泥火山甚低頻電磁測勘之研究－分析及反演

Abstract

本論文利用甚低頻電磁方法，結合資料處理的新技術，總體經驗模組分解法與正規化反演，以單一測線和二維等值圖分析研究泥火山地區的地下形貌。數據處理上使用總體經驗模組分解法方法濾除地質雜波，再以包含有限元素法順推計算的正規化反演法求取單一測線之地下電阻率分布剖面圖。此新技術可提升甚低頻測勘在單一測線的準確性，結果令人滿意。 野外案例以前後3年的野外測勘，監測位於南台灣高雄縣燕巢鄉烏山頂的泥火山。研究結果成功地預測到2007年噴發的泥錐位置，且提出測區泥火山地下泥漿通道的模型，說明泥火山錐，噴泥盆和裂隙噴發的機制。數據模型顯示，烏山頂泥火山的泥漿通道在淺層處並非呈點狀或管狀，而是由位於較深處泥漿庫的泥漿，在上升過程中沿裂隙噴發，造成多個泥漿通道。因此噴出地表的泥漿大多分散形成泥錐或小型噴泥盆。此結果可證明旗山斷層通過本研究區域處為接近垂直的高角度逆衝斷層。This dissertation presents a study using the very low frequency electromagnetic (VLF-EM) method with a new data processing technique, ensemble empirical mode decomposition (EEMD), and the 2D regularized inversion to investigate the subsurface structure of a mud volcanic site. The EEMD technique was served as a filter bank to enhance the signal-to-noise (S/N) ratio of the data. After the data were processed by the EEMD, a regularized inversion with finite-element forward modeling scheme was utilized to calculate the subsurface resistivity model of a single profile. Inversion results were confirmed by surface 2D contour analysis. The results indicate that the EEMD technique is critical in improving the model accuracy of the inversion. To demonstrate the effectiveness of this new data processing scheme in studying mud volcanoes, secular data collection and analysis in the Wu-Shan-Ding (WSD) mud volcano nature reserve in southwest Taiwan were conducted sporadically over the period 2005 to 2008. This study successfully predicted the evolving of a gryphon, and proposed a model for the shallow structure of the eruption site. Examining the inversion results, fluid content of the mud, distribution of gryphons and mud pools, and erupting events of the study area, an active Chi-shan fault model is also suggested in this study.