運用地磁響應測深探討臺灣深部電性構造;Utilizing Geomagnetic Depth Sounding to Analyze Deep Structure Electrical Conductivity Beneath Taiwan

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Title:	運用地磁響應測深探討臺灣深部電性構造;Utilizing Geomagnetic Depth Sounding to Analyze Deep Structure Electrical Conductivity Beneath Taiwan
Authors:	林鼎竣;Lin, Ding-Jiun
Contributors:	地球科學學系
Keywords:	地磁響應測深;C響應;地函;導電率;電磁模型;海洋效應;Geomagnetic depth sounding;C-response;Mantle;Electrical conductivity;Electromagnetic modeling;Ocean effect
Date:	2024-11-13
Issue Date:	2025-04-09 16:53:37 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究的主要目的是利用地磁響應測深法（Geomagnetic Depth Sounding, GDS）分析來自地磁觀測站的長時序資料研究台灣下方的深部結構來估算C響應函數。GDS主要為分析垂直向量場與水平向量場在不同自然磁場周期下的響應變化。在本研究中，外部地磁場的空間變化可以用簡易球諧函數P01來充分描述。我們分析臺灣中央氣象署提供的七個地磁觀測站的地磁資料，並使用了三個世界資料中心(Word Data Center, WDC) 的國際地磁站，計算周期範圍為1.3至21.3天的C響應函數。由於C響應函數受海水和海洋沉積物引起的海洋感應效應的影響，尤其鄰近海邊的測站。因此我們應用3-D 球型正演模型，加入具有橫向異質性導電層的情況來代表海洋及海洋沈積物分佈的外層模型，推導全球平均的1-D導電結構模型，並將校正因子應對海洋感應效應的影響。正演模型顯示，對於外層模型的不同網格解析度（0.1°×0.1°和1°×1°），越密集的網格對於區域性研究能夠提供更多變化細節。此外，為了避免過度或低估模擬結果，我們發現以100 Ohm·m在外層模型中作為陸地的電阻率值能與顯示與觀測值相符。將海洋效應進行修正後，C響應被轉換為表觀電阻率，並進行1-D反演以推導導電率-深度剖面。台灣的1-D導電模型在300至900公里深，導電率從0.06 S/m隨深度增加至0.86 S/m。在上部地函，台灣的平均導電率較全球平均高，推測主要受到板塊隱沒影響，而下部地函中，導電率與全球模型相符，顯示出台灣在下部地函沒有明顯的異質性。對於未來研究，需要探討更深的下部地函的導電模型並加入海底電磁法的資料分析。;The main objective of this research is to utilize Geomagnetic Depth Sounding (GDS) for estimating C-response using data from geomagnetic observatories to study the deep structure beneath Taiwan. GDS involves analyzing variations between the vertical vector field and horizontal vector field responses to different periods of natural magnetic fields. In our study, spatial variations of the external geomagnetic field can be adequately described by a simple spherical harmonic, P01. We analyzed geomagnetic data from seven geomagnetic observatories, provided by the Central Weather Administration of Taiwan, and three international stations from the World Data Center to calculate C-responses over periods ranging from 1.3-21.3 days. The C-responses at each site are influenced by the oceanic induction effect caused by the seawater and oceanic sediment. Therefore, we applied a correction factor based on the ratio between C-responses, simulated through a global average 1-D conductivity structure model, with and without a 3-D surface laterally heterogeneous surface conductance layer expressing the ocean distribution. Comparison of different mesh resolutions (0.1°×0.1° and 1°×1°) for the shell model indicated that a denser mesh provides better detail of induction variation. To avoid over- or underestimating the simulated C-response, we used a continental resistivity value of 100 Ohm.m in the shell model. After correcting the response for oceanic effects, the C-responses were converted to apparent resistivity, and 1-D inversions was performed to derive the conductivity-depth profiles. The resulting 1-D conductivity model for Taiwan ranges from 0.06 to 0.86 S/m between 300 km and 900 km depth. In the lower mantle, the conductivity converges with global models, indicating less heterogeneity beneath Taiwan. However, further investigation of require the conductivity model in further deeper mantle and derived with 3-D inversion.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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