Additional file 1 of Fault geometry of M6-class normal-faulting earthquakes in the outer trench slope of Japan Trench from ocean bottom seismograph observations
Creators: name: Obana, Koichiro
name: Takahashi, Tsutomu
name: Yamamoto, Yojiro
name: Iinuma, Takeshi
name: Nakamura, Yasuyuki
name: Fujie, Gou
name: Miura, Seiichi
name: Kodaira, Shuichi
Publisher: name: figshare
Year: 2024
Subjects: subject: Geophysics
subject: FOS: Earth and related environmental sciences

description: Additional file 1: Fig. S1. Distribution of initial hypocenters determined using 1-D velocity structure. a Distribution of the initial hypocenters. Colored circles are the events used for the double-difference tomographic analysis. Open and solid inverted triangles are the OBSs seaward and landward of the trench axis, respectively. b Cross section of the initial hypocenters along the profile X–X’ shown in (a). c 1-D Vp models used for the OBSs seaward (S) and landward (L) of the trench axis. Fig. S2. Model configuration and initial velocity model of the tomographic analysis. a Map showing the initial Vp model at a depth of 15 km. Crosses indicate grid nodes of the velocity model. The red line is the survey line of Ito et al. (2005), used as a reference for the initial velocity model. Inverted triangles indicate the OBS locations. Bathymetric contours in meters. b Cross section of the initial Vp model along axis X. Dashed black lines indicate the top of the oceanic crust (Ito et al. 2005) and the approximate depth of the Moho, which is 7 km below the seafloor seaward of the trench and 6 km below the top of the oceanic crust landward of the trench. Inverted triangles indicate the projected locations of OBSs. White contours are iso-velocity contours of Vp. Fig. S3. Results of the tomographic analysis and checkerboard resolution test. a Map showing the obtained Vp model at a depth of 15 km. Symbols are the same as in Fig. S2. b, c Cross sections of Vp (b) and Vs (c) model along the profile X–X’ on panel (a). d Map showing the results of the checkerboard resolution test for Vp at a depth of 15 km. e, f Cross sections of the results for Vp (e) and Vs (f) along the profile X–X’ on panel (d). Fig. S4. Location errors of the hypocenters estimated from 100 bootstrap samples. aMap showing error ellipsoids of hypocenter locations. Error ellipsoids are color-coded by location errors. Open stars are the epicenter of three M6-class earthquakes. b Cross section of hypocenter errors projected along the profile indicated by a thick solid line on panel (a). Fig. S5. Temporal evolution of aftershock activity for the first 24 h of the September 20, 2017 earthquake. a–f Maps and cross sections showing aftershock hypocenters for each time range, represented with circles. The origin time of the mainshock is 16:37. Aftershocks within the first hour of the mainshock are indicated in panel (a). Green stars indicate the hypocenter location of the mainshock. The time ranges displayed on each panel vary from 1 to 8 h. Cross sections indicate hypocenters projected along the thick solid line on the map, which represents profile A–A’ in Fig. 3. Inverted triangles indicate the OBS locations. The seafloor and the approximate depth of the Moho, 7 km below the seafloor, are indicated on the cross sections with solid and dashed lines, respectively. Fig. S6. Coulomb stress changes at aftershock hypocenters for the September 20, 2017 earthquake. a Map and cross section indicating the definition of the west, mainshock, and east areas used in panel (b). Green stars are the hypocenter of the mainshock. The green rectangle on the map view and thick green line on the cross section are the assumed faults of the mainshock for case 1, in which the rupture extends both in the oceanic crust and uppermost oceanic mantle. Inverted triangles indicate the OBS locations. Open circles are the aftershocks that occurred until September 22, 2017, which are the same as the colored events in Fig. 3. b Frequency distribution of Coulomb stress changes (dCFF) at aftershock hypocenters. The stress changes on both westward and eastward-dipping normal faults with a 70° dipping angle were calculated for the aftershocks that occurred within the map area in panel (a) until September 22, 2017.