Repeated occurrence of surface-sediment remobilization along the landward slope of the Japan Trench by great earthquakes

Ken Ikehara,Toshiya Kanamatsu,Kazuko Usami

doi:10.1186/s40623-020-01241-y

Abstract

Deep-sea turbidites have been utilized to understand the history of past large earthquakes. Surface-sediment remobilization is considered to be a mechanism for the initiation of earthquake-induced turbidity currents, based on the studies on the event deposits formed by recent great earthquakes, such as the 2011 Tohoku-oki earthquake, although submarine slope failure has been considered to be a major contributor. However, it is still unclear that the surface-sediment remobilization has actually occurred in past great earthquakes. We examined a sediment core recovered from the mid-slope terrace (MST) along the Japan Trench to find evidence of past earthquake-induced surface-sediment remobilization. Coupled radiocarbon dates for turbidite and hemipelagic muds in the core show small age differences (less than a few 100 years) and suggest that initiation of turbidity currents caused by the earthquake-induced surface-sediment remobilization has occurred repeatedly during the last 2300 years. On the other hand, two turbidites among the examined 11 turbidites show relatively large age differences (~ 5000 years) that indicate the occurrence of large sea-floor disturbances such as submarine slope failures. The sedimentological (i.e., of diatomaceous nature and high sedimentation rates) and tectonic (i.e., continuous subsidence and isolated small basins) settings of the MST sedimentary basins provide favorable conditions for the repeated initiation of turbidity currents and for deposition and preservation of fine-grained turbidites. The MST small basin is a suitable site for examining deep-sea turbidite paleoseismology.

Highlights

Deep-sea turbidites are a potential tool for submarine paleoseismology (e.g., Adams 1990; Goldfinger et al 2007, 2012)
*Correspondence: k‐ikehara@aist.go.jp 1 Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 7, 1‐1‐1 Higashi, Tsukuba, Ibaraki 305‐8567, Japan Full list of author information is available at the end of the article 2000; Goldfinger et al 2012; Pickering and Hiscott 2015). It is well-known that earthquake-induced submarine slope failures have generated turbidity currents; e.g., the 1929 Grand Banks earthquake, NW Atlantic (Heezen and Ewing 1952), the 1954 Orleansville earthquake, Algeria (Heezen and Ewing 1955) and the 2006 Pingtung earthquake, Taiwan (Hsu et al 2008)
The radiocarbon dates for some horizons are slightly older than those of the underlying horizons, the relationship between the radiocarbon ages and the turbidite-free depths shows a linear relationship with a calculated averaged sedimentation rate of ~ 200 cm/ky

Summary

Introduction

Deep-sea turbidites are a potential tool for submarine paleoseismology (e.g., Adams 1990; Goldfinger et al 2007, 2012). Bao et al (2018) indicated very small differences in the radiocarbon ages of bulk organic matter in marine sediments between the 2011 event beds and the underlying hemipelagic muds in the core of the Japan Trench. We wish to determine the age differences between turbidite muds and the underlying hemipelagic muds in a sediment core from the MST, and to examine the repeated occurrence of surface-sediment remobilization due to past earthquakes.

Results

Conclusion