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This paper discusses the variability of the stress parameter as a robust descriptor for high-frequency source scaling in earthquakes. It emphasizes the importance of accommodating site amplification and addresses the convenience of using a single parameter to estimate source variability. The study examines Ground Motion Prediction Equations (GMPEs) that include site variability, providing consistency checks on Central and Eastern North America (CENA) aleatory variability. Through various analyses, including comparisons with WNA data, the research aims to enhance the understanding of stress drops, depth inversions, and incorporates site/crustal amplification for better predictive modeling.
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Stress Parameter Variability Walter Silva Pacific Engineering and Analysis September 30, 2009
Stress Parameter, Robust Descriptor of High-Frequency Source Scaling - Appropriate Accommodation of Site-Amplification • Stress Parameter Variability, Convenient Single Parameter Estimate of Source Variability • GMPEs Include Site Variability • Provides Consistency Check on CENA Aleatory Variability
Small Magnitude σΔσsp • WNA, CENA Comparison • Similarity Suggests Comparable Source Variability • Accommodation of Epistemic Components • Mechanism • Depth
Inversions - Easy, 95% Work is in Developing FAS - Also Get Kappa - Incorporate Site/Crustal Amplification - Recommend Multiple Approaches
[1] Correlation between static stress drops and stress parameters
Figure 1. Estimates of static stress drops (circular rupture) computed for the NGA earthquakes listed in Table 1 verses magnitude (M). Note Chi-chi aftershocks and Cape Mendocino earthquake not included.
Figure 2. Estimates of static stress drops computed for the subset (24, Table 1) of NGA earthquakes with stress parameters verses magnitude (M). Shallow slip defined as greater than (or equal) 20% moment released to a depth of 5 km. Deep slip with less than 20% moment released over the top 5 km of the crust.
Figure 3. Estimates of static stress drops (circular rupture) computed for the NGA earthquakes listed in Table 1 verses depth to to-of-rupture (TOR, Table 1). Note Chi-chi aftershocks and Cape Mendocino earthquake not included.
Figure 4. Estimates of static stress drops computed for the subset (24, Table 1) of NGA earthquakes with stress parameters verses depth to top-of-rupture (TOR, Table 1). Shallow slip defined as greater than (or equal) 20% moment released to a depth of 5 km. Deep slip with less than 20% moment released over the top 5 km of the crust.
Figure 5. Estimates of stress parameters computed for the subset (24, Table 1) of NGA earthquakes verses magnitude (M). Shallow slip defined as greater than (or equal) 20% moment released to a depth of 5 km. Deep slip with less than 20% moment released over the top 5 km of the crust.
Figure 6. Estimates of stress parameters computed for the subset (24, Table 1) of NGA earthquakes verses depth to top-of-rupture (TOR, Table 1). Shallow slip defined as greater than (or equal) 20% moment released to a depth of 5 km. Deep slip with less than 20% moment released over the top 5 km of the crust.
