| Title | Fault Exploration based on the Microcrack Distribution Pattern: the Example of the Tsukiyoshi Fault, Central Japan |
|---|---|
| Authors | Tomoyuki OHTANI, Kazunari OKAZAKI, Yuki NISHIMURA, Satoru KOJIMA, Koji KUBOSHIMA, Eiji SASAO, Tadahiko TSURUTA |
| Year | 2013 |
| Conference | Stanford Geothermal Workshop |
| Keywords | fault exploration, microcrack distribution pattern |
| Abstract | Faults are important conduits for the geothermal fluids in the crust. The boreholes for the geothermal exploration often need to penetrate faults to produce the hot water. If the cuttings or core samples could provide the information on the presense of the fault below the bottom of the drill hole, the decision to continue drilling would become easier. It is known by experimental studies that the microcrack distribution pattern is different near the fault from that of the intact rock. The purpose of this study is to understand the microcrack distribution pattern near a fault from that at other parts and to assess the applicability of microcrack distribution to fault exploration. The studied borehole is MIU-3 drilled by Japan Atomic Energy Agency (JAEA). MIU-3 borehole is c.1000 m length and penetrates the Tsukiyoshi fault at the depth of 707 m. The host rock of the Tsukiyoshi fault is the Late-Cretaceous Toki Granite. Several granite samples from the different depth of the MIU-3 borehole were used for this study. Attitude of healed and sealed microcracks developed in quartz grains in the granite are measured under the optical microscope with the universal stage. The previous study indicated that the microcrack pattern far from the fault forms two or three perpendicular planes. In this study, several granite samples from the different depth of the MIU-3 borehole show a different microcrack pattern that is combination of perpendicular planes and oblique planes. This suggests that microcrack pattern can be a potential tool to assess the presence of a fault. |