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The rupture behavior of large‐scale thrust faults has become an increasingly important topic in active tectonic and seismic studies. This is especially true for the 2008 Wenchuan earthquake (Mw 7.9), which occurred along the Longmenshan thrust fault (LMS) in China. While this earthquake has been the subject of many studies to date, paleoseismic studies along the LMS are still lacking. In this study, results from trenching at the town of Bailu, as well as radiocarbon and Optical‐Stimulated Luminescence dating, are used to constrain the timing of the penultimate and earlier events, respectively: 3.3 ± 0.6 to 4.4 ± 0.6 ka and 4.8 ± 0.6 to 5.8 ± 0.8 ka. Further, coseismic displacement produced by the two events is similar to that produced by the 2008 event. The results suggest that fault segments along the Yingxiu‐Beichuan and Jiangyou‐Guanxian faults likely ruptured coseismically with similar offsets and that the northern segment of the LMS possesses independent rupture behavior. The magnitude of the penultimate seismic event was likely lower than that of the 2008 event, which indicates a characteristic slip‐rupture pattern along the LMS. Key Points: New trenches were opened for paleoseismic studies on the Longmenshan thrust faultTrenches reveal evidence of three paleoseismic events with similar recurrence intervals and coseismic offsetsLongmenshan thrust fault shows a characteristic coseismic slip‐rupturing pattern [ABSTRACT FROM AUTHOR]

Following the Lushan M7.0 earthquake on 20 April 2013, a topic of much concern is whether events of M7 or greater could occur again on the southern segment of the Longmenshan fault zone. In providing evidence to answer this question, this work analyzes the tectonic relationship between the Lushan event and the 2008 Wenchuan earthquake and the rupture history of the southern segment of the Longmenshan fault zone, through field investigations of active tectonics and paleoearthquake research, and our preliminary conclusions are as follows. The activity of the southern segment of the Longmenshan fault zone is much different to that of its central section, and the late Quaternary activity has propagated forward to the basin in the east. The seismogenic structure of the 2008 Wenchuan earthquake is the central-fore-range fault system, whereas that of the 2013 Lushan event is attributed to the fore-range-range-front fault system, rather than the central fault. The southern segment of the Longmenshan fault zone becomes wider towards the south with an increasing number of secondary faults, of which the individual faults exhibit much weaker surface activity. Therefore, this section is not as capable of generating a major earthquake as is the central segment. It is most likely that the 2013 earthquake fills the seismic gap around Lushan on the southern segment of the Longmenshan fault zone. [ABSTRACT FROM AUTHOR]

Abstract: In historical records, no earthquake of magnitude comparable with that of the Wenchuan Mw 7.9 earthquake has ever been reported in Chengdu and Longmenshan regions. It is important, therefore, to assess if there is any evidence of prior large earthquakes in the recent geological record. In order to explore this problem, 3 trenches were excavated separately at 3 sites along the surface rupture zones in the middle segment of the Beichuan–Yingxiu Fault and Jiangyou–Guanxian Fault of the Longmenshan fault zone, and the offsets of geomorphic surfaces were measured in the trenches. The basic facts of recurrence of large earthquake on the seismogenic fault of the Wenchuan earthquake are demonstrated in this paper on the basis of the accumulated deformation amounts of old and young geomorphic surfaces as well as the paleoearthquake events revealed in the trenches. The document that at Leigu along the Beichuan–Yingxiu Fault, at Bailu along the Jiangyou–Guanxian Fault, and Xiaoyudong on a NW-trending fault, the height of fault scarp on the second terrace has a multiple relationship to that on the first terrace after the Wenchuan earthquake of 12, May. The elevation difference of the marker horizon (the yellow sandy clay bed) of the second terrace revealed in the trenches on both sides of the fault is nearly twice (or three times larger in Bailu) of that produced by the Wenchuan earthquake. These observations suggest the occurrences of paleoearthquake events with surface deformation comparable to that produced by the Wenchuan Mw 7.9 earthquake. According to the dating data and the fact that there is no such slip of comparable paleoearthquakes in the 2300-year-long historic literature in Longmenshan region, we suggest that the penultimate event occurred between 2300aBP and 3300aBP. [ABSTRACT FROM AUTHOR]