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| Titel |
Early aftershocks statistics: first results of prospective test of alarm-based model (EAST) |
| VerfasserIn |
Peter Shebalin, Clement Narteau, Matthias Holschneider, Danijel Schorlemmer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039125
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| Zusammenfassung |
| It was shown recently that the c-value systematically changes across different faulting styles
and thus may reflect the state of stress. Hypothesizing that smaller c-values indicate
places more vulnerable to moderate and large earthquakes, we suggested a simple
alarm-based forecasting model, called EAST, submitted for the test in CSEP in California
(3-month, M -¥ 4 class); the official test was started on July 1, 2009. We replaced the
c-value by more robust parameter, the geometric average of the aftershock elapsed
times (the ea-value). We normalize the ea-value calculated for last 5 years by the
value calculated for preceding 25 years. When and where the normalized ea-value
exceeds a given threshold, an “alarm” is issued: an earthquake is expected to occur
within the next 3 months. Retrospective tests of the model show good and stable
results (even better for targets M -¥ 5). During the first 6 months of the prospective
test 22 target earthquakes took place in the testing area. 14 of them (more than
60%) were forecasted with the alarm threshold resulting in only 1% of space-time
occupied by alarms (5% if space is normalized by past earthquake frequencies). This
highly encouraging result was obtained mostly due to successful forecast of the
sequence of 11 earthquakes near Lone Pine in 1-9 October 2009. However, if we
disregard aftershocks as targets, then 4 out of 9 main shocks occurred in alarms with
normalized ea-value threshold resulting in 2.5% of normalized space-time occupied by
alarms, the result is also impossible to get by chance at a significance level 1%. To
expand the evaluation of the EAST model relative to larger number of forecast
models, we have developed its frequency-based version. We estimate the expected
frequency of earthquakes using joint retrospective statistics of targets and the ea-value. |
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