Exploratory Data Analysis July 19, 2004 NGA Workshop

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

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

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

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

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

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

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

Y Cos()

No Yes Unknown SS 17 17 38 NM 3 5 14 RV 18 4 11 RV-OB 7 3 1 NM-OB 1 1 4 Unknown 0 0 28

Exploratory Outliers do show up