Final Project Summary — PEER Lifelines Program
Project Title—ID Number
Start/End Dates
Project Leader (boldface) and
Other Team Members

Next Generation Attenuation (NGA) Models, WUS Shallow Crustal
Earthquake—1L01
Budget/8/1/02 – 6/30/04$352,630 / CaltransFunding Source
Power (Geomatrix)

1. Project goals and objectives

The overall goal of the project is to develop Next Generation Attenuation (NGA) relationships
for shallow crustal earthquakes in the western United States. These attenuation relationships will
have a substantially better scientific basis than current relationships because they are developed
through the efforts of five selected attenuation relationship developer teams working in a highlyinteractive process with other researchers who are: (a) developing an expanded and improved
data base of strong ground motion recordings and supporting information on the causative
earthquakes, the source-to-site travel path characteristics, and the site and structure conditions atground motion recording stations; (b) conducting research to provide improved understanding of
the effects of various parameters and effects on ground motions that are used to constrain
attenuation models; and (c) developing improved statistical methods used to develop attenuation
relationships including uncertainty quantification.
2. Benefits of the results of this project to develop technologies and protocols to mitigate thevulnerability of electric systems and other lifelines to damage directly and indirectly caused byearthquakes. Also, benefits to develop assessment techniques to evaluate damage to electricsystems caused by earthquakes and to assess fiscal impacts due to the loss of electric service tothe community.

The assessment of the damage that earthquakes can cause to electrical systems and other lifelines
depends significantly on how well the vibratory ground motions can be predicted as a function of
the seismic environment characteristics, including earthquake magnitude and other earthquake
source characteristics, source-to-site-distance and other travel path characteristics, and thestiffness and depth of the geologic media in which lifelines are founded. This project greatly
improves the reliability and the quantification of uncertainty associated with ground motion
predictions, thus allowing more reliable assessments of damage to, and design of, lifelines.
3. Brief description of the accomplishments of the project

The project accomplishments to date are summarized as follows.
(1) The PEER data base of ground motion recordings and supporting information, which is vitalfor developing attenuation relationships, has been substantially improved through the addition ofa large number of recordings, evaluation of the characteristics of recordings (e.g. better
understanding of the usable period range for response spectra of the recordings), and researchand quality assurance that has resulted in more accurate and increased information about theearthquake source, path, and recording station parameters. The additions of records to the PEER
data base is shown in Figure 1.
(2) Selected research and synthesis of current and previous research by PEER, PEER-LL, U.S.
Geological Survey, Southern California Earthquake Center, and others, has been conducted todevelop increased understanding of the various earthquake source, travel path, and site factors
affecting earthquake ground motions and thus provide better constraints on empirically-based
attenuation relationships. The research synthesis includes findings from the following projects:1(a) rock motion simulations; (b) basin response simulations; (c) site response simulations; (d)attenuation at moderate distances; (e) effects of rupture directivity on ground motions; (e) andsynthesis of empirical studies on site response.
(3) Six two-day NGA workshops have been held in 2003 and 2004 following a two-day kickoff
meeting on October 2002. These workshops, each attended by approximately 40 to 45
researchers and stakeholders in the NGA project, have facilitated review of interim results for theproject. Presentations from the workshops have been placed on the PEER web site. In additionto the workshops, a number of less formal meetings of NGA working groups and of the NGA
developers have been held for project review and interaction. The working groups have been anintegral part of the project for review of selected research and data base findings. Six working
groups, each consisting of five to thirteen scientists and engineers involved in various project
activities have been active: #1Strong Ground Motion Data Processing; #2 Validation of Ground
Motion Database; #3 Validation of 1D Rock Motion simulations; #4 Source and Path Effects; #5
Site Classification and Site Effects; and #6 Statistical Modeling of Data.
(4) Preliminary results for effects modeled in NGA relationships were presented by the five
NGA attenuation developer teams at Workshop #6 in July 2004. Examples of analysis of effects
of soil type and soil depth on ground motions are shown in Figures 2 and3. Results arescheduled to be finalized during October and presented at a final workshop for this phase inNovember 2004. In addition to preparation of comprehensive project reports covering the newattenuation relationships, the new data base, and the supporting research, it is planned that the
new attenuation relationships will be presented at special sessions at conferences and publishedtogether in a special issue of a widely read professional journal.
4. Describe any instances where you are aware that your results have been used in industry

The final project results are not yet available. When available later this year, extensive use of the
new attenuation relationships is anticipated in engineering practice, including in the developmentof future ground motion maps for California, the United States, and in national building codes, aswell as for site-specific ground motion definition. The data base developed for the project will
be a major resource to the entire engineering and seismological community as a source of well
documented strong motion records and supporting information. Reports of supporting research
for the NGA project will similarly be used to advance the practice of ground motion definition
for new construction and retrofit projects.
5. Methodology employed

The methodology developed and its implementation is summarized in items (1) and (3) above.
6. Other related work conducted within and/or outside PEER

The NGA project is unique in providing a focused, coordinated, and highly interactive effort
involving participation of five selected expert attenuation relationship developer teams,development of an improved and expanded data base of ground motion recordings andsupporting data required for attenuation relationship development, conduct and synthesis of
supporting research on the processes of earthquake generation, seismic wave propagation, andsite response to provide better physical constraints on attenuation relationships, development ofbetter statistical methods for attenuation relationship development, and integration of all project2

elements through a series of workshops and meetings of working groups and attenuation
relationship developers.
7. Recommendations for the future work: what do you think should be done next?

The present project is limited to development of attenuation relationships for horizontal elastic
response spectral acceleration and horizontal PGA, PGV, and PGD of ground motions forshallow crustal earthquakes in the western U.S. Future phases of attenuation relationships
development may be conducted for: (1) vertical ground motions; (2) other ground motion
parameters found to be important in determining earthquake damage to structures (e.g. inelastic
response spectral accelerations); and (3) western U.S. subduction zone earthquakes. The present
project is also limited to the use of ground motion recordings from actual earthquakes in thestatistical analyses for attenuation relationship development. Simulated earthquake recordings,
although used in the present project to guide the modeling of effects in attenuation relationshipdevelopment, and not used as data in developing attenuation relationships. Future phases may
consider incorporating simulated recorded data directly along with the actual data for conditions
that are not well represented in or well constrained by the existing recorded data (e.g. recordings
from large earthquake magnitudes at close distances).
8. Author(s), Title, and Date for the final report for this project

The final report will be submitted later in 2004. Final reports will be submitted by eachattenuation relationship development team. In addition, the series of a final reports will(a)compare attenuation relationships from all of the development teams; (b) document the database of ground motion recordings and supporting information developed for the project;(c)document and synthesize research conducted in support of NGA relationship development.

3Figure 1
Magnitude – Distance Distribution of NGA Data Base

Previous Data

New EQ Data
87Magnitude- Kobe- Kocaeli- ChiChi- Duzce- Hector Mine
- Denali- Moderatemagnitude
earthquake
aftershocks

6540.1

1

10100

1000

Distance (km)4

Figure 2
Effects of NEHRP Soil Type on 3-Sec Spectral Acceleration

NEHRP
AB
CDEE

NEHRP

DCB

A-2-101Residuals of T3.000S5

Figure 3Soil Type on 3-Sec Spectral
Effects of Depth to NEHRP
Bedrock

Residuals of T3.000S

ABCDE

10-10500

1000

1500

2000

2500

3000

Z1.5

Depth to Bedrock (taken as depth to rock with Vs = 1.5 km/sec)

6