Technical Updates: 2014, Second Quarter

Summary

The latest status of NGA-East’s project was presented in a SSHAC Workshop in July 2014 through a series of presentations followed by discussions. Unless otherwise specified, presentations linked below are from the July 2014 SSHAC Workshop. All the presentations for this workshop are available here.

Significant progress has been made in in the last few months with the completion of many scientific research and development tasks. Key milestones include the internal release of ground motions database products, the completion of the regionalization task, the conclusion of the finite fault simulations validation exercise, the publication of the reference rock site conditions paper as well as significant progress on other supporting tasks. See Project status (C.Goulet) for more details.

Data Sets (Task A)

The database was finalized and preliminary ground motion products have been shared internally for further QA by model developers. The NGA-East database is the largest, most complete database of uniformly processed ground motions for the Central and Eastern North America region. It contains more than 30,000 recorded components. More details are provided in the presentations below:
• Summary, status and ground motion products (T. Kishida)
• Source metadata (B. Youngs)
• Station metadata (Y. Hashash)

Reference rock and site amplification models (Task B)

The Geotechnical Working Group (GWG) continues to meet monthly.
• The group is making further progress on setting-up their large scale site response simulations.
• They recently published their paper on reference rock:
  Hashash, YMA, AR Kottke, JP Stewart, KW Campbell, B Kim, C Moss, S Nikolaou, EM Rathje, WJ Silva (2014). “Reference rock site condition for central and eastern North America,” Bull. Seism. Soc. Am., 104(2), 684-701.

Regionalization & Source/Path Studies (Tasks C and D)

Teams led by Dr. Mooney (USGS) and Prof. Chapman (Virginia Tech) completed a large regionalization task. The final report documenting the various tasks and results has been submitted for publication as a PEER report. The key results relevant to the TI team are summarized in the following presentations:
• Regionalization: summary of regionalization tasks and simulation results, proposed regions (G. Atkinson, W. Mooney, M. Chapman)

 
Additional presentations on regionalization issues:

• Regionalization: depth-dependent stress-parameter (R. Graves, J. Boatwright)
• Paths contained in CENA regions (C. Goulet)
• Preliminary treatment of the Gulf Coast/Mississippi Embayment, reference velocity and kappa adjustments (M. Chapman)

Finite Fault and Stochastic Simulations (Tasks E and F)

• NGA-East held a Working Meeting at PEER on April 7^th 2014 to review validation results from the latest release of the SCEC BroadBand Platform (V.14.3). The validation included seven Western U.S. (WUS), two Japanese and three CENA events in addition to a series of WUS GMPE scenarios. The TI team evaluated the results following the criteria developed by the SCEC-based review panel established in May 2013. Four methods have passed this round of evaluation and are considered for use in NGA-East.
• Graves and Pitarka (led by Dr. Graves, USGS)
• San Diego State University method (led by Prof. Olsen, SDSU)
• EXSIM (led by Dr. Assatourians and Prof. Atkinson, University of Western Ontario)
• UC Santa Barbara (led by Prof. Archuleta and Mr. Crempien, UCSB)
• The collaborative simulations group (PEER and SCEC) continued to have their weekly phone calls and forward simulations have been initiated for CENA.
• A collection of eight papers has been submitted to the Seismological Research Letters on the validation of the Broadband Platform V.14.3. The “evaluation” paper is authored by the SCEC-based review panel and their findings are consistent with the TI team findings.
• The most recent validation results and method summaries (consistent with V. 14.3 of the BBP) have also been summarized at the July workshop:
• Simulations: validation exercise, finite-fault (FF) methods (C. Goulet)
• Simulations: methods selected, FF and point source (PS) (D. Dreger)
• Simulations: focus on validation for CENA. Results summary for Mineral, Riviere-du-Loup and Saguenay (C. Goulet) and Saguenay modeling details (R. Graves)

Development of Median Ground Motion Prediction Equations (Task H)

This task progressed significantly in the last few months. NGA-East is tackling the development of GMPEs starting from regressions on Fourier amplitude spectra (FAS). This has the advantage of properly including seismological constraints, including kappa effects (site-specific attenuation of high frequencies), into the regression. Kappa is a controlling factor for high frequencies, especially for CENA where the attenuation is generally low compared to other seismic regions. The final GMPEs will produce pseudo-spectral acceleration (PSA) which will be obtained from the FAS models using the random vibration theory (RVT). In the last few months, progress was made with the (1) creation of a RVT working group to address RVT-related issues and progress on numerous sub-tasks and (2) development of regression codes and production of initial regressions results based on FAS using the recently assembled database. Key items are summarized in the presentations linked below:
• NGA-East approaches for median GMPE development in Fourier spectral space: summary, preliminary regression results and key issues (N. Abrahamson/J. Hollenback).
• Kappa estimation and related issues (O. Ktenidou)
• Development of duration model for empirical FAS (N. Kuehn)
• Development of duration model for the SMSIM point-source stochastic method (D. Boore)

 
Summary of additional proponent models and methods considered by NGA-East were also presented:

• Summary of EPRI (2004-2006) Review Project Model (R. Youngs)
• Cramer and Al Norman ENA Empirical Model (C. Cramer)
• Preliminary Graizer-14 GMPE for CEUS (V. Graizer)
• The Hybrid Empirical Approach (K. Campbell)

Sigma (Standard Deviation) (Task J)

The Sigma Working Group has completed their model for the WUS. The next step is to extend the Sigma models for CENA. The summary of that work along with the CENA-specific development is summarized in:
• NGA-East approach for standard deviation modeling (L. Al Atik)

Evaluation of Epistemic Uncertainty (Task K)

The evaluation of epistemic uncertainty has evolved substantially in the last few years. The evolution of the process is summarized in:
• Epistemic uncertainty: previous approaches (N. Abrahamson)

 
Recent developments supported by the SWUS project led to a new method that offers numerous advantages relative to previous approaches. The method, how it was applied to the WUS as part of the SWUS project and implementation aspects specific to NGA-East are addressed in:

• Proposed approach for NGA-East (N. Kuehn)

Other related efforts

A series of presentations were made on various tasks at the SSA Annual Meeting, Anchorage, AK, April 30-May 2 2014 (see online abstracts for abstracts and link to posters and presentations, when applicable). The work summarized in these presentations was either funded by NGA-East or made use of preliminary version of the NGA-East Database.
• “Comparing the CENA GMPEs Using NGA-East Ground Motion Database”, Ogweno, L. P. and Cramer, C. H.
• “Defining the Usable Bandwidth for Response Spectra From Records with Different Sampling Rates and Anti-Aliasing Filters”, Goulet, C. A. and Boore, D. M
• “Initial ENA Empirical GMPEs Using the NGA-East Database”, Al Noman, M. N. and Cramer, C. H.
• “Referenced Empirical Ground-Motion Model for Eastern North America, Based on the NGA-West 2 GMPE”, Hassani, B. and Atkinson, G.
• “Refinements to the Graves and Pitarka (2010) Broadband Simulation Method”, Graves, R. W
• “Regional Study of Fourier Amplitude Drop of Lg-Wave Acceleration In Central United States”, Chapman, M. C., Pezeshk, S., Hosseini, M., and Conn, A.
• “Summary of a Large Scale Validation Project Using the SCEC Broadband Strong Ground Motion Simulation Platform”, Goulet, C. A. and the BBP Validation Group
• “The SDSU Broadband Ground Motion Generation Module Version 1.5”, Olsen, K. B. and Takedatsu, R.
• “Validation of the Stochastic Finite Fault Module (EXSIM) Implemented on the SCEC Broadband Platform”, Assatourians, K. and Atkinson, G.