A search for silent/slow earthquakes around Japan islands

1989年、1992年和1994年，日本海沟沿着39.0 ° N至40.6 ° N的地区发生了三陆冲地震。本文在总结地震抗震性的基础上，提出了“地震大地耦合”和“矩释放间隙”两个新概念。它们的地震矩之和为（4.8-6.6）× 10 ~（-1）<20>Nm，它们与各自主震后一天到一年的震源时间的超慢断层活动有关。超慢速断层释放的板间力矩分别为1.4、（1-4）、4.2 × 10 ~ 4 <20>Nm，相当于Mw7.3 ~ 7.7级地震的板间力矩。地震断层和非地震断层释放的力矩之和为（11-16）× 10 ~<20>（-1）Nm，在180 km的区域内，板间力矩累积为（19-23）× 10 <20>~（-1）Nm（39.0 ~ 40.6）× 150 km（三陆海岸与日本海沟之间的高地震活动区宽度），从1968年的十胜冲8.2级地震到1989-1994年的超慢地震间隔为21-27年，板块相对运动为8 cm/年，（11-16）× 10^<20>Nm与（19-23）× 10^ Nm的比值为1.5 × 10^ Nm。<20>根据Nm的估算，鄂霍次克板块与俯冲太平洋板块之间的“地震-大地耦合系数”约为50- 85%，而普通地震耦合系数约为20-30%。这将成为未来三陆冲地区板间地震中长期预测的基础。

We had the 1989,1992 and 1994 Sanriku-Oki earthquakes in the region form 39.0ﾟN to 40.6ﾟ N along the Japan trench. Summarizing the aseismic nature of the earthquakes, we propose two new concepts "seismo-geodetic coupling" and "a gap of the moment release". The sum of their seismic moments is (4.8-6.6) *10^<20>Nm.These events were associated with aseismic ultra-slow faulting of source times of a day to a year following the respective main seismic shocks. The ultra-slow faultings respectively released interplate moments, 1.4, (1-4), 4.2*10^<20>Nm, equivalent to those of Mw7.3 to 7.7 seismic events. The sum of the moments released by both seismic and aseismic faultings amounts to (11-16) *10^<20>Nm.The interplate moment is accumulated as (19-23) *10^<20>Nm for the area of 180km (39.0ﾟ N to 40.6ﾟN) *150km (width of high seismicity region between the Sanriku coast and the Japan trench), with the relative plate motion of 8 cm/yr and the interval of 21-27 years from the 1968 Tokachi-Oki earthquake of Mw8.2 to the 1989-1994 ultra-slow earthquakes.The ratio of (11-16) *10^<20>Nm to (19-23) *10^<20> Nm leads to the rough estimate of "seismo-geodetic coupling coefficient" of 50-85%, where the ordinary seismic coupling coefficient has been estimated to be 20-30% between the Okhotsk and subducting Pacific plates.Based on the spatiotemporal distribution of the interplate moments including the ultra-slow earthquakes, three gaps of the moment release are suggested for the Sanriku-Oki region. This would serve as a basis for the mid-term/long-term prediction of future interplate earthquakes in the Sanriku-Oki region.