Fig. 4

Result of seismic velocity tomography: cross-sections. a Map view of Vp/Vs at a depth of 18 km. The ellipse with broken line shows the approximate location of the inherited caldera suggested by the gravity anomaly in Fig. 3a. Earthquakes within a ±3 km depth range are plotted. b A cross-section along C’-C for Vp/Vs and c cross section along B’-B for Vp/Vs, d cross section along C’-C for Vp at a latitude of 37.45 degrees, e a cross-section along B-B’ for Vp. In b–d earthquakes within a ± 3 km width are plotted. The high Vp/Vs and high Vp area and the low-Vp/Vs and low Vp area are marked by a broken-line ellipse and square, respectively. The white and black stars in a, c, and e denote the M5.4 earthquake on June 19, 2022, and the M6.5 earthquake on May 5, 2023, respectively. Grey in d and e or white in a, b, and c, and black dots denote the earthquake from 2019 before the M6.5 earthquake and after the M6.5 earthquake, respectively. Red small squares in a denote the seismic stations used in this study