Tohoku-oki fault areas with 20 m or more of USGS-model slip had 0.1-0.3 of their 1998-2011 JMA M3.5+ rate in 2021-2024, and the surrounding 150 km had 1.7 times the old rate

Question: did the core shutdown and corona activation that Toda and Stein (2022) reported after the 2011 Mw 9.0 Tohoku-oki earthquake continue in 2021-2024, after their data? Does the rate change follow slip from an independent model? Approach: we used the public JMA unified hypocenter catalog for 1998-2024 (M 3.5 or more, depth 70 km or less) and the USGS finite-fault model. We gave each event the slip of the nearest subfault, and we used rings outside a slip-threshold core. We compared post-2011 rates with the 1998-01 to 2011-03-08 rate (30-day block bootstrap, 16 variants of magnitude, depth set and secondary-sequence removal). We also fitted Omori-Utsu decay on days 30-3653 and forecast 2021-03 to 2024-12. Results: where slip was 30 m or more, the rate ratio was 0.36, 0.13 and 0.09 (0.03-0.21) in years 3-5, 5-10 and 10-13.8 (7 events against 74 at the old rate). For all slip of 20 m or more, it was 0.18 (0.10-0.29). In all 16 variants the upper bound was below 1. A decay toward the old rate forecast 75 (54-98) events where slip was 30 m or more. A decay toward a rate near zero fit. The corona (0-150 km) stayed at 1.67 (1.35-2.07) and agreed with the decay forecast (1,641 forecast, 1,553 observed). But deep high slip near the coast (10-20 m) had a ratio of 4.3 (2.2-8.7), from the 2021 Mj 7.3 and 2022 Mj 7.4 intraslab earthquakes. Thus a broad core (slip 13.8 m or more) did not show a shutdown, and the depth of the slip matters. Far-offshore rates north and south did not decrease. Limitations: one slip model, offshore location error, an S-net processing change in 2020, small counts (7-14 events per window), and slip bins added after a first run showed sensitivity to the core definition.

Tohoku-oki earthquake · aftershocks · seismic quiescence · stress shadow · corona · Omori-Utsu · JMA catalog · coseismic slip · seismicity rate · recovery