Time-dependent probabilistic seismic hazard assessment for Taiwan: Development of a time-dependent approach and implementation of the Taiwan Earthquake Model parameters

Tuesday, 16 December 2014
Chung-Han Chan1,2, Yu Wang1, Yu-Ju Wang3,4, Ya-Ting Lee4, J Bruce H Shyu2, Marco Pagani5 and Graeme Weatherill5, (1)EOS, Nanyang Technological Univ., Singapore, Singapore, (2)National Taiwan University, Taipei, Taiwan, (3)Academia Sinica, Jhongli City, Taoyuan County, Taiwan, (4)National Central Univ., Jhongli, Taiwan, (5)GEM FOUNDATION, Pavia, Italy
To assess time-dependent probabilistic seismic hazard for Taiwan, we develop a new approach and implement the state-of-the-art parameters of seismogenic sources obtained by Taiwan Earthquake Model (TEM). Based on the information on tectonic setting, geology, geomorphology, and earthquake catalog, four categories of seismogenic source were identified. Those are: (a) regional source, (b) crustal fault source, (c) subduction interface source, and (d) subduction intraslab source. For the treatment of time-dependency, both long-term and short-term impacts are considered. In order to evaluate seismic probability evolution during a long-term period, several recurrence interval models for crustal fault sources were introduced. We examined their feasibility through comparison with observed return periods acquired from excavation data. By implementing occurrence time of last event obtained by instrumental and historical catalogs, long-term evolutions of the occurrence probabilities for crustal fault sources were obtained. The results show lower occurrence probabilities for the faults, which just ruptured at a recent time. For evaluation of short-term rate change, earthquake interaction between different sources in form of stress change was investigated. An increased stress state promoted occurrence of consequent events, while stress decrease inhibits future seismic activity. Through considering ground motion prediction equations for different types of sources and site conditions, time-dependent probabilistic seismic hazard was assessed. Obtained high hazards can mainly be attributed to the crustal active faults with short recurrence intervals or/and long elapsed time of the last events. Thus, higher hazards were evaluated near the active faults in the Coastal Plain in western Taiwan and along the Longitudinal Valley to the East. In northern Taiwan, by contrast, a low hazard level is obtained. It corresponds to inactive tectonics and faults in this region as well as its vicinity. Generally, since there is no significant large events took place recently in Taiwan, the short-term impact in current version is trivial. The time-dependent hazard map can be updated when a significant event take place in the future.