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147 NEW HAZARD MAPS FOR RIVERSIDE COUNTY NEW HAZARD MAPS FOR RIVERSIDE COUNTY, CALIFORNIA W. Richard Laton, Ph.D. California State University, Fullerton Earth Consultants International [email protected] Rene Perez California State University, Fullerton Earth Consultants International [email protected] Doug Bausch, Ph.D. Earth Consultants International Northern Arizona University [email protected] ABSTRACT Riverside County, California is a complex area of differing geologic and hydrologic conditions representing many differing hazards. Hazard iden- tification defines the magnitude and associated probabilities of natural haz- ards that may pose threats to human interests in specific areas. Utilizing geographical information systems (GIS), the following maps of the Temecula area of Riverside County were developed: raster image, digital elevation, geologic, landslide and slope instability, seismic activity (earthquakes), sur- face fault rupture susceptibility (including Alquist-Priolo earthquake fault zones – state and county), liquefaction susceptibility, subsidence suscepti- bility, and shallow groundwater. These completed maps and associated tech- nical documents will aid the County in its future design and policy initia- tives so that they are consistent throughout the entire County. Utilizing the available data, planners are able to make appropriate choices in land use management.

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Page 1: NEW HAZARD MAPS FOR RIVERSIDE COUNTY, CALIFORNIAgroundwater.fullerton.edu/Groundwater_Web/Professional_Publications... · NEW HAZARD MAPS FOR RIVERSIDE COUNTY NEW HAZARD MAPS FOR

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NEW HAZARD MAPS FOR RIVERSIDE COUNTY

NEW HAZARD MAPS FORRIVERSIDE COUNTY,

CALIFORNIA

W. Richard Laton, Ph.D.California State University, FullertonEarth Consultants [email protected]

Rene PerezCalifornia State University, FullertonEarth Consultants [email protected]

Doug Bausch, Ph.D.Earth Consultants InternationalNorthern Arizona [email protected]

ABSTRACT

Riverside County, California is a complex area of differing geologicand hydrologic conditions representing many differing hazards. Hazard iden-tification defines the magnitude and associated probabilities of natural haz-ards that may pose threats to human interests in specific areas. Utilizinggeographical information systems (GIS), the following maps of the Temeculaarea of Riverside County were developed: raster image, digital elevation,geologic, landslide and slope instability, seismic activity (earthquakes), sur-face fault rupture susceptibility (including Alquist-Priolo earthquake faultzones – state and county), liquefaction susceptibility, subsidence suscepti-bility, and shallow groundwater. These completed maps and associated tech-nical documents will aid the County in its future design and policy initia-tives so that they are consistent throughout the entire County. Utilizing theavailable data, planners are able to make appropriate choices in land usemanagement.

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GEOLOGY AND ENOLOGY OF THE TEMECULA VALLEY

INTRODUCTION

DISASTER. It strikes anytime, anywhere. It takes many forms - a hurri-cane, an earthquake, a tornado, a flood, a fire or a hazardous spill, anact of nature or an act of terrorism. It builds over days or weeks, or hitssuddenly, without warning. Every year, millions of Americans face di-saster, and its terrifying consequences (2000, FEMA).

The County of Riverside covers approximately 7,000 square miles ofthe geologically complex southern California region. The County stretchesfrom the Arizona border at the Colorado River to within about ten miles ofthe Pacific Ocean. As a result, Riverside County contains many differentgeologic and geomorphic units with many varying hazards associated witheach of them. The following maps of the Temecula area are in draft formand are being reviewed by the county at present time. These maps are avail-able for viewing at the Earth Consultants, Int’l. website atwww.earthconsultants.com and are included as reduced-size black and whiteversions in this article. Each map was created utilizing various sources ofinformation in many varying formats.

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DIGITAL ELEVATION MAP (DEM)

A digital elevation map (DEM) of Riverside County was constructedusing data from the United States Geological Survey (USGS). This mapwas used in the analysis of slope for the landslide hazard map as well as aconstraining map for flood and dam inundation. The DEM data from 7.5-minute units correspond to the USGS 1:24,000 and 1:25,000 scale topo-graphic quadrangle map series for all of the United States and its territories.Each 7.5-minute DEM is based on 30- by 30-meter data spacing with theUniversal Transverse Mercator (UTM) projection. Each 7.5- by 7.5-minuteblock provides the same coverage as the standard USGS 7.5-minute mapseries.

GEOLOGIC MAP

Detailed digital Geologic and Engineering Geologic maps for RiversideCounty were prepared for this study. No field mapping was done but ratherwas compiled from existing geologic maps of the area. The accuracy of theoverall Geology and Engineering Geology maps is 1:100,000. The engi-neering map is a consolidation and grouping of geologic units for the pur-pose of providing a like materials map. These maps were utilized in variousqueries to construct landslide, liquefaction and subsidence hazard maps.The engineering materials map is useful in evaluating areas for constructionand potential mitigation of geological hazards. Map references: 1) Prelimi-nary Geologic Map of the Blythe 30' by 60' Quadrangle, CA and AZ; 2)

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Geologic Map of California, Salton Sea Sheet; 3) Geologic Map of Califor-nia, Santa Ana Sheet; 4) Distribution and Geologic Relations of Fault Sys-tems in the Vicinity of the Central Transverse Ranges, Southern California;5) Geologic Map of California, San Bernardino Quadrangle; 6) GeologicMap of the Big Maria Mountains NE Quadrangle, Riverside County, Cali-fornia, and Yuma County Arizona; 7) Geologic Map of California, NeedlesSheet; 8) Digital map of the Santa Ana Sheet, California – provided by Dr.Morton of the USGS.

LANDSLIDES AND SLOPE INSTABILITY MAP

Earthquakes have caused rockfalls, rock avalanches, debris flows, bluffcollapses, and other types of potentially damaging landslide movements.Landslides tend to occur in loosely consolidated, saturated soils on slopingterrain. Landslides also tend to form distinctive landforms (scarps, troughs,disrupted drainages, etc.) that can be recognized by most trained geologists.Other types of oversteepened slopes (cliffs, stream banks, saturated soil-filled swales, man-made cuts and fills, etc.) are often prone to collapse whenshaken by an earthquake. Research has shown that landslide deposits andcertain geologic formations and other earth materials are prone to landslidefailure.

The following is the procedure used to define the landslide susceptiblemaps for Riverside and the subsequent landslide hazard maps.

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• Created a slope map for Riverside County by creating a gridmap of the USGS DEM for the County. A 30m-grid cell sizewas used.

• Created a grid map of the Engineering Geology using a 30m-grid cell size.

• Queried both grid maps for areas that meet the parameters forslope instability and landslide susceptibility.

SEISMIC ACTIVITY

Historic Earthquakes in the Riverside County area were plotted for theirmagnitude, depth and epicenter. Earthquake risk varies from very high inthe western portion of the County, due to the presence of two of California’smost active faults, the San Andreas and San Jacinto, to moderate in theeastern portion of the County that includes Blythe.

Earthquake locations for events occurring prior to 1931 (1858 – 1931)were plotted based on Blake, T. F., 1996, EQFAULT- Computer softwarefor deterministic site parameters, Version 2.20. Earthquake locations forevents occurring from 1932 to 1980 (Earthquake data recorded by the South-ern California Seismic Network (SCSN), and catalogued by the SouthernCalifornia Earthquake Center (SCEC), which operated jointly by the Seis-mological Laboratory at Caltech and the U.S. Geological Survey, Pasa-

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dena, California.) were used. Data collected by Hauksson, E., 1999 (inpress), (Crustal structure and seismicity distribution adjacent to the Pacificand North America plate boundary in southern California: submitted to Jour-nal of Geophysical Research, 1999.) was used to locate earthquake eventsoccurring from 1981 to 1999.

SURFACE FAULT RUPTURE SUSCEPTIBILITY MAP

The surface fault rupture map is comprised of two maps. The first is amap of all the referenced faults with their respective ages color-coded. Sec-ond is a map showing the Alquist-Priolo Earthquake Fault Zones (AP-zones)for the State as well as County fault zones. The source map used for thesecoverage’s was a 1974 State of California, The Resources agency, Depart-ment of Conservation 7.5 minute quadrangle topographic map. This cover-age may not show all potentially active faults, either within the special stud-ies zones or outside their boundaries. The faults shown on the map were notfield checked and the “quality of data” used is highly varied.

The faults shown on this map are typically accurate to within 100 to500 feet; however, some faults are better constrained than others as a conse-quence of the geologic field relations (exposures of the fault), or the qualityof the geologic maps from which the data were acquired. Most of the faultsthat are Holocene to Late Quaternary in age are accurate to within 100 to300 feet because their locations were typically retrieved from detailed (small-

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scale) geologic maps. However, in regions where these faults are “con-cealed” by younger sediments, their locations become progressively lessaccurate.

LIQUEFACTION SUSCEPTIBILITY MAP

Liquefaction is a process by which water-saturated materials (includingsoil, sediment, and certain types of volcanic deposits) lose strength and mayfail during strong ground shaking. Liquefaction is defined as “the transfor-mation of a granular material from a solid state into a liquefied state as aconsequence of increased pore-water pressure” (Youd, 1973). Four kindsof ground failure commonly result from liquefaction: lateral spread, flowfailure, ground oscillation, and loss of bearing strength. Portions of theCounty of Riverside are susceptible to liquefaction, which is a very destruc-tive secondary effect of strong seismic shaking. Liquefaction occurs prima-rily in saturated, loose, and fine to medium-grained soils in areas where theground water table is 50 feet or less below the ground surface. Severalprocedures have been developed to identify areas prone to ground failure.Although we know that loosely packed, unconsolidated, saturated depositsare most likely to liquefy, site-specific geotechnical studies are the only prac-tical and reliable way of determining the liquefaction potential of a site.The following is the liquefaction hazard rating system used for this mappingproject (Table 1).

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Table 1General Liquefaction Potential Zones for Riverside County

Rank Ground Water General+ Sediment Recommended Policies*Depth# Type General

ConstructionCritical Facilities

High < 30 feet very susceptible study required study required

Moderate< 30 feet susceptible study required study required

30-50 feet very susceptible study required study required

Low > 30 feet susceptible none study required

Very Low30-50 feet susceptible

50-100 very susceptible none study required

ExtremelyLow

50-100 feet susceptible none study required

None> 100 feet susceptible none none

no data bedrock none none

*: Ground shaking potential in easternmost Riverside County is considered below the threshold forliquefaction as shown on Figure 1-10, and site-specific investigations should not be required for generalconstruction projects#: Ground water depth is based on the historic high measurement+: Very susceptible sediment type includes generally granular Holocene sediments; susceptible includesgenerally granular Pleistocene sediments.

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SUBSIDENCE SUSCEPTIBILITY MAP

Certain areas of Riverside County are prone to regional downwarpingand rapid subsidence. Withdrawal of underground fluids, and tectonic el-evation changes produced during extremely large earthquakes are most im-portant in terms of potential causes. This map focused on land subsidenceassociated with the withdrawal of ground water.

SHALLOW GROUNDWATER MAP

Groundwater was mapped using data from the Regional Water Qualityboard, SAWPA, and USGS reports on groundwater within Riverside County.The groundwater is reported as the highest recorded elevation. Groundwa-ter is only mapped in areas where sufficient data was available. There couldbe areas of perched water that have not been mapped throughout the county.Contours were created based on data collected from the various water dis-tricts through Santa Ana Watershed Project Authority. Reports located atthe Regional Water Quality board were used to augment the data collectedfrom the various water districts. All data was analyzed for highest histori-cal recorded elevation. This data should be only considered for regionalanalysis only.

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CONCLUSION

While many natural and man-made hazards have the potential to impactthe County of Riverside and the Temecula area on a relatively frequent ba-sis, the event with the greatest potential for loss of life, property and eco-nomic damages in the County is an earthquake. Earthquakes trigger variousgeologic phenomena that can cause severe property damage and loss of life.These hazards in Riverside County include ground shaking, fault rupture,and landslides, foundation failures caused by liquefaction or subsidence,and seiche. Earthquakes can also cause a variety of localized, but not lessdestructive hazards such as urban fires, dam failures, and toxic chemicalreleases. This generalization is true for most of southern California and isdue to the fact that earthquakes impact regions of significant aerial extent.

Although it is not possible to prevent earthquakes from occurring, theirdestructive effects can be minimized. Comprehensive hazard mitigation pro-grams that include the identification and mapping of hazards, prudent plan-ning, emergency exercises, enforcement of building codes, and expedientretrofitting and rehabilitation of weak structures can reduce significantlythe scope of a disaster. Local governments, emergency relief organizations,and residents are advised to take action and develop and implement policiesand programs aimed at reducing the effects of earthquakes. Individuals

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should exercise prudent planning to provide for themselves and their fami-lies in the aftermath of a disaster. It’s through the process of producingcountywide hazard maps that enable the local and county officials to planahead accordingly and provide land use alternatives in areas of potentialrisk.

PARTIAL LIST OF REFERENCES USED IN THIS REPORT

Babbitt, D.H., 1993, Improving Seismic Safety of Dams in California: Depart-ment of Water Resources, California Division of Safety of Dams, 21 pgs.

Beatley, T. and Burke, P., 1990, Seismic Safety through Public Incentives: ThePalo Alto Seismic Hazard Identification Program, in Earthquake Spectra,Vol. 6, No. 1, pp. 57-80.

Blake, T. F., 1996, EQFAULT- Computer software for deterministic siteparameters, Version 2.20.

Bortugno, E.J., Spittler, T.E., 1986, Geologic Map of the San BernardinoQuadrangle, California Division of Mines and Geology, Regional GeologicMap Series, Map No. 3A (Geology), map scale 1:250,000.

California Division of Mines and Geology (CDMG), 2000, Currently AvailableSeismic Hazard Zone Maps and Planned Release Dates: Last Updated:February 14, 2000, http://www.consrv.ca.gov/dmg/shezp/schedule.htm

CDMG Special Publication 117 (http:///www.consrv.ca.gov/dmg/pubs/sp/117/)

California Governor’s Office of Emergency Services, 1999, Emergency Plan-ning Guide, Guidelines for Local Government, Vol. 1, 56 pgs.

Coachella Valley Water District, 2000, Water and the Coachella Valley: http://www.cvwd.org/water&cv.htm

County of Riverside, Transportation and Land Management Agency, 1997,Environmental Hazards Map for Riverside County, dated June 10, 1997,scale 1"=6 miles.

Dibblee, T.W., Jr., 1982, Geologic Quadrangle Maps of the San Jacinto Moun-tains and vicinity, California: South Coast Geological Society, GeologicMaps SCGS 1, 2, 3, 4 and 5, (15-minute quadrangle maps: Perris, Banning,Palm Springs, Hemet, Idyllwild), map scale 1:62,500.

Dibblee, T.W., Burnham, W.L. and Dutcher, L.C., Geologic Map of the SanTimoteo-Smiley Heights Area, Upper Santa Ana Valley, Southern Califor-nia, Showing Water Levels for 1967, 1968.

Elsinore Valley Municipal Water District, 2000, Website Documents: http://www.evmwd.com/

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Fault_Rupture Hazard Zones in California, 1980-1995, issued by the CaliforniaDivision of Mines and Geology, map scale 1:24,000.

Federal Emergency Management Agency, 2000, Website Documents: http://www.fema.gov.

Fife, D.L., Rodgers, D.A., Chase, D.W., Chapman, R.H., and Sprotte, E.C.,1976, Geologic Hazards in Southwestern San Bernardino County, Califor-nia, CDMG Special Report 113, 40p.

Greenwood, Richard B., Morton, Douglas M., Jachens, Robert C., Chapman,Rodger H., 1991, Geology and geophysics of the Santa Ana 1:100,000quadrangle, Southern California; a progress report: Abstracts with Programs_ Geological Society of America, vol. 23, n. 5, p. 478. [This map is alsoavailable on the internet : http://wrgis.wr.usgs.gov/open_file/of99_172/Open File Report 99-172. Preliminary digital geologic map of the SantaAna 30' x 60' quadrangle, Southern California, version 1.0, Compiled by:D.M. Morton, preparation by: Rachel M. Hauser and Kelly R. Ruppert].

Hamilton, W.B., 1984, Generalized Geologic map of the Big Maria Mountainsregion, northeastern Riverside county, southeastern California: U.S. Geo-logical Survey Open File Report 84-407, 7 p., (scale 1:48,000).

Hart, E. W. and Bryant, W.A., 1997, Fault Rupture Hazard Zones in California,Fault Rupture Hazard Zones in California: Department of Conservation,Division of Miners and Geology Special Publication 42, 26p.

Hart, E. W., 1984, Fault Rupture Hazard Zones in California, Alquist-PrioloSpecial Studies Zones Act of 1972 with Index to Special Studies ZonesMaps: California Department of Conservation, Division of Mines andGeology, 23p.

Holzer, T.L., 1984, Ground failure induced by ground-water withdrawal fromunconsolidated sediment: man-induced land subsidence: Reviews in Engi-neering Geology, Vol. 6, pp. 67-105.

Howard, K.A., Allen, C.M., 1988, Geologic Map of the Southern Part of theDale Lake 15_minute quadrangle, San Bernardino and Riverside Counties,California: United States Geological Society, Open File Report OFR 88-534,map scale 1:62,500.

Howard, K.A., Horringa, E.D., Miller, D.M., Stone, P., 1989, Geologic Map ofthe eastern parts of the Cadiz Lake and Cadiz Valley 15_minute quad-rangles, San Bernardino and Riverside Counties, California: United StatesGeological Society, Miscellaneous Field Studies Map MF_2086, map scale1:62,500.

Ikehara, M. E., Predmore, S.K., Swope, D.J., 1997, Geodetic Network toEvaluate Historical Elevation Changes and to Monitor Land Subsidence inLower Coachella Valley, California, 1996: U.S. Geological Survey, Poster.

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Jennings, C.W., 1967, Geologic Map of California Salton Sea Sheet: CaliforniaDivision of Mines and Geology, Regional Geologic Map Series, GAM-13,map scale 1:250,000.

Lofgren, B.E., 1976, Land Subsidence and aquifer system compaction in theSan Jacinto Valley, Riverside County, California. A progress report: U.S.Geological Survey Journal of Research, Vol. 4, No. 1, pp. 9-18.

Matti, J.C., Morton, D.M., and Cox, B.F., 1985, Distribution and geologicrelations of fault systems in the vicinity of the central Transverse Ranges,southern California. U.S. Geological Survey Open File Report 85-365, 23p.

Matti, J.C., Morton, D.M., Cox, B.F., 1992, The San Andreas Fault System inthe Vicinity of the Central Transverse Ranges Province, Southern Califor-nia: United States Geological Survey Open File Report 92-354, map scale1:250,000.

Metropolitan Water District (MWD), 2000, Website Documents: http://www.mwd.dst.ca.us

Moyle, W.R, 1973, Map of the Santa Rosa Rancho and Vicinity Riverside andSan Diego Counties, California, Showing Reconnaissance Geology andLocation of Wells and Springs.

National Inventory of Dams, 2000, U.S. Army Corp of Engineers websitedocuments: http://crunch.tec.army.mil/nid/webpages/nid.html

Onderdonk, N.W., (personal communication), 1998, Geologic maps of the HotSprings, Thomas Mountain and Claremont Faults of the San Jacinto FaultZone, map scale 1:24,000.

Powell, R.E., 1981, Geology of the crystalline basement complex, easternTransverse Ranges, southern California: Constraints on regional tectonicinterpretation [Ph.D. thesis]: Pasadena, California, California Institute ofTechnology, map scale 1:125,000.

Proctor, R.J., 1968, Geology of the Desert Hot Springs – Upper CoachellaValley Area, California: California Division of Mines and Geology, SpecialReport 94, 50p, map scale is 1: 62,500.

Rogers. T.H., 1965, Geologic Map of California, Santa Ana Sheet, scale1:250,000.

Rogers, T.H., 1966, Geologic Map of California Santa Ana Sheet: CaliforniaDivision of Mines and Geology, Regional Geologic Map Series, map scale1:250,000.

Seed, H. B., Idriss, I. M., and Arango, I., 1983, Evaluation of LiquefactionPotential Using Field Performance Data: American Society of Civil Engi-neers Journal of Geotechnical Engineering Division, Vol. 109, No. 3, pp.458-482.

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Shlemon, R.J., Barry, M.J., Alhadeff, C., and Kupferman, S.A., 1995, Legal,Geotechnical, and Political Aspects of Subsidence-Zone Formation inCalifornia: in Land Subsidence Case Studies and Current Research:Proceedings of the Dr. Joseph F. Poland Symposium on Land Subsidence,Special Publication No. 8, Association of Engineering Geologists, pp. 549-552.

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Shlemon, R.J., and Davis, P., 1992, Ground Fissures in the Temecula Area,Riverside County, California: in B.W. Pipkin and R.J. Proctor, eds., Engi-neering Geology Practice in Southern California: Association of Engineer-ing Geologists, Special Publication No. 4, pp. 275-288.

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Youd, T.L., and Perkins, D.M., 1978, Mapping liquefaction induced groundfailure potential: Proceedings of the American Society of Civil Engineers,Journal of the Geotechnical Engineering Division, Vol. 104, No. GT4, pp.433-446.