利用InSAR探討伊朗法爾斯弧鹽貫入體造成之地表變形與構造活動

Abstract

位於札格羅斯東南段的法爾斯弧為一個向南擴展的褶皺帶，與板塊碰撞相關的褶皺呈不規則狀並經常扭曲變形，褶皺軸短且兩翼不對稱。此區的斷層發育鮮少破裂至地表，且絕大多數都以盲斷層的形勢發生錯動，並且大地震好發於海拔1250公尺以下的簡單褶皺帶。埃迪卡拉紀至早寒武紀時期沉積的霍爾木茲鹽與晚始新世至早中新世時期沉積的法爾斯鹽影響鄰近波斯灣地區的地表形變，形成眾多衝出地表的鹽貫入體。鹽體的活動從早古生代延續至今，在霍爾木茲鹽沉積後不久就開始活動，這些早就存在的鹽貫入體影響後來沉積的地層與褶皺的走向和變形趨勢。本研究以法爾斯弧東南角為例，藉由合成孔徑雷達技術監測自2020年1月至2022年12月之地表變形，透過GMTSAR系統對衛星影像進行相位解纏，分解升軌與降軌影像所得之時間序列，拆解出垂直向與東西向的結果，並同時透過地震資料、時間序列數據分析構造的變形速度，藉此分析南波斯灣前陸盆地中鹽貫入體的變形行為。本研究結果顯示鹽貫入體波爾在時間序列中具有週期性變化，應是雨季造成的現象，是本研究區域內最為活躍的鹽貫入體。加希的圍岩活動性比中央鹽庫高，中心垂直抬升速度12.88 mm/yr，推測其仍具有穩定的活動性。霍爾木茲具有受壓後向四周擴張的行為，並形成異地鹽，溢出的鹽翼下部存在兩條生長斷層，先是下沉之後再抬升，將鹽翼向上推擠，應是使東側抬升速度增加的主因。拉拉克具有平均約25.83 mm/yr的向東速度，變形應由鹽貫入體中央鹽庫的流動行為主控。本研究區域的鹽貫入體因新生代的擠壓事件已經發展出異地鹽翼的後期構造，造成本區的鹽貫入體在水平方向上存在變形差異，過去研究著重討論鹽貫入體的垂直變形行為，本研究認為應該考慮到後期構造造成鹽貫入體的側向流動行為。

The Fars arc in the southeastern segment of the Zagros exhibits an irregular and often distorted pattern of folds associated with plate collision, characterized by short fold axes and asymmetric linbs. Faults in this region rarely reach the surface, with the majority exhibiting blind thrust faulting, and earthquakes are more common in Simple Fold Belts (SFB) below an elevation of 1250 meters. The deposition of Hormuz Salt during the Ediacaran to Early Cambrian and Fars Salt during the Late Miocene to Early Middle Miocene has influenced surface deformation in the neighboring Persian Gulf region, resulting in numerous salt diapirs penetrating the surface. The activity of these salt bodies has persisted from the Early Paleozoic to the present, initiating shortly after the deposition of Hormuz Salt. These pre-existing salt diapirs, active for a long time, have influenced the orientation and deformation trends of subsequently deposited strata and folds. Using the southeastern corner of the Fars arc as a case study, this research employs Interferometric Synthetic Aperture Radar (InSAR) to monitor surface deformation from January 2020 to December 2022. The GMTSAR software is used for the analysis of phase unwrapping in satellite images, and time series analysis of the resulting ascending and descending images is conducted to separate vertical and east-west components. Additionally, structural deformation rates are analyzed using seismic data and time series data to study the deformation behavior of salt diapirs in the South Persian Gulf Foreland Basin. The results indicate periodic variations in the time series of salt diapir Pol, making it the most active diapir in the study area. Gachin''s surrounding rock activity is higher than the central salt dome, with a vertical uplift rate of 12.88 mm/yr, suggesting stable activity. Hormuz demonstrates radial expansion after compression, forming allochthonous salt. Two growth faults exist beneath the lower part of the salt wing, sinking first and then uplifting, pushing the salt wing upward and contributing to the increased uplift rate on the eastern side. Larak has an average eastward velocity of about 25.83 mm/yr, indicating that the deformation is primarily controlled by the flow behavior of the central salt reservoir in the salt diapir. The salt diapirs in this study area have developed late-stage structures with allochthonous salt wings due to Neogene compressional events, leading to horizontal deformation differences in these salt diapirs. While previous studies focused on vertical deformation, this study emphasizes considering lateral flow behavior caused by late-stage structures in salt diapirs.