Block Modeling of Taiwan Active Faults and Its Application to Earthquake Hazard Analysis

Taiwan locates in a high seismic activity belt of the southeastern Asia. In central Taiwan, many large earthquakes occurred in historic time, such as the 1906 Meishan (Ml= 7.1), the 1935 Hsinchu-Taichung (Ml=7.1), and the 1999 Chi-Chi (Mw= 7.6) earthquakes. GPS horizontal velocities, in addition, also show a shortening rate of about 30 mm/yr across the Central Range to the Deformation Front in the central Taiwan. However, Earthquake forecasts are necessarily an underinformed process, and we have not witnessed enough earthquakes anywhere in the world to make accurate forecasts based solely on historical catalogs.Extensive use of geodesy in the form of Global Positioning System (GPS) observations is a new feature brought into the earthquake probability analysis in the past few years, such as the Working Group on California Earthquake Probabilities (WGCEP) forecasts for the Uniform California Earthquake Rupture Forecast, version 3 (UCERF3) model. Geodetic measurements are potentially more spatially comprehensive than geologic offset observations, however, geodetic observations require a modeling step to translate them into estimates of fault slip rate, and they have poor resolution on closely spaced, locked faults. Therefore the challenge is to use the geodetic and geologic data in the best, most complementary way. In this proposal we employ a block-modeling method, DEFNODE, which is constructed by dividing the crust into numerous closed, fault-bounded blocks, to evaluate the interseismic fault slip behaviors in Taiwan with constraints from updated geological evidence of long-term fault activity. This proposal intends to incorporate different geodetic observations such as GPS, precise leveling, and InSAR to evaluate the geodetic long-term slip, interseismic slip, and slip-deficit rates. By considering the effect of contemporary surface deformation, the results will provide a new insight into the method of probabilistic earthquake source rupture analysis, with better constraints than the traditional seismic hazard analysis that have used long-term average fault slip rates only.