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ETAS-positive Parameter Sets for Three Southern California Earthquake Catalogs

Description: 

Statistical analysis of seismicity is hindered by incomplete recording of earthquakes. One of the major sources of incompleteness is the overshadowing of smaller earthquakes by larger ones. “Positive” statistics works around this incompleteness by restricting the analysis to intervals between earthquakes where the second is larger than the first (by some margin). The main statistical model used in earthquake forecasting is the Epidemic Type Aftershock Sequence (ETAS), and this model can also be defined without reference to a magnitude of completeness using positive statistics (ETAS+). Here I present parameter sets estimated with ETAS+ for three classical and enhanced earthquake catalogs for Southern California. The catalogs comprise 1) the ANSS Comprehensive Catalog, 2) the Hauksson et al waveform relocated catalog, and 3) the Ross et al QTM catalog. Estimates are made at different minimum magnitude cutoffs and over a range of time intervals to capture temporal variability in the parameters. Results with ETAS+ are compared to classical ETAS estimates. With the classical approach, nearly all the parameters show a dependence on minimum magnitude, consistent with the expected variation with minimum magnitude due to incompleteness. This bias is present but reduced in the QTM enhanced catalog. On the other hand, estimates made with ETAS+ show very little systematic variation with the minimum magnitude. ETAS+ returns both Gutenberg-Richterb-values and productivity scaling parameter alpha close to one, for all magnitude cutoffs, suggesting self-similar clustering. The Omori c-parameter is estimated to be on the order of the smallest interevent times in the catalog, meaning it is likely only an upper bound. For the QTM catalog with a lower magnitude cutoff of M2, the minimum catalog interevent time is quite small, and thec-value is constrained to be less than 10 seconds.

Session: Improving the State of the Art of Earthquake Forecasting Through Models, Testing and Communication - I

Type: Oral

Date: 4/15/2025

Presentation Time: 02:45 PM (local time)

Presenting Author: Nicholas

Student Presenter: No

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