Satellite geodetic imaging reveals internal deformation of western Tibet

It is often assumed that the majority of the interseismic strain accumulates around the major mapped geological block boundaries. However, numerous recent earthquakes in the continents have occurred on faults that were previously unidentified. Existing deformation data from Tibet are insufficiently dense to map the distribution of interseismic strain. Here we combine 265 interferograms formed from 166 radar images with GPS data to constrain a high-resolution velocity field covering ∼200,000 km 2 of western Tibet. We confirm that the slip rate of the Karakoram Fault is low (<6 mm/yr), but show that areas of focused strain do not coincide with the major fault structures. Some of this strain is due to postseismic relaxation after a M w 6.8 earthquake that occurred in 1996 on a structure that is difficult to identify in satellite imagery. Models of seismic hazard that rely on imperfect knowledge of the boundaries of crustal blocks can therefore underestimate hazard from unknown faults. Copyright 2012 by the American Geophysical Union.