PEER has just published Report No. 2013/14 titled “Hanging-Wall Scaling using Finite-Fault Simulations” as a new addition to the PEER Report Series. It was authored by Jennifer L. Donahue of Geosyntec Consultants and Norman A. Abrahamson of the Department of Civil and Environmental Engineering at University of California, Berkeley. This report is part of the NGA-West2 research program sponsored by PEER and funded by the California Earthquake Authority, California Department of Transportation, and the Pacific Gas & Electric Company (PG&E).
The hanging-wall (HW) effect is defined as the increase in ground motions observed during a reverse earthquake event, when in close proximity and while on the hanging-wall side of a fault. As observed in the empirical data, the short period ground motions over the hanging-wall may be twice the amplitude of the ground motions recorded on the footwall at the same rupture distance. Because there are only a few earthquakes with near-fault recordings, there is insufficient empirical data to constrain the dependence of the HW effect. Using finite-fault simulations, 34 reverse earthquake events were simulated. The scenarios varied the magnitude between M6 and M7.8, dips from 20 to 70 degrees, and distances to top of rupture of 0 and 5 km. A simplified parametric model for the median hanging-wall effect was developed using the distance parameters Rx and Ry, magnitude, fault dip, fault width, and depth to top of rupture. The HW effect reaches it maximum over the bottom edge of the rupture. The residuals for the model fall within the range -0.2 to 0.2 natural log units. The scaling constraints derived in this study are being used in part or in whole in many of the NGA-West2 GMPEs and lead to more consistent HW effects.