台灣東北部北宜蘭構造的可能海域延伸;Offshore extension of North Ilan Structure in Northeastern Taiwan

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Title:	台灣東北部北宜蘭構造的可能海域延伸;Offshore extension of North Ilan Structure in Northeastern Taiwan
Authors:	張致嘉;Chang, Chih-Chia
Contributors:	地球科學學系
Keywords:	北宜蘭構造;電火花震測;底拖聲納;轉換拉張;斷塊旋轉;North Ilan Structure;Sparker reflection seismic;Sub-bottom profiler;Trantension;Tilted block faulting
Date:	2023-07-20
Issue Date:	2024-09-19 15:46:47 (UTC+8)
Publisher:	國立中央大學
Abstract:	菲律賓海板塊在臺灣東北部向西北方向隱沒至歐亞板塊之下，使得早期造山運動形成的隆起因而翻轉而沉陷，因此臺灣東北部處於後碰撞時期，而有一系列東北—西南走向的正斷層。其中之一是東北—西南走向的北宜蘭構造（NIS），位於宜蘭平原和雪山山脈交界處。根據2020年臺灣地震模型(TEM)團隊發表的報告，未來50年內在NIS地區發生地震矩規模Mw 6.9地震的機率估計約為13%。然而，若NIS延伸到東北海域，地震矩規模將會更大。本研究目的在了解NIS往台灣東北近海延伸的可能性，並分析其斷層活動性。為此，本研究根據既有水深資料所描繪的海底地形，在斷層可能分佈的位置收集了32條24頻道電火花反射震測剖面和6條覆蓋電火花震測剖面的底質剖面與側掃聲納，來更好的了解淺部地層構造。結果顯示兩個主要的斷層A1和C1在測區西南方明顯破裂至海床上，暗示此處斷層仍在活動。同時斷層A1幾乎縱貫整個研究區域並向西南延伸，可能與陸上的宜蘭斷層連接，而活動性較高的正斷層C1則似乎是較為區域性的斷層，並且兩大主要斷層在西南段都發育出數條分支斷層，以斷層帶的形式分佈，代表了向西南漸複雜的構造力，而東北段主要受弧後擴張所控制，以斷塊旋轉(Tilted block faulting)的斷層活動為主。其次，活動斷層C1的東北段與高角度大陸斜坡相連，揭露了將來發生海底山崩的可能，也代表海槽正在向西南擴張。最後，根據電火花震測剖面在正斷層A1與C1西南段發現的負花狀構造(Negative flower structure)，表示區域應力是轉換拉張(Transtension)。整體而言，臺灣東北部近海地區的正斷層似乎仍在活動，除東北部的斷塊旋轉(Tilted block faulting)外，經過正斷層A1和C1的側掃聲納影像與底質剖面顯示斷層C1為生長斷層且在海床形成線型構造，因此監測正斷層C1的活動至關重要，因為其持續的活動可能導致海底山崩並形成新的大陸斜坡。;The Philippine Sea Plate subducts northwestward beneath the Eurasian Plate in northeastern Taiwan, causing the previously formed mountain range collapse due to the reverse subduction polarity, which is also view as post-collisional stage and formed a series of NE-SW trending normal faults in NE Taiwan. Among these structures, the North Ilan Structure (NIS), is located at the junction of the Ilan Plain and the Hseushan Range. According to Taiwan Earthquake Model (TEM) in 2020, the estimated probability of an earthquake with a moment magnitude (Mw) of 6.9 occurring in the NIS area within next 50 years is 13%. However, if the NIS extends to the offshore area, the magnitude could be even greater. This study aims to understand the potential offshore extension of the NIS and analyze its activity. To achieve this, we collected 32 profiles of 24-channel sparker reflection seismic data and 6 sub-bottom profiles based on the possible fault distribution. The results indicate that two major normal faults, A1 and C1, are ruptured to the seafloor in SW part of the survey area, suggesting ongoing fault activity in this region. Fault A1 cross the entire study area and extends southwestward, possibly connecting to the onshore Ilan Fault, on the other hand, fault C1 appears to be a regional normal fault system. Both faults A1 and C1 have separated into multiple subsidiary faults in their SW segments, representing complex reginal forces. In contrast, the NE segments of these faults are controlled by post-arc extension, characterized by tilted block faulting along fault A1. Additionally, the NE segment of fault C1 is connected to a high-angle continental slope, indicating the potential occurrence of submarine landslide, suggesting the southwestward expansion of the south Okinawa Trough. Last, the negative flower structures observed in the SW segments of faults A1 and C1 in the sparker profiles indicate a transtensional stress regime. Overall, two major normal faults A1 and C1 in the offshore area of NE Taiwan appear to be active according to the side scan sonar image and sub-bottom profiles, therefore, monitoring the activity of growth fault C1 is crucial, as its continued activity could lead to submarine landslides and the formation of a new continental slope in NE offshore Taiwan.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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