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Post-seismic Effects of an M 7.2 Earthquake and Microseismicity in an Abandoned, Flooded, Deep Mine |
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| Authors: | H. Ogasawara Y. Kuwabara T. Miwa K. Fujimori N. Hirano M. Koizumi |
| Affiliation: | Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, 525-8577, Japan. E-mail: ogasawar@se.ritsumei.ac.jp, JP Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan., JP Research Center of Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011, Japan., JP |
| Abstract: | —?An M 7.2 earthquake took place 67?km southeast of an abandoned mine containing flooded, vertical ore veins at depth of 1?km. Multidisciplinary monitoring of the unweathered country rock within the mine was carried out for a distance of about one kilometer. The M 7.2 earthquake was followed by significant post-seismic changes in strain and tilt of ～10?6, with a self-potential of ～10?mV, and an increase in the water level in the mine of about 10?cm/day. These phenomena continued for several months before returning to pre-earthquake levels. Coseismic elastic deformations were too small to account for the observed post-seismic changes, and have different senses in strain and tilt from the observed post-seismic changes. The contractions in strain and the changes in the electric self-potential and water-elevation rate strongly suggest an increase in pore pressure. An increase in microseismic activity (M?M 7.2 earthquake. |
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