Rupture Process Of The Wenchuan Earthquake Based On The Near Field Strong Motion Data

As a big earthquake with complicated and large rupture fault, the5.12Wenchuan earthquake is important for realizing the large earthquake sourcemechanism. After the earthquake, several research groups have implementedthe source inversion using the far-field long-period teleseismic waveform dataand different fault model. Most results show that the earthquake rupturedmore than100s, and it formed2asperities in Yingxiu and Beichuan area.By now, all studies on source inversion of Wenchuan earthquake arebased on far-field long-period teleseismic waveform data, which can hardlygive the detail of the rupture due to the use of low frequency wave.During the earthquake, the strong-motion network of China EarthquakeAdministration recorded many three-component accelerograms and a lot ofsurface offset data are acquired through the field investigations. So in thispaper, based on3components velocity records of48near field strong motionstation and the field investigated surface rupture data, we inverse the sourcerupture process of the Wenchuan earthquake by the non-negative least-squaresmethod and the multiple-time widow technique. Two causative faults aretaking into inverse; one is the Beichuan-Yingxiu which is represented as acurved fault, the other is Jiangyou-Guanxian fault which is a single fault. Themain results include:(1) The fault rupture process are very complex, which lasted for90s, andthe rupture front propagate rapidly in the north direction with average velocityof about3.1km/s than that in the southwest direction.(2) In the middle and north part of the faults, whose surface near Yingxiu,Wenchuan, and Beichuan area, the fault persisted for a majority of slipsequence. The rupture result in3asperities in Beichuan fault with maximumslip of the8.2m and2small asperities in the Pengguan fault with maximumslip of5.2m.(3) The dynamical rupture process show that the rupture fronts are veryirregular, and it propagated in two directions (northeast and southwest), withdifferent rupture phenomenon in the north and south parts. In northern area,slip velocity is generally high and the total rupture duration time is relativelylonger than that in the south part, especially for the Yingxiu asperity regionwith rupture duration up to more than30s, and accompanied by rupture pauseand re-rupture. In the southern region, slip velocity is generally low, and thetotal rupture duration time is relatively short. In these asperities, the slipduration time sustained relatively long with most of them over25s, and thelongest one is more than58s in the Yingxiu area.