Fig. 2

Geologic map of study area. (a) Distribution of active faults (red lines) around the Osaka Bay (e.g., Kato et al. 2008). Black lines: seismic reflection survey lines in this study closed-up in (b). Dotted lines: deep seismic profiles by previous studies. Orange dots: location of boreholes referred in this study (Nakaseko 1987; Masuda et al. 2000; Masuda & Miyahara 2000; Nanayama et al. 2001; Kitada et al. 2001). OsF: Osaka Bay Fault. The Awaji Island Fault zone consist of the KaF: Kariya Fault, NoF: Nojima Fault, KsF: Kusumoto Fault, HgF: Higashiura Fault, KmF: Kamakuchi Fault, NdF: Nodao Fault, and SnF: Senzan Fault. WaF: Wadamisaki Fault. MaF: Maya Fault. RIF: Rokko Island Fault. YoF: Yokooyama Fault. TaF: Takatsukayama Fault. OtF: Otsuki Fault. R1-R10: Rokko Fault zone (R1: Nobata Fault. R2: Itami Fault. R3: Koyaike graben. R4: Nishinomiya flexure. R5: Koyo Fault. R6: Ashiya Fault. R7: Gosukebashi Fault. R8: Okamoto Fault. R9: Suwayama Fault. R10: Motomachi and Itayado flexures. R11: Suma Fault.). A1-A5: Arima-Takatsuki Fault zone (A1: Makami Faults. A2: Ai Fault. A3: Bojima Fault. A4: Kiyoshi-kojin Fault. A5: Rokko Fault). UeF: Uemachi Fault. IkF: Ikoma Fault. Blue stars show representative earthquakes. Focal mechanisms are based on Imanishi et al. (2020). Geologic map is modified from Geological Survey of Japan, AIST (2022). (b) Close-up of seismic reflection survey lines in this study. Green and black lines were acquired using an Airgun and a Boomer as active source, respectively