PAGE 4 CALIFORNIA GEOLOGICAL SURVEY NNOTOTEE RREGEGULULAATTOORRYY EAEARRTTHHQQUUAKEAKE HHAZAAZARDRD ZOZONNEESS 5454 EARTHQUAKE-INDUCED GROUND FAILURE HAZARDS SOUTHERN CALIFORNIA REGION

Liquefaction—as The California Geological Survey (CGS) establishes zones of liquefaction and earthquake-induced landslides. a geologic term, PhotoPhoto 11 Photo 3 zones that delineate areas where ground failure (due to Eighty-eight of the completed maps cover parts of Los refers to the loss of liquefaction, landslides or surface fault rupture) is more Angeles, Orange, Ventura, San Bernardino, and Riverside strength of saturated likely to increase earthquake damage. (The hazard of counties; these seismic hazard maps are compiled into soils during shaking. strong earthquake shaking is addressed separately by the one map inside this CGS Note. An earthquake can California Building Code.) These areas are commonly cause soil particles referred to as “Zones of Required Investigation” (ZORI). to shift and become Cities and counties are required by state law to withhold buoyant, as pore building permits within these zones until geologic/geo- spaces fill with technical investigations are conducted to assess seismic water, weakening hazards on a site-specific basis. If a liquefaction or earth- the ability of a soil quake-induced landslide hazard is identified, appropriate to support structures on the surface. As shown in Photo 1, lique- Surface rupture—occurs when design and/or ground improvement measures must be faction caused damage to gas, water, and power utility lines in the movement on a fault deep within the applied in order to reduce the potential for structural failures. More restrictive measures are applied within San Fernando Valley during the 1994 Northridge Earthquake earth breaks through to the surface. 500m (Photo 1 from the U.S. Geological Survey). Fault rupture almost always follows earthquake fault zones, where proposed structures must pre-existing faults, which are zones of avoid being placed across the trace of active faults. In all weakness. Rupture may occur suddenly cases, sellers of real property are required to check seismic Seismic hazard ZORI for earthquake-induced landslides (in during an earthquake or slowly in the zonation maps produced by CGS to determine whether PhotoPhoto 22 property being sold falls within a seismic hazard zone or blue) for a portion of Pacific Palisades (red arrow shows location form of fault creep. Sudden ruptures and view direction of Photo 2 on back page). are more damaging to structures because earthquake fault zone. The seller is required to provide a they are accompanied by shaking. As “Natural Hazard Disclosure Statement” to the buyer. Earthquake fault zones designated by CGS are delineated shown in Photo 3, there was over a meter on a separate series of maps. CGS geologists place earth- of vertical diplacement of the ground quake fault zones along traces of faults where mapping surface caused by rupture of the San demonstrates surface fault rupture has occurred within Fernando fault zone during the 1971 the past 11,000 years (Holocene time). Construction within San Fernando Earthquake (Photo 3 from these zones cannot be permitted until a geologic investiga- the U.S. Geological Survey). tion has been conducted to prove that a building planned for human occupancy will not be constructed across an active fault. These types of site evaluations address the precise location and recency of rupture along traces of the Landslides—are the downhill movement of ground caused primarily by gravity acting on weakened rock or soil. faults and typically are based on observations made in 500m Slopes are weakened by weathering, erosion, saturation, and the addition of weight in the form of artificial fill, trenches excavated across fault traces. As of October 2007, structures, snow, or rock. Landslides that occur during earthquakes typically originate from these steep and weak- CGS has released 547 official maps statewide. ened slopes. A number of landslides occurred in the coastal bluffs, as shown in Photo 2, and steep mountainous Seismic hazard ZORI for liquefaction (in green) for a portion areas in Southern California during the 1994 Northridge Earthquake (Photo 2 by Pamela Irvine, California of the San Fernando Valley (red arrow shows location and Geological Survey). view direction of Photo 1 on back page). Seismic Hazards Resources and Earthquake Education Information: CGS geologists delineate liquefaction zones by assessing Regulatory Seismic Zonation Maps - www.consrv.ca.gov/cgs/geologic_hazards/regulatory_hazard_zones/index.htm the engineering behavior of soils based on surface Earthquake Education Information - www.consrv.ca.gov/cgs/information/EdResCenter.htm geology and geomorphology, soil properties from sub- surface borings, the potential degree of soil saturation, Offices of the California Geological Survey: and the potential for such soils to liquefy under estimated Publications and Information Office Bay Area Regional Office Southern California Regional Office levels of ground shaking from future earthquakes. Earth- 801 K Street, MS 14-34 345 Middlefield Road, MS 520 888 South Figueroa Street, Suite 475 quake-induced landslide zones are based on a similar analysis that also includes mapping locations of existing 500m Sacramento, CA 95814-3532 Los Angeles, CA 90017 Menlo Park, CA 94025 landslides, and an analysis of rock strength, geologic (916) 445-5716 (650) 688-6327 (213) 239-0878 structure and surface topography in order to assess the Earthquake fault ZORI (in pale yellow) for a portion of stability of slopes under future earthquake shaking. As the San Fernando fault zone that ruptured during the 1971 www.conservation.ca.gov/cgs of October 2007, CGS has released 113 official maps San Fernando Earthquake (red arrow shows location and view covering about 7,000 square miles. These maps show direction of Photo 3 on back page) .

THE RESOURCES AGENCY STATE OF CALIFORNIA DEPARTMENT OF CONSERVATION MIKE CHRISMAN ARNOLD SCHWARZENEGGER BRIDGETT LUTHER ©California Department of Conservation, 2007. Reproduction of this CGS Note for classroom or public education purposes is encouraged and does not SECRETARY FOR RESOURCES GOVERNOR DIRECTOR require written permission. However, please cite California Geological Survey as source. The Department of Conservation makes no warranties as to the suitability of this product for any particular purpose. PAGE 2 PAGE 3

Seismic Hazard Zonation of 58 Southern California October 2007

MAP EXPLANATION

138 Zones of Required Investigation Liquefaction Ventura Areas where historic occurrence of liquefaction, or local geological, geotechnical and groundwater County 33 San Bernardino condtions indicate a potential for permanent ground displacements such that mitigation as defined in County Public Resources Code Section 2693(c) would be Area not Zoned required. 5 Area not Zoned Earthquake-Induced Landslides Areas where previous occurrence of landslide movement,

or local topographic, geological, geotechnical and 14 subsurface water conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693(c) would be required. 150 126 Earthquake Fault Zone Los Angeles Regulatory zones encompassing active faults wherein County 2 fault-rupture hazard investigations are required prior to building structures for human occupancy.

Area Not Zoned 39 Areas not zoned include land not likely to be developed Los Angeles Area not Zoned 15 23 5 within the National Forests and other remote areas. 210

1 134 210 2

110 66 210 405 2 10 10 110 E ls in o re 60 fa 10 u C lt 60 a 60 l R i I 71 VE 72 D R f V SI L Y DE 42 o B A D T W R S E A 142 Riverside K M O 110 r A IU R 105 L E D U R A 90 G E n I l T s E F in S o 57 County E re V N f 710 a L V u 90 I l i S 110t CA A A DEMY a S RD A C O N TT A E D V V W SU E 5 D L N A B S ET S 91 N BL A VD P 19 W T N BROADWAY TE 101 M S PL E S Y

T L S T A 15

A D D T Orange IU S G E 22 ls M IN in Y o WA R re P fa S u N lt County B N MAIN ST EV 39 ER T LY S BL AL VD PINE O ST D 55 A N R T VI 405 A W W S G Area V N D Index Map 3 2 A L R E D N S R A ST D D N 241 not S O S S W E I M T T S A W 1 M R W 6 S IS EN T A IL H W T M GO Zoned S S S L N H T 3 T E ST IR R A M E B Los Angeles D A L N C VD ST Y W ST 73 4 W 1 TH 74 W S 3R T T D 101 S 5T H ST W A S T 133 O O T S LY R Y T M 110 E W A S E E 1 O 73 P 7 3 ST ST T IC U T W IN R B IG H D D O LV W A S S D F S A M T P A C I F I C O C E A N 8 T O E S TH S N S R V E B A W T E 4 S S 5 T 9 T L H T H P M W H S A L T I P S S IC T E R S O E 6 T B 8 T I L N T H O VD E T S H S E 9 O E T N E S C VE T R S 4T N H T 7 R H T T I D S C S S E S E H D T S B Downtown T S A LV P T 5 N D N A A T Los Angeles S D A

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M F S E A E 7TH ST L O A T E A E O V O S E 1 L E S San Diego V 6T Y A H M S S P D T IC N B A LV County R E D G E WA V S SH A 60 ING R E TO E V N P Scale A BL O Miles E Geologic Information and Publications V O 8 D D TH N H ST 801 K Street, MS 14-34 A 0 0.2 0.4 0.8 1.2 1.6 2 R Miles Sacramento, CA 95814 G S (916) 445-5716 0 4 8 16 24 32 40 5 www.conservation.ca.gov/cgs