1. Exploratory Data Analysis
July 19, 2004
NGA Workshop

2. Step 1:
For each earthquake, fit data to the following model (functional form used by Sadigh et al.)
M = Earthquake magnitude
Rj = Closest distance to fault
All soil types are lumped together

3. C5 and C6 can’t be reliably estimated for most earthquakes  fixed to the values of Sadigh et al. (1997)
172 earthquakes  172 x 2 = 344 unknown coefficients
Rj < 70 km
Freefield records
California data vs. worldwide data

6. Step 2:
Examine estimated C1 and C4 for magnitude effects and functional form.

8. Step 3:
Modify the basic model to
C1  C1 + C2 M + C3 (M-8.5)2.5
C4  C4 + C5 M
Repeat regression

9. Step 4:
Examine estimated coefficients for
Magnitude scaling at short distances to large-magnitude earthquakes
Style of faulting effect
Effects of coseismic surface faulting

10. Step 4:
Examine residuals for
Site classification and site effects
FW/HW effects
Directivity effects

11. Observed trend may be explained by more than one explanatory variables
Z1.5 ~ Vs30 (NEHRP)
Style of faulting ~ Surface Rupture
FW/HW ~ Directivity

13. Y Cos()

14. No Yes Unknown SS NM RV
RV-OB
NM-OB
Unknown

15. Exploratory
Outliers do show up