Rapid Assessment of High Seismic Intensity Areas of the 2008 Mw 7.9 Wenchuan Earthquake Using Satellite SAR Data

Abstract

Online Material : Two figures containing comparison of satellite-geodetic surveys with isoseismal contours. One of the largest inland earthquakes ever recorded struck Wenchuan, China on 12 May 2008. It devastated huge regions and triggered over 11,000 catastrophic landslides, slope collapses, and debris flows (Huang and Li, 2009) spanning 300 km along the Longmen Shan (LMS) fault zone. The great disaster resulted in 69,226 fatalities, 17,923 missing, 374,643 injuries, and 14,565 heavily affected villages as of 25 August 2008 (State Council of China, 2008). The M w 7.9 earthquake epicenter was located on the southwestern end of the LMS faults; however, the most damaged regions were Yinxue (seismic intensity XI), Beichuan (XI), and Qingchuan (IX), distributed over a distance of 290 km toward the northeast as the LMS faults ruptured (Fig. 1a). Some of the high-intensity areas were not revealed in the immediate days after the earthquake since the epicenter was determined by initial P waves from far-field seismological observations. Lack of information on inaccessible areas such as mountainous regions led to more fatalities and injuries. On-line instrumental surveys of seismic intensity have dramatically revolutionized the method for assessing earthquake damage from the conventional field investigations. More than 4,200 strong-motion seismographs were installed to survey seismic intensity in Japan and allow information to be automatically publicized within minutes following an earthquake (Japan Meteorological Agency [JMA], 1996; Kinoshita, 1998; Okada et al. , 2004). Unfortunately, the other countries frequently affected by earthquakes lack such a dense array of seismographs. leading to delayed reporting. For example, after the Wenchuan earthquake, a field-investigation-based seismic intensity map (Fig. 1b) was not produced until 14 weeks post-quake due to widespread damages (China Earthquake Administration [CEA], 2008; Yuan, 2008). As earthquake survivors in devastated regions waited for rescue, responders had no detailed knowledge of …