Satellite observations of the Wenchuan Earthquake, 12 May 2008

The Wenchuan Earthquake (latitude 31.0 N, longitude 103.4 E), magnitude 7.9 according to the United States Geological Survey (USGS) and 8.0 according to the Chinese Meteorological Authority, occurred on 12 May 2008 in southwest China (Pan and Tang 2010). It took away about 65 000 lives, made millions of people homeless, damaged buildings and caused changes on the Earth’s surface, both in the epicentral region and also as far away as in Taiwan and India (Wang et al. 2009, Singh et al. 2010). Increases and decreases in ground-water levels were observed at a few locations in southwest Taiwan, and a release of gases was observed near Kolkata in India (Das et al. 2009); these show changes in the stress regime in the Earth’s crust. Recently, remote-sensing satellites have become popular in providing information about the land, land cover, atmosphere and meteorological parameters at a small to large scale, and such information is commonly used by scientists to monitor changes on the Earth’s surface and in the atmosphere (Singh et al. 2002, 2006, 2007, 2010). Multi-satellite sensor data are being used for damage assessment and also for providing early-warning information about some of the natural hazards such as volcanoes, floods, droughts, forest fires and cyclones/hurricanes/typhoons. After each damaging earthquake, multi-satellite sensor data are used for damage assessment and also for relief work and rescue operations (Kumar et al. 2007, Pesaresi et al. 2007, Tan et al. 2007, Yang et al. 2007, Balz and Liao 2010, Li et al. 2010, Liou et al. 2010). The use of satellite data is increasing, and the integration of such data with Geographic Information Systems (GISs) has opened a new dimension for scientists and planners/managers to organize rescue operations and relief work soon after any deadly natural hazards and even in future planning. Soon after the Wenchuan Earthquake, multi-sensor data were analysed for damage assessment (Pan and Tang 2010), urban-building-damage detection (Li et al. 2010, Vu and Ban 2010), co-seismic landslides mapping (Ren and Lin 2010, Zhang et al. 2010a), post-earthquake disaster assessment (using FORMOSAT-2 images and images from the Disaster Management Constellation (DMC)) and damage-consequence chain mapping (Guo et al. 2010, Liou et al. 2010, Wu et al. 2010). Differential Interferometric Synthetic Aperture Radar (InSAR) data were used for the identification of macroand meso-scale land deformation caused by the Wenchuan Earthquake (Sowter 2010). A high-resolution Synthetic Aperture Radar (SAR) was used for building-damage detection (Balz and Liao 2010, Zhang et al. 2010b,c). The Wenchuan Earthquake and its aftershocks continuously shook the epicentral region; as a result, water was blocked in lakes from the fall of debris and due to landslides. Advanced Land Observing Satellite (ALOS) Advanced Visible and Near Infrared Radiometer type 2 (AVINER-2) data were used for mapping the change detection around barrier lakes (Xu et al. 2010). Zhuang et al. (2010) used high-resolution satellite data for the assessment of river blocking by debris flow in the epicentral region, and discussed the use of remote sensing