Three-dimensional S-wave attenuation structure in and around source area of the 2018 Hokkaido Eastern Iburi Earthquake, Japan

Abstract

Abstract We investigate S-wave attenuation (Qs) structure in and around Hokkaido, Japan, including the source area of the 2018 Hokkaido Eastern Iburi Earthquake (M 6.7) and its aftershocks. From the strong-motion seismograms recorded in the nationwide seismograph network in Japan, we compute spectrum amplitude at 1–10 Hz with every 1 Hz and then estimate Qs structure by adopting tomographic inversion technique. The obtained Qs structure suggests that lateral variations of Qs are remarkably formed in the study areas. The low-Qs anomalies distributing north to south are imaged in both sides of the Hidaka mountain range which is built in the central Hokkaido. These characteristics structures of Qs are extended from the ground surface to depths by about 50 km, indicating that heterogeneous structures resulted from the collision of the Kuril and northeastern Japan arcs develop at the depth ranges. Around the source area of the 2018 Hokkaido Eastern Iburi Earthquake, the abrupt changes of Qs values are identified. The 2018 Hokkaido Eastern Iburi Earthquake and its aftershocks seem to be arraigned on the high-Qs zones, whereas the low-Qs anomalies are also imaged next to the high-Qs zones. The boundary of the low- and high-Qs zones lies with near vertical, corresponding to aftershock distributions of the 2018 Hokkaido Eastern Iburi Earthquake. This agreement would propose that the heterogeneities formed due to the arc–arc collision would characterize faulting processes in the main shock of the Hokkaido Eastern Iburi Earthquake and the activities of its aftershocks.

Keywords

• The 2018 Hokkaido Eastern Iburi Earthquake
• S-wave attenuation
• The arc–arc collision zone
• Tomography