A special issue on the great 12 May 2008 Wenchuan earthquake (Mw7.9): Observations and unanswered questions

The 12 May 2008 Wenchuan earthquake (Mw 7.9) ruptured the active Longmen Shan thrust belt bounding the eastern margin of the Tibetan plateau against the Sichuan basin (Fig. 1) (Burchfiel et al., 2008). Initial observations of this devastating earthquake were reported in several short papers focusing on coseismic slip and earthquake-fault geometry (e.g., Wang et al., 2008; Xu et al., 2009; Lin et al., 2009; Liu-Zeng et al., 2009; Hubbard and Shaw, 2009; Shen et al., 2009; Feng et al., 2010). Subsequent work has addressed the questions of whether reservoir had triggered the earthquake (Ge et al., 2009) and if a weak middle and lower crust in eastern Tibet had controlled the location of the earthquake fault zone (Xu et al., 2010a; Zhang et al., 2010a). The early studies have established some of the basic facts about the Wenchuan earthquake. First, the main shock ruptured two northwest-dipping faults in the eastern part of the Longmen Shan thrust belt: the sub-parallel Beichuan–Yingxiu fault (∼230 km) in the northwest and the Pengguan fault (∼110 km) in the southeast (Fig. 2). Second, coseismic slip was accommodated dominantly by thrust motion on the Pengguan fault and by mixed right-slip and thrust motion on the Beichuan–Yingxiu fault. Specifically, coseismic slip on the Beichuan–Yingxiu fault changes systematically northeastward, from dominant thrust motion on shallowdipping rupture planes to nearly pure right-slip motion along fault strike. Third, the Longmen Shan thrust belt lies along a crustal-scale boundary between the younger and possibly weaker Triassic Songpan–Ganze terrane in the northwest from the much older and thus stronger South China block in the southeast. The current issue collects a total of 22 papers that expand greatly on the early reports of the Wenchuan earthquake. The volume covers the following six subjects: (1) coseismic slip, (2) evolution of static Coulomb stresses induced by the Wenchuan earthquake and recent seismicity in eastern Tibet, (3) recurrence times of late Quaternary seismicity, (4) tectonic setting and structural framework of the Longmen Shan thrust belt that hosts the Wenchuan earthquake fault, (5) lithospheric structure of the eastern Tibetan plateau, and (6) interplay between exhumation and tectonics across the Longmen Shan thrust belt at various time scales. Below I summarize the main points of the papers presented in this issue and outline some of the outstanding issues with regard to the Wenchuan earthquake and the tectonic evolution of the eastern Tibetan plateau.