Directivity in Preliminary NGA Residuals - 1M01

Project goals and objectives

Development and calibration of improved functional forms for directivity, based on isochrone theory, that can be used by NGA attenuation relation developers in their new attenuation models.

Role of this project in supporting PEER's mission (vision)

The PEER mission is to develop and disseminate technologies to support performance-based earthquake engineering (PBEE). The approach is aimed at improving decision-making about seismic risk by making the choice of performance goals and the tradeoffs that they entail apparent to facility owners and society at large. A crucial part of PBEE is the accurate assessment of the ground motion hazard for a site or a region. This project is aimed at improving the accuracy of predictions of ground motions for future earthquakes.

Methodology employed

Spudich et al, 2004, USGS Open File Report 2004-1268, http://pubs.usgs.gov/of/2004/1268 has proposed functional forms for directivity and ground motion polarization, based on isochrone theory, suitable for use in NGA ground motion prediction relations. These functional forms have some parameters that can only be derived by comparison with empirical data. I am examining residuals (observed FN, FP, and geometric mean 1-s and 3-s spectral accelerations minus corresponding predictions of non-directive relations) submitted to me by developers. I select for analysis a subset of earthquakes that are well-recorded aziumuthally. I (1) determine which of the proposed isochrone directivity parameters (IDPs, functional forms, p. 15 of Spudich et al., 2004), or other IDPs we have subsequently proposed is best, (2) use data to determine the undetermined empirical constants Dfloor, (Spudich and Chiou, memo to developers "Isochrone Directivity User's Guide v2", Aug. 1, 2005) and e, the radiation pattern water level (Spudich et al., 2004, eqn 15), and (3) report the results to developers. It is envisioned that the developers will take the results of this work and use/modify them as necessary to extend them to the entire period band, magnitude range and distance range of their prediction relations.

Brief Description of previous year's achievements, with emphasis on accomplishments during last year (Year 8)

First year project. For related previous activities on a different project, please see above "Methodology" section.

Other similar work being conducted within and outside PEER and how this project differs

Other work on near-fault ground motions and directivity is being done outside PEER, (e.g., Mavroeidis and Papageorgiou, BSSA, 2003; Hisada and Bielak, BSSA, 2003, B. Rowshandel, unpublished), but none of these works is using isochrone theory.

Describe any instances where you are aware that your results have been used in industry

First year project, no results yet.

Expected milestones & deliverables

Oral report on initial analysis of ground motion residuals compared to isochrone directivity, March 7, 2006 (achieved). Consultation with developers on proper implementation of theory (as needed). Written report on analysis of residuals compared to isochrone directivity, Sept. 30, 2006.