Measuring Earthquake Deformation Using SAR Imagery: The 2008 Sichuan, China Earthquake

The 12 May 2008 Mw 7.9 earthquake in Sichuan province, China occurred close to the front of the Longmenshan mountains, a region of dramatic relief marking the eastern extent of the Tibetan plateau. Existing archives of pre-earthquake imagery from multiple satellites, particularly the European Envisat and Japanese ALOS platforms, allow the possibility of measuring the coseismic deformation using both InSAR and pixel offsets from precise image matching. Although topography and vegetation cover are challenging, preliminary interferograms from both satellites show good coherence and multiple fringes on the flatlands east of the mountains, and the amount of ground deformation is sufficient such that pixel offset data can resolve motion across the mountains that is significantly above the noise level.

Preliminary modelling of ALOS image-matching offset data suggests around 4 m of oblique thrust/right-lateral strike-slip on a shallowly-dipping fault set back between 10 and 20 km from the range front, somewhat close to the mapped Beichuan fault (e.g. Densmore et al., 2007, Tectonics). Subsequent acquisitions on neighbouring tracks will permit substantial refinement of this first model. Although evidence of historical large earthquakes is limited, the absence of resolvable contraction, as measured using GPS, across the front of the Longmenshan, suggests that such events are relatively uncommon compared with events elsewhere at the fringes of the Tibetan plateau.