Arc-arc collision caused the 2018 Eastern Iburi earthquake (M 6.7) in Hokkaido, Japan

Yuanyuan Hua,Zewei Wang,Yixian Xu,Dapeng Zhao

doi:10.1038/s41598-019-50305-x

Yuanyuan Hua, Zewei Wang + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-50305-x

Copy DOI

Abstract

Inland crustal earthquakes usually occur in the brittle upper crust (0–20 km depths), but the 6 September 2018 Eastern Iburi earthquake (M 6.7) took place in southern Hokkaido with a focal depth of ~37 km, causing 41 fatalities and serious damage to the local infrastructure. The reason why this event was so deep and its causal mechanism are still unclear. In this work we study the three-dimensional P and S wave seismic attenuation (1/Q) structure in the source zone of the 2018 Iburi earthquake. Our results show that this event occurred at the boundary between the Sorachi-Yezo belt (low Q) and the dipping Northeastern (NE) Japan arc (high Q) that is descending beneath the Kuril arc. The collision between the NE Japan and Kuril arcs as well as fluids from dehydration of the subducting Pacific plate caused this big event and its unusual focal depth. Similar attenuation structures are revealed in source zones of the 1970 Hidaka earthquake (M 6.7) and the 1982 Urakawa-oki earthquake (M 7.1), suggesting that they were caused by similar processes. We think that large earthquakes will take place again on the active thrust faults in southern Hokkaido in the coming decades. Hence, we should pay much attention to the seismic risk and prepare for reduction of earthquake hazards there.

Highlights

Earthquakes in and around Hokkaido can be divided into three types, including megathrust earthquakes at depths of ~10–50 km along the upper boundary of the subducting Pacific plate, intra-slab events that occur within the subducting Pacific slab, and earthquakes in the overriding Okhotsk plate[2]
There have been a few studies of seismic attenuation tomography in Japan, such studies are still quite few as compared with seismic velocity tomography, in particular, in source zones of large earthquakes
P and S wave attenuation tomography of the source zone of the 2018 Eastern Iburi earthquake (M 6.7) is determined, which sheds new light on the causal mechanism of the Iburi earthquake that occurred at a boundary between low-Q and high-Q zones

Summary

Introduction

Earthquakes in and around Hokkaido can be divided into three types, including megathrust earthquakes at depths of ~10–50 km along the upper boundary of the subducting Pacific plate, intra-slab events that occur within the subducting Pacific slab, and earthquakes in the overriding Okhotsk plate[2]. The tectonic evolution of Hokkaido has been dominated by a series of accretions and the right-lateral oblique collision between the Kuril arc and the NE Japan arc, which have formed a west-vergent fold-thrust belt called the Hidaka collision zone and a series of nearly north-south trending geological units in central Hokkaido[6,7] (Fig. 1b). As wide-angle reflection seismic soundings[6,11], seismic velocity tomography[9,12,13,14], attenuation tomography[15,16], and P-wave anisotropic tomography[17,18,19,20] These previous studies have improved our understanding of the arc-arc collision and seismotectonics in the region. Our results shed new light on the causal mechanism of this damaging earthquake, as well as arc-arc collision and subduction dynamics in the study region

Methods

Results

Discussion

Conclusion