Distant M6.5+ earthquakes did not change regular JMA-catalogue earthquake rates in Japan in 1998-2024, but catalogued Nankai low-frequency events rose in the first hour after waves of 1 kPa or more

We tested remote dynamic triggering in Japan with the public JMA hypocentre catalogue for 1998-2024 and 957 shallow M6.5+ USGS ComCat earthquakes (885 foreign). For each pair of a trigger and a 0.5-degree cell at 1,000 km or more, we estimated the peak dynamic stress from an Ms amplitude formula. We compared catalogue counts after the surface-wave arrival with counts before the origin time, and we used placebo dates shifted by 5-120 days as the null. For foreign triggers at 1 kPa or more, regular earthquakes (M 1.0 or more, depth 30 km or less) did not change: 574 in the hour after arrival and 556 in the hour before origin (ratio 1.03; 95% placebo range 0.86-1.17; 192 triggers). No stress bin from below 1 kPa to 10 kPa or more gave a repeated excess in cell-activation, superposed-epoch or before/after tests. A single M 2.0 excess came from the 2009 Suruga Bay earthquake, which started before the Andaman surface waves arrived. The same tests detected higher regular rates at 1,000 km or more after the 2011 Tohoku earthquake (7 times the placebo median in the first hour at 10 kPa or more). Catalogued low-frequency events increased after foreign waves of 1 kPa or more: 211 after against 60 before (ratio 3.5; placebo range 0.46-2.13; p = 0.0008 with 5,000 placebos). This result held when any one trigger was removed. Of these 211 events, 201 were in the Nankai deep-tremor belt. Volcanic deep low-frequency events did not respond. Limitations: the stress estimates are approximate, the catalogue can miss small events during shaking, there are few foreign pairs at 10 kPa or more, and the null applies to catalogued events only.

dynamic triggering · remote triggering · JMA catalogue · low-frequency earthquakes · Nankai tremor · surface waves · placebo test · Japan · earthquake interaction · null result