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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/68315


    Title: Record of extreme events in marine sediments, offshore eastern Taiwan
    Authors: 雷米;Lehu,Remi
    Contributors: 地球科學學系
    Keywords: 台灣;極端事件;重力流;濁積岩;地震;marine sediments;paleoseismology;sedimentary gravity deposits
    Date: 2015-07-07
    Issue Date: 2015-09-23 11:19:40 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 台灣是世界上最活躍的年輕的山岳帶之一。自二十世紀初至今已有超過二十次的七級( Mw7)以上地震發生於此。然而就超過八級( Mw8)以上的大型地震問題仍存有爭議。在本課題中利用長期記錄為突破口去評價大地震的狀況。同時本課題也藉由近年來發展迅速的,通過研究重力沉積記錄為基礎的子水古地震學中相關理論去探討歷史長期地震活動情況。

    本課題的第一個方向探討了台灣東部的沉積體系。理解沉積形態特徵,沉積相和研究海底斜坡的演化進程,同時注意近期內的沉積影響因素。它們對沉積體系分析尤為重要。我們的研究結果表明當地有許多不同的沉積體係正在形成,並對台灣東側岸外坡產生影響。同時濁流作為侵蝕作用的主要因素,佔據了當地沉積記錄的60%。濁流主要受到構造運動和氣候運動這兩個重要控制因素影響。當濁流和構造運動相結合,可導致地震晃動,並將形成內陸斜坡盆地。在氣候因素的影響下,濁流可能在盆地及內陸河域導致特大洪澇或颱風。

    第二個方向應用古地震學中兩個時間軸上以濁積岩記錄為基礎的方法。首先我們通過測試並調整濁流沉積物和地震形成之間的對應關聯。一旦校准後我們將時間序列前調至最近的三次濁積岩層形成時間,分別為:公元2001 +-3,公元1950+-5以及公元1928+-8。我們將地下加速度,震級,震源通過經驗關係相連,分別驗證了沉積岩和三個地震的聯繫:2013年12月10日成功地震(Mw6.8),1951年11月24日台東地震(Mw 7.1 )以及1935年9月4日綠島地震(Mw 7.0)。年代測定以及年齡建模為過去的3000年提供了極端氣候事件年代表。通過對比不同觸發因素對濁流形成的影響,我們得出結論,地震是濁流形成的主要觸發機制。我們還猜測整體大陸邊緣與同步濁流事件共同作用,從而導致了公元前50年至公元600年間的8級大地震。這項研究為全新世極端事件重新排序做了良好開端。;Taiwan is a young mountain belt, known as one of the most active area in the world. Since the beginning of the
    20th century more than twenty Mw7 earthquakes have struck the island. However, the occurrence of larger
    events ( Mw8) is still a matter of debate. In this framework it is of key importance to obtain longer record
    in order to evaluate the occurrence of large past earthquakes. The sub-aqueous paleoseismology, based on the
    record of the sedimentary gravity deposits, appears as a serious alternative to approach this thematic and is a
    rapidly advancing field that has the potential to illuminate the long-term history of seismicity.
    The first part of this work was to investigate the present sedimentary systems off east Taiwan, essential to
    understand the morphosedimentary features, sedimentary facies and processes governing the evolution of the
    submarine slope, and the controlling factors of the recent sedimentation. Our results showed that the offshore
    slope east Taiwan is affected by a variety of sedimentary systems and processes, and that turbidity currents
    appear as the main erosional processes covering nearly 60% of the sedimentary record. Turbidity currents are
    generated by distinct controlling factors such as tectonic and climatic activity that enabled us to define two
    end-members relative to turbidity currents initiation: Turbidity currents preconditioned by tectonic activity and
    triggered by earthquakes shaking and likely deposited into intra-slope basin and turbidity currents driven by
    climatic activity such as extreme floods or typhoons, generated in basin directly connected with onland rivers.
    The second part consisted to apply a paleoseismic approach, based on turbidites record, at two time-scales. First,
    we tested and validated the method by correlating turbidites deposits with instrumental earthquakes. Then, once
    calibrated we extended the time-series back in time. We dated the three most recent turbidites layers circa AD
    2001 3, AD 1950 5 and AD 1928 8. Using empirical relationship that link peakground acceleration,
    distance and magnitude to calibrate the seismic sources, we correlate these three turbidites with instrumental
    earthquakes: the Chengkong Earthquake 12/10/2003 (Mw 6.8), the 11/24/1951 Taitung Earthquake (Mw 7.1)
    and the 9/4/1935 Lutao Earthquake (Mw 7.0) respectively. Dating and age modeling provided a chronology of
    extreme events since the last 3000 years. Applying criteria to discriminating the different triggering mechanisms
    for turbidity current generation, we propose that earthquakes are the main triggering mechanisms. We also
    estimate that synchronous turbidite events correlated over the whole margin were triggered by a Mw8 earthquake
    between 50 BC and 600 AD. This work represents a good starting-point for future investigations in order to better
    assess Holocene time series of extreme events.
    Appears in Collections:[地球物理研究所] 博碩士論文

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