碩士 / 國立臺灣大學 / 海洋研究所 / 100 / Since 2006, southern Taiwan has been through several big typhoons and earthquakes which triggered submarine landslides and turbidity currents and damaged many submarine cables off southwestern Taiwan. In this study, we integrate the results of sub-bottom profiles, sedimentological analysis, hydrological data, and time series of cable breakages to find how the natural hazards (e.g. typhoon and earthquake) caused submarine cable failures.
Off southwestern Taiwan, two major submarine canyons, the Gaoping Submarine Canyon (GPSC) and Fangliao Submarine Canyon (FLSC), are incising from continental shelf to deep sea floor and both of them transport considerable amounts of sediment to the South China Sea. GPSC is directly connected to the Gaoping River on land. During the flooding event, hyperpycnal flows following the GPSC down to deep sea. In contrast, the FLSC, which is smaller, younger and confined to the slope, does not associate with any river on land. The source of sediments might directly from the Central Mountain Range. Torrential rains induced landslides delivered large amount of slate fragments through narrow Gaoping shelf into the deep sea.
From sub-bottom profiles, the liquefaction structures and chaotic deposits are widely spread off southwestern Taiwan. In such unstable geological and hydrological setting, the submarine landslides can be easily triggered by earthquake or extreme flooding. According to time series of cable breakages in 2006 Pingtung Earthquake, we suggests that a series of aftershocks or sea floor sediment liquefactions might induced submarine landslides and sediment gravity flows. In 2009 typhoon Morakot, torrential rain induced hyperpycnal flow in GPSC may broke submarine cables at the junction of
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upper and middle reaches. During typhoon period, the groundwater levels raised in Pingtung Plain. The increased groundwater pressure might lead to high flux of submarine groundwater discharge and induced liquefaction on seafloor which could triggered submarine landslides and damaged submarine cables.
Most of the broken cable sites are along the GPSC and FLSC axis, indicating that canyon might be the major transport path of sediment. Cores collected from the GPSC and FLSC have observed turbidites、wood fragments and broken shells. It shows that sediments are transported rapidly through the submarine canyons. The total 210
Pb activity profiles in cores collected from Gaoping intraslope basin III show an exponential decrease with depths, which suggests there is no severe sediment-laden flow pass through in the past 10 decades. Coarse slate fragments are widely distributed along the FLSC. In contrast, we do not find any coarse grain sediment in the middle reach of GPSC. Our finding suggests that the deep sea coarse slates might be generated from the FLSC.
| Identifer | oai:union.ndltd.org:TW/100NTU05279005 |
| Date | January 2012 |
| Creators | Yi-Ya Cheng, 鄭屹雅 |
| Contributors | Chih-Chieh, Su, 蘇志杰 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 98 |
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