岩石的流變性質對於研究地球岩石圈內之應力演變及地表形變與地震週期間的關連上是項很重要的控制量。本研究計畫主要利用測地資料如GPS及InSAR對地表運動的觀測，研究美國西部山間地震帶（Intermountain seismic belt，ISB）幾個活動構造下岩石圈的流變特性，區域涵蓋了Hebgen Lake和Wasatch正斷層帶以及一個著名的內陸火山系統─ 黃石火山系統。資料方面主要是由美國EarthScope PBO大型計畫所建立超過100站的連續GPS觀測網觀測所得，並佐以其他相關地球物理資料如地震與重力等。研究中將利用二維的黏彈解析模型及地表運動之觀測對岩石圈的流變結構進行模式化，並進一步以三維有限元素法來分析複雜地體系統中如火山及斷層等構造間的應力交互作用。這項三年的研究計畫將針對ISB中的三個區域，以不同的地殼形變機制對流變模式進行探討。摘要如下：（1）利用1959年Hebgen Lake地震（規模7.5）之震後形變量來反演岩石圈之流變結構。由於此斷層帶緊臨黃石火山系統的西北部，故將使用側向變化的二維流變模型；（2）黃石火山口自2004年中開始以每年3-7公分的速率上升。此階段之計畫將利用這一時期的GPS時間序列來分析地表應變率之變化，進而結合第一階段計畫之結果來探討此火山系統的流變特性以及火山活動（如岩漿遷移）與地震間的時空關連；（3）此階段計畫將以GPS觀測及古地震資料（至~6000年前）為主，利用有限元素法對沿美國落磯山脈東側長370公里的Wasatch斷層帶進行三維流變模式分析。並以此模式推算的應變與應力的時空演化，探討此斷層之地震週期性及其對時變地震災害分析的影響。特別注意的是，這個三年計畫的研究區域涵蓋比較簡單的地體系統；而且計畫主持人對此區域有十年以上之研究經驗，故在執行上比直接研究台灣地區有效率。此計畫後我會將所獲得的流變模式分析之經驗與結果，完全利用在複雜的台灣弧陸碰撞及造山系統上。這將對台灣地區的地體動力研究提供基本且重要的參考流變模型。 ; The rheology of viscously deforming rocks at depth is of fundamental importance when trying to understand stress evolution of the earthquake cycle and therefore time-dependent seismic hazard along active faults. This research project is focused on studying the lithospheric rheology of the Intermountain seismic belt (ISB) and the world’s premier mid-continental Yellowstone volcanic system of the western United States interior based mainly on continuous GPS measurements and other geophysical observations such as seismic and gravity data. Note that the EarthScope PBO (Plate Boundary Observatory) has deployed more than 100 continuous GPS stations along the study area since 2004 that provide excellent observations of ground motion for the studies of continental deformation. Both 2-D semi-analytic and 3-D finite-element viscoelastic modeling will be employed to evaluate the effect of the tectonic complexity and time-dependent stress interactions among geological structures. This three-year project will focus on the Hebgen Lake-Yellowstone area of extensional and volcanic regime (Phases I and II) and the Wasatch normal fault zone that extends 370 km along populated areas of Utah (Phase III). Time-dependent changes in crustal motion were determined by GPS measurements since 1987 following the 18 August 1959 Ms=7.5 Hebgen Lake earthquake, the largest historic normal-faulting earthquake of the western U.S. interior. The data were used to assess intraplate post-seismic deformation and to model lithospheric rheology. The proximity of the Hebgen Lake fault zone to the Yellowstone volcanic system also makes this area suitable for studying the mechanism of interaction between earthquakes and volcanoes. In addition, contemporary crustal deformation along the 370 km-long Wasatch fault, Utah, has been measured by GPS and modeled for elastic and viscoelastic mechanisms. This research project will employ a finite element modeling method to evaluate the viscoelastic effect on lithospheric stress evolution and its relation to the earthquake cycle based on the time history of paleoearthquakes of the fault zone. I also expect to apply the methodology and experiences obtained from this research project to future studies of the lithospheric rheology of the Taiwan area. ; 研究期間 9710 ~ 9807
