Predictability study on the aftershock sequence following the 2011 Tohoku-Oki, Japan, earthquake: first results

Kazuyoshi Z. Nanjo, Hiroshi Tsuruoka, Sayoko Yokoi, Yosihiko Ogata, Giuseppe Falcone, Naoshi Hirata, Yuzo Ishigaki, Thomas H. Jordan, K. Kasahara, Kazushige Obara, Danijel Schorlemmer, Katsuhiko Shiomi, & Jiancang Zhuang

Published November 2012, SCEC Contribution #1663

Although no deterministic and reliable earthquake precursor is known to date, we are steadily gaining insight into probabilistic forecasting that draws on space–time characteristics of earthquake clustering. Clustering-based models aiming to forecast earthquakes within the next 24 hr
are under test in the global project ‘Collaboratory for the Study of Earthquake Predictability’ (CSEP). The 2011 March 11 magnitude 9.0 Tohoku-Oki earthquake in Japan provides a unique opportunity to test the existing 1-day CSEP models against its unprecedentedly active aftershock sequence. The original CSEP experiment performs tests after the catalogue
is finalized to avoid bias due to poor data quality. However, this study differs from this tradition and uses the preliminary catalogue revised and updated by the Japan Meteorological Agency (JMA), which is often incomplete but is immediately available. This study is intended as a first
step towards operability-oriented earthquake forecasting in Japan. Encouragingly, at least one model passed the test in most combinations of the target day and the testing method, although the models could not take account of the megaquake in advance and the catalogue used for forecast generation was incomplete. However, it is also seen that important forecasts that are immediately after the quake are difficult for all models. Our conclusion does not change when the preliminary JMA catalogue is replaced by the finalized one, implying that the models perform stably over the catalogue replacement and are applicable to operational earthquake
forecasting. However, we emphasize the need of further research on model improvement to assure the reliability of forecasts for the days immediately after the main quake. Seismicity is expected to remain high in all parts of Japan over the coming years. Our results present a way to answer the urgent need to promote research on time-dependent earthquake predictability to prepare for subsequent large earthquakes in the near future in Japan.

Nanjo, K. Z., Tsuruoka, H., Yokoi, S., Ogata, Y., Falcone, G., Hirata, N., Ishigaki, Y., Jordan, T. H., Kasahara, K., Obara, K., Schorlemmer, D., Shiomi, K., & Zhuang, J. (2012). Predictability study on the aftershock sequence following the 2011 Tohoku-Oki, Japan, earthquake: first results. Geophysical Journal International, 191(2), 653-658. doi: 10.1111/j.1365-246X.2012.05626.x.