The Wenchuan earthquake(Ms=8.0) suddenly happened on May 12th 2008 in Sichuan Province,China. This earthquake produced a 240 km-long co-seismic surface rupture along the Longmenshan Central Fault. We mainly focus on three regions along the co-seismic surface rupture: the Nanba Town and the Fenghuang Village on the northern segment of the rupture, the theYingxiu Town on the southern segment of the rupture, and we study the river terraces in these regions cut by the active fault. We measured the surface rupture and the fault scarps on the multilevel terraces. We obtain the height of the fault scarps on the terrace of each level through data calculation and analysis, and the height of the scarps is namely the cumulative vertical slip of the active fault recorded by terrace. If we use the vertical slip of this earthquake as the average vertical slip of the paleoearthquakes, then the ratio of the cumulative vertical slip of each terrace to this average vertical slip is namely the cumulative times of the paleoearthquakes record by each terrace. The research results shows that T1 of every study area undergoes only 1 time of the paleoearthquake since its formation, T2 undergoes about 5 times of the paleoearthquakes since its formation, T3 undergoes about 9–11 times of the paleoearthquakes since its formation and T4 undergoes about 20 times of the paleoearthquakes since its formation. Based on the research result of this paper, combined with the previously dating ages of the terraces,we can obtain some reliable data about the recurrence intervals of the paleoearthquakes.
On May 12th, 2008, an Ms8.0 earthquake occured on the Longmenshan tectonic belt in Sichuan Province in China. The longmenshan tectonic belt is considered as a thrust nappe structure, and its cacavity of triggering earthquakes has been underestimated for a long time.