Join t estimation for rupture processes of the 2008 Wenchuan earthquake from regional and near source seism ic array observations

Bor-Shouh Huang(黃柏壽),Jiuhui Chen,Qiyuan L iu,Yue-Gau Chenand Xiwei Xu

1)Institute of Earth Sciences,Academia Sinica,Taipei 115 2)Institute of Geology,China Earthquake Administration,Beijing 100081 3)Department of Geosciences,Taiwan University,Taipei 10617

Source rupture of the 2008 Wenchuan earthquake w ere estimated based on backward projection of seismic waves to its source plane.Observations from regional seismic arrays and near source stations were employed to study the rupture behavior in its different spatial and tempo ral stages.Regional broadband arrays from Taiwan and northern Vietnam were used to determine the overall rupture processes of this earthquake. With high density of station distribution of both seismic arrays,the rupture processes of this earthquake were determined.Seismic energy determined from array waveform s have been back-projected to the rup ture p lane of earthquake to determine its slip distributions in fault p lane.The rup ture p rocesses have been reconstructed based on time-dependent imaged seismic energy radiated from earthquake fault p lane.Analyzed results of this study indicated that the 2008 Wenchuan earthquake has rupture duration more than 80 seconds with major asperities radiated its energy on several secondsafter the earthquake rupture initiation.The radiated seismic energy showed comp lex spatial distribution on the fault p lane.The rupture initiated at its epicenter and extended to its no rtheast direction about 250 km.The averaged rupture velocity of this earthquake is determined to be near 3.3 km/s.According to near source records,the first large amplitude arrivals were delayed by seconds with respect to the origin time and w ere p receded by a small-scale slip.Based on a beam forming analysis,some near source recordings were used in this study to investigate the initial rupture process of this event. We will discuss the rupture behavior in multiple scales using both near fault and regional arrays for source images in its different stages.