Technical Updates: 2014, Fourth Quarter


      The focus of the NGA-East project has been shifting from scientific development to the Ground Motion Characterization (GMC) model building by the Technical Integration team (TI team). The GMC model building involves the evaluation and integration of the different median and standard deviation Ground Motion Models (GMMs), also referred to as Ground Motion Prediction Equations (GMPEs). The TI team is also making use of products from scientific tasks completed previously, such as the Database, Regionalization and Simulations tasks. This issue of the Technical Updates is therefore focused on (but not limited to) model building, Project Plan Tasks H, J, K, and L (see below).
      For an update on additional NGA-East tasks, one can access a series of presentations at the October 29-30 SSHAC Workshop held at UC Berkeley.

Data Sets (Task A)

      A new web portal is being developed to allow the dissemination of NGA-East time series. The NGA-East web portal is scheduled for a public release in April 2015, after it has been tested internally. The response spectra of the recorded ground motions have already been released to the public in form of a “flatfile” (Appendix C of the PEER NGA-East Database Report).

Finite Fault and Stochastic Simulations (Tasks E and F)

    • The collaborative simulations group (PEER, SWUS and SCEC) published a series of nine papers as a Focus Section of the Seismological Research Letters journal. The Focus Section documents the validation exercise, the Broadband platform (BBP), the evaluation of simulation methods and papers detailing the different simulation methodologies evaluated as part of the effort. Figure 1 shows the SRL cover, which features an image from the Focus Issue.

      F1_SRL_V86_1_BBPValidationFigure 1. SRL cover with image taken from the Focus Issue.

    • Following the October Workshop, modeling of the simulation results was completed to include a better functional form to accommodate the magnitude scaling of ground motions in terms of distance and depth to top of rupture (Figure 2).

      F2_Ztor5Figure 2. Modeled magnitude scaling of ground motions based on the Graves and Pitarka simulation method, depth to top of rupture of 5 km.

Development of Median Ground Motion Models (Task H)

      Following the October Workshop, the GMM developers were given until mid-December to finalize their models. Final models, model predictions and a short summary of the method were then submitted to the TI team. Each team is preparing a detailed chapter documenting their model(s) and their model development process. These chapters will be aggregated into a NGA-East GMPE PEER report in the first quarter of 2015.

Sigma (Standard Deviation) (Task J)

      The Sigma Working Group has developed initial Sigma models for CENA, which were presented at the October Workshop. The models have been refined in the last Quarter of 2014 following a series of recommendations collected at the Workshop. The new models are currently being reviewed by the TI team and a proposed model will be presented at Workshop 3B in March 2015.

Evaluation of Epistemic Uncertainty (Task K) and Logic Tree building (Task L)

    • The TI Team approach for median logic tree development and the consideration of epistemic uncertainty (Task K) was summarized at the October Workshop. The approach makes use of Sammon’s maps. Following the updates of the GMMs (delivered in mid-December), new Sammon’s maps have been created (Figure 3). The evaluation work from the TI team was also formally initiated.

      F3_sammon_withsamplesFigure 3. Sample Sammon’s map for 1 Hz 5%-damped response spectral values. Large black dots represent candidate GMMs (sample subset), small grey dots represent new GMMs developed from the covariance of the candidate GMMs, large red dots represent the mean ground motions scaled by a factor of 0.5 and 2. Units are natural of “g”.

    • A PEER report on the use of visualization for the quantification of epistemic uncertainty is under preparation.