Focusing Seismic Energy along Faults through Time-Variable Rupture Modes: Wenchuan Earthquake, China  

作　　者：Timothy M Kusky Abduwasit Ghulam 王璐 刘建国 李中全 陈骁 

机构地区：[1]Three Gorges Research Center for Geo-hazard, Ministry of Education and State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences [2]Center for Environmental Sciences, Saint Louis University [3]Three Gorges Research Center for Geo-hazard, Ministry of Education, China University of Geosciences [4]Department of Marine Geology, Ocean University of China [5]Department of Earth Science and Engineering, Imperial College [6]Department of Geosciences, Chengdu University of Technology

出　　处：《Journal of Earth Science》2010年第6期910-922,共13页地球科学学刊（英文版）

基　　金：supported by NASA to Abduwasit Ghulam and Timothy M Kusky (No. 08-182);the National Natural Science Foundation of China (No. 40821061);Ministry of Education of China (No. B07039)

摘　　要：Field analysis and differential interferometry derived from Synthetic Aperture Radar （PALSAR） of the epicentral area of the May 12 2008 Mw 8.0 Wenchuan （汶川） earthquake zone reveal details about fault ruptures and ground displacements, with field-documented vertical offsets reaching 12 m along the trace of the main fault rupture, and PALSAR-measured horizontal displacements reaching 12.3 m. We document slip indicators on the fault scarp that show initially sub-horizontal then progressively steeper slip increments with time along the same fault during the 2 min earthquake, suggesting that the rupture propagated as a mixed Mode Ⅱ-Ⅲ fracture, with strike-slip movement at the tip directing energy from the initial rupture to points north of the epicenter, followed by vertical displacement in the interior of the slipped region. Field, seismic, and PALSAR-measured displacements are dominantly thrust near the epicentral region, and dextral in northeasterly areas, showing that slipwas partitioned along the fault in space and time during the earthquake. The changing slip directions may correlate with three main pulses of energy release at 0, 23, and 57 s during the earthquake as recorded by seismograms. The earthquake generated massive landsfides 〉100 km north of the epicenter along the trace of the fault. These massive sturzstroms formed where entire mountainsides collapsed and moved at high velocity down populated mountain valleys, jumping smaller mountains and ricocheting off steep canyon walls. These avalanches rode on cushions of water and compressed air that generated air blasts from beneath the debris, knocking down trees high on opposing mountain slopes. The concentration of massive landslides and ground deformation so far north of the epicenter was related to the Mode Ⅱ-Ⅲ fracture propagation focusing seismic energy along the fault towards the north, explaining why so much devastation occurred 〉100 km from the epicenter, such as in the destroyed city of Beichuan （北川）. Understanding nField analysis and differential interferometry derived from Synthetic Aperture Radar （PALSAR） of the epicentral area of the May 12 2008 Mw 8.0 Wenchuan （汶川） earthquake zone reveal details about fault ruptures and ground displacements, with field-documented vertical offsets reaching 12 m along the trace of the main fault rupture, and PALSAR-measured horizontal displacements reaching 12.3 m. We document slip indicators on the fault scarp that show initially sub-horizontal then progressively steeper slip increments with time along the same fault during the 2 min earthquake, suggesting that the rupture propagated as a mixed Mode Ⅱ-Ⅲ fracture, with strike-slip movement at the tip directing energy from the initial rupture to points north of the epicenter, followed by vertical displacement in the interior of the slipped region. Field, seismic, and PALSAR-measured displacements are dominantly thrust near the epicentral region, and dextral in northeasterly areas, showing that slipwas partitioned along the fault in space and time during the earthquake. The changing slip directions may correlate with three main pulses of energy release at 0, 23, and 57 s during the earthquake as recorded by seismograms. The earthquake generated massive landsfides 〉100 km north of the epicenter along the trace of the fault. These massive sturzstroms formed where entire mountainsides collapsed and moved at high velocity down populated mountain valleys, jumping smaller mountains and ricocheting off steep canyon walls. These avalanches rode on cushions of water and compressed air that generated air blasts from beneath the debris, knocking down trees high on opposing mountain slopes. The concentration of massive landslides and ground deformation so far north of the epicenter was related to the Mode Ⅱ-Ⅲ fracture propagation focusing seismic energy along the fault towards the north, explaining why so much devastation occurred 〉100 km from the epicenter, such as in the destroyed city of Beichuan （北川）. Understanding n

关 键 词：China Wenchuan earthquake LONGMENSHAN NEOTECTONICS PALSAR. 

分 类 号：P315.2[天文地球—地震学]