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physics.geo-ph · Geophysics

The Tohoku-oki high-slip area b-value stayed 0.26 above its 1998-2011 level in 2016-2024 at JMA M 2.5 or more, while five other regions changed by 0.05 or less

Question: after the 2011 Mw 9.0 Tohoku-oki earthquake, did the b-value of the high-slip area stay at its 1998-2011 level? A 2015 study reported a quick return and used it as evidence of rapid stress recovery. Approach: we used the JMA unified hypocenter catalog for 1998-2024 (4.93 M events) in a high-slip box (37.5-39.0 N, 142.5-144.0 E, depth 60 km or less), two rupture-zone boxes and three control regions. We used Aki-Utsu b-values at fixed cutoffs, b-positive, a month-block bootstrap, step tests at 119 monthly dates, and GCMT faulting types. Result: in the high-slip area, b was 0.68 in 1998 to March 2011 and 0.93 in 2016-2024 at M 2.5 or more. The change was +0.26 (95% interval +0.18 to +0.33), and it was +0.27 at M 3.0 or more. The other regions changed by 0.05 or less, and the difference from the controls was +0.26 (+0.17 to +0.34). At M 3.0 or more, b was already 0.87 in 2013-2015. An apparent return in that window occurs only with a cutoff below completeness. At M 2.5 or more, b did not step when JMA added S-net seafloor stations on 1 September 2020. But b-positive had its largest step (+0.27) at that date in the high-slip area, and steps also occurred in the other S-net regions. Thus low-cutoff estimates offshore Tohoku are not stable across this processing change. M 4 or more events in the high-slip area fell to 1.6 per year in 2020-2024, against a median of 8 per year before 2011. GCMT had no Mw 5 or more events there in 2016-2020. Limitations: the box edges are approximate, the pre-2011 b-value was not constant, and against 1998-2001 only the change is +0.13 at M 2.5 and not clear at M 3.0. A changed source population can also explain a higher b-value, and this catalog cannot separate it from lower stress.

b-value · Tohoku-oki earthquake · Gutenberg-Richter · stress recovery · JMA catalog · S-net · catalog artifacts · b-positive · Japan Trench · seismicity rate

Admitted 1 citing publication

References

10
  1. challengesdoi:10.1038/ngeo2343

    Reports a quick return of the high-slip b-value to pre-mainshock levels. We test whether the b-value stayed at that level through 2024.

  2. supportsdoi:10.1038/ngeo2649

    Argues for slow reloading and for population effects on b. Our late high b-value agrees with this view.

  3. usesdoi:10.1029/2020JB021027

    b-positive estimator.

  4. usesdoi:10.1016/j.pepi.2012.04.002

    Global CMT catalog used for faulting types.

  5. doi:10.1038/nature04094

    Faulting-type dependence of b-values.

  6. useshttps://www.data.jma.go.jp/eqev/data/bulletin/data/hypo/

    JMA unified hypocenter catalog files h1998.zip to h2024.zip.

  7. useshttps://www.data.jma.go.jp/svd/eqev/data/bulletin/catalog/notes_e.html

    Dates of JMA processing changes and hypocenter flag codes.

  8. useshttps://www.ldeo.columbia.edu/~gcmt/projects/CMT/catalog/jan76_dec20.ndk

    GCMT 1976-2020 NDK file.

  9. Automated b-value traffic lights classified 9 of 65 Japanese M5+ foreshock sequences before the larger event, and over 80% of red alarms were false (JMA, 2000-2024) sci:sha256:fa1ecaf76a35a728cb3a28a1681cf4de4583abd4d733a872948959bbb1f10eed

    Earlier campaign work with JMA b-values for foreshock traffic lights.

  10. An automatic b-value foreshock traffic light did not identify shallow Japanese M5+ earthquakes followed by larger events in 2002-2024; most larger events came before a decision sci:sha256:b5cd81d20d9e2873c84b81ace2bdff56790bcd3d7d001813ce52d8c07ce9e43c

    Earlier campaign work with automatic JMA b-value alarms.

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