| 摘要: | 台灣地區因處歐亞板塊與菲律賓海板塊碰撞邊界，因此構造活動劇烈，地震活動度也相當高。中央地質調查所在2012年對全島公布了33條活動斷層分布圖，若能了解這些斷層的震間滑移行為及未來發震潛勢，將可貢獻於建立建築物耐震係數或地震保險精算上，對民眾生命財產提供更多的保障。近年來全球衛星定位系統 (Global Navigation Satellite System, GNSS)發展快速，學術及政府機關在台灣各地廣設了300多個連續觀測站， 其中許多站的資料時間已超過10年。有了長時間的地表運動紀錄，除了可獲得更詳細的地表形變，也可以得到累積在區域內的應變大小。然而地表測地資料必須藉由設立斷層模型才能推求斷層的滑移行為，前人文獻曾使用GPS資料並套用不同的斷層及塊體模型對台灣地區進行研究，其中包含了二維板塊模型(2D plane models)、二維斷層剖面模型(2D cross‐section models)及三維塊體模型(3D block models)等。本研究計劃的前兩期利用了全台的連續與移動GPS並輔以精密水準觀測資料，再利用三維塊體模型DEFNODE估算各斷層上之長期滑移速率及滑移虧損率，並對台灣地區的地表速度場做整體的分析解釋。雖然水準資料提供了空間解析度較高及較精確的垂直變形分量，但由於其測站為線型分布，在與面狀分布的GPS資料整合時引入較多的問題。本期計畫欲加入PSInSAR觀測，以增加二維空間的地表垂直變形解析能力。由於這三種測地資料各有不同的誤差精度與測點密度，我們將透過一些內插技術與嘗試不同的權重比例，將它們整合並利用於塊體模型，以期對dip-slip faults分佈為主的台灣活斷層系統建立較為合理的分析模式。 ;Taiwan locates in a high seismic activity belt of the southeastern Asia. In central Taiwan, many large earthquakes occurred in historic time. 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. |
