Fig. 4

Horizontal slices of the final 3-D resistivity structure at various depths below sea level (b.s.l). Topographic contour interval is 200 m. Details are as in Fig. 2. The distinctive structures C1 and R1 are labeled. White lines show faults in the survey region (CF Chijiwa Fault, KF Kusenbu Fault, OF Oshidorino-Ike Fault), while red dots represent pressure sources identified by Kohno et al. (2008). The black line in the center of the top left panel marks the north–south cross section shown in Fig. 5b and 8b. The purple star and dashed black line indicate the USDP-4 drilling location and its subsurface trajectory. Note that the structure away from the profile is not constrained (for example, the sensitivity tests around pressure sources A and C show the small difference in RMS)