淺海型海底電磁儀的研發與元件驗證方法

Abstract

大地電磁法(Magnetotellurics, MT) 是一種非破壞性被動源的地球物理探勘方法，被廣泛應用在能源探勘和地球構造研究。臺灣位處於歐亞板塊和菲律賓板塊交界帶，地殼活動頻繁，自從MT法引入臺灣之後，已有許多學者與研究機構利用此套方法研究臺灣的電性構造。海洋電磁法(Marine magnetotelluric)是其中一種在海域進行的MT探勘技術，各國爭相發展海底大地電磁儀(Ocean Bottom Electro -magnetometer, OBEM)進行海底探勘的同時，國內也自主研發出佈放於深海的OBEM。儘管過去數十年來OBEM在深海探勘研究已經蓬勃發展，但水深小於300公尺的淺海區僅有少量MT測量相關研究。與深海探勘相比，淺水及沿海地區進行地球物理探勘相對複雜，MT方法需要測量的電磁訊號頻段容易受到海浪運動雜訊和人為設施的干擾。此外，具有足夠載重的研究船因吃水深度緣故在淺海地區難以行駛，頻繁的漁業活動也不利於研究進行，綜合上述原因，我們在前人的研究基礎之上，以深海型OBEM為參考，開發出可以使用小型船隻進行佈放與收回作業的淺海型OBEM，並期望運用此儀器進行淺海區域的大地電磁高密度探測，解析臺灣淺海及附近區域地下構造。

Magnetotellurics (MT) is a non-destructive passive source geophysical exploration method widely used in energy exploration and Earth structure research. Taiwan is located at the convergence zone of the Eurasian Plate and the Philippine Sea Plate, with frequent crustal activities. Since the introduction of the MT method to Taiwan, many scholars and research institutions have utilized this method to study Taiwan''s electrical structure. Marine Magnetotellurics (Marine MT) is one of the MT survey techniques conducted in marine areas. While countries worldwide are actively developing Ocean Bottom Electro-magnetometers (OBEM) for seafloor exploration, domestic efforts have also independently developed OBEMs for deployment in deep-sea environments. Despite the flourishing development of OBEMs in deep-sea exploration over the past decades, there has been limited research on MT measurements in shallow waters with depths less than 300 meters. Compared to deep-sea exploration, conducting geophysical exploration in shallow and coastal areas is relatively complex. The frequency range of electromagnetic signals that MT methods require measurements for is susceptible to interference from wave-induced motion noise and human-made facilities. Additionally, research vessels with sufficient payload capacity face challenges navigating in shallow sea areas due to draft limitations. Frequent fishing activities also hinder research efforts. Considering these factors and building upon previous research, we developed a shallow-water OBEM based on deep-sea OBEMs that can be deployed using small vessels. We aim to utilize this instrument for high-density electromagnetic exploration in shallow-sea regions, unraveling the underground structures of Taiwan''s shallow seas and nearby areas.