Serving professionals in engineering, environmental, and groundwater geology
MONTHLY DINNER MEETING
||*** Tuesday, March 13th ***
||Shaking Things Up with a Modified ‘Active Fault’ Definition:
A Case History of a School Site near the 1971 San Fernando Fault
||Jeffrey R. Keaton, PhD, PE, PG, F.ASCE
Senior Principal Engineering Geologist
MACTEC Engineering and Consulting, Inc
||Steven’s Steak House, 5332 Stevens Place, Commerce, CA
||5:30 p.m.-Social Hour; 6:30 p.m.-Dinner; 7:30 p.m.-Presentation
||$30 per person with reservations (no-shows charged full amount), $15 for students with a valid Student ID
||Please call Peter Thams at (805) 644-7976 or email email@example.com
A site on the hanging-wall block approximately 300 m away from the main trace of the 1971 San Fernando fault rupture (Sylmar segment) experienced strong ground shaking and minor surface faulting. An elementary school occupied the site at the time of the earthquake and two single-story wood-frame buildings were damaged by displacements of about 7.5 cm in their slab-on-grade foundations. A structural engineering evaluation conducted within days of the earthquake concluded that the damage did not present a collapse hazard. The buildings were repaired and returned to service. The San Fernando fault, including the minor faults at the school site, was included in a state-designated fault-rupture-hazard zone. Post-earthquake geologic mapping documented four faults on the school site with a maximum slip of 2 cm right-lateral and 5 cm down-to-the-north.
The school district undertook a program in 2005 to evaluate several schools located with state-designated fault-rupture-hazard zones, including the one damaged in 1971. Three trenches excavated in gravelly fluvial deposits intersected four minor fault projections; geologic evidence of one fault was found. The lack of geologic evidence along three faults suggests that the 1971 displacements may have been first-time ruptures. Future ruptures of similar magnitude were considered to be possible virtually anywhere on the site.
New school buildings in California are prohibited from being constructed within 50 feet of active (Holocene) faults. Therefore, new buildings cannot be built at the school site and substantial remodeling of existing buildings cannot be done even though the wood-frame structural systems received full-scale seismic testing in 1971.
The current definition of ‘active fault’ in California is based solely on age of most recent displacement without regard to the amount of displacement. Salt Lake County, Utah, defines an active fault as “A fault displaying evidence of greater than four inches of displacement along one or more of its traces during Holocene time (about 10,000 years ago to the present).” Guidelines for evaluating and mitigating seismically induced landslides in California (SR117) have gotten away from a simple factor-of-safety approach and recognized that “Newmark displacements of 0 to 10 cm are unlikely to correspond to serious landslide movement and damage.” Now may be a reasonable time for a modification of the ‘active fault’ definition to include a minimum displacement, which would be consistent with seismic landslide movements. Reasonable fault-rupture-hazard mitigation might allow some categories of structures to be build closer than 50 feet from well-defined active faults with acceptable displacements, at least in certain geologic settings.
|Speaker Brief Biography:
Jeffrey R. Keaton is a Senior Principal Engineering Geologist in the Los Angeles office of MACTEC Engineering and Consulting, Inc. His education consists of a BS degree in Geological Engineering from the University of Arizona (1971), a MS degree in Engineering (Geotechnical) from the University of California, Los Angeles (1972), and a PhD degree in Geology from Texas A&M University (1988). He is registered as a Professional Engineer in California, Utah, Alaska, and Arizona. He is also registered as a Professional Geologist in California, Arizona, and Utah, and certified as an Engineering Geologist in California and Washington.
Keaton was employed by Dames & Moore in Los Angeles (1970-1979) and Salt Lake City (1979-1988). He was employed by Sergent, Hauskins & Beckwith (which became AGRA Earth & Environmental, and then AMEC Earth & Environmental) in Salt Lake City (1988-1996), Phoenix (1996-2001), and Anaheim (2001-2005). He joined MACTEC in July 2005.
Keaton is a Fellow of the American Society of Civil Engineers and the Geological Society of America. He is beginning a three-year appointment as a member of the Geo-Institute Technical Coordination Council. He served as Chairman of the Utah Section of the Association of Engineering Geologists (AEG) in 1980-1982 and was the President of AEG in 1992-1993. He was Chairman of the Engineering Geology Division of the Geological Society of America in 1989-1990. He served as Chairman of the Transportation Research Board Committee on Engineering Geology (A2L05) from 1991 to 1997, as Chairman of TRB Committee on Exploration and Classification of Earth Materials (A2L01) from 1997 to 2002, and as Chairman of TRB Subcommittee on Scour Research (A2L05-2) from 1996 to 2002. In 2002, he became the Chairman of TRB Section L, housing the seven committees that deal with Geology and Properties of Earth Materials. Keaton was one of the 11 members of TRB Task Force A2T61 which produced TRB Special Report 247 Landslides: Investigation and Mitigation in 1996; Keaton was principal author of Chapter 9, Surface Observation and Geologic Mapping, and Chapter 16, Important Considerations in Slope Design. He was selected for the 1999 Professional Fellowship in Earthquake Engineering by the Earthquake Engineering Research Institute and Federal Emergency Management Agency for his proposed research on synthetic ground motions from normal-faulting earthquakes.
Keaton also is a member of American Geophysical Union, Earthquake Engineering Research Institute, Seismological Society of America, and the Society for Mining, Metallurgy, and Exploration (SME). He participates in the Accreditation Board for Engineering and Technology (ABET) through SME, making accreditation visits to undergraduate programs in geological engineering.
Keaton specializes in quantifying hazardous natural processes for use in design and risk analysis. He has written numerous articles regarding engineering geology mapping, debris flows, landslides, collapsible soils, subsidence, fault rupture, earthquake-induced liquefaction, earthquake ground motion, and case histories.