Coseismic horizontal shortening associated with the 2008 Wenchuan Earthquake along the Baishahe segment from high resolution satellite images

Many coseismic deformation data from the Wenchuan Earthquake of 12 May, 2008, have been published; however, most of the data record strike-slip and vertical offsets, and there is little information on the horizontal shortening components. To determine the amount of horizontal shortening, we suggest a new method of measuring the differences in the positions of geometrical markers observed in satellite images before and after the earthquake. We found two roads that run nearly parallel to the earthquake rupture but on opposite sides, and we examined the spacing between them before and after the earthquake. We were able to measure horizontal shortenings that average 6.6 +/- 1.84 m, with a maximum of 11.0 m and a minimum of 1.1 m. As an alternative method, we used a GPS RTK field survey system to measure the spacing of the two roads after the earthquake, and then measured the difference between that and the spacing determined from satellite images before the earthquake. This method gave horizontal shortenings that average 7.1 +/- 1.3 m, with a maximum of 9.85 m and a minimum of 3.8 m. The shortenings measured, using either of these two methods, are larger than those directly measured in the field in the immediate vicinity of the fault, which suggests that the coseismic horizontal shortening is distributed over a wider area that extends some distance away from the brittle fault scarp itself. Finally, the results support a low-angle fault model for the Wenchuan Earthquake, and they provide useful insights into the seismotectonics of eastern Tibet, especially the building of the Longmenshan range. (C) 2012 Elsevier Ltd. All rights reserved.