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Figure 59. The short-term rates after 2011/03/09 MW7.5
foreshock and before the MW9.1 Tohoku event – at the
foreshock epicenter the short-term rates are about 100 times
higher than the long-term rates. From annual report of Kagan.
SCEC Research Accomplishments | Report
windows mean that the CSEP tests should produce meaningful
results in a reasonable time frame. Kagan (“Testing Global
Long-Term Earthquake Forecasts”) produced an improved
global earthquake forecast that is updated daily. This model is
based on smoothed seismicity, and includes focal mechanism
forecasts. Because of the daily update of the model, it
successfully forecast a high earthquake probability at the
location and time of the 2011 M9.0 Tohoku, Japan, earthquake,
based on the occurrence of the M7.5 foreshock two days earlier
(Figure 59). This model is less successful for great earthquakes
that were not preceded by foreshocks, such as the 2004 M9.3
Sumatra earthquake.
Testing Methodology
One of the concerns about CSEP, particularly for the regional
testing areas such as California, is that the relatively low rate of
earthquakes means that it could take a long time to accumulate
enough events to meaningfully distinguish between models.
Gerstenberger et al. (“How Long Will it Take to Obtain
Meaningful Test Results (and Distinguish Models) in CSEP?”)
quantified how long it would take to distinguish between the 5year
RELM models for southern California, and find that it
would take between 5 and 13 M≥4.95 earthquakes to distinguish
between the spatial distributions of two models, depending on
which two models are being compared, implying that a 5-year
testing period is not enough. They also find that catalog
variations between different 5-year (or longer) testing periods
may lead to substantially different results. These are important considerations for interpreting the results of the RELM and
CSEP tests.
Schoenberg et al. (“Evaluating and improving models for seismicity forecasting using modern residual analysis techniques”)
explored several residual analysis techniques, which are well-suited to exploring where and when an earthquake forecast
model over- or under-predicts the observed earthquake rate. They found that some residual analysis techniques have more
power than the existing CSEP tests. With the large number of earthquake forecasts that are being submitted to CSEP, it’s
important to be able to evaluate the relative strengths and weaknesses of each model. The current tests implemented in CSEP
provide an assessment of the overall performance of each model, while the residual analysis techniques could give the
developers more detailed feedback on how the next generation of their models could be improved.
Additionally, SCEC supported travel for international participants in CSEP to attend SCEC and CSEP activities, collaborate
with SCEC scientists, and work on CSEP development in collaboration with the Southern California CSEP testing center.
SCEC supported travel for Gerstenberger and Rhoades of the New Zealand CSEP testing center (“CSEP Forecast Test
Methodology: Development and Participation”) and Werner et al. of the European CSEP testing center in Switzerland (“Travel
Funds for CSEP Integration and Development”).
Observational Constraints
Earthquake forecasts, particularly frequently-updated time-dependent forecasts, could be improved through a better
understanding of what triggers earthquakes. Bürgmann et al. (“Static vs. Dynamic Triggering of Earthquakes and Tremor at
Parkfield”) found that repeating earthquakes at Parkfield tend to be preceded, at higher rates that expected, by up to several
days by earthquake that transfer >1 kPa of static stress. Immediate triggering, within a few seconds to minutes, can happen
when the separation distance is within a few km. Short-term triggering only occurs when the triggered repeating event is
already late in its recurrence cycle, so the regularity of the repeating events is not substantially impacted. Dahmen and Ben-
Zion (“Earthquake nucleation mechanisms and damage healing in heterogeneous fault zones”) studied earthquake triggering
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