1L10b - Supplemental SASW Work by USGS for NGA Project

Project Title/ID Number	Supplemental SASW Work by USGS for NGA Project—1L10b
Start/End Dates	11/25/03 – 6/30/04
Project Leader	Robert Kayen (USGS/F)
Team Members	Eric Thompson (UNC/O), Diane Minasian (USGS/O), Brad Carkin (USGS/O)

F=faculty; GS=graduate student; US=undergraduate student; PD=post-doc; I=industrial collaborator; O=other

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1. Project Goals/Objectives:

Spectral analysis of surface waves (SASW) testing at strong motion recording (SMR) sites for the Next Generation Attenuation modeling (NGA) project.

2. Role of this project in supporting PEER’s mission (vision):

Quantitative site characteristics for strong motion recording stations in California are critical to the success of the NGA project. This supplemental project is fulfilling this critical element of the NGA effort.

3. Methodology Employed:

New acquisition of spectral analysis of surface waves (SASW)-based cross power spectra data using frequency controlled harmonic sine-wave source at strong motion instrumentation sites selected by PEER-LL for the NGA project.
Computation of dispersion curves and shear wave velocities using a constrained non-linear least-square inversion method for data from group dispersion curves of each test site.
Computation of Vs-30 site velocities and designation of NEHRP site class.

4. Brief Description of past year’s accomplishments (Year 6) & more detail on expected Year 7 accomplishments:

New Year 7 Project:

In Year 7, USGS will perform all of the fieldwork processing and reporting, with supervision by Kayen and field assistance by Thompson, Carkin and Minasian. The requisition will support one month of salary and travel per diem for University of North Carolina Ph. D. student Thompson to conduct the field data. USGS will cost share and supply a field vehicle, SASW apparatus, general fieldwork equipment, a generator, and cover cost for fuel.
Data collection will average 2-3 sites per-day depending on transit distance between stations and ease of site access. Between December 12 and and January 15 we performed SASW testing at a total of 60 SMR. Work is be clustered in spatial bins to optimize and maximize the number of sites collected.
Data processing was be performed on field data immediately following collection. A password-protected FTP/Web site (via mac.com) has been set up so for daily upload of field data files and rapid dissemination of results to PEER. PEER-LL NGA staff has access to the FTP/WEB site to get daily updates on field-testing, view site photos, and correspond with participants. Inversion analysis will be done at the USGS Geotechnical data processing lab. Vs Profiles will be used to compute an average 30-meter velocity and a simplified NEHRP classification will be determined for each site.

5. Other Similar Work Being Conducted Within and Outside PEER and How This Project Differs:

Other work on SASW-based shear wave characterization of strong motion sites by our group includes strong motion recording (SMR) instrumentation sites of the ALYESKA Pipeline Services Company, Anchorage, Alaska. That work is not connected with this proposal.

6. Plans for Year 8 if project is expected to be continued:

This short-term project has been highly successful for characterizing a large number of SMR sites for the NGA project effort. The USGS has worked to optimize all aspects of the field data collection and processing of SASW data such that we were able to test and document 60 sites/month. Many hundreds of SMR stations in California remain unclassified and therefore of limited usage in the NGA effort. If this project is renewed in Year 8 for additional SASW testing, we can make great inroads toward quantitatively characterizing many of these sites. This effort would have great significance and impact for elevating the knowledge base of California strong motion instrumentation sites for site response assessment, attenuation model development, and characterization of motions recorded during large damaging earthquakes.

7. Describe any actual instances where you are aware your results have been used in industry:

The California Strong Motion Instrumentation Program, USGS, and PEER-LL NGA effort have put these studies to immediate use in February and March 2004. The project was specifically designed to have a direct results-pipeline to the sponsors to facilitate immediate usage by industry.

8. Expected Milestones & Deliverables:

Acquisition of data from all 60-field sites by January 20, 2004.
Presentation of a initial data report, in downloadable FTB/Web format, documenting:
1. Site investigated;
2. Dispersion curve computation;
3. Inverted shear wave velocity profile; and
4. Tabulated NEHRP site classification designators were delivered to PEER-LL and NGA staff on February 1, 2004.
Presentation of a final report, in FTP/Web, written, and CD format, documenting methodologies used to acquire and process field surface wave data, and a presentation of all shear wave velocity profiles will be delivered by the June 1, 2004. NGA workshop.