Publication Date:
2014-12-05
Description:
The Next Generation Attenuation-West 2 (NGA-West 2) 2014 ground-motion prediction equations (GMPEs) model ground motions as a function of magnitude and distance, using empirically derived coefficients (e.g., Bozorgnia et al. , 2014 ); as such, these GMPEs do not clearly employ earthquake source parameters beyond moment magnitude ( M ) and focal mechanism. To better understand the magnitude-dependent trends in the GMPEs, we build a comprehensive earthquake source-based model to explain the magnitude dependence of peak ground acceleration and peak ground velocity in the NGA-West 2 ground-motion databases and GMPEs. Our model employs existing models ( Hanks and McGuire, 1981 ; Boore, 1983 , 1986 ; Anderson and Hough, 1984 ) that incorporate a point-source Brune model, including a constant stress drop and the high-frequency attenuation parameter 0 , random vibration theory, and a finite-fault assumption at the large magnitudes to describe the data from magnitudes 3 to 8. We partition this range into four different magnitude regions, each of which has different functional dependences on M . Use of the four magnitude partitions separately allows greater understanding of what happens in any one subrange, as well as the limiting conditions between the subranges. This model provides a remarkably good fit to the NGA data for magnitudes from 3〈 M 〈8 at close rupture distances ( R rup ≤20 km). We explore the trade-offs between and 0 in ground-motion models and data, which play an important role in understanding small-magnitude data, for which the corner frequency is masked by the attenuation of high frequencies. That this simple, source-based model matches the NGA-West 2 GMPEs and data so well suggests that considerable simplicity underlies the parametrically complex NGA GMPEs. Online Material: Figures providing detail on the V S 30 distribution in the subset of the Next Generation Attenuation-West 2 (NGA-West 2) data used, the quarter-wavelength amplifications used in the model, the statistical test for the large magnitude portion of the model, and the magnitude dependence.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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