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  • 學位論文

應用持久性散射體差分干涉法研究台灣西南部活動變形

Monitoring of Surface Deformation in Southwestern Taiwan Based on Persistent Scatterers SAR Interferometry

指導教授 : 胡植慶

摘要


台灣位在歐亞板塊與菲律賓海板塊的碰撞縫合帶,西南海岸平原雖然地勢平緩,地表不同程度的抬升和沉降,可能反應褶皺逆衝帶初期發展的特性。為掌握更多地表變形資訊及研究西南海岸平原區潛在的活動構造,本研究應用持久性散射體差分合成孔徑雷達干涉技術(PSInSAR),以ENVISAT ASAR衛星降冪期(descending)軌道編號: Track 232/Frame 3141共20幅影像資訊,使用StaMPS演算分析,獲得2005年5月19日至2008年9月25日間的西南台灣大範圍的地表變形成果,衛星斜距方向位移(Slant Range Displacement, SRD)結果顯示研究地區的八掌溪以北濱海有沈陷的變形,但曾文溪中游南岸到新化斷層以北,以及曾文溪下游兩側皆為抬升變形,台南台地在此期間的變形行為與1996-2000年間的觀測資料比較,則有顯著改變。台南台地北段在視衛星方向(Line of sight)的抬升速率比南段快了近5 mm/yr。位在台地東側的大灣低地同樣也顯示抬升變形,最大斜距方向變形速率達9.6 mm/yr,比台南台地部分地區顯著,此一結果和使用1996年至2000年ERS-1/-2影像,利用差分合成孔徑雷達干涉法(D-InSAR)或持久性散射體差分合成孔徑雷達干涉技術所獲得地表變動不同,然而同一期間精密水準測量及全球衛星定位系統(GPS)等其他大地監測方法,均獲得相同的變形行為。此短暫時間內台南台地和大灣低地變形模式改變的構造因素仍不清楚,可能與泥岩貫入體活動或其它末知構造再活動有關,需要進一步研究。在曾文溪南岸和新化斷層以北之間的台南科學園區也呈現明顯的抬升變形,最大視衛星方向的抬升速率達13 mm/yr,曾文溪口北岸至北側將軍溪出海同樣均呈現抬升變形。本研究將PSI結果與水準資料和GPS比較,所得變形結果非常相近。本研究進而分析影響地表變形的可能因素,包括水文因素和活動構造可能造成地表變形的程度,地下水的影響較微弱,附近的斷層構造變形可提供較大程度的變形,但總結以上因素所有貢獻未能涵蓋此區變形速率,可能近期構造活動更加活躍,顯示在西南地區平坦的沖積層之下有活化的盲斷層或活動構造正在發育,因此臺灣西南部變形前緣的位置應該更往西移。

並列摘要


Taiwan is situated along the collision boundary between the Eurasian plate and Philippine Sea plate. Although the morphology of western Taiwan is flat, however subsurface deformation is characterized by various subsiding or uplift rate in response to the incipient development of fold-and-thrust belt. This study aims to unmask the deformation pattern of the major structures and active blind structures in the coastal plain of southwestern Taiwan area for the assessment of seismic hazard of blind fault systems. Persistent Scatterers SAR Interferometry (PSInSAR) was employed to monitor surface deformation in southwestern Taiwan using 20 Advanced Synthetic Aperture Radar (ASAR) images from the ENVISAT satellite taken during the period from 2005 May 19 to 2008 September 25. The result of slant range displacement (SRD) demonstrates that significant subsidence observed in the coastal area of north part of Bazhangxi River. Meanwhile the significant uplift rate is observed in the south area and both sides of downstream area of Tsengwen River as well as along the Hsinhua fault. We also found that the uplift rate of the northern Tainan tableland is 5 mm/yr faster than that in the southern tableland. The SRD rate for the area north along the precise leveling array is about 5 to 10 mm/yr with respect to the western edge of the Tainan tableland, whereas the SRD rate for the area south of the leveling array is about 1 to 5 mm/yr. In addition, the uplifted area extends eastward to the Tawan lowland with a maximum SRD rate of 9.6 mm/yr, which is almost the same as the rate of the Tainan tableland. Results of this study differ from those suggested in previous researches that employed ERS-1/2 radar images taken from the Differential Interferometry Synthetic Aperture Radar (D-InSAR) technique and PSInSAR. However, the SRD rate observed in 2005-2008 period is consistent with those from precise leveling and GPS measurement. For instance, the tectonic implication of this transient deformation in different period is unclear; it may be related to reactivation of mud diapir or the unknown active structures. The most interesting appearance arises from a wide and unequivocally uplifting area along the north side of E-W trending Hsinhua fault and to the south side of the Tsengwen River. The maximum SRD rate is about 13 mm/yr. In comparison with leveling and GPS data, the results are fairly consistent. The analysis of possible factors affecting the surface deformation including the contributions from underground water and the movement of major faults fail to meet the observed deformation rate. It implies that the subsurface structures might be reactived in response to the compressional regime in study area. Thus the westward propagation of fold-and-thrust belts could result in the westward migration of the deformation front in coastal plain of SW Taiwan.

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