井下電測(Well Logging)為一種地球物理探勘方法，具有獨特的優勢，能夠提供連續性的地下資訊。進而幫助科學家和工程師更準確地了解地下結構和地層的性質，進而從基礎工程開始預防更嚴重的災害發生。這種技術的發明和應用，對於石油勘探、礦產資源勘探、地下水資源評估以及地質工程等領域都具有重要意義。後續學者們將該方法運用至瞭解地層應力狀態，透過井下影像觀察井孔崩裂與裂隙方向推估出該地的應力狀態。
1951年10月22日與2018年2月6日的縱谷地震系列與花蓮地震分別發生芮氏規模7.3與6.2的強烈地震，本研究為了解米崙斷層及其周圍地質力學之行為模式，透過「花蓮米崙斷層科學鑽探：地震活動及前兆井下監測(MiDAS)」計畫於花蓮新城地區的科學鑽井，施測地球物理井下測量取得自然伽瑪電測、電阻電測、聲波電測、聲波造影電測。藉由井測資料推估該地方之岩石特性，應力大小及方向。並透過Baker Hughes公司推出的軟體GMI‧SFIB建立米崙斷層相關之一維地質動力學模型以了解該區域之應力狀況。
研究結果顯示井下影像觀察到新城地區的最大水平應力方向呈現東南-西北走向，且與鄰近應力場的大地應力方向相似。在鑽井深度420公尺處，由於斷層的影響，最大水平應力方向從東南-西北走向逐漸轉變至東-西走向，但深度達到600公尺後，模擬結果顯示最大水平應力方向又逐漸恢復至東南-西北走向。震前的應力狀態從淺層的逆斷層機制逐漸轉變成走向滑移機制。2018年花蓮地震後，從深度362公尺處轉變成走向滑移機制，但在520公尺處又重新轉變成逆斷層機制，該深度的應力值大小也從震前的Shmin=12.7 Mpa、SHmax=21.0 Mpa，震後變成Shmin=11.7 Mpa、SHmax=20.5 Mpa。本研究透過分析該口井的物理特性，並建立該地區的一維地質動力學模型，透過該模型可以對該米崙斷層的應力狀態有進一步的了解。

Well logging, a geophysical method, offers vital continuous underground data aiding precise understanding of subsurface structures and properties. It holds significance in various fields like oil and mineral exploration, groundwater assessment, and geological engineering. By observing borehole collapses and fracture orientations, it aids in estimating strata stress states.
This study delves into the Milun Fault's behavior and geomechanics, focusing on the 1951 Longitudinal Valley earthquakes and the 2018 Hualien earthquake. Conducted in Xincheng, Hualien, the "Milun fault Drilling and All-inclusive Sensing (MiDAS)" employed geophysical borehole measurements, including natural gamma, electrical, sonic, and sonic imaging logging. Utilizing Baker Hughes' GMI-SFIB software, a one-dimensional Geomechanical model was developed to comprehend the stress state.

Results reveal the Xincheng area's maximum horizontal stress direction trending southeast-northwest, akin to the regional stress field. At 420 meters depth, the stress direction shifts to east-west due to fault influence, reverting to southeast-northwest at 600 meters. Pre-2018 earthquake, stress shifts from shallow thrust fault to strike-slip mechanism. Post-earthquake, stress at 362 meters shifts to strike-slip, reverting to thrust fault at 520 meters, with stress magnitude changes from Shmin=12.7 Mpa, SHmax=21.0 Mpa to Shmin=11.7 Mpa, SHmax=20.5 Mpa. This study offers insights into the Milun Fault's stress state through a one-dimensional Geomechanical model.

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