Earthquake Engineering Research Institute (EERI) will be publishing a special issue of its journal Earthquake Spectra (EQS) about PEER’s NGA-West2 project. The print version of the special issue of EQS will be published in August 2014. However, as a new part of its publishing process, EERI now releases electronic pre-prints of EQS papers for download before final formatting and print publication is completed.

To view the accepted pre-prints of the NGA-West2 papers, visit: http://earthquakespectra.org/toc/eqsa/0/0

More pre-prints of NGA-West2 papers will be posted as they become available.

The site amplification factors used to develop design-basis ground motions will be changing in the next revisions of several building code documents due to research conducted as a part of PEER’s NGA-West2 project.  These factors, commonly called F_a, F_v, and F_PGA are found in Tables 11.4-1, 11.4-2, and 11.8-1 of the ASCE-7 code and have not been updated in several decades. 
 
The new site factors have been approved by the Provisions Update Committee of the Building Seismic Safety Council and are expected to appear in the 2015 version of the NEHRP Provisions, followed shortly thereafter by ASCE-7 and various building code documents. 
 
“After several years of comprehensive and extensive research, PEER is proud to have spurred this long awaited update,” said Yousef Bozorgnia, PEER’s Executive Director and Project Manager for the NGA-West2 project. 
 
Engineers use site factors to modify ground motions from a reference rock site condition to reflect the influence of geologic conditions at the site of interest, i.e. the location where a new building is being constructed. 
 
The current NEHRP site factors are based on a very small database of recordings in the San Francisco Bay Area from the 1989 Loma Prieta earthquake, which established relatively weak motion amplification empirically, in combination with nonlinear effects established from numerical simulations performed in the early 1990s.  Over the years misfits have been identified between NEHRP site factors and more modern ground motion prediction tools, such as the 2008 ground motion prediction equations (GMPEs) developed in PEER’s NGA-West1 project.
 
Not surprisingly, experience in practice and from research indicates that the site factor discrepancies are consequential for ground motion hazard analyses, loss estimation and other applications.  To resolve these issues, the new NGA-West2 ground motion data set was used by PEER researchers to develop a new site amplification model, which was then used to update the NEHRP site factors.   Because the updated site factors operate seamlessly with the NGA-West2 GMPEs (which will soon be applied for the next-generation of seismic hazard maps used in the code), a long-standing problem in earthquake engineering will be resolved.
 
PEER researcher Jonathan Stewart from UCLA led this effort and is the first author of PEER Report 2013/13 that proposed the new factors.  This report titled “Semi-Empirical Nonlinear Site Amplification and its Application in NEHRP Site Factors” was just published by PEER on November 7^th and is available for free download at the PEER website.
 
“This long-awaited change will allow engineers and earthquake financial loss modelers to have more accurate ground motion hazard estimates when using generic building code procedures or site-specific analyses,” said Professor Stewart.  “This will likely lead to more confidence in the levels of seismic risk considered in design and loss estimation practices. In some areas ground motions estimates will rise as a result of the change, in other cases they will fall. In either case, the ground motions that buildings are designed for will be more scientifically sound.” 
 
NGA-West2 has been financially supported by the California Earthquake Authority (CEA), California Department of Transportation (Caltrans) and Pacific Gas & Electric Company (PG&E).  Other products from this project, including final project reports describing the newly updated GMPEs and the database flatfiles, can be found at the NGA-West2 website.

PEER’s NGA-West2 Program, one of our largest multi-year multidisciplinary mega research projects, is reaching its conclusion on various tasks and the first of its final products are now available! These products include many published reports describing the newly updated ground motion prediction equations (GMPEs) and other research studies supporting GMPE development, along with the NGA-West2 Database Flatfile.

NGA-West2, which is the Phase 2 of the Next Generation Attenuation relationships for shallow crustal earthquakes in active tectonic regions, has been coordinated by PEER and financially supported by the California Earthquake Authority (CEA), California Department of Transportation (Caltrans) and Pacific Gas & Electric Company (PG&E). Similar to the previous phase, NGA-West2 will have major impacts on the entire earthquake engineering community. For example, the USGS is reviewing the NGA-West2 GMPEs to consider their adoption for the upcoming US National Seismic Hazard Maps. Site-specific applications will also be affected by the NGA-West2 products.

Flatfile

In the tradition of the openness, the NGA-West2 database “flatfiles” used in various research components of NGA-West2 have also been posted at PEER website: http://peer.berkeley.edu/ngawest2/databases/

The actual time series of the database for download are being incorporated into an updated version of the online user-friendly PEER Ground Motion Database which will be completed later in 2013.

Reports

The following final reports from various NGA-West2 sub-projects are now available for free download at http://peer.berkeley.edu/publications/peer_reports_complete.html:

PEER 2013/03 – PEER NGA-West2 Database
by Timothy D. Ancheta, Robert B. Darragh, Jonathan P. Stewart, Emel Seyhan, Walter J. Silva, Brian S.J. Chiou, Katie E. Wooddell, Robert W. Graves, Albert R. Kottke, David M. Boore, Tadahiro Kishida, and Jennifer L. Donahue

PEER 2013/04 – Update of the AS08 Ground-Motion Prediction Equations Based on the NGA-West2 Data Set
by Norman A. Abrahamson, Walter J. Silva, and Ronnie Kamai

PEER 2013/05 – NGA-West2 Equations for Predicting Response Spectral Accelerations for Shallow Crustal Earthquakes
by David M. Boore, Jonathan P. Stewart, Emel Seyhan, and Gail M. Atkinson

PEER 2013/06 – NGA-West2 Campbell-Bozorgnia Ground Motion Model for the Horizontal Components of PGA, PGV, and 5%-Damped Elastic Pseudo-Acceleration Response Spectra for Periods Ranging from 0.01 to 10 sec
by Kenneth W. Campbell and Yousef Bozorgnia

PEER 2013/07 – Update of the Chiou and Youngs NGA Ground Motion Model for Average Horizontal Component of Peak Ground Motion and Response Spectra
by Brian S.J. Chiou and Robert R. Youngs

PEER 2013/08 – NGA-West2 Model for Estimating Average Horizontal Values of Pseudo-Absolute Spectral Accelerations Generated by Crustal Earthquakes
by I. M. Idriss

PEER 2013/09 – Final Report of the NGA-West2 Directivity Working Group
by Paul Spudich, Jeffrey R. Bayless, Jack W. Baker, Brian S.J. Chiou, Badie Rowshandel, Shrey K. Shahi, and Paul Somerville

PEER 2013/10 – NGA-West2 Models for Ground-Motion Directionality
by Shrey K. Shahi and Jack W. Baker

PEER 2013/11 – Epistemic Uncertainty for NGA-West2 Models
by Linda Al Atik and Robert R. Youngs

PEER 2013/12 – Nonlinear Horizontal Site Response for the NGA-West2 Project
by Ronnie Kamai, Norman A. Abrahamson, Walter J. Silva

PEER 2013/13 – Semi-Empirical Nonlinear Site Amplification and its Application in NEHRP Site Factors
by Jonathan P. Stewart and Emel Seyhan (available in summer 2013)

PEER 2013/14 – Hanging-Wall Scaling using Finite-Fault Simulations
by Jennifer L. Donahue and Norman A. Abrahamson (available in summer 2013)

PEER 2012/01 – Spectral Damping Scaling Factors for Shallow Crustal Earthquakes in Active Tectonic Regions
by Sanaz Rezaeian, Yousef Bozorgnia, I.M. Idriss, Kenneth Campbell, Norman Abrahamson and Walter Silva (sub-project previously published in 2012 on the issue of damping scaling of response spectra)

Next Steps

The task for vertical ground motion is still underway and will be completed in late summer 2013.
 
PEER and EERI are currently planning a traveling seminar series for Fall 2013 that will describe the NGA-West2 findings, discuss the implementation of the new GMPEs and other research outcomes, and summarize the impacts on the earthquake engineering community.  These seminars will be held in Southern California, Northern California, Seattle, and Utah.  More details will be sent as these events approach!

The first public workshop for PEER's NGA-West2 program will take place at UC Berkeley on November 15th.  This workshop will highlight and share the findings that have developed from the project team over the last 2 years, including the preliminary ground motion prediction equations (GMPEs), updated ground motion database, and results from other research tasks.  Researchers, practitioners, and any other interested parties are welcome and encouraged to attend.

Date: Thursday, November 15, 2012
Location: Auditorium in Room 310, Sutardja Dai Hall (CITRIS Building), University of California, Berkeley. Directions.
Registration: This one-day workshop is free, but advanced registration is required.  Register now.

More information including the full workshop program will be released to the NGA-West2 Preliminary Results Workshop web page as it becomes available.

The NGA-West 2 project was funded by the California Earthquake Authority (CEA), California Department of Transportation (Caltrans) and Pacific Gas & Electric Company (PG&E), to improve Next Generation Attenuation models for active tectonic regions such as Western US. During the multi-year, multidisciplinary project, the NGA-West 2 research teams have addressed several important issues in earthquake engineering, including updating a very comprehensive database of ground motions; modeling of directivity and directionality; update of NGA-West models using recent small, moderate and large magnitude events; scaling of GMPEs for different levels of damping; and evaluation of soil amplification factors in NGA models versus NEHRP site factors. More information about the project can be found at the NGA-West2 website.

Subsurface data for Taiwan Strong Motion Instrumentation Program (TSMIP) stations are now available in electronic form via the Engineering Geological Database for TSMIP (EGDT), a joint effort between the National Center for Research on Earthquake Engineering (NCREE) and the Central Weather Bureau (CWB) in Taiwan.

Between 2000 and 2010, NCREE completed site characterization, comprising of surface investigations and suspension PS-logging, at 469 strong-motion stations. Of these, 385 had PS-logging data reaching at least 30 m depth. These data have been used by PEER’s NGA-West projects to determine VS30 (the time-averaged S-wave velocity of the top 30 m of soil) of the TSMIP stations that recorded the 1999 ChiChi earthquake and some of its large aftershocks.

Given the enormous amount of TSMIP strong-motion data from both shallow crustal earthquakes and subduction zone earthquakes, this expanding database will be a valuable resource to the development of ground motion prediction equations as well as the studies of shallow soil effects on surface motion.

Free-field TSMIP stations in Taiwan. The blue circles are drilled stations; the red circles are stations surveyed but not drilled; open circles are stations not yet surveyed. (Kuo et al., Engineering Geology, 2012)

Visit the EGDT website to view and download detailed information about the site investigation at the TSMIP stations, including the instruction on how to obtain these data from EGDT.