Refinements to the Graves and Pitarka (2010) Broadband Ground Motion Simulation Method

Robert W. Graves, & Arben Pitarka

Published February 2014, SCEC Contribution #1947

This brief article describes refinements to the Graves and Pitarka (2010) broadband ground motion simulation methodology (GP2010 hereafter) that have been implemented in version 14.3 of the SCEC Broadband Platform (BBP). The updated version of our method on the current SCEC BBP is referred to as GP14.3. Our simulation technique is a hybrid approach that combines low-frequency and high-frequency motions computed with different methods into a single broadband response. In approaches like ours, the separate low- and high-frequency components have traditionally been referred to as “deterministic” and “stochastic”, respectively; however, this is very much an oversimplification. In reality, the low-frequency computation includes many stochastic elements, and likewise, the high-frequency computation includes many deterministic elements. While the traditional terminology will likely remain in use by the broader modeling community, in the remainder of this paper, we refer to these using the generic terminology “low-frequency” and “high-frequency” approaches.

In the validation of GP2010, strong motions from four California earthquakes were modeled. While the method performed well overall, several issues were identified including the tendency to over-predict the level of longer period (2-5 sec) motions and the effects of rupture directivity. Some of the refinements incorporated in GP14.3 are aimed at addressing these issues with application to the simulation of earthquakes in Western US (WUS). These refinements include the addition of a deep weak zone to the rupture characterization and the perturbation of the correlation structure for rise time and rupture speed parameterization. Additionally, we have extended the parameterization of GP14.3 so that it is also applicable for simulating Eastern North America (ENA) earthquakes. This work has been guided by the comprehensive set of validation studies described in Goulet and Abrahamson (2014) and Dreger et al. (2014). The GP14.3 method shows improved performance relative to GP2010, and we direct the interested reader to Dreger et al. (2014) for a detailed assessment of the current methodology. In this paper, we concentrate on describing the modifications in more detail, and also discussing additional refinements that are currently being developed.

Citation
Graves, R. W., & Pitarka, A. (2014). Refinements to the Graves and Pitarka (2010) Broadband Ground Motion Simulation Method. Seismological Research Letters, 86(1), 75-80. doi: 10.1785/0220140101.

Related Projects & Working Groups
Ground-Motion Prediction