Seismically Induced Ground Failure

Transcription

1 Seismically Induced Ground Failure by William A. Bryant Seismic Hazards Zoning California Geological Survey 100 th Anniversary Earthquake Conference Commemorating the 1906 San Francisco Earthquake April 18 22, 2006

2 CGS Seismic Ground Failure Zonation Programs Alquist-Priolo Earthquake Fault Zoning Act of 1972 Seismic Hazards Mapping Act of 1990

3 Alquist-Priolo Earthquake Fault Zoning Act of 1972 This Act resulted from the Mw San Fernando earthquake. The AP Act originally was referred to as the Alquist-Priolo Geologic Hazards Act and was intended to address a broader scope of ground deformation hazards. Immediately following the 1989 Mw 6.9 Loma Prieta Earthquake, legislation was introduced and the following year enactment of the Seismic Hazards Mapping Act of 1990

4 Seismic Hazards Mapping Act of 1990 Liquefaction Seismically Induced Landslides 1989 Mw 6.9 Loma Prieta Earthquake

5 CGS Seismic Ground Failure Zonation Programs Identify where ground failure hazards are more likely to occur Delineate zones of required investigation Trigger geologic or geotechnical hazards reports that lead to earthquake resilient construction in hazardous areas

6 Comparison of Seismic Hazards Mapping Act and Alquist-Priolo Act The Seismic Hazards Mapping Act (SHMA) is modeled after the Alquist-Priolo (AP) Act. Implementation of the SHMA generally is the same as for the AP Act. An important distinction is that where the AP Act mitigates surface fault rupture hazard by avoidance,, the SHMA allows mitigation by engineering design.

7 Seismic Hazards Zoning State Mining & Geology Board Advisory Committee Adopts Mandated Policies Receives Review Comments Provides Technical Advice State Geologist Evaluates Regional Seismic Hazard Designates Seismic Hazard Zones Provides Advisory Services Cities & Counties Requires Site Investigations Updates General Plans Reviews and Approves Projects Applies For Waivers Property Owners Developers Determines Hazard at Site Mitigates Hazard Discloses

8 ALQUIST-PRIOLO EARTHQUAKE FAULT ZONING ACT OF 1972

9 Intent of Act is to Avoid Surface Fault Rupture Hazard 1971 San Fernando Earthquake

10 Alquist-Priolo Earthquake Fault Zoning Act The AP Act addresses the seismic hazard of surface fault rupture by prohibiting placing most structures for human occupancy across the traces of active faults. The Act also requires sellers and real estate agents to inform buyers whether real property being sold is within a state- designated Earthquake Fault Zone. Earthquake Fault Zone (EFZ) maps are issued in order to assist cities and counties in avoiding the hazard of surface fault rupture ure

11 Damage to Residential Structure 1992 Mw 7.3 Landers Earthquake

12 Foundation Damage Landers Earthquake Photo by E. Hart Photo by E. Hart Photo by D. Murbach

13 1999 Chi Chi (Taiwan) Earthquake and Alquist-Priolo Earthquake Fault Zoning Act...if development along the Chelungpu fault had occurred under AP regulations, the loss of life and property would have been greatly reduced. from Rubin and others, 2001, EOS, v. 82, #47

14 Faults in California

15 Quaternary and Younger Faults

16 STRIKE-SLIP SLIP FAULT 1992 M 7.3 Landers Earthquake

17 REVERSE FAULT 1999 M 7.5 Chi Chi (Taiwan) Earthquake Photo by K. Kelson

18 NORMAL FAULT Photo by K. Steinbrugge 1954 M 7.0 Fairview Peak Earthquake

19 Alquist-Priolo Earthquake Fault Zoning Act of 1972 Surface fault rupture hazard is mitigated by avoiding placing structures across traces of hazardous faults. Earthquake Fault Zones encompass hazardous faults, which are defined as those faults that are sufficiently active and well-defined defined. Sufficiently active faults exhibit evidence of Holocene displacement (approx. last 11,000 years). Well-defined - trace detectable by trained geologist.

20 Surface Fault Rupture Usually Occurs Along Pre-Existing Faults Imperial Fault and 1979 Earthquakes

21 Evidence of Multiple Earthquakes SAN ANDREAS FAULT - WALLACE CREEK 53 events 13.3 ka 42 events 10.5 ka 14 events 3.7 ka 9 m 1857 Photo by R. Wallace

22 STATE GEOLOGIST Delineates Earthquake Fault Zones 10-Region Project Reviews New Data for New and Revised Earthquake Fault Zones Grants Waiver Requests Continuing Program

23 How the Maps are Made

24 California Geological Survey 10 Region Fault Evaluation and Zoning Program DEL NORTE SISKIYOU MODOC TRINITY SHASTA LASSEN HUMBOLDT TEHAMA MENDOCINO BUTTE GLENN PLUMAS SIERRA LAKE COLUSA SUTTER NEVADA PLACER EL DORADO YOLO SONOMA NAPA ALPINE SOLANO MARIN SAN CONTRA COSTA JOAQUIN SANTA CLARA SANTA CRUZ SACRAMENTO AMADOR SAN FRANCISCO ALAMEDA MARIPOSA SAN MATEO STANISLAUS CALAVERAS MERCED TUOLUMNE MADERA MONO MONTEREY SAN BENITO FRESNO INYO KINGS TULARE SAN LUIS OBISPO KERN SANTA BARBARA 1976 VENTURA SAN BERNARDINO LOS ANGELES miles kilometers 1977 ORANGE 1978 SAN DIEGO RIVERSIDE IMPERIAL

25 Alquist-Priolo Fault Evaluation and Zoning Program Faults with evidence of late Quaternary displacement were evaluated for possible zoning. Evaluations consisted of: Literature Review Air Photo Interpretation Field mapping Results are summarized in 248 Fault Evaluation Reports.

26 Fault Evaluation Report Literature Review Critical evaluation of available literature, both published and unpublished, including existing site-specific specific investigations. Age of geologic units: note youngest unit offset and oldest unit not offset. Evaluate accuracy of fault locations mapped by others.

27 Summary of Previous Mapping

28 Fault Evaluation Report Air Photo Interpretation Evaluate the geomorphic expression of fault, looking for young fault-produced landforms. Identify youthful geomorphic surfaces and deposits that are offset and not offset. Accurately plot surface traces on appropriate base maps, generally at a scale of 1:24,000.

29 Air Photo Interpretation Use of Pre-development Photos is Essential

30 Geomorphic Expression Recently Active Faults From Wallace, 1990

31 Geomorphic Expression Active Strike Slip Faults right-laterally offset drainages linear sidehill benches Photo by E. Hart

32 Geomorphic Expression Active Strike Slip Faults right-laterally offset drainages linear drainage beheaded drainages linear west-facing scarp on alluvial fans Photo by R. Wallace

33 Geomorphic Expression Active Reverse and Thrust Faults Photo by D. Morton

34 Fault Evaluation Report Field Reconnaissance

35 Field Reconnaissance Verify Features Interpreted From Air Photos Observe and Map Small Scale Features Not Visible on Air Photos Estimate Ages of Surfaces Offset and Not Offset

36 Fault Evaluation Report Annotated Fault Map

37 Fault Evaluation Report Green Valley Fault Fault Evaluation Report (FER) summarizes evidence for or against fault recency. FER provides recommendations for or against encompassing faults in an Earthquake Fault Zone.

38 Official Earthquake Fault Zone Map Released After 6 Month Review Period

39 Index to Alquist-Priolo Earthquake Fault Zone Maps ( ) 547 Earthquake Fault Zone Maps issued as of 1/1/2006 San Francisco Sacramento 36 Counties and 104 Cities affected Los Angeles

40 Site-Specific Specific Investigations Objective is to accurately locate active faults in order to avoid placing most structures for human occupancy over potentially hazardous faults.

41 Fault Investigation Methods Include: Literature Review Aerial Photographic Interpretation Site Observations/Geologic Mapping Subsurface Investigation Trenching Borings and Test Pits Cone Penetrometer Testing (CPT) Geophysical Investigations High Resolution Seismic Reflection Ground Penetrating Radar Other (Seismic Refraction, Magnetic, Electrical, Resistivity, Gravity

42 Project Site Within Hayward Fault Zone Niles Quadrangle

43 Trench Excavation Site-Specific Specific Fault-Rupture Hazard Investigation

44 Trench Locations for Specific Structure Footprint From UGS, Misc. Pub. 03-6

45 Trench Locations for Project Site From UGS, Misc. Pub. 03-6

46 Hayward Fault Zone Site Investigation for Condominium Complex

47 Logs for Trenches TT-C C and TT-C

48 Trench Considerations Bonilla and Lienkaemper, 1991, Factors affecting the recognition of faults exposed in exploratory trenches: : USGS Bulletin Required reading for geologists who write or review reports evaluating fault activity Bonilla and Lienkaemper (1991) concluded that 45% of faults die out upward, even though rupture continued to the ground surface. Strike-slip and reverse faults comprise greater than 70% of this fraction. Therefore, a fault strand overlain by an apparently undisturbed deposit is not necessarily older than the deposit. Faults in unconsolidated deposits: Gouge reported in only 15% of exposures Slickensides noted in only about 10% of exposures

49 Age-Dating Techniques Relative Dating Methods: Soil Profile Development Degree of Land Surface Preservation Isotopic Methods 14 C Cosmogenic Nuclide Radiogenic Methods Thermoluminescence (TL) Optically Stimulated Luminescence (OSL) Correlation Methods Tephrochronology Marine Terrace Correlation Glacial Event Correlation

50 Result of Fault Investigation CONDOMINIUMS SET BACK FROM HAYWARD FAULT Photo by C. Real

51 Setbacks Setback from active fault generally 50 feet (15 m). Language in California Code of Regulations (sec 3603) states..as the area within 50 feet of such active faults shall be presumed to be underlain by active branches of that fault unless proven otherwise by an appropriate geologic investigation no such structures shall be permitted in this area. Setback recommendations should consider the style and complexity of faulting at the site and the accuracy of fault location. In general, the hanging wall of dip-slip faults will have a greater setback width than the footwall.

52 Digital AP Products

53 Selected References Bonilla and Lienkaemper, 1991, Factors affecting the recognition of faults exposed in exploratory trenches: U.S. Geological Survey Bulletin California Geological Survey, 2002, Guidelines for evaluating the hazard of surface fault rupture: California Geological Survey Note 49. California Geological Survey, 2002, General guidelines for reviewing geologic reports: California Geological Survey Note 41. Christenson, G.E., Batatian, L.D., and Nelson, C.V., 2003, Guidelines for evaluating surface-fault-rupture hazards in Utah: Utah Geological Survey Miscellaneous Publication Hart, E.W., and Bryant, W.A., 1999, Fault-rupture hazard zones in California: Division of Mines and Geology Special Publication 42. McCalpin, J.P., (ed), 1996, Paleoseismology: Academic Press. Noller, J.S., Sowers, J.M., and Lettis, W.R. (eds), 2000, Quaternary geochronology, methods and applications: Washington D.C., American Geophysical Union AGU Reference Shelf 4.

54 Internet Resources Alquist-Priolo Act Special Publication 42 ftp://ftp.consrv.ca.gov/pub/dmg/pubs/sp/sp42.pdf CGS Fault Rupture Guidelines (Note 49) Utah Geological Survey Fault Rupture Guidelines CGS Digital Fault Activity Map CGS Digital Fault Activity Map QuaternaryFaults_ver2.htm

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