Design Ground Motion Library (DGML)

DGML Database

      The source of the database for the DGML is the PEER Next-Generation Attenuation (NGA) project database of ground motion recordings and supporting information (http://peer.berkeley.edu/nga/). This database was developed as the principal resource for the development of updated attenuation relationships in the NGA research project coordinated by PEER-Lifelines Program (PEER-LL), in partnership with the U.S. Geological Survey (USGS) and the Southern California Earthquake Center (SCEC) (Power et al.  2008; Chiou et al. 2008). The database represents a comprehensive update and expansion of the pre-existing PEER database (Chiou et al., 2008). The ground motion records are originally from strong motion networks and databases of CGS-CSMIP and USGS and other reliable sources, including selected record sets from international sources. The PEER NGA database includes 3551 three-component recordings from 173 earthquakes and 1456 recording stations. 354 records from the PEER NGA database were not included in the current DGML database of 3197 records for various reasons. The figure below shows the magnitude and distance distribution of the included records.

Develop the Target Spectrum

     Three options are provided within the DGML for developing the target spectrum: Option 1 – Specify Code Spectrum. For this option, the target spectrum is the design earthquake spectrum or the maximum considered earthquake (MCE) spectrum as formulated in the NEHRP Provisions, (BSSC 2003), ASCE Standard ASCE/SEI 7-05 (ASCE 2006), and the International Building Code, (ICC 2006). Option 2 – User-Defined Spectrum. The user may enter any response spectrum as a table of periods and response spectral accelerations and the tool constructs and plots the spectrum. Option 3 – Spectra based on PEER Next Generation Attenuation (NGA) Relationships. DGML constructs a deterministic scenario earthquake spectrum using a user-selected set of ground motion attenuation models for western United States shallow crustal earthquakes developed in the NGA project. Five different attenuation models were implemented in DGML (Abrahamson and Silva 2008; Boore and Atkinson 2008; Campbell and Bozorgnia 2008; Chiou and Youngs 2008; and Idriss 2008) . The user also has the option of constructing the response spectrum as a conditional mean spectrum using the correlation model of Baker and Jayaram (2008).  The DGML graphic interface for generating target spectrum is shown as follows.

Specifying Criteria and Limits for Searches for Time History Records

      A basic criterion used by the DGML to select a representative acceleration time history is that the spectrum of the time history provide a “good match” to the user’s target spectrum over the spectral period range of interest. The user defines the period range of interest. The quantitative measure used to evaluate how well a time history conforms to the target spectrum is the mean squared error (MSE) of the difference between the spectral accelerations of the record and the target spectrum. The focus of the DGML is on selecting “as recorded” strong ground motion acceleration time histories for use in seismic analyses.  Therefore, DGML does not alter the frequency content of the recordings to better match a target spectrum. However, it does provided the ability to linearly scale recorded time histories to improve their match to the target spectrum and select time histories that have the best spectral match.

      The user specifies the ranges of parameters over which searches are to be conducted and other limits and restrictions on the searches  These may include: magnitude range; type of faulting; distance range; VS30 range; significant duration range; whether records are to exclude, include, or be limited to pulse records; limits on the scale factor f; and restrictions on directional component (i.e., arbitrary FN or FP components [no restriction]; FN components only; FP component only; or FN and FP components in pair). If three dimensional analyses are to be conducted requiring pairs of horizontal components, ordinarily FN and FP components in pairs would be searched for and scaled by the same factor.

Search of Database, Selection of Records, and Saving of Records, Plots and Supporting Information

      The DGML scans the database, selects all records meeting user-specified criteria and limits for searches as summarized above, scales records to match the target spectrum, and ranks records in order of increasing MSE. In addition, DGML provides capability to search for specific records according to specified NGA record sequence number or by earthquake name or recording station name. Selected records are scaled and ranked by MSE and can be incorporated into final data sets as desired by the user. This search capability was added to DGML so that users can examine any record or group of records and further fine-tune the search results based on user preferences. DGML also provides powerful features for the selected records to be easily visualized, inspected and exported for use in seismic analysis of civil infrastructure.

Project Team

      The DGML has been developed by a project team that includes experts in the selection of time history record sets and use of time histories in dynamic analysis of structures. The primary project team members includes: Dr. Robert Youngs, Dr. Gang Wang, Mr.  Maurice Power, Dr. Zhihua Li, Dr. Faiz Makdisi, and Dr. Chih-Cheng Chin (AMEC Geomatrix); The following individuals served as technical review committee, including  Prof. Allin Cornell (deceased, Stanford University) and Prof. Jack Baker (Stanford University); and Prof. Stephen Mahin (University of California, Berkeley); Mr. Ronald Hamburger and Dr. Ronald Mayes (Simpson Gumpertz & Heger, Inc. ); Mr. Roupen Donikian (Parsons Brinckerhoff ); Dr. Yusof Ghanaat (Quest Structures); Dr. Walter Silva (Pacific Engineering & Analysis); Dr. Paul Somerville (URS Corporation); Mr. Ignatius Po Lam (Earth Mechanics).  Acknowledgement also goes to Dr. Brian Chiou (California Department of Transportation) for his helpful discussion, and Dr. Tony Yang (University of California, Berkeley) for help compiling the DGML software package.

      The DGML project is jointly sponsored by the California Geological Survey - Strong Motion Instrumentation Program (CGS-SMIP) and the Pacific Earthquake Engineering Research Center - Lifelines Program (PEER-LL).