Research On The Wenchuan Earthquake Rupture Process Of Joint Inversion And High-frequency Radiation

The Wenchuan earthquake is a complex process occurring on imbricate fault.The Beichuan-Yingxiu fault and Guanxian-Jiangyou fault have surface ruputre,meanwhile the Xiaoyudong fault which perpendicular to these faults also has surface ruputre.Kinematics and dynamics studies have shown that the fault rupture extended to the intersection of the three faults and important transformations may occurred.Therefore,the rupture sequence of the Beichuan fault,Pengguan fault and Xiaoyudong fault is the key to reverse the rupture process of Wenchuan earthquake.First,we establish a reasonable 3D complex fault model.Joint inversion of teleseismic,strong motion,GPS and surface rupture data,the fine rupture process of Wenchuan earthquake is inversed,besides a reasonable rupture sequence is given,using parallel nonnegative least square method and multitime window.Next,based on the near filed strong motion and differential evolution method,the high-frequencywave radiation areas of the Wenchuan earthquake is inversed.The difference between high and low frequency seismic radiation is analyzed and compared.The main results are as follows:1.Comprehensive consideration of the research results of the three-dimensional fault model,aftershock distribution and surface rupture investigation,we establish a realistic fault model of Wenchuan earhtquake.Based on the parallel nonnegative least square method and multitime window,the rupture prcoss of Wenchuan earthuqake is inversed,using 36 vertical teleseismic P waveforms.The results show that:?1?Most research about rupture process of Wenchuan earthquake presume a unilateral rupture,leading the surface area between Hongkou and Yingxiu has no surface rupture,which is inconsistent with the field investigation.The PGF triggered by the Xiaoyudong fault will generate large slips about 4m on the southwestern part of PGF,which is contradictive to the zero surface offset on these areas.Whereas,the sourthern part of Beichuan fault with high dip angle is riggered by the Xiaoyudong fault,the surface area between Hongkou and Yingxiu has larger surface offset agreement with the field investigation.It is considered that a bilaterally rupture of southwestern part of BCF is accordant with actual situation.?2?The teleseisimic waveforms can not distinguish the slip on the southern part of Beichuan fault or that on the Pengguan fault,owing to the two fault yield nearly identical green function.Meanwhile the slip on the southern part of Beichuan fault is more reliable than that on the Pengguan fault.2.By the near field strong-motion records with uniform azimuthal coverage,the the rupture process is inversed,usiing the parallel nonnegative least square method and multitime window.The results show that:?1?Similar to the teleseismic records inversion result,unilateral rupture and the PGF triggered by the Xiaoyudong fault has no dislocation in the shallow ares of Hongkou and Yingxiu in Beichuan fault.In order to make the slip of the Hongkou and Yingxiu area coincide with the field investigation,only the Beichuan fault has a bilateral rupture on the point of intersection of Xiaoyudong fault.In the high dip area of the southwest Beichuan fault,there are obvious rupture pause and two rupture,and the duration can reach about 15s in some areas.?2?The larger HPGV at the stations 51MZQ,51SFB,51MXN and 51MXT are in good agreement with the adjacent region of the fault plane with larger slip velocity.The fault plane produces large slip velocity,the around stations tend to have peak ground velocities.3.In order to overcome the defects of single data with low resolution,combined the teleseismic,strong motion,GPS and coseismic displacement data,the rupture process of Wenchuan earthquake is inversed.Research shows:?1?Combined teleseismic records and near-field records have improved the identification ability of slip distribution in the high dip angle area on southwestern part of Beichuan fault the southern part of the PGF,and the area around Beichuan on northeastern part of Beichuan fault.?2?The GPS data can well control the slip distribution in the shallow part of the fault and the northern section of the Beichuan fault.?3?The joint inversion results show that the rupture duration of Wenchuan earthquake is 100s,and the seismic moment is 1.058×10²¹N·m.There are 5asperities on the fault plane,which indicate that the earthquake is composed of at least5 subevents.The slip is mainly distributed on the Beichuan fault,indicating that the Beichuan fault is the main fracture surface.On the southern part of Beichuan fault,the dislocation underside the Longmenshan area and Hongkou-Yingxiu near surface area are dominated by thrust,and the maximum slip is 12m,located on the underside of Hongkou.Slip between the Yuejiashan and Qingping area is dominated by thrust,the maximum slip is about 10m.On the northern part of Beichuan fault,slip is mainly thrust near Beichuan area with maximum slip 10m,the area from Nanba to Qingchuan is strike slip,and the maximum slip is 10m.The dislocation downside of Bailu is also dominated by thrust,with maximun slip 8m.4.Based on the line source model,the high-frequency?>1Hz?wave radiation areas on the Wenchuan earthquake fault plane is inversed by the differential evolution method,using acceleration envelopes attenuation relationship of Lushan earthquake and envelopes of 30 near-field stations acceleration seismograms in Wenchuan earthquake.The results are as follows:?1?The high-frequency wave radiation areas are very nonuniform,with most of the high-frequency waves radiated in:the surface rupture areas,including Yingxiu,Beichuan and Nanba areas;the areas close to the boundaries of the asperities,including that with epicentral distance from 60 to 90 km northeast of epicenter,and areas 30 km northeast of Beichuan and Nanba;the area within 30 km length near the fault northeastern tip.Both high and low frequency wave radiation were very higher in areas of Yingxiu,Beichuan and Nanba with large surface rupture.?2?The accelerations in areas with no seismic records are synthesized by the synthetic envelopes and a stationary stochastic process extracted from its near station with similar site conditions.The results could be used as the earthquake input for analyzing seismic damage of structures in Wenchuan earthquake.