地貌分析揭示的越南中北部活動斷層;Active faulting in the north Central Vietnam illuminated by geomorphic analysis

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题名:	地貌分析揭示的越南中北部活動斷層;Active faulting in the north Central Vietnam illuminated by geomorphic analysis
作者:	武安道;Dao, Vu Anh
贡献者:	地球科學學系
关键词:	越南中部;活動斷層;流域不對稱;河流剖面;谷底寬高比;歸一化陡度指數（ksn）;Central Vietnam;Active fault;River profile;Normalized steepness index (ksn);Drainage basin asymmetry;Valley floor width-to-height ratio
日期:	2022-09-13
上传时间:	2022-10-04 11:12:47 (UTC+8)
出版者:	國立中央大學
摘要:	越南中北部和廣南盆地最近經歷了幾次地震，隨之而來的地質災害，如滑坡和局部隆起/沉降。然而，關於越南中部新構造變形的研究很少。本研究將現場觀測數據與新提取的河流網絡地貌指數相結合，以說明廣南盆地的變形模式和潛在的活動運動。使用 12.5 米 ALOS DEM 量化斷層和地貌之間的關係，以提取渠道和盆地指標，包括流域不對稱 (AF)、谷底寬高比 (Vf)、歸一化陡度指數 (ksn) 和臨界點模擬河流縱向剖面。幾個裂點來自不同可蝕性的岩性邊界；然而，沿大斷層走向分佈的許多裂點表明構造起源。歸一化陡度指數（ksn）的結果在與NE-SW到E-W斷層系統相交的通道上表現出相對較高的值，在近期斷崖的剪切感應指標中被認為是正常斷層。此外，廣南盆地流域不對稱（AF=60.1）表明地勢向北傾斜，這可以解釋為該地區活動構造的影響。北翼谷底寬高比（Vf=0.11~0.61）低於南翼（Vf=0.4~3.72），表明北翼下沉率較高。這項研究的結果提供了存在活動斷層分佈的地貌證據，這些活動斷層可能對越南中部的廣南地區構成地震威脅。;North Central Vietnam as well as the Quang Nam basin recently experienced several earthquakes with consequent geohazards such as landslides and local uplift/subsidence. However, there has been little research regarding neotectonics deformation in central Vietnam. This study compiles field observation data with new extracted geomorphic indices of the fluvial network to illustrate deformation patterns and potential active movements in the Quang Nam basin. The relationship between faults and geomorphology is quantified using 12.5-m ALOS DEM to extract channel and basin metrics including drainage basin asymmetry (AF), Valley floor width-to-height ratio (Vf), normalized steepness index (ksn), and knickpoints of modeled river longitudinal profiles. Several knickpoints arise locally from lithological boundaries of different erodibility; however, many knickpoints distributed along-strike of major faults indicate a tectonic origin. The results of the normalized steepness index (ksn) exhibit relatively higher values on the channels intersecting with the NE-SW to E-W fault system which is regarded as normal faults by shear-sense indicators on recent fault scarps. Furthermore, the drainage basin asymmetry (AF=60.1) of the Quang Nam basin shows that the topography is tilted to the north which may be interpreted as the influence of active tectonics in the region. The valley floor width-to-height ratio on the northern flank (Vf=0.11–0.61) is lower than the southern one (Vf=0.4-3.72), indicating a higher subsidence rate on the northern flank. The results of this study provide the geomorphic evidence of the existence of a distribution of active faults which might pose a seismic threat to the Quang Nam area in central Vietnam.
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