Revisions of the M 8.0 Wenchuan earthquake seismic intensity map based on co-seismic landslide abundance

Hundreds of thousands of landslides were triggered by the May 12, 2008, Mw 7.9 Wenchuan earthquake in China. A detailed inventory of landslides triggered by the earthquake was prepared based on geographic information systems and remote sensing technology. Visual interpretation of high-resolution satellite images and aerial photos taken pre- and post-earthquake and selected field investigation showed that at least 197,481 co-seismic landslides related to the earthquake were triggered throughout an area of approximately 110,000 km(2). These co-seismic landslides are delineated as individual solid polygons. The landslides cover a total area of approximately 1,160 km(2). Most of the landslides are distributed in an approximate ellipse area with a total area of approximately 44,031 km(2). In this paper, quantitative co-seismic landslide criteria for seismic intensity zonation were constructed based on the original "M 8.0 Wenchuan Earthquake Seismic Intensity Map" (MWESIM) and co-seismic landslide abundance analyses. These quantitative criteria, which correspond to landslide area percentages (LAP), indicate the percentage of the area affected by landslides in certain calculation windows and are listed as follows: Areas of LAP a parts per thousand yen70 % correspond to the XII intensity district; areas of 20 % a parts per thousand currency sign LAP < 70 % correspond to the XI intensity district; areas of 1 % a parts per thousand currency sign LAP < 5 % correspond to the IX intensity district; and areas of LAP < 1 % correspond to the VIII and less-than-VIII intensity districts. The VII and greater-than-VII intensity districts of the original MWESIM, which constituted an area of approximately 123,832 km(2), were corrected based on the above quantitative criteria. The degrees of fit of the original and revised MWESIMs with the co-seismic landslides were 93.8 and 95.8 %, respectively, indicating a 2.0 % improvement. The quantitative criteria of the constructed earthquake-triggered landslides for seismic intensity zonation can provide a scientific reference, standard, and basis for seismic intensity zonation in other earthquake events, especially those occurring in mountainous areas.