14:45 〜 15:00
[SSS03-05] Resolving Stress Singularities: a Retrospective Japan Rate-and-State Earthquake Forecast
キーワード：forecast, seismology, Coulomb stress
Retrospective evaluations of rate-and-state Coulomb stress transfer have shown consistent as-
sociations between increased Coulomb stress and seismicity rates. However, stress singularities
occurring at the ends of fault dislocation patches tend to provide an unrealistic calculated stress
field near active faults, where most earthquakes occur. The effects of such stress calculation artefacts
may be mitigated through implementation of an inverse rate-and-state model, where seismicity rate
variations are inverted to obtain Coulomb stress steps over time. The resulting stress variations,
from which expected seismicity rates are derived, show potential near the Tohoku rupture plane in
a short-term prospective Japan forecast due to low magnitude completeness thresholds, which allow
for comprehensive delineation of the Coulomb stress field. An additional advantage of the stress
inversion model is that it does not require receiver plane orientations or focal mechanisms, which
add uncertainty to the calculated stress field and are not always available, limiting the reliability
of applying the forward model in a global earthquake forecast. We retrospectively test our forecast
within all Japan CSEP (Collaboratory for the Study of Earthquake Predictability) testing regions,
just after the 2011 Tohoku earthquake. To determine whether the observed seismicity rate varia-
tions are sufficient to define Coulomb stress field variations, we combine our forecast with ETAS
forecasts currently being tested in the Japan CSEP testing center. At the 95% significance level,
the rate-and-state forecast displays potential in defining the magnitude distribution of future earth-
quakes, but does not yet reliably constrain the number, or the spatial distribution of earthquakes
away from the mainshock, indicating that the inverse forecast may be most effectively applied in
an ensemble earthquake forecast model, where it contributes more to forecasted seismicity rates near areas with recent seismicity.
sociations between increased Coulomb stress and seismicity rates. However, stress singularities
occurring at the ends of fault dislocation patches tend to provide an unrealistic calculated stress
field near active faults, where most earthquakes occur. The effects of such stress calculation artefacts
may be mitigated through implementation of an inverse rate-and-state model, where seismicity rate
variations are inverted to obtain Coulomb stress steps over time. The resulting stress variations,
from which expected seismicity rates are derived, show potential near the Tohoku rupture plane in
a short-term prospective Japan forecast due to low magnitude completeness thresholds, which allow
for comprehensive delineation of the Coulomb stress field. An additional advantage of the stress
inversion model is that it does not require receiver plane orientations or focal mechanisms, which
add uncertainty to the calculated stress field and are not always available, limiting the reliability
of applying the forward model in a global earthquake forecast. We retrospectively test our forecast
within all Japan CSEP (Collaboratory for the Study of Earthquake Predictability) testing regions,
just after the 2011 Tohoku earthquake. To determine whether the observed seismicity rate varia-
tions are sufficient to define Coulomb stress field variations, we combine our forecast with ETAS
forecasts currently being tested in the Japan CSEP testing center. At the 95% significance level,
the rate-and-state forecast displays potential in defining the magnitude distribution of future earth-
quakes, but does not yet reliably constrain the number, or the spatial distribution of earthquakes
away from the mainshock, indicating that the inverse forecast may be most effectively applied in
an ensemble earthquake forecast model, where it contributes more to forecasted seismicity rates near areas with recent seismicity.