Cause of destructive strong ground motion within 1–2 s in Mukawa town during the 2018 Mw 6.6 Hokkaido eastern Iburi earthquake

Abstract

We investigated the cause of destructive ground motion during the 2018 Hokkaido eastern Iburi earthquake. We conducted strong motion observations of aftershocks and microtremors and the surface wave method in the damaged areas of the town of Mukawa, Hokkaido prefecture, Japan. The ground accelerations were continuously recorded during a period of approximately 3 months after the main shock on September 6, 2018. The heavily damaged buildings were mainly situated around the strong motion station (HKD126) in Mukawa town. Such concentration of damage can be explained by the strong power that was observed in the 1-2 s period of the response spectrum at this station. We estimated the S-wave velocity profiles of this station site and a temporary station site that was installed on a nearby hill. The estimated S-wave velocity, which was inverted from phase velocity structures with the microtremor array and the surface wave method observations explained the difference in the SH-wave amplification characteristics between the two sites. An analysis of HKD126 and the temporarily observed records clearly indicates the strong effects of the local geological conditions on the heavily damaged area of Mukawa. The strong ground motion power generated during the main shock in Mukawa for 1-2 s period was mainly amplified by this shallow underground velocity structure. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Source and strong-motion characteristics of two M > 6 buried earthquakes in southwest Taiwan

“…This implies that this thick-mudstone-layer region in southern Taiwan plays a critical role in seismic hazards. A recent study by Takai et al (2019) also found that the cause of destructive ground motion, which had a predominant period of 1-2 s, during the 2018 Mw 6.6 Hokkaido eastern Iburi earthquake was nonlinear amplification by the shallow underground velocity structure. Thus, investigating the site effects of the mudstone layer in southern Taiwan is crucial because of its complex behavior and influence, and these factors should be considered to the application of seismic hazard mitigation.…”

Deposits’ Morphology of the 2018 Hokkaido Iburi-Tobu Earthquake Mass Movements from LiDAR & Aerial Photographs

“…The sudden energy release is supposed to have originated from a major slip along the faulting plane [7,8]. This subterranean slip then translated at the surface into strong motion, notably under the amplification of the near-subsurface structure [9]. The near-subsurface is made of +/−9000 years old air-fall lapilli-sized pumice soil layers (about 1.5 m thick).…”

Estimation of Subsurface Structure Based on Microtremor and Seismic Observations in Area Damaged by 2018 Hokkaido Eastern Iburi Earthquake, Hokkaido, Japan

“…For the soil type of the alluvium, the layers of clay, gravel, and silt are alternated in Mukawa, according to the PS-logging information of K-NET (HKD126). In addition, it was reported that a non-linear ground response occurred at the earthquake observation point (HKD126) in Mukawa [11], which may be related to building damage. In the future, it will be necessary to study the nonlinear ground response based on the ground structure model obtained in this study and to clarify the factors causing the damage.…”