Intermediate-term precursors of great subduction zone earthquakes: An application for predicting the Tokai earthquake

The Philippine Sea coast of central-southwest Japan tilts oceanward during interseismic periods and peninsulas uplift suddenly at the time of great earthquakes. Tide gauge data indicate that precursory uplifts of the peninsulas occurred during about the decade prior to the occurrence of recent earthquakes. I construct a model to interpret the precursory uplifts on the basis of the model which assumes a fractal distribution of asperities. I calculate uplifts due to slow failures of smaller asperities contained in the rupture zone, assuming that the probability of breakage of the smallest unit asperity increases linearly over time. The time of breakage of one of the largest asperities is the time of the occurrence of a great earthquake, tf. I conduct a least squares fitting to the residual uplift data prior to great earthquakes to constrain tf. Applications to tide gauge data before the 1923 and 1946 earthquakes give tf = 1923.2 (±1.6), and 1943.7 (±2.7), respectively. For the expected Tokai earthquake, I obtain tf = 2007.6 (−5.4, +2.8) using precise leveling data. The intermediate-term precursors of a decade may be useful to limit the expected time of occurrence of coming great earthquakes, filling the gap between long-term and short-term earthquake predictions.