由於衛星遙測技術的快速發展，利用測地資料（如GPS、InSAR）來監測活動斷層的震間地殼形變在近十年來對研究斷層應力累積及地震週期行為有很重要的貢獻。本研究利用美國EarthScope PBO（Plate Boundary Observatory）計劃在Utah州建立的50多個連續GPS 站的觀測資料為主，對位於Utah東部總長約350公里的Wasatch正斷層系統進行震間（interseismic）地殼形變及斷層滑移模型進行研究。Wasatch斷層屬於板塊內部（intraplate）的活斷層系統，穿過Utah人口最稠密的地區（包括其首府Salt Lake City），因此這個斷層的活動狀況直接關係到約200萬人口的生活安全。古地震資料顯示最近一次發生在此斷層上的大地震（M>7）約在600年前，近期的GPS觀測也發現斷層兩側約有0.02 μstrain/yr的擴張應變速率。這些證據都顯示Wasatch斷層持續在震間期累積應力，因此美國政府在其 NEHPR（National Earthquake Hazards Reduction Program）計劃中一直將Wasatch fault研究視為重要的項目之一，USGS的National Hazard Map也顯示此斷層附近屬於高地震災害區。 EarthScope PBO在此所設立的連續GPS測站運轉最長已有五年之久，對研究此斷層的震間活動及滑移模式提供了重要的資料。第二期的研究計劃主要集中於整合式機率地震災害分析（probabilistic seismic hazard analysis，PSHA）方法的建立。傳統PSHA只利用了地質（包括古地震）及地震資料，並沒有適當方法將GPS的觀測結果引入分析中。本期研究會將第一期所得到的跨斷層地表形變率及最佳化逆推所得的震間斷層面滑移模型適當的引入PSHA，評估這些資料對災害評估所造成的影響。特別注意的是這個方法的建立未來將可應用輿台灣地區。由於本島位於較複雜的弧陸碰撞及造山系統中，因此由相對簡單的Wasatch fault地體系統（幾近單向的內板塊擴張）切入上述的研究較為容易。加上計畫主持人對Wasatch地區有近十年的研究經驗，以及EarthScope PBO的資料較易取得，因此在完成研究進度上較為容易。這個研究計劃的最大目標之一就是將所得的經驗用於台灣地區，讓我們未來對地震災害評估有更好及更先進的方法。 Geodetic measurement of crustal deformation across active fault zones can provide important information on the interseismic fault behaviors such as strain energy accumulation and fault loading rate. These observations must be integrated into probabilistic seismic hazard analysis to evaluate temporal variation of fault parameters such as rupture recurrence rates. The contemporary deformation field across the 370 km-long Wasatch fault zone, Utah, has been measured by continuous and campaign GPS observations since 1992, providing key constraints on modeling the geometry and loading (creeping) rate of the fault. Using the horizontal deformation results from the GPS measurements, we have done nonlinear inversions for fault geometry, locking depth, and loading rates corresponding to the interseismic loading part of the Wasatch fault. Preliminary results suggest that a dislocation dipping 27º and creeping at 7 mm/yr from depths of 9-20 km is the optimal model based on the current GPS data [Chang and Smith, 2004]. The second phase of this proposal will focus on incorporating GPS observations for time-dependent analysis of earthquake hazard by estimating the released seismic moment rate of historic earthquakes and compare the values with the accumulated geodetic moment rate for a better estimate of the amount of strain energy accumulation in the crust. The techniques and knowledge obtained from this project can be practical for future studies on fault-stress interaction, earthquake cycles, and seismic hazard assessments of the Taiwan area, where prevalent active fault systems and tectonic features make the analysis very crucial to publics. Specific goals include: 1. Derive the spatial variation of strain rate from observed GPS velocity field and then calculate the accumulating rate of geodetic moment in the elastic part of the crust; 2. Estimate the released seismic moment rate of historic earthquakes and compare the values with the accumulated geodetic moment rate for a better estimate of the amount of strain energy accumulation in the crust; 3. Analyze the time series of GPS stations to derive the temporal variation of the strain-rate field and their implications on time-dependent earthquake hazard analysis. 研究期間：10008 ~ 10107
