Effects from the Wenchuan Earthquake and seismic hazard in the Longmenshan Mountains at the eastern margin of the Tibetan Plateau

Effects from the disastrous Ms 8.0 Wenchuan Earthquake of May 12, 2008 show that the seismic hazard is closely related to the proximity of active faults and elevated areas of unstable rock as well as the recurrence rate of large earthquakes. Dextral-slip thrusting in the Longmenshan Mountains formed large displacement along ~ 250 km of the Central Longmenshan Fault and smaller offsets along sub-parallel faults. The distribution pattern of the major destruction has a strong northeast–southwest orientation closely related to the ruptured faults and decreases noticeably 3–5 km away from the Central Longmenshan Fault and ~ 2 km from the other faults. Thousands of landslides, rock falls and debris flows triggered by the earthquake lie chiefly adjacent to the principal fault, and smaller-scale landslides along the other faults as well as in distant areas. Some landslides formed dams whose impounded waters threatened downstream cities. Future landslides, rock falls and debris flows will result from rock loosened by the earthquake during rainy seasons or subsequent earthquakes.The Central Longmenshan Fault had maximum displacements of 4.6 m dip-slip and 6.1 m dextral-slip and the total dip and dextral-slip displacement for all faults is 5.9 m and 7.0 m, respectively. These faults apparently converge at depth and account for the crustal shortening in the region. Their displacements coupled with convergence rates determined by GPS measurements provide an estimated recurrence interval for an Ms 8.0 earthquake along the Central Longmenshan Fault of between 4600 and 6600 years and that for the entire Longmenshan Mountains between 1000 and 3000 years.

► The 8.0 magnitude Wenchuan earthquake caused a 250 km long northeast-trending rupture.
► Dextral-slip thrust oblique offset along all the faults involved totals ~9.2 m.
► Damage closely follows the fault geometry and drops off sharply to either side.
► Estimated recurrence interval for this earthquake in the region is 1,000 to 3,000 years.