We present a new empirical ground motion model, commonly referred to as an attenuation relationship, which we developed as part of the PEER Next Generation Attenuation of Ground Motion (NGA) Project. Using a common database of worldwide strong motion recordings, we selected a subset of ground motion data and predictor variables that we believed were appropriate for use in developing our model. Consistent with the requirements of the PEER NGA Project, we developed both a median and aleatory uncertainty model for peak ground acceleration (PGA). peak ground velocity (PGV), peak ground displacement (PGD), and response spectral acceleration (PSA) and displacement (SD) for oscillator periods ranging from 0.01—10.0 s, magnitudes ranging from 4.0—8.0, and distances ranging from 0—200 km. We consider the set models to be valid for use in the western United States and in other similar tectonically active regions of shallow crustal faulting worldwide. A comparison of our NGA model with our previous ground motion models, (Campbell, 1997, 2000, 2001; Campbell and Bozorgnia, 1994, 2003a 2003b, 2003c, 2004) showed that the biggest differences in these models occur for sites located at small-to-moderate distances from large-magnitude earthquakes for near reverse faults with surface rupture, where the NGA model predicts lower ground motion, and for sites located on the hanging wall of dipping strike-slip and normal faults, where the NGA model predicts higher ground motion. We also found that eh standard deviation is no longer a direct function of magnitude, which increase aleatory uncertainty for large-magnitude earthquakes and decreases it for small-magnitude earthquakes for stiff sites, compared to our previous models. However, the dependence of the standard deviation on nonlinear site effects in our new model can lead to less aleatory uncertainty for soft sites even at large magnitudes as compared to our previous models.
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