Noise correlation functions from two seismic arrays deployed in the vicinity of the Pengguan complex in the Longmenshan, eastern margin of the Tibetan plateau, China

Understanding the lithospheric structure of and the processes operating at plateau margins is important as these margins can host destructive earthquakes e.g. the May 2008 Wenchuan earthquake with a magnitude of about 8, in the Longmenshan at the eastern margin of the Tibetan plateau. From the deployment of 125 seismographs, including a dense profile of 45 seismographs, in the vicinity of the epicentre of the Wenchuan earthquake, 3-D compressional- and shear-wave velocity models of the crust in this part of the Longmenshan have been derived. These models show that the old Pengguan complex which cores this part of the Longmenshan is about 20 km thick and displays high velocities and low Poisson’s ratios. However, along the dense profile, the complex is underlain between 20 and 40 km depth, by low shear-wave velocities which likely extend out beneath the Sichuan basin in a 10 km thick basal crustal layer. These zones of low shear-wave velocities have high Poisson’s ratios and can be explained as a result of the push exerted by the high plateau, causing processes such as ductile shearing and fluid/melt infiltration to occur.