Toru Matsuzawa Title/Affiliation Specialized Field Research Subject Professor/ Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University Earthquake-generating process Elucidation of the rupturing process of asperities Research objectives and summary of results: In order to clarify the generating process of interplate earthquakes, and to verify and sophisticate the asperity model, we studied an M~5 repeating earthquake sequence off Kamaishi, northeastern Honshu, Japan. Recent studies including ours indicate that there are seismic patches called 'asperities' (interplate regions that connect the two plates firmly and can generate seismic waves when they rupture) on plate boundaries, and aseismic slip regions surround the asperities. This hypothesis corresponds to a slight modification of the asperity model that was originally proposed by Kanamori's group in 1980's. The off-kamaishi repeating earthquake sequence is one of the seismic activities that contributed to the improvement of the asperity model. In the sequence, M~5 earthquakes have repeatedly occurred with a recurrence interval of around five and a half years. After the 2001 event, we predicted that the next event with M~5 would occur within the period from September 2006 to January 2008 with 68 % probability (i.e., within +/- 1σ range, where σ is the standard deviation of the recurrence interval) and the period from August 2005 to February 2009 with 99 % probability (i.e., within +/- 2.57 σ range). The size of the event was expected to be Mj4.7-4.9 (where Mj denotes the JMA magnitude) [Matsuzawa et al., 2002]. The expected event of Mj4.7 occurred on January 11, 2008. We investigated the source processes of the 1995, 2001 and 2008 events and found that all the events rupture the same region whose diameter is around 1 km. This result indicates that the off-kamaishi sequence is caused by repeated ruptures of an asperity. Detailed analyses of the seismic wave data show that the slip distributions and rupture processes of the recent two events are slightly different causing the difference in the high-frequency components of waveforms. The difference in the slip distribution between the two events is inferred to be caused by the difference in the smaller event activities just before the occurrences of the M~5 earthquakes. These results show the correctness of the asperity model providing a basis for long-term forecasts of earthquakes. Publications: Journals: 1. Goltz, C., D. L. Turcotte, S. G. Abaimov, R. M. Nadeau, N. Uchida, and T. Matsuzawa, Rescaled earthquake recurrence time statistics: application to microrepeaters, Geophys. J. Int., 176(1), 256-264, 2009. 2. Uchida, N., J. Nakajima, A. Hasegawa, and T. Matsuzawa, What controls interplate coupling? :
Evidence for abrupt change in coupling across a border between two overlying plates in the NE Japan subduction zone, Earth Planet. Sci. Lett., 283, 111-121, 2009. 3. Uchida, N., S. Yui, S. Miura, T. Matsuzawa, A. Hasegawa, Y. Motoya, and M. Kasahara, Quasi-static slip on the plate boundary associated with the 2003 M8.0 Tokachi-oki and 2004 M7.1 off-kushiro earthquakes, Gondwana Research, doi:10.1016/j.gr.2009.04.002., 2009 in press. 4. Hasegawa, A., J. Nakajima, N. Uchida, T. Okada, D. Zhao, T. Matsuzawa, and N. Umino, Plate subduction, and generation of earthquakes and magmas in Japan as inferred from seismic observations: An overview, Gondwana Research, doi:10.1016/j.gr.2009.03.007., 2009 in press. 5. Nakajima, J., Y. Tsuji, A. Hasegawa, S. Kita, T. Okada and T. Matsuzawa, Tomographic imaging of hydrated crust and mantle in the subducting Pacific slab beneath Hokkaido, Japan: Evidence for dehydration embrittlement as a cause of intraslab earthquakes, Gondwana Research, doi:10.1016/j.gr.2008.12.010, 2009 in press. 6. Ariyoshi, K., T. Hori, J. Ampuero, Y. Kaneda, T. Matsuzawa, R. Hino and A. Hasegawa, Influence of interaction between small asperities on various types of slow earthquakes in a 3-D simulation for a subduction plate boundary, Gondwana Research, doi:10.1016/j.gr.2009.03.006., 2009 in press. 7. Ariyoshi, K., T. Matsuzawa, Y. Yabe, N. Kato, R. Hino and A. Hasegawa, Character of slip and stress due to interaction between fault segments along the dip direction of a subduction zone, Journal of Geodynamics, 48, 55-67, 2009. 8. Hasegawa, A., J. Nakajima, S. Kita, Y, Tsuji, K. Nii, T. Okada, T. Matsuzawa, and D. Zhao, Transportation of H 2 O in the NE Japan subduction zone as inferred from seismic observations: Supply of H 2 O from the slab to the arc crust, J. Geography, 117(1), 59-75, 2008. 9. Kawada, Y., H. Nagahama, N. Uchida, and T. Matsuzawa, Afterslip associated with interplate earthquakes and viscoelastic behavior of rocks, J. Geol. Soc. Japan., 2009 in press. 10. Matsuzawa, T., Interplate earthquakes and the asperity model, Zisin2, 2009 in press. 11. Matsuzawa, T., and N. Uchida, A regular seismic activity off Kamaishi and the asperity model, Nawihuru, 67, 4-5, 2008. Contribution to books: 1. Matsuzawa, T., The Miyagi-oki earthquake (M7.2) on August 16, 2005, in "Forty Years of the Coordinating Committee for Earthquake Prediction", 2009 in press. 1. Matsuzawa, T., Recent progress in the earthquake prediction research at Tohoku University, in "Forty Years of the Coordinating Committee for Earthquake Prediction", 2009 in press. Symposium Participations: 1. Uchida, N., T. Matsuzawa, J. Nakajima, A. Hasegawa, and F. Hirose, Subduction of Izu-Bonin forearc 'wedge' and its effect on interplate coupling around Kanto, Japan, 7th International Seminar on Seismic Tomography of Far-East-Asia and related works, Daejeon, Korea Institute of Geoscience and Mineral Resources, August, 2008. (Invited) 2. Uchida, N., J. Nakajima, A. Hasegawa, and T. Matsuzawa, Abrupt change in interplate coupling on the Pacific plate across a border of two overlying plates east off Kanto, Japan, The 7th General Assembly of Asisan Seismological Commission, Tsukuba, Tsukuba international congress center, November, 2008.
3. Uchida, N., M. Mishina, and T. Matsuzawa, Afterslip of the 2008 off Ibaraki (M7.0) and off Fukushima (M6.9) earthquakes estimated from small repeating earthquakes, The 7th General Assembly of Asisan Seismological Commission, Tsukuba, Tsukuba international congress center, November, 2008. 4. Uchida, N., A. Hasegawa, J. Nakajima, and T. Matsuzawa, What controls interplate coupling?implications from abrupt change in coupling on the Pacific plate across a border between two overlying plates in the southernmost extent of the NE Japan subduction zone, AGU 2008 Fall meeting, San Francisco, Moscone Center, December, 2008. 5. Ito, Y., K. Obara, T. Matsuzawa, and T. Maeda, Very-low-frequency earthquakes accompanied with episodic tremors and slips on the plate boundary in the transition zone from locked to aseismic interface, AGU 2008 Fall meeting, San Francisco, Moscone Center, December, 2008. 6. Matsuzawa, T., K. Shimamura, N. Uchida, T. Okada, Y. Ito, T. Kono, and A. Hasegawa, Repeating Earthquake Activity off Kamaishi, Iwate Prefecture, Japan, GCOE International Symposium (Invited) 7. Kawada, Y., H. Nagahama, N. Uchida, and T. Matsuzawa, Time-scale invariance in afterslip and mechanical relaxation of rocks, Frontiers of Seismology - A meeting for the UK seismological community, Edinburgh, Our Dynamic Earth, April, 2009 8. Shimamura, K., T. Matsuzawa, T. Okada, N. Uchida, T. Kono, and A. Hasegawa, A Detailed analysis of the off-kamaishi earthquake sequence, The 7th General Assembly of Asisan Seismological Commission, Tsukuba, November, 2008. 9. Omuralieva, A., T. Okada, J. Nakajima, T. Matsuzawa, and A. Hasegawa, Spatial variation of lower limit of the shallow inland seismogenic layer and its seismic velocity structure in northeastern Japan, AGU 2008 Fall meeting, San Francisco, Moscone Center, December, 2008. 10. Kita, S., T. Okada, J. Nakajima and T. Matsuzawa, A. Hasegawa, and K. Katsumata, Anomalous deepening of upper-plane seismic belt in the Pacific slab beneath the Hokkaido corner, The 7th General Assembly of Asisan Seismological Commission, Tsukuba, November, 2008. 11. Shimamura, K., T. Matsuzawa, T. Okada, N. Uchida, T. Kono, and A. Hasegawa, Rupture Processes of the 2001 and 2008 Repeating Earthquakes off Kamaishi, NE Japan, GCOE International Symposium 12. Kita, S., T. Okada, A. Hasegawa, J. Nakajima, and T. Matsuzawa, Upper-plane seismic belt of the double seismic zone and its anomalous deepening beneath the Hokkaido, GCOE International Symposium Circum-Pacific Subduction Zones, Sendai, Katahira Sakura Hall, Tohoku University, February, 2009. 13. Omuralieva, A., T. Okada, J. Nakajima, T. Matsuzawa, and A. Hasegawa, Shallow inland earthquakes and seismic velocity structure of the crust in northeastern Japan, GCOE International Symposium 14. Ariyoshi, K., J.-P. Ampuero, T. Hori, Y. Kaneda, T. Matsuzawa, R. Hino, and A. Hasegawa, A trial to simulate deep low-frequency earthquakes occurring on the subducting plate boundary, JPGU Meeting 2008, May 25-30, 2008, 15. Ariyoshi, K., T. Matsuzawa, T. Hori, R. Hino, Y. Kaneda, and A. Hasegawa, Estimation of frictional properties by comparing propagaation speed of post seismic slip with numerical simulation results, PGU
Meeting 2008, May 25-30, 2008, 16. Uchida, N., T. Matsuzawa, T. Okada, K. Shimamura, A. Hasegawa, K. Imanishi, and W. L. Ellsworth, The 2008 off-kamaishi repeating earthquake and micro earthquake activity around the event, JPGU Meeting 2008, May 25-30, 2008, 17. Uchida, N., S. H. Kirby, T. Okada, S. Kita, Y. Tsuji, Y. Yamamoto, S. S.N. Gamage, R. Hino, T. Matsuzawa, A. Hasegawa, Seismological evidence for supraslab earthquake clusters above the subduction plate boundary of offshore Sanriku, NE Japan, JPGU Meeting 2008,May 25-30, 2008, 18. Matsuzawa, T., K. Shimamura, N. Uchida, T. Okada, Y. Ito, T. Kono, A. Hasegawa, On the long-term prediction of the characteristic earthquake activity off Kamaishi, Iwate prefecture, Japan, JPGU Meeting 2008, May 25-30, 2008, 19. Matsuzawa, T., On the characteristics of the Iwate-Miyagi Nairiku earthquake (M7.2) in 2008, The 2008 Fall Meeting of the Japanese Society for Active Fault Studies, November 2008, Tokyo, Japan. (Invited) 20. Hasegawa, A., J. Nakajima, F. Hirose, Y. Tsuji, S. Kita, T. Okada, T. Matsuzawa, Anomalous distribution of intraslab earthquakes beneath Kanto and phase transformation depth, JPGU Meeting 21. Kawada, Y., H. Nagahama, N. Uchida, T. Matsuzawa, Temporal pattern in afterslip and mechanical relaxation of rocks, JPGU Meeting 22. Kita S., T. Okada, A. Hasegawa, J. Nakajima, T. Matsuzawa, K. Katsumata, Anomalous deepening of Upper-plane seismic belt of double seismic zone beneath Hokkaido corner: Shielding effect of sliver material, JPGU Meeting (Invited) 23. Uchida, N., T. Matsuzawa, J. Nakajima, A. Hasegawa, S. H. Kirby, Moho depth variation in the forearc region of the northeastern Japan subduction zone estimated from converted waves, JPGU Meeting 2009, May 16-21, 2009, 24. Obara, K., T. Kanazawa, N. Hirata, Y. Iio, T. Mogi, T. Matsuzawa, Y. Yamanaka, S. Matsumoto, Y, Ogawa, H. Sato, S. Kodaira, T. Sagiya, T. Imaizumi, Y. Okamura, H. Fujiwara, T. Iwata, K. Koketsu, K. Satake, R. Matsu'ura, Multidisciplinary research project on the zones of high strain rate, JPGU Meeting 25. Arao, M., T. Matsuzawa, N. Uchida, K. Ariyoshi, and A. Hasegawa, Are there any regularities in the fluctuated slip behavior of the small repeating earthquakes?, JPGU Meeting 2008,May 25-30, 2008, 26. Shimamura, K., T. Okada, T. Matsuzawa, and A. Hasegawa, Rupture area of M5.6 earthquake off Iwaki on October 22, 2005 estimated from seismic waveform inversion, JPGU Meeting 2008,May 25-30, 2008, 27. Shimamura, K., T. Okada, N. Uchida, T. Matsuzawa, T. Kono, and A. Hasegawa, Comparison of source areas between the M4.8 earthquake on January 11, 2008 and the previous two earthquakes off Kamaishi, NE Japan, JPGU Meeting 2008,May 25-30, 2008, 28. Omuralieva, A., J. Nakajima, T. Okada, T. Matsuzawa, and A. Hasegawa, Regional variation of the bottom of seismogenic layer beneath the Japan Islands, JPGU Meeting 2008,May 25-30, 2008,
29. Shimamura, K., T. Matsuzawa, T. Okada, N. Uchida, T. Kono, A. Hasegawa, Comparison of rupture processes of the 2008 and 2001 small repeating earthquakes off Kamaishi, NE Japan, JPGU Meeting