Risk Evaluation and Disaster Mitigation Research Division
Inland Earthquake and Volcano Lab
Earthquake Disaster Prevention for Urban Areas Lab (OYO Corporation) (Concurrent)

Concurrent: Graduate School of Science
Research Subject(s)
My research straddles paleoseismology, tectonic geomorphology, seismology and geophysics to best perform long-term earthquake forecasting, particlarly focusing on fault-to-fault interaction and earthquake clusttering in time and space.
Key Words
Active Fault / Inland Earthquake / Seismicity / Earthquake Probability
Research Activities

Large inland earthquakes greater than magnitude 7 are caused by the movement of active faults. There are more than 2,000 active faults found in the Japanese archipelago. We are investigating not only their distributions but also the ages and slips of the prehistoric earthquakes (paleo-earthquakes) by observing recent sediments exposed on trench walls across major active faults for estimating probabilities of the future inland earthquakes. The photo shows the excavation survey in Mashiki Town of the Futagawa Fault that has been ruptured every 2,000 to 3,000 years and caused the 2016 Kumamoto Earthquake as the most recent event.

While a large earthquake releases cumulative stress on a fault, the stress is transferred to the faults nearby. It tends to trigger aftershocks not only on the source fault but also in the areas stress is loaded. We are conducting research to predict aftershocks by calculating the stress change on a computer. The figure demonstrates the stress imparted by the Kumamoto earthquake, which divides the entire region into two, areas where seismic activity is expected to increase (warm colors) and areas where dormancy is expected (cold colors). The green dots, one-month aftershocks, mostly occurred in the warm color areas.

Selected Works

Toda, S., and R. S. Stein (2020) Long‐ and Short‐Term Stress Interaction of the 2019 Ridgecrest Sequence and Coulomb‐Based Earthquake Forecasts, Bulletin of Seismological Society of America, 110, 1765-1780.

Toda, S., and R. S. Stein (2018) Why aftershock duration matters for probabilistic seismic hazard assessment, Bulletin of Seismological Society of America, 108, 1414-1426.

Toda, S., Kaneda, H., Okada, S., Ishimura, D., and Mildon, Z. (2016) Slip-partitioned surface ruptures for the Mw 7.0 16 April 2016 Kumamoto, Japan, earthquake, Earth, Planets and Space, 68, 188.

Toda, S., and H. Tsutsumi (2013) Simultaneous reactivation of two, sub-parallel, inland normal faults during the Mw 6.6 11 April 2011 Iwaki earthquake triggered by the Mw 9.0 Tohoku-oki, Japan, earthquake, Bull. Seismol. Soc. Amer., 103, 1584-1602.

Toda S., Stein R. S., Beroza G. C., Marsan D. (2012) Aftershocks halted by static stress shadows, Nature Geoscience, 5, 410-413, 10.1038/ngeo1465.

Selected Memberships
  • Seismological Society of Japan
  • Japan Geoscience Union
  • Japan Society of Engineering Geology
  • Japanese Society for Active Fault Studies
  • American Geophysical Union
  • Seismological Society of America