【A級國家核心科技研究計畫】臺灣南部外海極端事件之沈積紀錄研究(Ⅳ)

Offshore southern Taiwan, a variety of geological hazards may be present,including earthquakes, submarine landslides, tsunami and turbidity currents. Thestudy area locates in the northern Manila subduction zone, where plate-interfacemegathrust and splay fault are capable of generating great (M > 8) earthquakes,which may cause tsunamis with devastating effects on the nuclear facility andpopulated coastal regions nearby the epicenters. The river-connected GaopingCanyon, has witnessed recent major floods (e.g., flooding during 2009 Morakottyphoon) and submarine landslides caused by earthquakes (e.g., 2006 Pingtungearthquake) in the form of turbidity currents and their ensuing deposits. Theturbidite layers, therefore, provide with us an opportunity to reconstruct the spatialand temporal variability of the extreme events in the study area.There is an array of core material being collected in offshore southern Taiwan inthe past. These cores, including giant piston cores, collected onboard R/V MarionDufresne (i.e., research cruises of 2010 MD178, 2018 EAGER, and 2018HydroSed), R/V Ocean Researcher I (e.g., OR1-930, 1138), and R/V OceanResearcher V (i.e., OR5-0032), are available for this study. The cores are locatedin two types of depositional settings. One type of cores is located in perchedslope basins in the accretionary wedge without connection with canyons. Theother type of cores located in the Gaoping Canyon. Turbidites in the perchedbasins are used to study the paleoseismology while hyperpycnites and seismoturbiditesare both occurring in the Gaoping Canyon and the dynamics andcontrols on sediment transfer from Taiwan to the South China Sea can bedeciphered from these canyon cores.Objectives of this multi-year project are to (1) study the paleoseismology in thenorthern Manila subduction zone for the past tens of thousands of years, (2)decipher the dynamics and controls on sediment transfer from Taiwan to theSouth China Sea through the study of cores collected in the Gaoping Canyon, (3)distinguish hyperpycnites from seismo-turbidites, and (4) collect new cores inother perched basins to decipher possible segmentation of major seismogenicfaults. Results of this multi-year project will lead us to better understand the lateQuaternary spatial and temporal development of extreme events in the studyarea. This will provide some essential parameters for future assessment ofseismic and tsunami risks in southern Taiwan and neighboring countries. Majorcontrols on sediment delivery from Taiwan to the South China Sea can also bedeciphered.Results for previous project year reveal that the sediments along the Gaopingand Penghu canyons are dominated by Taiwan-derived sediments and the rest ofstudy area off SW Taiwan the sedimentation is significantly modulated by thebranch of the Kuroshio Current. Study of MD18-3548 core reveals that the returnperiod of extreme event is around 1 ka in perched basins. Objectives for thisfourth project year are: (1) detailed chronology and stable oxygen and carbonisotope variations for MD18-3568 cores; (2) sedimentary geomorphology,sediment facies, event deposits along the Gaoping Canyon; and (3) recurrenceintervals for great earthquakes and event correlation among perched basins.