Geological and historical evidence of irregular recurrent earthquakes in Japan

Abstract

Great (M∼8) earthquakes repeatedly occur along the subduction zones around Japan and cause fault slip of a few to several metres releasing strains accumulated from decades to centuries of plate motions. Assuming a simple 'characteristic earthquake' model that similar earthquakes repeat at regular intervals, probabilities of future earthquake occurrence have been calculated by a government committee. However, recent studies on past earthquakes including geological traces from giant (M∼9) earthquakes indicate a variety of size and recurrence interval of interplate earthquakes. Along the Kuril Trench off Hokkaido, limited historical records indicate that average recurrence interval of great earthquakes is approximately 100 years, but the tsunami deposits show that giant earthquakes occurred at a much longer interval of approximately 400 years. Along the Japan Trench off northern Honshu, recurrence of giant earthquakes similar to the 2011 Tohoku earthquake with an interval of approximately 600 years is inferred from historical records and tsunami deposits. Along the Sagami Trough near Tokyo, two types of Kanto earthquakes with recurrence interval of a few hundred years and a few thousand years had been recognized, but studies show that the recent three Kanto earthquakes had different source extents. Along the Nankai Trough off western Japan, recurrence of great earthquakes with an interval of approximately 100 years has been identified from historical literature, but tsunami deposits indicate that the sizes of the recurrent earthquakes are variable. Such variability makes it difficult to apply a simple 'characteristic earthquake' model for the long-term forecast, and several attempts such as use of geological data for the evaluation of future earthquake probabilities or the estimation of maximum earthquake size in each subduction zone are being conducted by government committees.

Tsunamis: bridging science, engineering and society

“…Given that most of the relative plate motion in the eastern Mediterranean is aseismic, 'the modern record of seismicity provides little or no information about the faults that are likely to generate large earthquakes'. A similar conclusion is implicit in Satake's [11] analysis of the irregular nature of recurrent earthquakes in Japan.…”

“…The forecast failed as the 2011 event was much larger. Satake [11] compares limited historic records, recorded seismicity and palaeotsunami deposit studies and concludes that there is evidence of much larger earthquakes with longer recurrence intervals than documented in recent centuries. Most importantly, he finds that the sizes of recurrent earthquakes are highly variable.…”

“…A substantial paradigm shift in the estimation of earthquake hazard required for assessing tsunami potential is currently underway in Japan, as discussed by Satake [11]. Probabilities of future earthquakes had been traditionally calculated there using the characteristic earthquake model.…”

Determination of Mmax from Background Seismicity and Moment Conservation

“…For example, the analysis of 92 years of historical data (Satake, 2015) yielded a b-value of 0.88, and the aftershocks of Tohoku-Oki yielded a b-value range of 0.9-1.2 (Omi et al, 2013;Toda and Stein, 2013). However, it is clear that b-values can vary in space and time (Wiemer and Wyss, 2002).…”

“…Japan is another well-documented area with a spread of values but a general convergence of b-values around 1 (e.g., Bird and Kagan, 2004;Grunewald and Stein, 2006;Parsons et al, 2012;Omi et al, 2013;Toda and Stein, 2013;Satake, 2015). For example, the analysis of 92 years of historical data (Satake, 2015) yielded a b-value of 0.88, and the aftershocks of Tohoku-Oki yielded a b-value range of 0.9-1.2 (Omi et al, 2013;Toda and Stein, 2013).…”