Detailed paleoseismic history of the Hinagu fault zone revealed by the high‐density radiocarbon dating and trenching survey across a surface rupture of the 2016 Kumamoto earthquake, Kyushu, Japan

Abstract

The NE-trending Hinagu fault zone, length 81 km, is one of the major active faults in Kyushu, Japan. From north to south, it is divided into three segments based on geomorphic features and paleoseismic behavior: the Takano-Shirahata, Hinagu, and Yatsushiro Sea segments. The 2016 Kumamoto earthquake produced a 6-km-long surface rupture with a dextral strike-slip displacement on the northern part of the Takano-Shirahata segment.Surface rupture, a faint east-side-up flexure with a vertical offset of less than 8 cm, was observed near the middle of the Takano-Shirahata segment. To examine past surfacerupturing earthquakes on the Takano-Shirahata segment, including rupture frequency and timing, we conducted a paleoseismic study with boring and trenching at Yamaide. A trench across the surface rupture exposed multiple fault strands associated with multiple surfacerupturing events that deformed several strata of fine-grained sediments. By structural and stratigraphic interpretation, high-density radiocarbon dating and tephra analysis, and Bayesian modeling, we constrained the timing of seven events, Events 1-7, to 0.84-1.25, 1.

Radiocarbon dating

“…Thus, application of radiocarbon dating is frequently accompanied with the use of other dating techniques such as dendrochronology, optically-stimulated luminescence, uranium-thorium dating, lead-210 dating, varve counting or tephrochronology. The combinations of methods can be used to date volcanic eruptions [155][156][157][158] , landslides [159][160][161] , earthquakes 162,163 , tsunamis 164,165 and floods 166,167 .…”