Recurrent large earthquakes related with an active fault-volcano system, southwest Japan

Aiming Lin,Koichiro Sado,Peng Chen

doi:10.1038/s41598-018-32140-8

Abstract

Based on fieldworks, trench excavation, archaeological evidence, and radiocarbon dating ages, we have identified at least three large normal faulting events within Aso caldera in the past ~3000 years, excluding the 2016 Mw 7.1 Kumamoto earthquake. These events took place in AD ~1000, BC ~100, and BC ~1100, respectively, suggesting an average recurrence interval of ~1000 years. These events coincide with the timings of three large inferred paleoearthquakes within the Hinagu–Futagawa Fault Zone (HFFZ), where the 2016 Kumamoto earthquake rupture began. On the basis of geological, geophysical, and seismic data, we conclude that the recurrent normal faulting events within Aso caldera were triggered by the active faults of the HFFZ. As for the 2016 Kumamoto earthquake, seismic rupture initiated on the southwest side of the caldera, propagated northeastward, and terminated inside it. These findings demonstrate that large recurring earthquakes within an active fault-volcano system can be studied to improve our understanding of the termination of coseismic rupture propagation, and that the magma chamber beneath Mt. Aso probably hinders the propagation of coseismic rupture during large earthquakes.

Highlights

Large recurring earthquakes generally occur on mature, active faults, and often accompany or precede volcanic eruptions[1,2,3,4,5,6,7,8]
Two historical/paleoseismic events prior to the 2016 Mw 7.1 Kumamoto earthquake are identified on the Hinagu–Futagawa Fault Zone (HFFZ)-Aso volcano system in this work; the magnitudes and epicenters of these earthquakes cannot be determined because no historically or instrumentally recorded earthquakes of M ≥ 6.5 have occurred within Aso caldera
Historical and instrumental records show that eight large earthquakes (6.7 ≥ M ≥ 6.0) have occurred in central Kumamoto Prefecture around the HFFZ in the past 400 years, and M ≤ 6.3 earthquakes occurred within Aso caldera in 1894 and 189515

Summary

Introduction

Large recurring earthquakes generally occur on mature, active faults, and often accompany or precede volcanic eruptions[1,2,3,4,5,6,7,8]. Previous studies reveal that the 2016 Mw 7.1 Kumamoto earthquake produced a ~40 km long coseismic surface rupture zone, mostly along the pre-existing active faults of the Hinagu–Futagawa Fault Zone (HFFZ); the rupture zone extends into Aso caldera in central Kyushu Island, southwest Japan[3,4,9] (Figs 1 and 2a). After the 2016 Kumamoto earthquake, Aso began to erupt on 8 October 2016 after 36 years of dormancy, suggesting a close relationship between volcanic eruptions and faulting in this case[4]. To better understand the relationship between the paleoseismicity and fault-volcano system structure, we conducted a comprehensive study of the active faults of the HFFZ–Aso volcano system

Methods

Discussion

Conclusion