T245 Scientific Ocean Drilling’s Impact on Geoscience: Past, Present, and Future

Wednesday, 25 September 2019
8:00 AM - 12:00 PM
Room 228AB, North Building

EXTRACTING THE SEDIMENT RECORD OF MEGATHRUST RUPTURES IN THE JAPAN TRENCH THROUGH SCIENTIFIC OCEAN DRILLING

Paper number: T245-7
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

Scientific Ocean Drilling has evolved to meet society scientific challenges since its beginning in 1950’s. Natural hazards has become a priority after the catastrophic 2004 Mw9.2 Sumatra and 2011 Mw9.0 Tohoku earthquakes and tsunamis and Scientific Ocean Drilling is meeting the challenges these events pose to heavily populated coasts. Submarine earthquake geology studies of recent megathrust ruptures, specifically the tsunamigenic 2011 Tohoku event, have provided excellent data. The International Ocean Discovery Program (IODP) Expedition 386 will take cores in the 8 km deep Japan Trench in 2020. One major objective is to document the location, time and size of large tsunamigenic megathrust ruptures from their sedimentary signature to help improve geohazards.

Surface sediment remobilization by the 2011 Tohoku earthquake was documented from short-lived radioisotopes for 260km along the mid-slope terrace, in the Japan slope and for 200km in the Japan Trench. The remobilized sediment is centimeters to 2m thick and widely distributed from 600-8000m of water depth. The 2011 deposits are generally acoustically transparent and lithologically homogeneous but classic single or amalgamated turbidities, and large-scale mass-wasting events have also been documented. Up to 7m thick acoustically homogeneous deposits recovered in 10m long cores in the trench likely resulted from M~9 paleoearthquakes. The Sr, Nd and Pb isotopic ratios within these deposits have a narrow range in composition. Surficial sediment remobilized from large areas of the slope is consistent with such thick and isotopically homogeneous deposits. In contrast, the Sr, Nd and Pb ratios of smaller, younger and older turbidites reflect a wide range in isotopic composition as expected from diverse sources and possibly smaller magnitude events. Great tsunamigenic earthquakes recorded in the stratigraphy of the Japan Trench and dated by tephrachronology include the 1454 Kyotoku and 869 Jogan events.

New techniques are being successfully developed to constrain megathrust ruptures back in time and below the CCD in the upcoming IODP Expedition 386 such as the application of paleomagnetic secular variability for dating, the use of isotopes for deposit identification and the quantification of organic carbon remobilized to the trench during megathrust ruptures.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-332750

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