Abstract
Understanding the impact of earthquakes on subaqueous environments is key for submarine paleoseismological investigations seeking to provide long‐term records of past earthquakes. For this purpose, event deposits (e.g., turbidites) are, among others, identified and stratigraphically correlated over broad areas to test for synchronous occurrence of gravity flows. Hence, detailed spatiotemporal petrographic and geochemical fingerprints of such deposits are required to advance the knowledge about sediment source and the underlying remobilization processes induced by past earthquakes. In this study, we develop for the first time in paleoseismology a multivariate statistical approach using X‐ray fluorescence core scanning, magnetic susceptibility, and wet bulk density data that allow to test, confirm, and enhance the previous visual and lithostratigraphic correlation across two isolated basins in the central Japan Trench. The statistical correlation is further confirmed by petrographic heavy grain analysis of the turbidites and additionally combined with our novel erosion model based on previously reported bulk organic carbon 14C dates. We find surficial sediment remobilization, a process whereby strong seismic shaking remobilizes the uppermost few centimeters of surficial slope sediment, to be a predominant remobilization process, which partly initiates deeper sediment remobilization downslope during strong earthquakes at the Japan Trench. These findings shed new light on source‐to‐sink transport processes in hadal trenches during earthquakes and help to assess the completeness of the turbidite paleoseismic record. Our results further suggest that shallow‐buried tephra on the slope might significantly influence sediment remobilization and the geochemical and petrographic fingerprints of the resulting event deposits.
Highlights
Ever since the Grand Banks earthquake in 1929, it has been known that ground shaking can trigger submarine slope failures, evolving downslope into debris flows and turbidity currentsSCHWESTERMANN ET AL.Geochemistry, Geophysics, Geosystems (Heezen & Ewing, 1952) and depositing in terminal basins as event deposits
We develop for the first time in paleoseismology a multivariate statistical approach using X‐ray fluorescence core scanning, magnetic susceptibility, and wet bulk density data that allow to test, confirm, and enhance the previous visual and lithostratigraphic correlation across two isolated basins in the central Japan Trench
The statistical correlation is further confirmed by petrographic heavy grain analysis of the turbidites and combined with our novel erosion model based on previously reported bulk organic carbon 14C dates
Summary
Ever since the Grand Banks earthquake in 1929, it has been known that ground shaking can trigger submarine slope failures (e.g., slumps and slides), evolving downslope into debris flows and turbidity currentsSCHWESTERMANN ET AL.Geochemistry, Geophysics, Geosystems (Heezen & Ewing, 1952) and depositing in terminal basins as event deposits (e.g., mass‐transport deposits and turbidites). Besides correlating distinct time horizons within the stratigraphic record (e.g., tephra layers) and establishing a precise chronology (e.g., by tephra stratigraphy and radiocarbon dating), many other approaches using sedimentological, petrographical, geochemical, geophysical, and micropaleontological proxies have been proposed to establish a stratigraphic framework and to identify the sedimentologic characteristics and provenances of event deposits (e.g., Beckers et al, 2017; Çağatay et al, 2012; Goldfinger, 2009; Goldfinger et al, 2017, 2012; McHugh et al, 2014; Polonia et al, 2013; Usami et al, 2017) Such “fingerprinting” information provides the spatial and temporal correlations of turbidite records that allow testing for event synchronicity and eventually inferring source and seismic ground motion characteristics of the areas from where sediment has been remobilized. A comprehensive, high‐resolution, and multiproxy approach is needed to develop a robust statistical basis for deciphering the fingerprint of each event deposit
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