Revealing coseismic displacements and the deformation zones of the 1999 Chi-Chi earthquake in the Tsaotung area, central Taiwan, using digital cadastral data

Abstract

[1] The 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6) was the largest earthquake to strike Taiwan in the twentieth century. This earthquake is associated with a 100 km long surface rupture. In order to reveal the details of displacement near the surface rupture, we use a digital cadastral system to calculate coseismic displacement around the Tsaotung area, central Taiwan. The digital cadastral system was originally conceived to survey land and building boundaries. In the Tsaotung area, Taiwan authorities have taken digital cadastral measurements before and after the Chi-Chi earthquake. The cadastral system affords high-density control points that reach ∼1421 points/km2, a system denser than that of the GPS. Accuracy is to within ±11 cm, a level that is higher than spot imaging and one that allows us to study surface deformation in detail. Coseismic displacement is ∼4.3-4.6 m at distance from the surface rupture and decreases to 3-4 m near the surface rupture. The azimuth of horizontal displacements is ∼310°-315° and rotates to 280°-305° near the surface rupture. This produced a compression, left-lateral deformation zone with ∼10-3 compression strain near the surface rupture. Coseismic displacement of the footwall is 1-1.2 m in 110°, which is similar to that from using GPS data. In the Tsaotung thrust slice, we observed that the azimuth of horizontal displacement rotates from a NW trend to a south trend as a result of slip partitioning and gravity slide effect. © Copyright 2010 by the American Geophysical Union. © Copyright 2010 by the American Geophysical Union.