The 2008 Wenchuan earthquake,a major intraplate earthquake with Mw7.9,occurred on the slowly deforming Longmenshan fault.To better understand the causes of this devastating earthquake,we need knowledge of the regional stress field and the underlying geodynamic processes.Here,we determine focal mechanism solutions(FMSs)of the 2008 Wenchuan earthquake sequence(WES)using both P-wave first-motion polarity data and SH/P amplitude ratio(AR)data.As P-wave polarities are more reliable information,they are given priority over SH/P AR,the latter of which are used only when the former has loose constraint on the FMSs.We collect data from three categories:(1)permanent stations deployed by the China Earthquake Administration(CEA);(2)the Western Sichuan Passive Seismic Array(WSPSA)deployed by Institute of Geology,CEA;(3)global stations from Incorporated Research Institutions for Seismology.Finally,129 events with magnitude over Ms4.0 in the 2008 WES are identified to have well-constrained FMSs.Among them,83 are well constrained by P-wave polarities only as shown by Cai et al.(Earthq Sci 24(1):115–125,2011),andthe rest of which are newly constrained by incorporating SH/P AR.Based on the spatial distribution and FMSs of the WES,we draw following conclusions:(1)the principle compressional directions of most FMSs of the WES are subhorizontal,generally in agreement with the conclusion given by Cai et al.(2011)but with a few modifications that the compressional directions are WNW–ESE around Wenchuan and ENE–WSW around Qingchuan,respectively.The subhorizontal compressional direction along the Longmenshan fault from SW to NE seems to have a leftlateral rotation,which agrees well with regional stress field inverted by former researchers(e.g.,Xu et al.,Acta Seismol Sin 30(5),1987;Acta Geophys Sin 32(6),1989;Cui et al.,Seismol Geol 27(2):234–242,2005);(2)the FMSs of the events not only reflected the regional stress state of the Longmenshan region,but also were obviously controlled by the faults to some extent,which was pointed out by Cai et al.(2011)and Yi et al.(Chin J Geophys55(4):1213–1227,2012);(3)while the 2008 Wenchuan earthquake and some of its strong aftershocks released most of the elastic energy accumulated on the Longmenshan fault,some other aftershocks seem to occur just for releasing the elastic energy promptly created by the 2008Wenchuan earthquake and some of its strong aftershocks.(4)Our results further suggest that the Longmenshan fault from Wenchuan to Beichuan was nearly fully destroyed by the 2008 Wenchuan earthquake and accordingly propose that there is less probability for great earthquakes in the middle part of the Longmenshan fault in the near future,although there might be a barrier to the southwest of Wenchuan and it is needed to pay some attention on it in the near future. The 2008 Wenchuan earthquake, a major intraplate earthquake with Mw7.9, occurred on the slowly deforming Longmenshan fault. Better way for this devastating earthquake, we need knowledge of the regional stress field and the underlying geodynamic processes. Here, we determine focal mechanism solutions (FMSs) of the 2008 Wenchuan earthquake sequence (WES) using both P-wave first-motion polarity data and SH / P amplitude ratio (AR) data. As P-wave polarities are more reliable information, they are given priority over SH / P AR, the latter of which are used only when the former has loose constraint on the FMSs.We collect data from three categories: (1) permanent stations deployed by the China Earthquake Administration (CEA); (2) the Western Sichuan Passive Seismic Array (WSPSA) deployed by Institute of Geology, CEA; (3) global stations from Incorporated Research Institutions for Seismology. Fundually, 129 events with magnitude over Ms 4.0 in the 2008 WES are well-constrained FMSs. Among They, 83 are well constrained by P-wave polarities only as shown by Cai et al. (Earthq Sci 24 (1): 115-125, 2011), and the rest of which are newly constrained by incorporating SH / P AR.Based on the spatial distribution and FMSs of the WES, we draw the following conclusions: (1) the principle compressional directions of most FMSs of the WES are subhorizontal, generally in agreement with the conclusion given by Cai et al. (2011) but with a few modifications that the compressional directions are WNW-ESE around Wenchuan and ENE-WSW around Qingchuan, respectively. The subhorizontal compressional direction along the Longmenshan fault from SW to NE stress to have a leftlateral rotation, which agrees well with regional stress field inverted by former researchers ( eg, Xu et al., Acta Seismol Sin 30 (5), 1987; Acta Geophys Sin 32 (6), 1989; Cui et al., Seismol Geol 27 (2): 234-242, 2005) FMSs of the events not only reflected the regional stress state of the Longmenshan region, but also were obviously controlled b y the faults to some extent, which was pointed out by Cai et al. (2011) and Yi et al. (Chin J Geophys 55 (4): 1213-1227, 2012); (3) while the 2008 Wenchuan earthquake and some of its strong aftershocks released most of the elastic energy accumulated on the Longmenshan fault, some other aftershocks seem to occur just for releasing the elastic energy promptly created by the 2008 Wenchuan earthquake and some of its strong aftershocks. (4) Our results further suggest that the Longmenshan fault from Wenchuan to Beichuan was nearly fully destroyed by the 2008 Wenchuan earthquake and accordingly offered that there is less for for great earthquakes in the middle part of the Longmenshan fault in the near future, although there might be a barrier to the southwest of Wenchuan and it is needed to pay some attention on it in the near future