1

Comments on Potential Geologic and 

Seismic Hazards Affecting Coastal Ventura 

County, California

By Stephanie L. Ross1, David M. Boore1, Michael A. Fisher1, 

Arthur D. Frankel3, Eric L. Geist1, Kenneth W. Hudnut2, Robert E. Kayen1, 

Homa J. Lee1, William R. Normark1, and Florence L. Wong1

Open-File Report 2004-1286

2004

Any use of trade, firm, or product names is for descriptive purposes only and does not 

imply endorsement by the U.S. Government

1 Menlo Park, Calif.

2 Pasadena, Calif.

3 Golden, Colo.

U.S. Department of the Interior

U.S. Geological Survey
2

Executive Summary

This report examines the regional seismic and geologic hazards that could affect proposed 

liquefied natural gas (LNG) facilities in coastal Ventura County, California. Faults throughout 

this area are thought to be capable of producing earthquakes of magnitude 6.5 to 7.5, which 

could produce surface fault offsets of as much as 15 feet. Many of these faults are sufficiently 

well understood to be included in the current generation of the National Seismic Hazard Maps; 

others may become candidates for inclusion in future revisions as research proceeds. 

Strong shaking is the primary hazard that causes damage from earthquakes and this area is zoned 

with a high level of shaking hazard. The estimated probability of a magnitude 6.5 or larger 

earthquake (comparable in size to the 2003 San Simeon quake) occurring in the next 30 years 

within 30 miles of Platform Grace is 50-60%; for Cabrillo Port, the estimate is a 35% likelihood. 

Combining these probabilities of earthquake occurrence with relationships that give expected 

ground motions yields the estimated seismic-shaking hazard. In parts of the project area, the 

estimated shaking hazard is as high as along the San Andreas Fault. The combination of longperiod basin waves and LNG installations with large long-period resonances potentially increases 

this hazard. 

Other hazards that need to be considered include:

• The potential for earthquake-induced liquefaction of wet and loose sandy material 

and several other potential causes of instability should be addressed as portions of the 

proposed projects may be developed on artificial fill. Such fill generally performs poorly 

during earthquakes if it was not properly engineered. Other portions may be developed 

on naturally deposited sediments with similarly poor performance during earthquakes. 

• High-resolution bathymetric mapping of the Santa Barbara Channel has revealed the 

remains of a number of very large submarine landslides. However, we cannot fully 

assess the hazard of smaller landslides without higher resolution data; therefore, because 

submarine slope failure hazards exist, surveys for pipeline routes should include highresolution multibeam bathymetric imagery and slope stability analysis.

• All of the proposed pipelines from Cabrillo Port cross the delta of the Santa Clara River, 

a large undersea pile of sediment cut by a series of steep marine canyons. This would 

expose planned pipelines to hazards from turbidity currents and debris flows. 

• The coastal region of Ventura and Santa Barbara Counties has been impacted by 

tsunamis, 20 feet or more feet, from a variety of sources in the past and, thus, hazards 

from future tsunamis could potentially affect proposed LNG sites. Tsunamis can be 

generated by very large magnitude earthquakes distant from the site or from local 

submarine earthquakes and landslides near the site.

Additional studies that would help reduce the uncertainty in our hazards assessments include the 

following:

• Collecting sediment cores offshore, to date past earthquakes and determine fault slip 

rates, to improve estimates of the likelihood of future earthquakes
3

• Detailed mapping of soil and sediment layers in targeted coastal regions to develop a 

chronology of large prehistoric tsunamis and determine the potential for ground failure 

and liquefaction 

• Offshore high-resolution multibeam bathymetric data to locate active faults on the 

seafloor and identify past landslides

• Utilization of marine seismic reflection data, collected by private industry along the 

west coast in the 1970’s and 1980’s for oil and gas exploration, to improve our knowledge 

of the location and subsurface geometry of offshore faults (and hence their earthquake 

potential). The USGS is currently involved in efforts to rescue these data.

Introduction

In a letter to the U.S. Geological Survey (USGS) dated June 25, 2004, Representative Lois Capps 

(CA 23rd district) requested advice on geologic hazards that should be considered in the review 

of two proposed liquefied natural gas (LNG) facilities offshore Ventura County, CA (Figure 

1). In this report, we address the questions raised in her letter and her request for advice on 

any additional studies that might be needed to evaluate the proposed LNG facilities. The report 

is based on previously compiled, publicly available data and did not involve additional field 

studies or site-specific investigations. We have considered hazards posed to the offshore facilities 

Cabrillo Port (moored, http://www.cabrilloport.ene.com) and Platform Grace (on an existing oildrilling platform, http://www.crystalenergyllc.com), to their onshore distribution installations, 

and to the proposed pipeline routes that connect them.

These facilities are being proposed in a region of known geologic hazards that arise from 

both the potential for strong earthquakes and geologic processes related to the high rate 

of sediment transport and accumulation in the offshore environment. The probability of a 

damaging earthquake (considered here as magnitude 6.5 or greater) in the next 30 years within 

about 30 miles (50 km) of the two proposed locations ranges from 30 to 60%. Earthquakes 

of this magnitude are capable of producing strong shaking, surface fault offsets, liquefaction 

phenomena, landslides, underwater turbidity currents and debris flow avalanches, and tsunamis. 

Local geologic conditions may further aggravate these hazards. For example, some of the 

onshore portions of the proposed pipelines would cross materials with a high susceptibility 

to liquefaction. Offshore sections of pipelines also risk rupture from seabed earthquake fault 

rupture as well as submarine landslides. These hazards should be considered as part of the 

evaluation of the suitability of the proposed sites, as well as during any future design review 

process.

This brief report outlines the geologic hazards that need to be considered, but is not intended 

to provide an extensive discussion of each of the identified geologic hazards or how they might 

affect the proposed facilities. In particular, we have not made any attempt to review proposed 

engineering plans as this is beyond the scope of our expertise.
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Cabrillo

Grace

Malibu

Oxnard

Ventura

Camarillo

Simi Valley

Port Hueneme

Santa Barbara

Thousand Oaks

119 40'0"W 119 20'0" W 119 0'0" W 118 40'0"W

3400'0"N3420'0"N

Mercator Projection

Santa Clara R.

Explanation

Earthquakes ofmagnitude 4 andgreater since 1812

4.0-4.9

5.0-5.9

6.0-6.9

Cabrillo Port

Platform Grace

proposed pipeline

existing pipeline

alternate route

fault used inNational SeismicHazard maps

other identifiedfaults, offshore

County line

Roads

Aug 04 multibeamsurvey

Existing multibeambathymetry data

Santa ClaraRiver delta,approx. extent

North Channel Slope Northri

Los Angeles

Ventura

Malibu Coast

Oak Ridge Pita s Point

Red Mo u nt a in

Santa Ynez

Anacapa - Dume

Oak Ridge - Midchannel

101 Oak Ridge

Simi - Santa Rosa

Santa Monica Basin

Ormond Beach

Hueneme

Canyon

Mugu

Ca

nyon

Goleta

Carpinteria

Santa Barbara Channel

0 5 10 

0 5 10 

Santa Cruz Island

Figure 1. Map showing faults (Petersen and others, 1996; USGS, 2004a), earthquake epicenters (SCEC,2004; USGS 2004b), delta of Santa Clara River and related drainages (Normark and others, 1998), andextent of offshore multibeam bathymetric data in relation to proposed liquefied natural gas facilities.Additional offshore faults after Sorlein and others (2000).
5

If a more extensive hazard analysis is required, some of the issues raised here will be difficult 

to resolve without additional data. Collection of high-resolution bathymetric data in the project 

areas would help to resolve uncertainties about the hazard posed by small- to medium-sized 

landslides that potentially threaten the proposed pipelines. These studies would also help us 

better locate the surface traces of faults and determine their potential for rupturing the seafloor in 

earthquakes. In addition, collecting cores of sediments near offshore faults would help improve 

estimates of earthquake probabilities.

A more complete understanding of other potential hazards will require a much more thorough 

analysis of existing data. In particular, extensive seismic reflection data covering offshore 

Ventura County was gathered by the oil exploration industry over the past 30 years. These data 

would be invaluable for assessing the location, geometry and earthquake potential of the offshore 

faults and the hazards they might pose to facilities. These critical data could not be collected 

today because environmental restrictions make it impossible to conduct seismic reflection 

surveys in these areas. The USGS is currently working with industry to safeguard and archive 

these data and make them available to the broad research and consulting community. However, 

additional effort could speed the collection and interpretation of the relevant data.

Regional Earthquake History

In the relatively short time we have records of earthquake observations (since the early 19th

century), the faults in this region have produced several notable earthquakes (Weber and 

Kiessling, 1975; 1978; Ellsworth, 1990). In 1812, an earthquake of about magnitude (M) 7 

occurred, probably in the Santa Barbara Channel. This event severely damaged the mission in 

Ventura (Mission San Buenaventura), and created a damaging tsunami throughout the region 

(Townley and Allen, 1939). In 1857, a large earthquake (about M 8) ruptured 200 miles of 

the inland San Andreas Fault, from Cholame (near Paso Robles) to Wrightwood. This event, 

known as the great Fort Tejon earthquake, also severely damaged Mission San Buenaventura. 

Earthquakes in the Santa Barbara Channel in 1925 (M 6.3), 1941 (M 5.5), and 1978 (M 5.1) 

caused some damage in Ventura (fallen chimneys, broken plate glass, surface cracks in buildings) 

(Bailey, 1925; Townley and Allen, 1939). The 1933 M 6.4 Long Beach earthquake (located 60 

miles away) caused similar damage in the Ventura area. In 1973, an earthquake offshore of Point 

Mugu (M 5.2) caused widespread damage in the Oxnard area, including some structural damage 

to buildings (Lander, 1973). The 1994 M 6.7 Northridge earthquake caused widespread minor 

damage in coastal Ventura County (Dewey and others, 1995).

All of these earthquakes are the result of large-scale earth processes in which the Pacific plate 

slides northwestward relative to the North American plate at about 2 inches/year. This plate 

motion results in horizontal slip (primarily on the San Andreas “strike-slip” fault) as well as a 

component of compression that has created the series of east-west trending “thrust” faults with 

vertical motion that are responsible for the prominent mountain ranges and intervening valleys 

situated between Santa Monica and Santa Barbara. Although slower moving than the strikeslip faults of the San Andreas system, these numerous thrust faults account for over half of the 

significant earthquakes that occurred in southern California during the past century, including 
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the damaging 1971 M 6.6 San Fernando, 1994 M 6.7 Northridge, and 2003 M 6.5 San Simeon 

earthquakes.

The historical earthquake record in southern California only covers about 200 years, so potential 

seismic damage is not limited to what has already been experienced at any given location. For 

example, the 1999 M 7.1 Hector Mine earthquake in the Mojave Desert occurred on a fault that 

geologists determined had not ruptured in more than 30,000 years.

What are the locations of active faults in proximity to each site and what potential hazards 

could result from ground rupture?

Figure 1 shows the locations of numerous faults that may pose hazards throughout this region. 

The thick black lines are faults used in the USGS National Seismic Hazard Maps (http://

eqhazmaps.usgs.gov/; Frankel and others, 1996 and 2002; Petersen and others, 1996). These 

maps are produced by the USGS every 3 to 5 years and are the basis for seismic provisions in 

both the International Building Code and the International Residential Code. The faults shown 

in Figure 1 were determined to pose a quantifiable seismic hazard by a consensus of USGS, 

California Geological Survey, and outside experts. To fall into this category, they must have 

evidence of fault slip during the past 1.6 million years (a short time in geologic history) as well 

as a scientifically established rate of fault slip or a history of past earthquakes from evidence such 

as trenches excavated across faults. In general, the fault traces are better known and documented 

for onshore than for offshore faults. Therefore, we also show (in dashed black lines, Figure 1) 

recognized offshore faults that are not currently included in the National Seismic Hazard Maps 

and represent the result of additional research, e.g. Sorlien and others (2000); these faults may 

be included in future updates of the National Maps as more information on them is developed.

All faults shown on Figure 1 have the potential to produce M 6.5 or greater earthquakes that 

would result in locally strong ground shaking and some combination of ground-surface breaks, 

liquefaction of near surface sediments both onshore and offshore, landslide triggering of both 

coastal bluffs and underwater slopes, and generating tsunamis. These effects have occurred as the 

result of past earthquakes in this region and thus are expected to occur in future earthquakes.

The maximum magnitude of an earthquake is related to fault length: the longer the fault, the 

larger the potential earthquake can be (Wells and Coppersmith, 1994). For example, the Oak 

Ridge Fault offshore, which, as shown on the National Seismic Hazard Maps, runs near Platform 

Grace and parallel to a proposed pipeline connecting Platform Grace to the Southern California 

Gas Company facility; this fault is estimated to produce earthquakes as great as M 7.1. In 

comparison, the much longer Anacapa-Dume Fault, near Cabrillo Port, is thought to be capable 

of producing earthquakes as great as M 7.5 (for comparison, the great San Francisco 1906 

earthquake was M 7.8). As we learn more, connections between different faults are sometimes 

found, increasing total fault length and the sizes of potential earthquakes. The offshore region is 

more difficult to study, but acquiring additional high-resolution (“swath”) bathymetric data and 

seismic reflection data will help define fault structure, and sediment cores may help estimate fault 

slip rates and the times of past earthquakes.
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The offshore facilities and the offshore and on land pipeline routes will be subject to hazard 

from surface fault breaks during future large earthquakes on crossing or nearby faults. The 

faults in this region are thought to be capable of producing earthquakes as great as M 6.5 to 

7.5, which could produce surface offsets as large as 15 feet. New techniques, in conjunction 

with knowledge of prehistoric earthquake activity on these faults, make it possible to calculate 

the probabilities, amounts and locations of surface rupture affecting the proposed facilities and 

pipelines. However, these methods have not been widely applied yet, and, for many of the faults 

in the study area, little information exists, so such calculations would be highly uncertain unless 

additional studies could also be conducted on prehistoric faulting. 

The offshore portion of the Oak Ridge Fault runs very close to Platform Grace (Greene 

and others, 1978; Dahlen, 1992; Shaw and Suppe, 1994; Kamerling and Nicholson, 1996; 

Kamerling and others, 1998; Sorlien and others, 2000). The onshore portion of the Oak Ridge 

Fault appears to be the westward continuation of the thrust fault that caused the 1994 M 6.7 

Northridge earthquake (Yeats and Huftile, 1995). Onshore, the Oak Ridge Fault slips at about 

1.6 inches per decade, on a long-term average. Offshore, the National Seismic Hazard Maps 

distribute this slip across the more southerly Oak Ridge Fault (estimated at 1.2 inches per 

decade) and the Oakridge-Midchannel Fault trend estimated (at 0.4 inches per decade). Faultrelated compression may also be transferred to other nearby faults and folds in the Santa Barbara 

Channel (Yeats and others, 1988; Huftile and Yeats, 1995). During a large earthquake, surface 

rupture would not likely occur on the offshore Oak Ridge Fault because it is primarily a “blind” 

thrust fault; that means its main strands are below ground and do not clearly reach the seafloor. 

However, significant surface deformation, such as warping, and offset across mapped subsidiary 

structures (shown on figure 1), poses a significant hazard. A pipeline extending northward from 

Platform Grace to Carpenteria crosses the Oakridge-Midchannel Fault trend, the Red Mountain 

Fault Zone, and the Pitas Point Fault Zone (Yeats and others, 1987; Yerkes and others, 1987; 

Kamerling and Sorlien, 1999).

The moored Cabrillo Port would connect to shore via a pipeline across a major east-west fault 

system that includes, among others, the Santa Cruz Island Fault, the Anacapa-Dume Fault, and 

the Malibu Coast Fault (Ellsworth and others, 1973; Stierman and Ellsworth, 1976; Dibblee, 

1982; Dibblee and Ehrenspeck, 1993; Drumm, 1992). Although only the onshore segment of the 

Malibu Coast Fault was included in the National Seismic Hazard Maps, an offshore extension 

of this fault identified in other studies is shown in Figure 1 (Greene and Kennedy, 1986; Sorlien, 

1999; Sorlien and others, 2000). This fault system comprises numerous fault strands, including 

one or more deep thrust faults that might produce large earthquakes. As previously noted, the 

Anacapa-Dume Fault has the potential for producing the largest earthquakes in the region, up to 

M 7.5.

What potential hazards could result from shaking?

Strong shaking is the primary hazard that causes damage from earthquakes and this area has 

been zoned with a high level of seismic shaking hazard. The goal of the USGS National 
8

Seismic Hazard Mapping effort is to quantify the level of shaking that may occur with sufficient 

frequency that it should be considered in the development of building codes or the design of 

specific projects. For example, some of the maps show the amount of earthquake shaking with 

a 2% chance of being exceeded in 50 years. Thus, if a project is built to withstand this level of 

shaking, but no more, there would be a 2% chance of incurring damage during the next 50 years.

While the USGS provides estimates of the ground-shaking hazard for any probability level, 

engineers and public policy experts must decide on the appropriate probability level to be used in 

the design of a facility or project. This probability level is determined by the acceptable level of 

risk, which will vary depending on the consequences of structural failure. For example, the U.S. 

Nuclear Regulatory Commission now specifies a hazard level for nuclear power plants that has a 

probability 40 times stricter than the 2% in 50-year hazard level.

Figure 2a is a map of the estimated probability of having a magnitude 6.5 or larger earthquake 

within 30 miles of each location on the map in the next 30 years. For the Platform Grace site, the 

estimated probability is about 50 to 60%. The probability is about 35% for the moored Cabrillo 

Port site. The probabilities of moderate and large earthquakes increase inland, with probabilities 

of 60% or more along the on land pipeline route north of Ormond Beach. Thus, there is a high 

likelihood of having earthquakes somewhere in this region with M 6.5 or higher in the next 30 

years.

Figure 2b shows an expanded view of one of the USGS National Seismic Hazard Maps (Frankel 

and others, 2002). This map shows the peak acceleration of the shaking as a percent of the 

acceleration of gravity for the 2% in 50 years hazard level for a site on “firm rock” (as opposed 

to softer sediments). These maps represent a conservative estimate of the shaking hazard. For 

areas filled with soft sediment, such as coastal valleys, the expected shaking levels will be higher. 

The proposed facilities are in areas of high hazard from earthquake ground shaking. For example, 

near Cabrillo Port there is a 2% chance that there will be ground shaking of 60% or more of the 

acceleration of gravity (60%g) in the next 50 years. Higher values (around 85%g) are found for 

the Platform Grace site and 120%g is calculated along the proposed pipeline route northeast of 

Oxnard. The latter value is similar to the hazard along much of the San Andreas Fault. To put 

these numbers into context, the highest horizontal accelerations observed during the Northridge 

earthquake (M 6.7) were about 90% of the acceleration of gravity. Thus, there is a 2% chance 

in the next 50 years of much of this area experiencing ground motions equal to or higher than 

the highest ground motions observed during the Northridge earthquake. If a stricter risk level is 

chosen with lower probability, then the hazard assessment ground motions will increase.

There are additional factors that could increase the estimated ground-shaking hazard to the 

proposed facilities. For example, structures are prone to damage from shaking at their resonant 

period (the duration in seconds at which the structure preferentially oscillates when disturbed). 

Offshore platforms and storage tanks are large structures that can have relatively long resonant 

periods, in excess of 1 second. Compounding the earthquake hazard is the existence of “basin” 

waves, which are not included in the National Seismic Hazard Maps. Basin waves are seismic 

waves that echo inside the sediment that fills underground valleys in the harder bedrock, 

producing amplified shaking at long periods (e.g. Joyner, 2000). If these periods match the 
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60 10 miles

60

80

80

80

100

100

100

100

100

120

120 Oak R

160

idge

Oak Ridge - Midchannel

Pitas Point

Red Mountain

Anacapa - Dume

North Channel Slope

Santa Ynez

Malibu Coast

Northridge

Oak Ridge

Simi -``Santa Rosa

119°40'0"W 119°20'0"W 119°0'0"W 118°40'0"W

34°20'0"N 34°00'0"N

Camarillo

Santa Barbara

Ventura

Malibu

Port Hueneme

Pacific Ocean

Santa Barbara Channel

Santa Cruz Island

Oxnard

Simi Valley

Grace

Cabrillo

0

4

6

8

10

12

14

16

18

20

30

40

50

60

80

100

120

160

200

300

%g

10 miles

Camarillo

Santa Barbara

Ventura

Malibu

Port Hueneme

Pacific Ocean

Santa Barbara Channel

Santa Cruz Island

Oxnard

Simi Valley

Grace

Cabrillo

Oak Ridge

Oak Ridge - Midchannel

Pitas Point

Red Mountain

Anacapa - Dume

North Channel Slope

Santa Ynez

Malibu Coast

Northridge

Simi - Santa Rosa

Oak Ridge

119°40'0"W 119°20'0"W 119°0'0"W 118°40'0"W

34°20'0"N 34°00'0"N

10

20

30

40

50

60

70

80

90

Prob. %

Figure 2a. Percent probability of a magnitude 6.5 or greater earthquake within

30 years and 50 km (31 miles). Only faults used in the National Seismic Hazard

Maps are shown (Petersen and others, 1996).

Figure 2b. Earthquake ground motion (peak acceleration) as a percent of the

acceleration of gravity with a 2% chance of being exceeded in 50 years. Data

and faults from USGS National Seismic Hazard Map, firm rock site condition

(Frankel and others, 2002).
10

resonant frequencies of the structures, then the hazard increases for these structures. For 

example, an earthquake recording from a site offshore of Long Beach of waves traversing the 

Los Angeles Basin contains substantial energy at periods as long as 7 seconds (Boore, 1999); 

therefore, large structures offshore of Long Beach with resonant periods in this range would face 

greater hazards than represented in the hazard maps. Structures in the Santa Monica Basin might 

similarly be subject to basin wave effects. Another concern for structures with long resonant 

periods is that they can be influenced by large earthquakes at relatively great distance from the 

site; this effect is also not well represented in the maps. For example, a repeat of the 1857 Fort 

Tejon earthquake on the San Andreas Fault would produce long period motion in the project 

area. If the proposed LNG facilities contain platforms, tanks or pipelines with long resonant 

periods, then these factors must be considered to determine if they are applicable to the specific 

sites.

It is important to emphasize the uncertainties in the parameters used to make these hazard 

assessments. The locations and subsurface geometry of the offshore faults are poorly known. The 

slip rates of these faults are also poorly constrained, so that estimates of earthquake recurrence 

rates are poorly determined. In the hazard maps, alternative models of faulting are used to reflect 

differing views by various geoscientists. For example, it is not known how much of the slip on 

these faults occurs during earthquakes and how much may be due to slow movement on faults 

that does not produce shaking.

Which specific earthquake hazards should be considered in more detail?

(In answering, we also discuss related geologic hazards)

Engineering Foundation Stability, Ground Failure, and Liquefaction

The potential for earthquake-induced liquefaction of wet and loose sandy material and several 

other potential causes of instability should be addressed for this project. Portions of the proposed 

projects may be developed on coastal areas of artificial fill, which generally performs poorly 

during earthquakes if not properly engineered. For example, liquefaction of artificial fills in the 

coastal town of Oceano, California, caused significant damage to buildings and lifelines despite 

being 30 miles from the 2003 M 6.5 San Simeon earthquake. Other portions of the proposed 

projects may be developed on naturally deposited sediments with similarly poor performance 

during earthquakes. For example, sandy continental shelf deposits in the Klamath Delta area of 

far northern California liquefied and flowed during a 1980 M 7.0 earthquake. The flow failures 

produced a 3 to 6 foot high scarp. Such failures could also occur on the continental shelf of the 

Santa Barbara Channel and might impact offshore pipelines. Thus, it is necessary to assess the 

ability of underlying geologic materials and fills to stably support the foundations of buried and 

surface engineered structures.

When soils liquefy during strong shaking, horizontal displacements as large as tens of feet 

may occur and are especially damaging to buried utilities and unsupported foundations. The 

venting of ground water as it is expelled from the liquefied sands can unevenly displace and tilt 

foundations, affecting both buried and surface structures. In addition, large areas that are only 
11

slightly above sea level could lose elevation and be submerged. Clayey soils do not liquefy but 

may also be subject to large displacements due to earthquake shaking. Earthquake-induced 

displacements and cracking may also occur at boundaries between different soils and between 

soil and rock. Geologically young clay soils, like bay mud, may consolidate slowly when 

subjected to loads from new structures, causing these structures to settle. This process involves 

the slow expulsion of pore water and can occur over decades.

The onshore section of the pipeline from Platform Grace to the distribution facilities may require 

special care in engineering and design due to liquefaction and ground failure hazards. This is 

because the proposed onshore pipeline parallels both the Oak Ridge Fault and the Santa Clara 

River channel for 6 miles. This entire onshore section of the pipeline runs through recently 

deposited sediments that are identified by the California Geological Survey for their potential 

liquefaction hazard during seismically induced shaking. The Santa Clara River channel is 

particularly susceptible to liquefaction and other forms of ground failure, and is also close to the 

mapped trace of the Oak Ridge Fault, making it particularly important to address these hazards 

there.

For all of these aspects of foundation stability, routine and well-developed site investigation 

techniques are available to characterize the physical properties of soils, and widely accepted 

geotechnical engineering models exist to evaluate potential deformation hazards.

Submarine Landsides 

Multibeam bathymetric imaging of the Santa Barbara Channel has shown the remains of a 

number of very large submarine landslides (Eichhubl and others, 2002). The largest is located 

offshore of Goleta and 18 miles west of Platform Grace; the “Goleta Slide” measures 8.5 miles 

long and 6.5 miles wide, and probably occurred within the past 6000 years. Mathematical 

modeling indicates that when this landslide occurred, it could have generated a tsunami with a 

height at the coast ranging from 6 to 65 feet (Borrero and others, 2001). There are also buried 

remains of other landslides. The estimated recurrence interval for these very large landslides is 

about 15,000 years (Lee and others, 2004).

Several medium-sized submarine landslide deposits also exist in Santa Barbara Channel; the best 

known is the Gaviota Slide (Lee and others, 2004). This slide, 28 miles west of Platform Grace, 

measures over a mile on each side and likely occurred in the last 300 years. It may have been 

triggered by the 1812 Santa Barbara earthquake.

The area near Platform Grace has not been mapped using high-resolution bathymetric 

(“multibeam”) techniques, so the existence of small to medium-sized submarine landslide 

deposits cannot be discerned. This platform does lie on a 150-m high slope near a submerged 

channel, so there is some possibility of a slope failure at the site. Multibeam mapping and slope 

stability analysis for this site should be conducted to identify previous failures and determine the 

risk of future failures. Currently available low-resolution bathymetric data show that pipelines 

connecting Platform Grace to the shore pass through generally flat seafloor areas that are 
12

probably unlikely locations for large submarine landslides. However, we cannot fully assess the 

hazard of smaller landslides without higher resolution data. Therefore, because submarine slope 

failure hazards may still exist, surveys for pipeline routes should include multibeam bathymetric 

imagery and slope stability analysis.

Turbidity Currents and Debris Flows

All of the proposed pipelines extending on land from Cabrillo Port cross the delta of the Santa 

Clara River (Dahlen and others, 1990), exposing them to hazards from mass movements of loose 

sediment and rock slurries (known as turbidity currents and debris flows). The delta, a large 

undersea pile of sediment, fed by the Santa Clara River, is cut by five north-south canyons on the 

delta slope. The Hueneme Canyon, largest and most active of the five, is the major conduit for 

turbidity currents and debris flows (Normark and others, 1998; Piper and others, 1999). Figure 1 

shows Hueneme and Mugu Canyons, the outermost of the five.

Some river systems, including the Santa Clara River, carry substantial sediment in suspension 

during major flood events, and commonly this slurry of fresh river water and sediment is 

denser than sea water (Warrick and Milliman, 2003). When this occurs, gravity pulls the slurry 

downslope, forming high-speed turbulent flows known as hyperpycnal flows, which are a type of 

turbidity current (Mulder and Syvitski, 1995). Turbidity currents, especially on steeper slopes in 

submarine canyons, move with such speed and power that the only comparable on land processes 

are the catastrophic volcanic flows that rush down the flanks of volcanoes during explosive 

eruptions. A turbidity current in the Laurentian Fan, off of Nova Scotia, broke submarine 

telecommunications cables and is thought to have traveled at 45 miles per hour (see review of 

turbidity current processes in Normark and Piper, 1991). The Santa Monica Basin has less relief 

than the Laurentian Fan, so turbidity currents there would not reach the same speed. Reynolds 

(1987) documents a turbidity current event in the Santa Monica Basin about 100 years ago that 

transported more than a million cubic yards of sediment at speeds of 2 miles per hour. This 

event is suggested to have resulted from the southern California flood of 1884. A much larger 

turbidity current that transported more than 10 million cubic yards of sediment occurred about 

200 years ago; it transported coarser (larger grain-size) sediment and its velocity must have been 

substantially greater (Malouta and others, 1981). This earlier event is suggested to have been 

generated as a result of sediment failure during the 1812 Santa Barbara earthquake.

Turbidity currents capable of transporting sand-sized sediment more than 35 miles from the 

Hueneme Canyon to the basin floor have occurred about every 200 years on average during the 

last 3000 years (Normark and McGann, 2004). Triggered commonly by earthquakes and large 

storms, these flows are typically 150 feet high (Piper and others, 2003). The proposed site for 

the Cabrillo Port facility is directly in the path of such energetic flows. Several of the smaller 

canyons on the delta slope east of Hueneme Canyon are filled by deposits of past debris flows up 

to 35 feet thick (Piper and others, 1999). These debris flows were probably generated by seismic 

shaking from nearby earthquakes. All of the proposed pipeline routes to move gas from Cabrillo 
13

Port to the coast cross one or more of the canyons and channels on the young and still active 

submarine delta slope.

Improved assessment of the hazards from these turbidity currents and debris flows will require 

research to answer the following questions. How stable are the deep channels cut into the 

submarine delta? How often do large storms, such as those related to El Niño

events, create hyperpycnal flows? How often do earthquakes cause debris flows and turbidity 

currents? How often do submarine landslides cause debris flows and turbidity currents? How 

can pipeline design protect against hazards from thick, energetic turbidity currents and muddy 

debris flows?

What is the vulnerability of offshore LNG facilities to tsunamis generated by nearby 

offshore earthquakes or potentially large coastal bluff landslides?

The coastal region of Ventura and Santa Barbara Counties has been impacted by tsunamis from 

a variety of sources in the past (Lander, Lockridge, and Kozuch, 1993) and, thus, hazards from 

future tsunamis could potentially affect proposed LNG sites. A tsunami is a series of waves 

whose height increases as water depth shallows. In the deep, open ocean, their height will only 

be a few feet and they are unrecognizable. However, they grow as they approach shore, and they 

can reach heights exceeding 100 feet in coastal waters. Hazards from tsunamis include: (1) runup 

where tsunami waves wash ashore at heights above normal wave action, and (2) strong currents 

that can affect marine terminals. 

Tsunamis can be generated by very large magnitude earthquakes distant from the site (termed 

far-field tsunamis) or from local submarine earthquakes and landslides near the site (termed local 

tsunamis). An example of a far-field or trans-oceanic tsunami is the one generated by the 1964 

M 9.2 Alaska earthquake that caused considerable damage along much of the west coast of the 

United States (Lander, Lockridge, and Kozuch, 1993). In southern California, this tsunami was 

observed as multiple surges as high as 10 feet accompanied by very strong currents. The latter 

caused most of the damage in ports and harbors, with smaller boats capsizing and larger ships 

ramming into docks and piers. In Los Angeles harbor, an oil tanker ripped out a 175-foot section 

of dock. A local M 5.2 earthquake in 1930 was followed by a tsunami with 20 feet of runup 

in Santa Monica, which caused a fatality in Redondo Beach (Lander, Lockridge, and Kozuch, 

1993); the tsunami was probably caused by a submarine landslide triggered by the earthquake.

The inter-agency National Tsunami Hazard Mitigation Program (NTHMP), which includes the 

National Oceanic and Atmospheric Administration (NOAA), the USGS, the Federal Emergency 

Management Agency (FEMA), the National Science Foundation (NSF), and the five western 

Pacific states, is dedicated to mitigating tsunami hazards in the U.S. (http://www.pmel.noaa.

gov/tsunami-hazard/). The NTHMP develops tsunami inundation maps, showing regions 

near the ocean that are likely to be flooded during a major tsunami (González and others, 

2001). They are used primarily to determine evacuation routes and in long-term planning for 

vulnerable coastal communities. Preliminary inundation maps have been completed for Los 

Angeles, Ventura, and Santa Barbara counties, and are in development for San Luis Obispo 
14

County (Eisner, Borrero, and Synolakis, 2001). In addition, a FEMA study has been undertaken 

jointly by the Marine Facilities Division of the California State Lands Commission and the 

University of Southern California to develop standards and guidelines for marine terminals in 

Los Angeles, Ventura and Orange Counties (Synolakis, Eskijian, and others, 2003). 100-year and 

500-year tsunami probabilities were estimated in a 1974 U.S. Army Corps of Engineers Report 

(see Eisner, Borrero, and Synolakis, 2001) for Ventura at 10.5 feet and 21.7 feet, respectively. 

These estimates, however, need considerable refinement given the current state of knowledge of 

tsunami generation and dynamics and are the subject of an ongoing FEMA-sponsored pilot study 

for the National Flood Insurance Program that involves members of the NTHMP.

Improving the tsunami hazard assessments will require making detailed inundation maps 

for engineering assessment of specific marine facilities. This includes determining accurate 

wave heights and currents at higher spatial resolution (165 feet or less) than used for the 

current inundation maps. Tsunami probabilities also need to be refined in line with current 

understanding of tsunami generation and modeling capabilities.

Please describe the scope of any additional studies that may be needed for evaluation of 

both proposals.

Beyond the issues raised above, additional research is needed to reduce uncertainties in the 

hazard assessments:

• Global Positioning System (GPS) measurements to provide the overall rate of tectonic 

compression across the region in order to constrain the expected rate of large earthquakes. 

• Geophysical and sonar studies to identify, map, and characterize the underwater traces of 

the faults. 

• Determining the chronology of prehistoric earthquakes and fault slip rates through 

trenching studies on land and sediment coring offshore. Knowledge of the rates of these 

past earthquakes reduces the uncertainty in the earthquake probabilities. 

• Detailed mapping of soil and sediment layers in targeted coastal regions to develop a 

chronology of large prehistoric tsunamis and determine the potential for ground failure 

and liquefaction. 

• High-resolution topographic mapping using airborne lasers (LIDAR) to locate active faults 

on land, and possibly to map subtle landscape features indicative of blind faults. The 

LIDAR data are also used to identify places on these faults suitable for trenching studies.

• Offshore high-resolution multibeam bathymetric data to locate active faults on the 

seafloor and identify past landslides. Figure 3a shows the existing multibeam bathymetric 

coverage in this region; the area around Platform Grace is scheduled to be collected in 

August, 2004 (a joint USGS-Minerals Management Service project) but important gaps 

will remain over Cabrillo Port and parts of the pipeline routes.
15

Figure 3 a. Coverage of existing multibeam bathymetric data in study area (MBARI, 2001; Gardner

and Dartnell, 2002). b. Tracklines of seismic reflection data collected by Western Geco (USGS,

2004c). Shaded relief basemap generated from NOAA (2004) data.

Cabrillo

Grace

Malibu

Oxnard

Newhall

Ventura

Camarillo

Simi Valley

Port Hueneme

Santa Barbara

Thousand Oaks

119 40'0"W 119 20'0"W 119 0'0"W 118 40'0"W

34 0'0"N 34 20'0"N

Mercator Projection, NAD 83

20 Kilometers

Santa Clara R.

Los Angeles

Ventura

15 Miles

Explanation

Cabrillo Port

Platform Grace

proposed pipeline

existing pipeline

alternate route

W-23-81-SC

W-30-81-SC

W-5-82-SC

W-33-82-SC

W-36-83-SC

W-37-84-SC

W-40-85-SC

5

101

b.

Cabrillo

Grace

121 0'0"W 120 0'0"W 119 0'0"W

34 0'0"N

Mercator Projection, NAD 83

20 Kilometers

Santa Clara R.

Explanation

Cabrillo Port

Platform Grace

proposed pipeline

existing pipeline

alternate route

Aug 04 multibeam

survey

Existing multibeam

bathymetry data

Los An geles

Ventura

15 Miles

5

101

Santa Barbara

a.

34 30'0"N
16

• Utilization of marine seismic reflection data, collected by private industry along the

west coast in the 1970’s and 1980’s for oil and gas exploration, to improve our

knowledge of the location and subsurface geometry of offshore faults (and hence

their earthquake potential). The USGS is currently involved in efforts to rescue

these data (Figure 3b and http://walrus.wr.usgs.gov/NAMSS/), which is critical

because they are irreplaceable due to new environmental restrictions on the use of

marine seismic sources such as airguns. The rescue efforts cost much less than 1%

of what it would cost to collect the data again and will insure that this priceless

resource is available to the public.

Acknowledgments

This document was greatly improved through reviews by Samuel Johnson and Mary Lou 

Zoback, and by additional advice from David Applegate, James Devine, William Ellsworth,

Lucile Jones, Andrew Michael, and Bruce Rogers. Stephen Harmsen provided the

earthquake probability map, Figure 2a. We thank Michael Diggles for formatting the web 

version and Carolyn Donlin for additional web support.

References

Boore, D.M., 1999, Basin waves on a seafloor recording of the 1990 Upland, California,

earthquake: Implications for ground motions from a larger earthquake, Bull. Seism.

Soc. Am, v. 89, p. 317-324.

Borrero, J. C., Dolan, J. F., Synolakis, C. E., 2001. Tsunamis within the eastern Santa

Barbara Channel. Geophy. Res. Let., 28, pp.643-646.

Dahlen, M. Z., 1992, Sequence Stratigraphy, depositional history, and middle to late

Quaternary sea levels of the Ventura shelf, California: Quaternary Research, v. 38,

p. 234-245.

Dahlen, M. Z., Osborne, R. H., and Gorsline, D. S., 1990, Late Quaternary history of the

Ventura mainland shelf, California: Marine Geology, v. 94, p. 317-340.

Dewey, J. W., Dengler, L., and Reagor, B. G., 1995, Spatial variations of intensity in the

Northridge earthquake, in The Northridge, California, Earthquake of 17 January,

1994, ed. Woods, M.C., and Seiple, W. R., California Division of Mines and 

Geology Special Publication 116, p. 39-46.

Dibblee, T. W., 1982, Geology of the Santa Monica Mountains and Simi Hills, southern 

California, in Fife, D. L., and Minch, J. A., eds., Geology and mineral wealth of the

California Transverse Ranges: Santa Ana, CA, South Coast Geological Society,

Inc., p. 94-130.

Dibblee, T. W., and Ehrenspeck, H. E., 1993, Geologic map of the Point Dume quadrangle

Los Angeles and Ventura Counties, California: Dibblee Geological Foundation 

Map #DF-48, p. 1 sheet.

Drumm, P. L., 1992, Holocene displacement of the central splay of the Malibu Coast fault

zone, Latigo Canyon, Malibu, in Pipkin, B. W., and Proctor, R. J., eds.,

Engineering Geology Practice in southern California, Special Publication 4,

Association of Engineering Geologists: Belmont, CA, Star Publishing Company, p.

247-254.
17

Eichhubl, P., Greene, H.G. and N. Maher, N., 2002. Physiography of an active transpressive 

margin basin; high-resolution bathymetry of the Santa Barbara Basin, southern California 

continental borderland. Mar. Geol., 184, 95-120.

Eisner, R.K., Borrero, J.C., and Synolakis, C.E., 2001, Inundation maps for the State of 

California, in International Tsunami Symposium 2001, Seattle, WA, p. 67-81.

Ellsworth, 1990, Earthquake history, 1769-1989, in The San Andreas Fault System, California, 

ed. Wallace, R.E., USGS Professional Paper 1515, p. 153-188.

Ellsworth, W. L., Campbell, R. H., Hill, D. P., Page, R. A., Alewine, R. W., Hanks, T. C., Heaton, 

T. H., Hileman, J. A., Kanamori, H., Minster, B., and Whitcomb, J. H., 1973, Point 

Mugu, California, earthquake of 21 February 1973 and its aftershocks: Science, v. 182, p. 

1127-1129.

Frankel, A., Mueller, C., Barnhard, T., Perkins, D., Leyendecker, E., Dickman, N., Hanson, S., 

and Hopper, M., 1996. National seismic-hazard maps: documentation June 1996, USGS 

Open-file Report 96-532, 110 pp.

Frankel, A., Petersen, M., Mueller, C., Haller, K., Wheeler, R., Leyendecker, E., Wesson, R., 

Harmsen, S., Cramer, C., Perkins, D., and Rukstales, K., 2002, Documentation for the 

2002 update of the national seismic hazard maps: U.S. Geological Survey Open-File 

Report 02-420, 39 pages, http://pubs.usgs.gov/of/2002/ofr-02-420/

Gardner, J. V., and Dartnell, P., 2002, Multibeam Mapping of the Los Angeles, California 

Margin: U.S. Geological Survey Open-file Report 02-162, http://geopubs.wr.usgs.gov/

open-file/of02-162/

González, F.I., Titov, V.V., Mofjeld, H.O., Venturato, A.J., and Newman, J.C., 2001, The 

NTHMP Inundation Mapping Program, in International Tsunami Symposium 2001, 

Seattle, WA, p. 29-54.

Greene, H. G., and Kennedy, M. P., 1986, Geology of the mid-southern California continental 

margin, California Continental Margin Geologic Map Series, Area 2, California 

Department of Conservation, Division of Mines and Geology, 4 sheets 

Greene, H. G., Wolf, S. C., and Blom, K. G., 1978, The marine geology of the eastern Santa 

Barbara Channel with particular emphasis on the ground water basins offshore from the 

Oxnard plain, southern California: U.S. Geological Survey Open-file report 78-305, p. 

104 p.

Huftile, G. J., and Yeats, R. S., 1995, Convergence rates across a displacement transfer zone in 

the western Transverse Ranges, Ventura basin, California: Journal Geophysical Research, 

v. 100, p. 2043-2067.

Joyner, W.B., 2000, Strong motion from surface waves in deep sedimentary basins, Bull. Seism. 

Soc. Am, v. 90, p. S95--S112. 

Kamerling, M., and Nicholson, C., 1996, The Oak Ridge fault and fold system, eastern Santa 

Barbara Channel, California: Southern California Earthquake Center Annual Report, v. 

11, p. C26-C30.

Kamerling, M. J., Sorlien, C., and Alex, C. M., 1998, Map restoration of a Quaternary horizon 

across the Oak Ridge fault, offshore and onshore Ventura Basin, California: American 

Association Petroleum Geologists Bulletin, v. 82, p. 850.

Kamerling, M. J., and Sorlien, C. C., 1999, Quaternary slip and geometry of the Red Mountain 

and Pitas Point-North Channel faults, California: Eos, Transactions, American 

Geophysical Union, v. 80(46), p. 1003.
18

Lander, J.F., ed., 1973, Seismological Notes: January - February 1973. Bulletin of the 

Seismological Society of America, Vol. 63, No. 5, pp. 1841-1846.

Lander, J.F., Lockridge, P.A., and Kozuch, M.J., 1993, Tsunamis affecting the west coast of 

the United States 1806-1992: U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, NGDC Key to Geophysical Records Documentation No. 

29, 242 p.

Lee, H.J., Normark, W.R., Fisher, M.A., Greene, H.G., Brian D. Edwards, B.D.; and Locat, 

J., 2004. Timing and Extent of Submarine Landslides in Southern California, Offshore 

Technology Conference Paper Number 16744, Houston, TX.

Malouta, D. N., Gorsline, D. S., and Thornton, S. E., 1981, Processes and rates of Recent 

(Holocene) basin filling in an active transform margin: Santa Monica Basin, California 

Continental Borderland. Journal Sedimentary Petrology, v. 51, p. 1077-1096.

Monterey Bay Aquarium Research Institute (MBARI), 2001, Santa Barbara Multibeam Survey: 

MBARI Digital Data Series No. 4, http://mbari.org/data/mapping/SBBasin/default.htm

Mulder, T., and Syvitski, J. P. M., 1995, Turbidity currents generated at mouths of rivers during 

exceptional discharges to the world oceans, Journal of Geology, v. 103, p. 285-299.

National Oceanic and Atmospheric Administration (NOAA), 2004, Coastal Relief Model http://

www.ngdc.noaa.gov/mgg/coastal/coastal.html

Normark, W. R., and McGann, M., in press, Late Quaternary deposition in the inner basins of the 

California Continental Borderland: Part A. Santa Monica Basin, U.S. Geological Survey 

Scientific Investigations Report, 2004-XXXX.

Normark, W. R. and Piper, D. J. W., 1991, Initiation processes and flow evolution of turbidity 

currents: implications for the depositional record, in Osborne, R. H. (ed), From Shoreline 

to Abyss, SEPM Special Publication No. 46, p. 207-230.

Normark, W. R., Piper. D. J. W., and Hiscott, R. N., 1998, Sea level controls on the textural 

characteristics and depositional architecture of the Hueneme and associated submarine 

fan systems, Santa Monica Basin, California, Sedimentology, v. 45, p. 53-70. 

Petersen, M. D., Bryant, W. A., Cramer, C. H., Cao, T., Reichle, M. S., Frankel, A. D., 

Lienkaemper, J. J., McCrory, P. A., and Schwartz, D. P., 1996, Probabilistic Seismic 

Hazard Assessment for the State of California, DMG Open-File Report 96-08 and USGS 

Open-File Report 96-706, 64 p., http://pubs.er.usgs.gov/pubs/ofr/ofr96706

Piper, D. J. W., Hiscott, R. N., and Normark, W. R., 1999, Outcrop-scale acoustic facies analysis 

and latest Quaternary development of Hueneme and Dume submarine fans, offshore 

California, Sedimentology, v. 46, p. 47-78.

Piper, D. J. W., Normark, W. R., and McGann, M., 2003, Variations in accumulation rate of late 

Quaternary turbidite deposits in Santa Monica Basin, offshore southern California: Eos 

Trans. AGU, 84(46), Fall Meet. Suppl., Abstract OS52B-0916.

Reynolds, S., 1987, A recent turbidity current event, Hueneme fan, California: reconstruction of 

flow properties: Sedimentology, v.34, p.129-137.

Shaw, J. H., and Suppe, J., 1994, Active faulting and growth folding in the eastern Santa Barbara 

Channel, California: Geological Society America Bulletin, v. 106, p. 607-626.

Sorlien, C. C., 1999, Rapid subsidence and south propagation of the active Santa Monica 

Mountains-Channel Islands thrust: Annual Report Southern California Earthquake 

Center, v. Available on the Internet at: http://www.scec.org/research/99research/, p. 5 p.
19

Sorlien, C. C., Gratier, J. P., Luyendyk, B. P., Hornafius, J. S., and Hopps, T. E., 2000, Map 

restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore 

and offshore Ventura basin, California: Geological Society America Bulletin, v. 112, p. 

1080-1090.

Southern California Earthquake Center Data Center (SCEC), 2004, Southern California catalogs: 

http://www.data.scec.org/catalog_search/

Stierman, D. J., and Ellsworth, W. L., 1976, Aftershocks of the February 21, 1973 Point Mugu, 

California earthquake: Bulletin Seismological Society America, v. 66, p. 1931-1952.

Synolakis, C.E., Eskijian, M., Borrero, J.C., and McCarthy, D., 2003, NEES tsunami “product” 

example: Standards and guidelines for construction of coastal structures [abs.]: Eos, 

Transactions American Geophysical Union, v. 84, p. F804-F805.

Townley, S. D., 1939, Earthquakes in California, 1769 to 1928. Bulletin of the Seismological 

Society of America, Vol. 29, No. 1, pp. 21-252.

Ulrich, F. P., 1941, The Imperial Valley Earthquakes of 1940. Bulletin of the Seismological 

Society of America, Vol. 31, No. 1, pp. 13-31, Figures 3, 7b, 10, 11, 14.

U.S. Geological Survey, 2004a, Quaternary Faults and Fold Database of the United States: http://

qfaults.cr.usgs.gov/

U.S. Geological Survey, 2004b, California Earthquake History 1769-Present: http://pasadena.

wr.usgs.gov/info/cahist_eqs.html

U.S. Geological Survey, 2004c, National Archive of Marine Seismic Surveys, WesternGeco 

Southern California Tracklines: http://walrus.wr.usgs.gov/NAMSS/wgtrackline_scs.html

Warrick, J. A., and Milliman, J. D., 2003, Hyperpycnal sediment discharge from semiarid 

southern California rivers: implications for coast sediment budgets. Geology, v. 31, p. 

781-784.

Weber, F. H., and Kiessling, E. W., 1975, General features of seismic hazards of Ventura County, 

California, in Seismic Hazards Study of Ventura County, California, California Division 

of Mines and Geology Open-File Report 76-5 L A, p. 8-218. 

Weber, F. H., and Kiessling, E. W., 1978, Historic earthquakes effects in Ventura County, 

California Geology, v. 31, p. 103-107.

Wells, D. L., and Coppersmith, K. J., 1994, New empirical relationships among magnitude, 

rupture length, rupture width, rupture area, and surface displacement: Bulletin 

Seismological Society America, v. 84, p. 974-1002.

Willis, Bailey, 1925, A Study of the Santa Barbara Earthquake of June 29, 1925. Bulletin of the 

Seismological Society of America, Vol. 15, No. 4, pp. 255-278.

Yeats, R. S., 1988, Late Quaternary slip rate on the Oak Ridge fault, Transverse Ranges, 

California: Implications for seismic risk: Journal of Geophysical Research, v. 93, p. 

12,137-12,150.

Yeats, R. S., and Huftile, G. J., 1995, The Oak Ridge fault system and the 1994 Northridge 

earthquake: Nature, v. 373, p. 418-420.

Yeats, R. S., Huftile, G. J., and Grigsby, F. B., 1988, Oak Ridge fault, Ventura fold belt, and the 

Sisar decollement, Ventura basin, California: Geology, v. 16, p. 1112-1116.

Yeats, R. S., Lee, W. H. K., and Yerkes, R. F., 1987, Geology and seismicity of the eastern Red 

Mountain Fault, Ventura County: U. S. Geological Survey Professional Paper 1339, p. 

161-167.
20

Yerkes, R. F., Sarna-Wojcicki, A. M., and LaJoie, K. R., 1987, Geology and Quaternary 

deformation of the Ventura area: in Recent reverse faulting in the Transverse Ranges, 

California: U.S. Geological Survey Professional Paper 1339, p. 169-178.