Spatial variability in sediment lithology and sedimentary processes along the Japan Trench: use of deep-sea turbidite records to reconstruct past large earthquakes

Abstract

Large earthquakes and related tsunamis serve as triggering mechanisms that generate turbidity currents which form turbidites. The event deposits from the recent 2011 Tohoku-oki earthquake and tsunami are observed throughout a wide area along the Pacific coast of Tohoku, northern Japan, extending from the coast through the shelf and slope, to the trench floor. Spatio-temporal correlation of turbidites and other tsunamigenic deposits, such as those generated in the 2011 event, can be used to reconstruct the recurrence history of large earthquakes and tsunamis. Here we use sediment cores and sub-bottom profiles to analyse the depositional setting along the Japan Trench, and show that the environment is ideal for preserving turbidites. The subducting Pacific Plate creates graben or basins along the trench floor that accommodate the episodic deposition of fine-grained turbidites; and interseismic hemipelagic deposits that form with high sedimentation rates along the Japan Trench effectively cover earthquake-induced turbidites and preserve the deposits as a geological record of large earthquakes. Therefore, small deep-sea basins with high sedimentation rates, such as in and around the Japan Trench floor, are favourable environments for studies of turbidite palaeoseismology.

Event Stratigraphy in a Hadal Oceanic Trench: The Japan Trench as Sedimentary Archive Recording Recurrent Giant Subduction Zone Earthquakes and Their Role in Organic Carbon Export to the Deep Sea

“…The AD 1454 M w ≥8.4 Kyotoku (Sawai et al, 2015) and AD 869 M w ≥8.6 Jogan earthquakes (Sawai et al, 2012;Namegaya and Satake, 2014) are modeled to occur offshore Miyagi Prefecture. Ikehara et al (2016Ikehara et al ( , 2018 and Bao et al (2018) reported thick event deposits from sediment cores along the central Japan Trench that are linked to the AD 2011 Tohoku-oki, AD 1454 Kyotoku, and AD 869 Jogan earthquakes. Similarly large earthquakes older than these events have also been documented from widespread tsunami deposits (Satake, 2015) and marine sediments on the mid-slope terrace (Usami et al, 2018).…”

“…The core locations were carefully determined with the help of bathymetry and onboard initial SBP data interpretation during these cruises. Core processing and analyses followed the same core description and investigation methods (including visual core description, radiograph image analyses, and multi-sensor core logging) to identify thick sedimentary events deposits as used by previous studies (Ikehara et al, 2016(Ikehara et al, , 2018Strasser et al, 2017;Bao et al, 2018;Kioka et al, 2019).…”

“…Remarkably, the 2011 earthquake delivered >1 Tg (10 12 g) of OC to the Japan Trench between 36.0 • and 39.5 • N through the resedimentation of spatially widespread remobilization of surficial sediment with a total volume of ∼0.2 km 3 (Kioka et al, 2019). Moreover, several cores from the central part of the Japan Trench document evidence for event deposits related to surficial sediment remobilization triggered by older large earthquakes in the last few thousands of years, including the well-known AD 1454 Kyotoku and AD 869 Jogan earthquakes (Ikehara et al, 2016(Ikehara et al, , 2018Usami et al, 2018). Yet, little is understood about (1) the temporal and spatial extent of the earthquake-triggered event deposits along the plate subduction zone, (2) whether older deposits may indicate prehistoric large earthquakes, and (3) the importance of recurrent large earthquakes for the carbon cycle at subduction margins.…”

Geochemical characterisation of the Late Quaternary widespread Japanese tephrostratigraphic markers and correlations to the Lake Suigetsu sedimentary archive (SG06 core)

“…Towada Hachinohe (To-H) (Hayakawa, 1985;Ikehara et al, 2017). Bourne et al (2016) 192 report ash from the To-H eruption in the Greenland ice cores which offers the most precise 193 age estimate (Table 1).…”

Tsunamis: geology, hazards and risks – introduction

“…There are three chapters relating to tsunami studies in Japan: Wallis et al (2017) investigate geological studies in tsunami research since the 2011 Tohoku earthquake; Goda et al (2017) present tsunami simulations of a wide range of realistic slip distribution and kinematic rupture processes, reflecting the current best understanding of what might happen due to a future mega-earthquake at the Nankai-Tonankai Trough; and Ikehara et al (2017) give an overview of spatial variability in sediment lithology and sedimentary processes along the Japan Trench, which can be used to reconstruct the recurrence history of large earthquakes and tsunamis.…”