Moment tensor solution, rupture process and rupture characteristics of the great Wenchuan M8.0 earthquake are studied by using 39 long-period P and SH waveforms with evenly azimuth coverage of stations. Our results reveal that the Wenchuan M8.0 event consisted of 5 sub-events of M w ≥7.3 occurring succesively in time and space. Rupture started with a M w 7.3 introductory strike-slip faulting in the first 12 s, then within 12−40 s, two sub-events with M w 7.6 and M w 7.4 occurred within 80 km northeast from the initial point with the dominant rupture type of thrust moving. From 40 to 62 s, a M w 7.5 and M w 7.4 right-lateral strike-slip type of sub-events occurred on the two sides of Beichuan, 120 km away northeast from the initial point. The whole rupture process lasted 105 s and unilaterally propagated from the initial point on the WS section of the Yingxiu-Beichuan fault to the NE direction, resulting in a 230-km-long surface rupture zone and the average surface dislocation is up to 4 m. Two asperities are identified and the whole rupture process is formed by WS and NE parts. In the WS part named Dujiangyang-Wenchuan, where the initial point is located, the rupture process showed reverse faulting with the maximum slip of 8.2 m. Around Mianzhu, rupture changed to right-lateral strike slip faulting and formed a Beichuan-Qingchuan large slip area. The rupture area on this part is about 10 km in depth, shallower than on the WS part. The maximum slip is 6.53 m. Consequently, there formed 2 segments with the surface dislocation larger than 6 m. One is the Dujiangyan-Wenchuan segment with the maximum surface displacement of 6.44 m, the other is the Beichuan-Qingchuan segment with the maximum surface displacement of 6.53 m. This segmentation may have its geological and tectonic background. Wenchuan earthquake, moment tensor solution, rupture process, fault segmentation characteristics Citation: Zhao C P, Chen Z L, Zhou L Q, et al. Rupture process of the Wenchuan M8.0 earthquake of Sichuan, China: the segmentation feature.At 14:28 on May 12, 2008, a great earthquake occurred in Wenchuan County of Sichuan Province, China. It caused the most severe damage and affected the largest area among other earthquakes since New China was founded, and resulted in tremendous injuries and deaths, as well as disaster. Study on its source rupture process using the digital seismic waveform data can provide information about the rupture scale, the way of fault moving, as well as slip distribution on the fault within several hours after a strong earthquake occurred. These estimations can not only rapidly provide the information on the seriously damaged area and the way of dislocation as well as important information for estimating the destructed scale and doing rescue work, but can also provide important information about the activity of the causative fault and the tendency of the earthquake sequence. After the Wenchuan M8.0 earthquake occurred, several research groups immediately carried out the source rupture process inversion. We also e...

In this study we obtained the tomography results of QLg in Sichuan‐Yunnan region, separately for each frequency, by using seismic wave data recorded by Yunnan and Sichuan seismic networks. The spatial resolution of our result is less than 100 km. Our results demonstrate that strong heterogeneity exists in the studied region, showing large difference between the highest and lowest Q value. The obvious high attenuation regions include the southeast edge of Sichuan‐Yunnan rhombic block, which extends from Xianshuihe fault zone to Anninghe fault zone, Simao‐Lancang‐Pu'e region, the Songpan‐Maowen region which is located to the west of Longmenshan fault zone, the Batang and Litang earthquake region. According to our result, high attenuation regions of Lg waves correspond to strong seismic active zones, ruptured area of large earthquakes, high terrestrial heat activity, and low velocity. It demonstrates that broken medium caused by strong tectonic activity or large earthquakes and heat flow upwelling along active faults may be the main reasons of low QLg in Sichuan‐Yunnan region. The obvious low attenuation regions include Sichuan basin, the eastern block of Yunnan region, and the middle part of Jinshajiang and Nujiang fault zones. The interior of Dianzhong block also shows lower attenuation than the nearby area. Low attenuation regions correspond to the stable tectonic block, weak tectonic activity and high velocity. It shows that low attenuation of Lg waves in Sichuan‐Yunnan region is correlated with small crustal deformation, low seismic activity, weak hydrothermal activities and stable block.

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Moment tensor solutions of 88 earthquakes were determined by using the broadband waveform data recorded in six stations within 450 km around the Wenchuan Earthquake sequence by means of the time domain moment tensor inversion method. It was found that the type of the focal mechanism solution is characteristic of obvious spatial segmentation. There are six segments along the main rupture zone from southwest to northeast, where initially the focal mechanism is of main thrust type, finally of main right-lateral strike-slip type and between these two areas there is a transition zone characterized in multiple types of focal mechanisms appearing in turn. Earthquakes of left-lateral strike-slip type perpendicular to the main rupture zone occurred near Xiaoyudong Town. The stress field of each segment is inversed by means of the FMSI program, and it was found that, along the main rupture zone from southwest to northeast, the direction of the maximum principal stress is gradually changing from near EW to NW-SE, and finally changing back to near EW.Wenchuan Earthquake, moment tensor inversion, stress field, segmentation characteristic On May 12, 2008, an earthquake of Ms8.0 occurred in Wenchuan County, Sichuan Province, China. The huge energy released from the earthquake has resulted in collapse of numerous houses and buildings and death of near 70 thousands people, and fatally destroyed Wenchuan County, Beichuan County, Qingchuan County, etc. Wenchuan Earthquake occurred in the middle segment of Longmenshan fault belt, which is a nearly 500-km-long tectonic boundary between the Bayanhar block at eastern part of the Qinghai-Tibet Plateau and the South China block. Longmenshan fault belt consists of four subparallel faults, i.e. Central Fault, Qianshan Fault, Houshan Fault and front blind fault of Lomengshan [1,2] . Wenchuan Earthquake occurred on the BeichuanYingxiu fault (Central fault). After the main shock the aftershocks were very active. Till August 31, 2008, more than 26600 aftershocks occurred among which there are 8 M6.0-6.9 aftershocks and 55 M5.0-5.9 aftershocks, forming an approximately 330-km-long aftershock belt (according to the catalog issued by the Earthquake Administration of Sichuan Province). The field investigation result shows that length of the main surface fracture zone of the Wenchuan Earthquake is about 240 km [1] .In this paper, the moment tensor solutions of the strong aftershocks of the Wenchuan Earthquake sequence were determined by using the broadband digital waveform datum and by means of the time domain moment tensor inversion method. Furthermore, the distribution characteristics of the stress fields along the seismic fault were analyzed. The above result will be helpful for knowing the origin of the Wenchuan Earthquake. In addition, it will provide important constraints for research of the dynamic rupture model of the Wenchuan Earthquake and the triggering model of the strong aftershocks.