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Evaluation of the Magnitude-Frequency Distribution of the Maximum Rupture Model for the Southern San Andreas and San Jacinto Faults

Session: Overdue?

Type: Oral

Date: 4/21/2021

Presentation Time: 10:15 AM Pacific

Description: 

The Maximum Rupture Model for the southern San Andreas and San Jacinto faults (Scharer and Yule, 2020) presents an end-member rupture history constructed to accommodate ground-rupturing paleoearthquake ages by the fewest and thus longest ruptures. Rupture length for pre-historic ruptures (prior to 1800 CE) is limited by the location of paleoseismic sites with contemporaneous events and is converted empirically to moment magnitude (Mw). Rupture length and Mw for historic ruptures (since 1800 CE) are taken from published sources and informed by mapping and shaking intensity. The model produces 50 ruptures in 1600 years but short paleoseismic records at the northern and southern ends of the faults reduce the total modeled length from 730 km since 1350 CE to 400 km in 400 CE. The average magnitude for the pre-historic and historic ruptures is similar (~Mw 7.2) but a few moderate (Mw 6.4-6.5) historic events broaden the magnitude distribution since ~1800 CE. A traditional magnitude-frequency distribution since 1350 CE shows a non-linear distribution for both the pre-historic and historic records, suggesting a relative dearth of events below ~Mw 7.2 range. To better examine the entire model, we scale moment release by the available fault extent. This approach reveals short-term (200-year) spikes and lulls in moment release around an otherwise linear trend over the last 1600 years. Overall, the results support the approach of long-term averaging employed by formal earthquake rupture forecasts but suggest that subregional clustering should be considered in earthquake mitigation planning.

Presenting Author: Katherine Scharer

Student Presenter: No

Authors