Stress Parameter Variability

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Stress Parameter Variability

• Walter Silva
• Pacific Engineering and Analysis
• September 30, 2009

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• 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

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• Small Magnitude s?ssp
• WNA, CENA Comparison
• Similarity Suggests Comparable Source Variability
• Accommodation of Epistemic Components
• Mechanism
• Depth

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• Inversions
• - Easy, 95 Work is in Developing FAS
• - Also Get Kappa
• - Incorporate Site/Crustal Amplification
• - Recommend Multiple Approaches

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WNA Stress Parameters WNA Stress Parameters WNA Stress Parameters
Set Stress Drop (bars) sln
All 46.9 0.47
Shallow Slip 30.6 0.37
Deep Slip 56.6 0.38
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NGA Earthquake Data Summary
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NGA Earthquake Summary(Cont.)
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Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters Table 2 Comparison of Static Stress Drops and Stress Parameters
Slip ?sstatic (bars) sln Number of Earthquakes ?sSP (bars) sln Number of Earthquakes Correlation1
NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models NGA Earthquakes with Finite Rupture Models
All 30.6 0.86 54
NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates) NGA Earthquakes With Stress Parameters (preliminary estimates)
All Slip 26.1 0.87 24 28.8 0.59 24 0.0
Shallow Slip 25.1 0.93 18 23.9 0.54 18 -0.1
Deep Slip 29.7 0.69 6 52.0 0.18 6 -0.6

1 Correlation between static stress drops and
stress parameters
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Earthquake Date MM/DY/YR HRMN M Mechanism ?s (bars) ?s (bars)
Earthquake Date MM/DY/YR HRMN M Mechanism Original Revised
Fruili 05/06/76 2000 6.20 reverse 780 139.6
Fruili 06/09/76 1848 4.40 reverse 353 75.4
Fruili 06/09/76 1716 4.65 reverse 242 87.4
Fruili 06/11/76 1631 5.20 reverse 325 47.6
Fruili 06/11/76 1635 5.30 reverse 406 102.3
Fruili 09/15/76 0315 5.90 reverse 430 40.0
Fruili 09/15/76 0921 5.90 reverse 386 56.7
Montenegro 04/15/79 0619 6.63 reverse 932 171.8
mean (ln) 438.2 80.4
s (ln) 0.45 0.51
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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.
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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.
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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.
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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.
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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.
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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.