運用大地電磁法探討北部屏東平原地下構造;Imaging the Subsurface Structures with the Magnetotelluric Method in the northern Pingtung Plain of Taiwan

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Title:	運用大地電磁法探討北部屏東平原地下構造;Imaging the Subsurface Structures with the Magnetotelluric Method in the northern Pingtung Plain of Taiwan
Authors:	韓怡娜;Amania, Haiyina Hasbia
Contributors:	地球科學學系
Keywords:	大地電磁法;屏東平原;近地表研究;Magnetotelluric;Pingtung Plain;Subsurface Study
Date:	2021-01-28
Issue Date:	2021-03-18 17:01:02 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究目的為應用大地電磁法探討台灣西南部屏東平原的地下構造。屏東平原位於馬尼拉俯衝帶與台灣碰撞帶之間的過渡帶，也是台灣最大的地下水補給區之一，由於構造活動和過多的地下水抽運而面臨快速沉降。鑽井資料顯示約500公尺的全新世-更新世厚沉積物覆蓋了大部分的平原淺層，然而稀疏的鑽井分佈對於區域地質了解有限。在本研究中，我們從屏東平原北部的10個站點收集了大地電磁數據，並應用一個遠端參考站作為校正，選擇晚上4個小時為週期的資料，以減少人為干擾影響，研究探測深度可達4公里深，可分成南北向和東西向兩個剖面成像。根據一維反演結果，我們發現未固結的沉積物與500公尺深處的基底接觸之間有一個清晰的邊界。上層的電阻率（<50Ωm）為沖積層，在500公尺深與中新世基底岩石接觸，其電阻率達到數千Ω-m。在此區域我們沒有發現泥火山構造或是河流，然而我們發現電阻率異常反應出類似斷層和構造。因此，可認為影響台灣西南部屏東平原河道方向的主要因素是地形效應而不是地質構造。;The use of Magnetotelluric method is implemented in attempt to image the subsurface structure in Pingtung Plain area of Southwestern Taiwan. The Plain is in the transition zone between the Manila subduction and Taiwan collision belt, and is considered as one of the country largest groundwater recharge area and is faced to rapid subsidence due to both tectonic activities along with excessive ground water pumping. Thick Holocene-Pleistocene sediments of less than 500m are covering most of the Plain surface. The sparse borehole data in the area provide limited geological information for the subsurface structure. In this study, we collected the Magnetotelluric data from 10 stations in the northern Pingtung Plain to explore to the depth of approximately less than 4km, divided into 2 profiles that is trending North-South and West-East. We also utilized 1 remote station, and selected 4-hours midnight timepiece to reduce the manmade artifacts and noise effects. From 1D inversion result, we obtained a sharp boundary between the unconsolidated sediments and the basement contact at 500m deep. The topmost conductive value belongs to the alluvium layer (<50Ωm) where it contacted the Miocene basement rock of resistivity reaching thousands Ω-m in the depth of approximately 500m. Most features observed in the study area shows a fault-like features and an anomalous volumetric body, thus hardly correlated with the surrounding mud diapir and volcanoes. Also, the topographical effect of SW Taiwan is assumed to be the dominant factor affecting the river course orientation rather than geological structure.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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