04409, doi:10.1029/2003JB002843.