City of Malibu, CA Existing Conditions

Faulting and Seismicity: The recently published foreword from "California at Risk, Reducing Earthquake Hazards 1992-1996" explains the State viewpoint on the importance of recognizing seismic hazards with the following:

It is government's primary duty to assure public safety. No California jurisdiction would ignore a major toxic spill threat, a big fire hazard, or any other such "clear and present danger." While the dangers posed by earthquakes are clear, many of the responsible government officials do not see them as clearly present and immediately threatening. Thus it is essential to emphasize the earthquake danger to public safety and economic stability. This ever-present hazard can be reduced and emergency response strengthened.

The State of California has aggressively embarked on its goal to significantly improve earthquake safety by the year 2000. An agenda of initiatives has been established that will involve dozens of state agencies, local agencies, the private sector, and volunteer groups. The state program includes 42 initiatives in five categories:

1.	Addressing the hazards associated with existing vulnerable facilities, including utility and transportation systems as well as buildings;
2.	Improving the seismic resistance of new facilities;
3.	Improving management of the emergency response and relief efforts;
4.	Improving disaster recovery; and
5.	Supporting research and public information and education.

The important initiatives that have resulted from the October 17, 1989, Loma Prieta earthquake in the San Francisco area are a clue to some of the important issues which could be important to Malibu as follows:

•	Initiative 1.1: Establish seismic evaluation and retrofit building standards.
•	Initiative 1.3: Improve safety of older public school buildings.
•	Initiative 1.8: Improve safety of homes. Improper wall bracing and anchorage can lead to condemned buildings and the number of homeless following a major quake.
•	Initiative 1.9: Improve safety of mobile homes.
•	Initiative 1.11: Reduce work-place hazards. Furniture, equipment, and stock often are not secured, causing loss of function, hazards to employees, and significant damage.
•	Initiative 1.16: Improve earthquake performance of transportation structures. A major effort is required to retrofit highway bridges.
•	Initiative 2.2: Map geologic hazards.
•	Initiative 3.1: Improve emergency communications systems.
•	Initiative 3.6: Improve shelter planning. Urban earthquake victims require shelter services for a longer period than victims of other disasters.
•	Initiative 4.1: Implement recovery guidelines.

In addition to the above, a review of the Initiatives in the "California at Risk, Reducing Earthquake Hazards 1992-1996" also outlines numerous other state initiatives which can serve as guidelines for the City of Malibu when picking its priorities. Summaries of these important initiatives have been reproduced in the Safety Element Background Report in Appendix B, Summary Of California Seismic Safety Commission Initiatives, 1992-1996. Actual State legislation which may affect Malibu is summarized in Appendix C, Legislation: The Last Five Years.

There are numerous faults surrounding and traversing the Malibu area, including the Malibu Coast Fault, the Santa Monica Fault, the Las Flores Reverse Fault, and the Anacapa Fault. These faults are not well defined as they are not generally visible on the surface. Maps provided in the Background Report to Safety Element of the General Plan delineate a 1,000-foot area on either side of all faults as areas which could be subject to seismic hazard; see also Figures S-2 and S-3.

The location, geometry, sense of displacement and magnitude of maximum credible earthquake (MCE) events along the following regional faults, each of which may generate strong ground shaking impacting the Malibu area, are described below. (The Maximum Credible Earthquake Event is the worst-case design earthquake magnitudes.) Historical and predicted maximum earthquake magnitudes are given as moment rather than the historically more common Richter magnitude, since the former is generally accepted as a better estimate of the seismic energy released during an earthquake because it is calculated from the actual physical dimensions of a fault zone (Wesnousky, 1986; Joyner and Fumal, 1985).

San Andreas Fault

Although it lies 81.5 miles east of the Malibu area, the southern segment of the San Andreas fault, running from Tejon Pass to Cajon Pass, is considered capable of generating a maximum 8.0 magnitude earthquake which could generate significant ground shaking in the City of Malibu. This design earthquake is supported by the historical record, including the great 1857 Fort Tejon earthquake, estimated at 7.9 magnitude, and the more recent 1992 Landers earthquake of magnitude 7.4. The San Andreas fault has strike-slip displacement, and a well-documented mean recurrence interval of approximately 130 years for great earthquakes. Recent data suggest that such large events may actually occur in temporal "clusters" separated by much larger time periods on the order of 300 to 400 years apart (Sieh, 1984; 1989).

Anacapa (Dume)-Santa Monica Fault Zone

Originally recognized on the basis of bathymetric contours in Santa Monica Bay, the Anacapa or Dume fault is a near-vertical offshore escarpment exceeding 600 meters locally, with a total length exceeding 62 miles (Yerkes and Wentworth, 1965; Junger and Wagner, 1977). It occurs as close as 3.6 miles offshore south of Malibu at its western end, but trends northeast where it apparently merges with the offshore segment(s) of the Santa Monica Fault Zone, thus lying as close as two miles south of the Malibu Beach/Carbon Beach area. This fault is assumed responsible for generating the historic 1930 M5.2 Santa Monica earthquake, the 1973 M5.3 Point Mugu earthquake, and the 1979 and 1989 Malibu earthquakes, each of which possessed a magnitude of 5.0 (Ziony and Yerkes, 1985; Hauksson, 1990). Analyses of the first-motion seismic waves produced by these latter three earthquake events suggests that the faults which produced them were north-dipping structures, and that the earthquakes resulted from south-vergent compression of the crust (Stierman and Ellsworth, 1976; Hauksson and Saldivar, 1986; 1989). Such studies are termed "first-motion" or "focal mechanism" solutions for the earthquakes, and suggest that the Anacapa fault is a south-vergent thrust fault. Because the Anacapa fault appears to truncate the northwest-striking, strike-slip Palos Verdes Fault Zone of Peninsular Ranges affinity, the former fault is considered the present-day southern margin of the zone of thrust faults which punctuate the Transverse Ranges province.

The Santa Monica Fault

The Santa Monica fault is interpreted as a 25 mile long zone with physiographic up-to-the-north scarp features along its trace which imply at least Late Quaternary displacement (Weber, 1980; Crook et al, 1983). The fault is truncated eastward by the Newport-Inglewood zone, implying that the latter behaves as a tear fault and possibly a segment boundary (Dolan and Sieh, 1992). Focal mechanism solutions of small-magnitude (micro seismicity) earthquakes at the eastern end of this fault suggest that it is active (Ziony and Yerkes, 1985) as a thrust fault with a minor component of left-lateral horizontal displacement; evidence for this left-lateral component can be seen in a series of en echelon left-stepping fault scarps (Dolan and Sieh, 1992). Hauksson (190) considers the Anacapa/Santa Monica fault zone as the westernmost segment of the Elysian Park Fold and Thrust Belt, a buried or "blind thrust" fault zone forming the southernmost boundary of the Transverse Ranges, and which was responsible for the 1987 M5.9 Whittier Narrows earthquake (Hauksson and Jones, 1989). This fault has not yet been fully evaluated under the Division of Mines and Geology Fault Evaluation Program (FER), and thus does not currently possess Alquist Priolo classification as an active fault.

Newport-lnglewood Structural Zone

Located between 18 and 31 miles east of the City of Malibu, the Newport-Inglewood zone consists of a series of enechelon, northwest-striking right-lateral strike-slip fault segments and related fold structures defined physiographically by a series of low hills crossing the Los Angeles coastal plain. The northernmost of these, the Inglewood segment, intersects the Santa Monica fault zone in the Cheviot Hills area, which represents the complex structural boundary between the Peninsular Ranges and Transverse Ranges. The fault has a potential to generate moment magnitude of 7.0 (Ziony and Yerkes, 1985; Toppozada et al, 1988). Total onshore length of the fault is 46.5 miles; all mapped surface deformation zones along the various segments of the fault have been granted Alquist-Priolo classification (Hart, 1990). The fault produced the 1920 magnitude 4.7 Inglewood earthquake and the great 1933 magnitude 6.2 Long Beach earthquake, and the 1989 magnitude 4.6 Newport Beach earthquake. This fault zone has more seismicity associated with it than any other Late Quaternary faults in the Los Angeles basin (Hauksson, 1990).

Palos Verdes Fault Zone

Located south of Malibu, the northernmost trace of this northwest-striking, right-reverse-slip fault occurs 7.5 miles south of the city limits, in Santa Monica Bay where it apparently intersects or merges with the Anacapa (Dume) fault discussed above. Its onshore segment forms the northwestern boundary of the Palos Verdes Hills and has significant reverse-slip component, whereas offshore it appears to be dominated by right-lateral displacement. The zone apparently displaces acoustically-transparent ocean-floor sediments in San Pedro Bay (Darrow and Fischer, 1983), interpreted to be water-saturated and thus formed recently in the Holocene period. The zone is about 50 miles long. Increases in recent seismicity along the Santa Monica Bay segment of this fault also imply Holocene displacement, although the spatial correlation of this seismicity with the geophysically-mapped offshore fault trace is not precise (Hauksson and Saldivar, 1989). Nevertheless, the fault is considered active and assumed capable of generating a maximum earthquake magnitude of 7.0; although it has not yet been granted active classification under Alquist-Priolo.

Ventura/Pitas Point Fault

Located 19.8 miles northwest of Malibu, this fault, like the San Fernando Fault, has a thrust or reverseslip sense of displacement. Although only 6.2 miles of onshore surface trace has been mapped, the fault extends offshore to the west for a minimum of 24.5 miles and displaces probable Holocene sediments (Greene and Kennedy, 1986). This fault has been zoned active under Alquist-Priolo, and was the probable source of a 7.1 magnitude 1812 event, a 6.8 magnitude 1925 event, a 5.0 magnitude 1930 event, and a 5.6 magnitude 1978 event, all of which had epicenters along the offshore extension of this fault in the Santa Barbara Channel. Therefore, a maximum design magnitude of 7.25 is assumed for this fault. Rates of crustal compression and tectonic uplift in the Southern California area are highest along this fault zone, based on the ages of uplifted and deformed marine terraces in the Ventura area (Lajoie et al, 1979).

San Fernando Fault

Located 14.8 miles northeast of Malibu, at the north end of the San Fernando Valley, this is a thrust fault with similar length, sense of displacement and character to the Malibu Coast Fault Zone and other Transverse Ranges-type faults. This fault generated the 1971 San Fernando earthquake of magnitude 6.6, which caused strong ground shaking in the Malibu area, and which was the impetus behind the Alquist-Priolo legislation. The fault is estimated to be able to yield a maximum 6.5 magnitude earthquake by Wesnousky (1986), based essentially on its mapped 10.5 miles of surface rupture during the 1971 event; however, Mualchin and Jones (1987) assume continuity with the Sierra Madre fault zone to the east, which has similar sense of displacement and a maximum design magnitude of 7.5 (Crook et al, 1987). A maximum earthquake magnitude of 7.0 is estimated herein. The entire fault zone, based on the surface rupture in 1971, is designated as active under Alquist-Priolo. On January 17, 1994, an estimated 6.7 magnitude earthquake occurred in the Northridge/Reseda area of the San Fernando Valley; preliminary analysis indicates that this earthquake was not part of the San Fernando Fault but was associated with the Oak Ridge Fault Zone or the Santa Susana Fault Zone.

Malibu Coast Fault Zone

The Malibu Coast fault zone runs in an east-west orientation onshore subparallel to and along the shoreline for a linear distance of about 17 miles through the Malibu City limits, but which also extends offshore to the east and west for a total length exceeding perhaps 37.5 miles (Junger and Wagner, 1.977; Greene and Kennedy, 1986). Onshore, this fault extends from Sequit Point in the west to Carbon Beach in the east (Yerkes and Campbell, 1980; Dibblee and Ehrenspeck, 1990), although recent mapping suggests that the Las Flores thrust fault may conceivably represent an onshore extension of this fault zone, thus pushing its onshore eastern limits to the Big Rock/Las Tunas beach areas (Dibblee and Ehrenspeck, 1992).

The onshore Malibu Coast fault zone involves a broad, wide zone of faulting and shearing as much as one mile in width; the Malibu Coast fault proper is only one fault splay within this broad deformation zone, but it is the most prominent feature within the zone because it juxtaposes two crustal blocks of extremely different character on either side of its length (Durrell, 1954; Schoellhamer and Yerkes, 1961; Yerkes and Wentworth, 1965). To the north, a basement terrain of granite and related igneous rocks, intruded into older metasedimentary-rocks termed the Santa Monica Slate, is overlain by a thick sequence of sedimentary rocks ranging in age from Late Cretaceous to Recent; to the south of the Malibu Coast fault proper, a basement terrain of high-pressure metamorphic rocks termed the Catalina Schist is overlain unconformably by a sequence of sedimentary rocks no older than Miocene, including the distinctive Monterey Formation, which is locally highly diatomaceous (Yerkes and Campbell, 1979). This latter crustal block south of the Malibu Coast fault is often termed a "Continental Borderland" terrain (Yerkes et al, 1965; Legg, 1992), because the Catalina Schist basement terrain underlies most of the offshore zone of southern California, which is conventionally known as the Continental Borderland.

The Malibu Coast Fault Zone (MCFZ) has not been officially designated as an active fault zone by the State of California and no Special Studies Zones have been delineated along any part of the fault zone under the Alquist-Priolo Act of 1971. However, evidence for Holocene activity (movement in the last 11,000 years) has been established in several locations along individual fault splays within the fault zone. Due to such evidence, several fault splays within the onshore portion of the fault zone are identified as active in the Seismic Element of the County of Los Angeles (Leighton and Associates; 1990). With reference to inferred active fault splays in Malibu, the Los Angeles County Seismic Safety Element map contains a note which states:

"A primary objective of this map is to increase public awareness of fault rupture hazards recognized by the state-mandated Alquist-Priolo Special Studies Zone Act (APSSZ). Additional faults inferred to be active are included on the map because there is published information or scientific opinion by staffs of authoritative agencies that indicate there is a reason to consider them active. Their inclusion is not intended to prohibit development, but to insure that proposed projects are supported by detailed geologic and seismic investigations that will provide the most accurate obtainable data on the presence or absence of a hazards and identify necessary mitigative measures."

In general, the City of Malibu has adopted of Los Angeles County Seismic Safety Element Map as discussed above and regards the Malibu Coast Fault Zone as active; however, it is recognized that individual splays within the fault zone may not necessarily be classified as active based upon site-specific geologic and seismic investigations.

Table 5-1 lists the large historic earthquakes recorded in Southern California. This list includes activity on all faults in Southern California, any of which might, during a major event, precipitate activity in Malibu; see, also, Figure S-4.

Liquefaction and Subsidence - Liquefaction is a process by which water-saturated sediment suddenly loses strength, which commonly accompanies strong ground motions caused by earthquakes. During an extended period of ground shaking or dynamic loading, porewater pressures increase and the ground is temporarily altered from a solid to a liquid state. Liquefaction is most likely to occur in unconsolidated, sandy sediments which are water-saturated within less than 30 feet of the ground surface (Tinsley et al., 1985).

Few areas of significant liquefaction susceptibility exist in the City of Malibu. These few areas are located along the beaches and in the flood plains of the major streams, such as Malibu Creek. Liquefaction susceptibility as used for this study is a qualitative measure of the fraction, or percent, of the area considered likely to be underlain by deposits susceptible to liquefy if strong shaking occurs. The susceptibility value is determined as the product of three important factors:

1.	The probability of finding cohesionless sediment in the area considered;
2.	The probability that the cohesionless sediment, when saturated, would be susceptible to liquefaction;
3.	The probability that the cohesionless sediment would be saturated.

The detailed information to determine these factors is only available for Los Angeles, San Diego and San Francisco. Because the USGS study of the Los Angeles region missed the Malibu area, susceptibility values based upon the values obtained nearby, at Santa Monica and Oxnard, were extrapolated into the City of Malibu.

Table 5-1 LARGE HISTORIC EARTHQUAKES RECORDED IN SOUTHERN CALIFORNIA
Date	Magnitude	Fault
Jan. 9, 1857	8.3+*	San Andreas Fault Zone
July 21, 1952	7.7	White Wolf Fault
Nov. 4, 1927	7.5	Undetermined fault off of Point Arguello
June 28, 1992	7.3	Landers (San Andreas Fault Zone)
May 19, 1940	7.0	Imperial (San Jacinto Fault Zone)
Dec. 8, 1812	7.0*	San Andreas Fault Zone
April 21, 1918	6.9	Claremont Fault (San Jacinto Fault Zone)
June 28, 1992	6.8	Big Bear (San Andreas Fault Zone)
Jan. 17, 1994	6.7	Oak Ridge or Santa Susana Fault Zone
Dec. 25, 1899	6.6*	Claremont Fault (San Jacinto Fault Zone)
Oct. 21, 1942	6.5	Coyote Creek (San Jacinto Fault Zone)
Oct. 15, 1979	6.5	Imperial (San Jacinto Fault Zone)
April 9, 1968	6.5	Coyote Creek (San Jacinto Fault Zone)
Feb. 9, 1971	6.4	San Fernando-Sunland Fault
April 10, 1947	6.4	Manix Fault in Mojave Desert
Mar. 19, 1953	6.4	Coyote Creek (San Jacinto Fault Zone)
Mar. 10, 1933	6.3	Newport-Inglewood Fault Zone
June 29, 1825	6.3	Undetermined fault in the Santa Barbara Channel
Dec. 4, 1948	6.0	Mission Creek
Apr. 4, 1893	6.0*	San Fernando-Santa Susana Fault
May 15, 1919	6.0	Glen Ivy (San Jacinto Fault Zone)
Oct. 23, 1916	6.0*	Tejon Pass Area (San Andreas Fault Zone, suspected)
Oct. 1, 1987	5.9	Elysian Park Fault
July 1, 1941	5.9	Undetermined Fault in the Santa Barbara Channel

* Estimated magnitude

Source: Parsons Environmental Services and Harland Bartholomew & Associates (1994)

Subsidence is the settling of the ground surface due to the compaction of underlying unconsolidated sediment. It is most common in uncompacted soils, thick unconsolidated alluvial material and improperly-constructed artificial fill. Subsidence is typically associated with the rapid removal of large volumes of groundwater or oil. It is also a secondary hazard associated with seismic activity, as groundshaking may cause the settling of loose, unconsolidated grains. Due to the fault zones and the unconsolidated alluvial sediments underlying much of the city and planning area, the potential for seismically-induced subsidence is considered high. Some subsidence could also be expected if large volumes of groundwater are withdrawn for developments in the area.

Landslides: Slope instability or landsliding is related to slope gradient, soil or rock type, and erosion susceptibility. Landsliding can also be seismically-induced, resulting from extended periods of groundshaking and high ground accelerations (see Figure S-5). Improper grading, and excessive rainfall or irrigation can also increase the probability of landsliding.

The 1990 Los Angeles County Safety Element (LACSE) prepared a map that was a generalized inventory of landslides that included:

•	Block Glides
•	Slumps
•	Debris Flows
•	Rockfalls

The minimum size of an individual landslide shown on the Landslide Inventory Map was five acres. Review of the Los Angeles County Landslide Inventory map indicates that the Malibu area, and the Santa Monica Mountains area in general, constitute one of the three areas of Los Angeles County that display a high propensity for landsliding. Only the Santa Susana Mountains and the Castaic area appear to equal the degree of landsliding displayed in the Malibu area; see, also, Figure S-6 and Figure S-7.

According to the 1992 review of landslides conducted by Philip Williams & Associates and Peter Warshall & Associates there are approximately 250 mapped landslides in the area. The 15 largest landslide areas contain 350 homes, not all of which are endangered, and are surrounded by at least 285 other homes which could be affected by sliding in the future.

Of the major slides listed in the Williams and Warshall report, sizes range from about eight acres up to the Big Rock Mesa landslide which is about 220 acres. Most of the large landslide areas involve housing units. Many of these are threatened. Public utilities have been affected, particularly those underground. To address the problem, underground piping has often been rerouted onto the ground surface with flexible connections.

The majority of slides in the study area are slump failures involving surficial deposits and weathered and faulted bedrock formational material. Of the numerous slides mapped by Weber and Wills as active in 1983, most were slump failures and 16 were reactivated during the winters of 1978-1980. The landslide limits have been plotted on a 1000-scale Geohazards Maps of Malibu available for inspection at City Hall, and the better known slides have been labeled with their commonly recognized name from the geologic literature and the listing provided in the 1992 Wastewater Management Study.

Debris Flow: The many canyons that drain the Santa Monica Mountains and cross through Malibu to empty into the ocean, provide avenues for future debris/mud flow events during wet winters and intense rain storms. Debris flow events have been experienced in Topanga Canyon, Las Flores Canyon, and others, and will occur again in the future. These phenomenon are potentially deadly to the public because many of the mountain failures that contribute soils and debris to the canyon bottoms tends to occur during the early A.M. hours following intense rainfall that is most likely during the night time. The public tends to be inside and asleep, not expecting catastrophic hillside failures to affect them.

Past storm tracks that caused significant debris flows in the 1982-83 storms, indicates that intense, continuous rainfall exceeding 0.25 inches per hour can, and does, occur in the Santa Monica Mountains.

The work of Russell H. Campbell (1975) for the Santa Monica Mountains indicates that when intense rain storms follow after the rainy season has experienced 10 to 15 inches of rainfall (antecedent rainfall), slopes steeper than 2:1 (26 degrees) up to steepness of 45 degrees, are prone to slippage and failure of the surficial several feet of slope. When there are numerous failures that take place within a short span of time, and that flow into main drainage courses, then there is the potential for downstream debris flow damage.

Debris flow potential from the Santa Monica Mountains has been greatly underestimated for its possible impact on the City of Malibu.

Mudflows have a potential for occurring wherever land development has constructed fill slopes that are steeper than 2:1. If such slopes are above other occupied properties, there is a potential for failure of these slopes during wet winters.

The generally recognized landslide areas in Malibu include (listed from east to west):

• Las Tunas Beach Slides	• Big Rock Mesa
• Eagle Pass-Las Flores Slide	• Rambla Pacifico
• Calle Del Barco	• Carbon Mesa Slides
• Carbon Canyon Slide	• Amarillo Beach Slides
• Puerco Beach Slides	• RV Park Slide
• Latigo Shore Slide	• Latigo Canyon Slide
• Malibu Cove Colony Slides	• Lower Encinal Canyon Slides
• LaChusa Highlands Slide

Soils: Soil types in the City of Malibu have been classified by the United States Department of Agriculture, Soil Conservation Service (SCS). These SCS classifications are associated with identified soil capabilities which may be used in planning for agricultural, urban, watershed, recreational and wilderness uses. SCS has identified 22 soil series and 45 soil phases in the Malibu area (Malibu Soil Survey, 1967).[1]

Expansive Soils: Of the various geologic hazards that affect the State of California, expansive soils have caused millions of dollars in damages, particularly to single-family residences and private property improvements. The State Department of Natural Resources estimates that to the year 2000, expansive soils will be a 150 million dollar problem in the state.

Each of the different geologic formations mapped in the Malibu area consists of various units which may possess expansive potential. Typically, these would be mudstones, claystones, siltstones, and clay fault gouge. Clay fault gouge is clay along the fault planes that slice through the rock. Silt and clay deposits near and around the Malibu Creek lagoon would possess expansion potential. Geologic units mapped as colluvium or slopewash, would commonly be expansive in nature. The terrace deposits shown along the coast also generally contain expansive soils.

Collapsible/Compressible Soils: Potential collapsible soils may exist in areas of Malibu where geologic units of alluvium or colluvium are present at the lower end of sloping terrain where it begins to flatten and become less steep, but particularly where debris flow deposits have been recognized (see Figure S-10). Russell H. Campbell (1980) mapped what he believes are old deposits from debris flows in the Point Dume-Zuma Beach area. Similar types of deposits are likely along Las Flores Canyon, Malibu Creek, Zuma Canyon, and Trancas Canyon. Compressible soils would be very likely in the Malibu Lagoon area, along Malibu Creek, Dume Canyon, and Trancas Canyon. Undetected, development on these type of soils may become distressed to collapse or consolidation of the foundation soils.

Coastal Hazards: Because of the age of the community (1920's, 1930's, to present), there are a wide range of buildings and coastal protective devices present along the Malibu coast. It has generally been observed by local geologists and engineers that during the major storms, construction that is most severely impacted is generally older construction.

In all situations, the potential exposure of a property is also a direct function of the setback of the structure from the ocean, the beach, and the cliff or bluff. Adequately setback construction provides the best protection.

Older bluff top properties with reduced bluff top setbacks, become more exposed to the risks of bluff failure and landsliding due to coastal erosion and earthquake ground shaking.

Some areas of the—Malibu coastal bluffs are retreating variably because of either the neglect, or special attention, given to surface drainage control. Rapid coastal bluff, or sea cliff top, retreat can occur when surface runoff is not controlled by collection and proper disposal. Damage to properties can be seen where concentrated surface runoff has generated surficial failures of the bluff, or where erosion has quickened the advance of gullies and ravines that have been cut into the bluff face and bluff top.

There still continues to be widespread debate among coastal experts and engineers regarding the possible adverse affect on beach widths relative to coastal protection. There is also wide disagreement about what types of coastal protection are best suited to a backshore. Economics of the property owner, or entity responsible for the protective device no doubt play a role in the type of coastal protection that is ultimately constructed.

Cooperative efforts to armour (protect) stretches of beach where protective devices may be hit, or miss, seem to provide the most appropriate methods to protect all the properties involved. Apparently, attempts by the County of Los Angeles in the past to coordinate homeowners has been largely unsuccessful.

There will be a continuing threat to beach structures from wood and floating debris that become battering rams when introduced to the surf during storms and coastal erosion events. As the building of decks, patios, housing, and other improvements become more sophisticated and permitted, the percentage of damages due to floating debris should be reduced.

Tsunamis and Seiches: Tsunamis, seismic sea waves, can be expected rarely from distant sources, but may be generated immediately offshore of Malibu by surface ground rupture of the faulting just offshore, or by the occurrence of submarine landslides immediately offshore. Displacement of the sea floor could generate a local wave and would include wave runup to elevations 12 feet above Mean Lower Low Water of the Pacific Ocean in this area. The runup heights for the Malibu coast in general are between five and seven feet for the 100-year zone and between eight and 12 feet for the 500-year zone. The higher runups occur in the eastern part of Malibu because of the amplification effects related to the Santa Monica Bay resonant oscillations. (See also Figures S-11 to S-15 and the Safety Background Report for a more detailed discussion.)

Most of the coastal dwellings and low lying coastal areas can expect to be damaged some time in the future by an earthquake generated tsunami. Damage due to flooding in the Malibu Civic Center area can be expected. The most vulnerable objects would be people on the beaches, houses or other buildings constructed on or near the beach, and bridges over the streams near the beach, such as along the Pacific Coast Highway at Malibu Creek and Corral Creek. People could be swept away by the waves and drowned; buildings and bridges could be undermined and collapse or carried away by the currents; buildings and other structures could be battered by debris carried by the currents.

Seiche, resonant oscillations in semi-enclosed water bodies such as Santa Monica Bay, may be triggered by moderate or larger local submarine earthquakes, and sometimes by large, more distant, regional earthquakes. Seiching was recorded at Santa Monica following moderate (Mw = 5.0-5.2) earthquakes under Santa Monica Bay in 1930, 1979, and 1989. The maximum height of these long period waves was about two feet. If such oscillations occurred during storm, conditions or unusually high tides, damaging coastal inundation could result. The duration of these oscillations may be several hours.

[1]

Soil series are soils that are grouped together because they have a similar set of soil profile characteristics. The soil phase is a division of the soil series in which the soils are grouped together by common surface and substrata characteristics. Important characteristics used to determine soil phase are surface texture, slope and quantity of stones.

• Alluvium (creek beds)	• Conglomerates	• Mudstones
• Beach and sand dune deposits	• Colluvium (foothill areas)	• Sandstones
• Cemented sandstones	• Debris flow deposits	• Shales
• Cherts	• Diatomaceous beds	• Siltstones
• Claystones	• Mixed-rock terrace deposits	• Various volcanic rocks

• Calabasas Formation	• Conejo Volcanics	• Coal Canyon Formation
• Llajas Formation	• Modelo Formation	• Monterey Shale
• Sespe Formation	• Topanga Canyon Formation	• Trancas Formation
• Tuna Canyon Formation	• Vaqueros Formation	• Zunia Volcanics

• Artificial fill	• Landslides and landslide deposits
• Coastal terrace deposits	• Stream terrace deposits
• Debris trains	• Undifferentiated surficial deposits
• Fan deposits

•	Elimination of wood shake roofs for new construction;
•	Establishment of minimum greenbelt systems along new subdivisions;
•	Improvement in existing water systems and vehicular access in a number of areas;
•	Improvements made in the "Incident Command System" used by the Los Angeles County Fire Department and in the emergency communications and coordination among various fire resource agencies;
•	Installation of smoke detectors in homes and sprinkler systems in commercial buildings; and
•	An aggressive brush clearance program that has been undertaken in the past few years.