A Study on Sedimentary Records of Extreme Events Offshore Southern Taiwan (II)

Extreme geological events may include floods, landslides, earthquakes, tsunamis, typhoons, and volcanic eruptions. Though extreme events are rare they are of geological importance and may bear significant societal impacts. Offshore southern Taiwan, a variety of geological hazards may be present, including earthquakes, submarine landslides, tsunami and turbidity currents. In particular, the study area in offshore southern Taiwan locates in the northern Manila subduction zone, where plate-interface megathrust and splay fault are capable of generating great (M > 8) earthquakes, which may cause tsunamis with devastating effects on the nuclear facility and populated coastal regions nearby the epicenters. The river-connected Gaoping Canyon, meandering through the accretionary wedge, has witnessed recent major floods (e.g., flooding during 2009 Morakot typhoon) and submarine landslides caused by earthquakes (e.g., 2006 Pingtung earthquake) in the form of turbidity currents and their ensuing deposits. The turbidite layers, therefore, provide with us an opportunity to reconstruct the spatial and temporal variability of the extreme events in the study area. There is an array of core material being collected in offshore southern Taiwan in the past. These cores, including giant piston cores, collected onboard R/V Marion Dufresne (i.e., research cruises of 2010 MD178, 2018 EAGER, and 2018 HydroSed), R/V Ocean Researcher I (i.e., OR1-930, 1138), and R/V Ocean Researcher V (i.e., OR5-0032), are available for this study. The cores are located in two types of depositional settings. One type of cores is located in perched slope basins in the accretionary wedge without connection with canyons. The other type of cores located in the Gaoping Canyon. Turbidites in the perched basins are used to study the paleoseismology while hyperpycnites and seismo-turbidites are both occurring in the Gaoping Canyon and the dynamics and controls on sediment transfer from Taiwan to the South China Sea can be deciphered from these canyon cores.The objectives of this second-year project are to (1) study the paleoseismology in the northern Manila subduction zone and to compare the sedimentology, characteristics, correlation, and timing of turbidites among cores recovered from perched basins and in the Gaoping Canyon, (2) decipher the dynamics and controls on sediment transfer from Taiwan to the South China Sea through the study of cores collected in the Gaoping Canyon, (3) attempt to distinguish hyperpycnites from seismo-turbidites, and (4) collect new cores in other perched basins to decipher possible segmentation of major seismogenic faults.The project results will lead us to better understand the late Quaternary spatial and temporal development of extreme events in the study area. This will provide some essential parameters (return periods for plate-interface megathrusts, for example) for future assessment of seismic and tsunami risks in southern Taiwan and neighboring countries. The major controls on sediment delivery from Taiwan to the South China Sea can also be deciphered.