EARTHQUAKE PLANNING SCENARIO For A Major Earthquake On The Newport-Inglewood Fault Zone
TOUSSON R. TOPPOZADA, JOHN H. BENNETT, GLENN BORCHARDT
RICHARD SAUL, and JAMES F. DAVIS
Division of Mines and Geology
CARL B. JOHNSON, HENRY J. LAGORIO, and KARL V. STEINBRUGGE
This article is adapted from Planning scenario for a major earthquake on the Newport-Inglewood fault zone, Division of Mines and Geology, Special Publication 99, 203 p., 16 plates, 1988 (in press).
The Newport-Inglewood fault zone was the source of the destructive 1933 Long Beach earthquake (Richter magnitude 6.3), which took 120 lives. A major earthquake (magnitude about 7) on this fault within the highly urbanized Los Angeles metropolitan area poses one of the greatest hazards to lives and property in the nation. Many of the possible consequences of a major earthquake on this fault are described in the scenario. Knowing the potential impact to transportation and utility lifelines and critical structures will allow emergency planners to coordinate preparedness and response plans to cope with this eventuality. Individuals can support public mitigation efforts and develop plans for themselves and their families to cope with the effects of earthquakes . . . [California Geology] editor
In 1981 the Federal Emergency Management Agency analyzed emergency response capabilities of all levels of government and the private sector and concluded that the collective capabilities would not be adequate to cope with a major destructive earthquake in a metropolitan area. Following this analysis, the Governor of California established the Emergency Task Force for Earthquake Preparedness in February 1981. Working with the Task Force, the Department of Conservation, Division of Mines and Geology (DMG) developed scenarios for two destructive earthquakes. One scenario is based on a repeat of the 1857 Fort Tejon earthquake (magnitude about 8) on the San Andreas fault zone in southern California (DMG Special Publication 60). The second scenario is based on a repeat of the 1906 San Francisco earthquake (magnitude about 8) on the portion of the San Andreas fault zone in northern California (DMG Special Publication 61).
A scenario for a magnitude (M) 7.5 earthquake on the Hayward fault in the San Francisco Bay area (DMG Special Publication 78) was prepared, and a scenario for a major earthquake in the San Diego area is being prepared.
An earthquake planning scenario assumes that a specific earthquake occurs in the future. The scenario event provides the opportunity for hypothetical assessments of the performance of certain critical facilities in the affected area. These assessments are based on the assumed surface fault rupture, intensity of shaking, and liquefaction related ground failure resulting from the scenario earthquake. The impacts of these effects upon structures and lifeline facilities then are considered.
Photo 1. Aerial view of metropolitan Los Angeles. Santa Monica Mountains are in the background. Photo courtesy of Port of Los Angeles.
The region that would be affected by a major earthquake on the Newport-Inglewood fault zone is centered in the Los Angeles metropolitan area (Photo 1). This area is approximately 30 miles wide and is bounded on the west by the Pacific coast from Santa Monica to San Juan Capistrano. The area includes the cities of San Fernando, Pasadena, and Orange on the east. Approximately 10 million people live in Los Angeles and Orange counties. This area encompasses virtually all of the region likely to experience Modified Mercalli (MM) intensities of VIII or greater resulting from this scenario earthquake, and thus, all areas within which significant structural damage can be expected (Figures 1, 2, and 5).
NEWPORT-INGLEWOOD FAULT ZONE
The alignment of hills and mesas from Newport to north of Inglewood first caused geologists to suspect that the uplifted features are related to a common, linear, underlying structural element, called the Newport-Inglewood fault (Figure 1). The landforms resulted from a combination of different rates of uplift and the effects of different agents of erosion at various localities along the zone (Barrows, 1974).
Late Pleistocene marine deposits are exposed on the surface of these low, rolling hills which range in elevation from 175 feet to about 510 feet. They are generally surrounded by south- or east-sloping alluvial terrain.
The northwest-trending zone of faulted anticlines which forms the surface topography in the Newport-Inglewood fault zone are structural traps for proven oil fields (Yeats, 1973) (Figure 1). From northwest to southeast these are the Cheviot Hills, Inglewood, Potrero, Howard Townsite, Rosecrans, Dominguez, Long Beach, Seal Beach, Sunset Beach, Huntington Beach, and West Newport oil fields. According to Yeats (1973), "on the northwest, the zone terminates abruptly against the Malibu Coast fault system in the vicinity of the Cheviot Hills oil field, but the extension of the zone to the southeast beyond the West Newport field is a matter of controversy." In this southeastern extension offshore of San Clemente and San Diego (the Rose Canyon and La Nacion faults), the faults have similar trends and projections (Ziony and Yerkes, 1985). The fault system is more than 145 miles long.
The oil producing anticlines and northwest trending surface features are underlain by a deep seated fault zone. At depth the Newport-Inglewood fault zone is a nearly vertical right-lateral strike-slip fault, with the Pacific Ocean side moving northwestward relative to Los Angeles (Harding, 1973). At the surface, the individual fault segments comprising the fault zone are discontinuous. For example, the Inglewood fault segment is 4 miles long. The sense of offset between surface fault segments is left stepping, which indicates a through-going right-lateral strike-slip fault at depth.
The zone of deformation along the Newport-Inglewood fault zone is about 1.2 miles wide; it includes the folds and faults that are the surface expressions of the inferred deep seated fault zone. Known Holocene (last 11,000 years) active fault traces in the zone of deformation have been mapped in the Alquist-Priolo Special Studies Zones (Figure 2).
Seventy small earthquakes (M 2.5 to M 3.8) that occurred in and bordering the Newport-Inglewood fault zone from 1973 to 1985 were analyzed by Hauksson (1987). The earthquake epicenters occurred along the fault zone from Dominguez Hills to Cheviot Hills. Adjacent to Long Beach, however, the earthquake epicenters are offset 2 to 3 miles to the east of the Newport-Inglewood fault zone, along the trend of the subsurface Los Alamitos fault. Most of the earthquakes occurred at depths of 4 to 7 miles, which is normal for earthquakes in southern California.
Figure 1. Newport-Inglewood fault zone, southern California, showing structural zone of folds and faults.
Figure 2. Alquist-Priolo Special Studies Zones maps in the Newport-Inglewood fault zone.
ALQUIST-PRIOLO SPECIAL STUDIES
The Alquist-Priolo Special Studies Zones Act was signed into law in 1972. The purpose of this Act is to prohibit the location of most structures for human occupancy across the traces of active faults and thus to mitigate the hazard of fault rupture. Under the Act, the State Geologist is required to delineate "Special Studies Zones" along known active faults in California. Cities and counties affected by the zones must regulate certain development projects within the zones. Permits for developing these sites within the zones are not issued until geologic investigations demonstrate that the sites are not threatened by surface displacement from future faulting (Hart, 1985).
Photo 2. Buildings damaged during the 1920 Inglewood earthquake, west side of Commerce Street (now Brea Avenue) in Inglewood. Photo from Taber 1920.
The first maps showing Special Studies Zones for the Newport-Inglewood fault zone were issued in 1976 and revised in 1986 (Figure 2). The active fault traces are discontinuous segments that are generally offset in a left-stepping pattern, as in Long Beach. Some of these traces show evidence of active movement during Holocene time --- the last 11,000 years (Bryant, 1988).
Active traces are not well located for some segments of the fault. The effectiveness of the Act varies, depending on how well the fault zone is defined. However, the law applies only to new real estate development and to structures for human occupancy. Many older structures sit astride active traces of the fault and the extent of damage produced by a major earthquake will depend on the amount of displacement that occurs locally on the fault and on the measures taken to mitigate the hazard.
Earthquakes were reported in the Los Angeles area by Spanish explorers as early as 1769. Members of the Portola expedition felt more than twenty-four earthquakes during one week in 1769 while traveling in the area between the Santa Ana and Los Angeles rivers.
The earthquakes of December 8, 1812 and December 21, 1812 were interpreted by Toppozada and others (1981) from documents written by Franciscan missionaries in December 1812 and January 1813. Dates of earthquakes and some of their effects are listed below.
December 8, 1812. An earthquake on this day destroyed the bell tower at Mission San Juan Capistrano (intensity VII), causing the roof of the church to cave in, and killing 40 Indians who were in the church. At Mission San Gabriel, statues in the church were broken, the bell tower was cracked, and other Mission buildings were extensively damaged (intensity VII). At Mission San Fernando, the walls of the church were damaged (intensity VII), and 30 beams were required to support them. The earthquake postulated in this scenario (M about 7) generates intensity in the low VIII range at San Juan Capistrano, San Gabriel, and San Fernando.
Intensity effects of the 1812 event are not sufficient to define the source fault. Jacoby and others (1987) found evidence from tree-rings for an 1812 earthquake on the San Andreas fault 30 miles northeast of San Gabriel, and hypothesized that it was the December 8 event.
December 21, 1812. Two separate events in southern California occurred in the same month and only about two weeks apart in time; this has caused some confusion and the mistaken impression that a single earthquake was destructive from Orange County to Santa Barbara County. The December 21, 1812 earthquake epicenter was probably located in the Santa Barbara channel (Toppozada and others, 1981). Earthquake damage was reported at missions at San Buenaventura, Santa Barbara, Santa Ynez, and Purisima Concepcion in Ventura and Santa Barbara counties.
July 10, 1855. This event was probably on one of the surface faults (Hollywood-Raymond, Whittier, or Newport-Inglewood) bordering the Los Angeles basin. It could also have been located on a concealed fault as was the case for the 1987 Whittier Narrows earthquake. During the July 10, 1855 quake, the bells of Mission San Gabriel were thrown down, and 26 buildings in Los Angeles were damaged. The earthquake was felt from San Bernardino to Santa Barbara.
June 21, 1920. This earthquake of magnitude 4.9 (Richter, 1970) was destructive only at Inglewood (Photo 2). Because of this, Taber (1920) assumed a shallow epicenter at or west of Inglewood. According to Taber (1920), "the damage to buildings was due to poor construction rather than to the intensity of the vibrations. Thin brick walls built as fronts to wooden buildings and not tied in properly, toppled outward into the street. Poorly built brick cornices and fire walls along the fronts of buildings were shaken off.
March 10, 1933. Long Beach Earthquake (Photos 3-5). The hypocenter of this M 6.3 earthquake (Figures 3 and 4) was just off the coast of Newport Beach at a depth of about 6 miles. Aftershocks (magnitude up to 5.5) occurred along the Newport-Inglewood fault zone from Newport Beach to Long Beach, a distance of 15 miles. This indicates that the earthquake was generated by about 15 miles of subsurface faulting that began near Newport Beach and propagated northwestward along the Newport-Inglewood fault zone toward Long Beach. Fault rupture was not identified at the surface, and no seismic sea waves were observed. The isoseismal map (Figure 4) shows that the area damaged at MM intensity VII to IX extended from Laguna Beach to Marina del Rey and inland to Whittier.
According to Richter (1958), "Loss of life is commonly stated as 120, and property damage at 50 million dollars." The 1933 earthquake stimulated passage of the Field Act and the Riley Act by the California legislature. Under the Field Act, the construction of public schools is regulated. Under the Riley Act, construction of buildings larger than two-family dwellings is regulated.
The March 1933 Long Beach earthquake was followed by a M 5.4 earthquake which occurred on October 2, 1933 centered near Signal Hill.
In 1941 two earthquakes caused damage in Torrance and Gardena. The first event (M 4.9) occurred on October 21, 1933 in the West Dominguez oil field and damaged wells at depths of 5,000 feet to 6,000 feet (Barrows, 1974). The second event (M 5.4) occurred on November 14 to the west of the Newport-Inglewood fault zone and caused damage in Torrance to structures inadequately repaired after the 1933 earthquake (Richter, 1958, p. 499). On June 18, 1944 two earthquakes of M 4.5 and M 4.4, respectively, occurred in the Dominguez Hills and damaged oil wells in the Rosecrans oil field at depths of 3,000 feet to 6,000 feet (Barrows, 1974).
Figure 3. Los Angeles metropolitan area and surroundings, showing major Quaternary faults and epicenters of earthquakes of M 5 or greater that occurred from 1927 to 1987.
Major Quaternary faults surround Los Angeles; the epicenters of earthquakes of magnitude 5 or greater that have occurred since 1927 are shown in Figure 3. The Newport-Inglewood fault zone (Photo 6) was selected for the scenario earthquake because:
(1) it is part of a fault system that is more than 145 miles long that extends to Baja California;
(2) it lies within the highly urbanized Los Angeles metropolitan area, a major (M about 7) earthquake has consequences potentially greater than those of a larger magnitude event on the more distant southern San Andreas fault;
(3) faults within this zone have been active during the Holocene epoch;
(4) the displacement rate on the fault zones during the last million years is 0.6 mm/yr (0.024 in/yr);
(5) historic record shows that an earthquake which occurred on December 8, 1912 severely damaged the missions at San Juan Capistrano, San Gabriel, and San Fernando, suggesting a magnitude of about 7 and an epicenter within 50 miles of these missions. The destructive Long Beach earthquake of 1933 (M 6.3) occurred on this fault zone, and small earthquakes continue to occur on this fault zone in the Los Angeles metropolitan area.
Figure 4. Isoseismal map of the 1933 Long Beach earthquake. Roman numerals indicate Modified Mercalli intensity areas. Arabic numerals indicate Modified Mercalli intensities at specific locations. From Toppozada and Parke, 1982.
Subsurface faulting extending 45 miles on the fault zone is postulated, with the northern end near Beverly Hills at the intersection of the Newport-Inglewood fault zone with the Santa Monica fault. The southern end is offshore from Laguna Beach. This zone of faulting overlaps and extends beyond the locations of the 1933 Long Beach earthquake and its after-shocks. Surface faulting will be discontinuous, and occur mainly on the Holocene active traces.
The 45 mile extent of faulting on this zone corresponds to M 7.4 using the relation of Bonilla and others (1984), to M 7.1 using the relation of Slemmons (1982), and to M 7.0 using the relation of Wyss (1979). For planning purposes, a maximum surface displacement of 6 feet is assumed. The more prevalent average displacement is usually half the maximum value (Slemmons, 1987, verbal communication), or about 3 feet. The displacement is assumed to be dominantly right-lateral strike-slip, and occurs on the Holocene active (Alquist-Priolo) fault traces (Figure 2). Minor dip slip or vertical components of faulting will occur locally. Where there are no known active faults in the fault zone, displacement occurs possibly on other unidentified faults within the approximately three-quarter mile wide zone of deformation. Warping and uplift of about 3 feet will also occur in the zone.
Potentially damaging ground shaking continues for about 25 seconds within 25 miles of the fault. Potentially damaging aftershocks occur for about a month following the main shock, with a few earthquakes in the magnitude 5.5 to 6.5 range.
The southernmost 8-mile segment of the postulated subsurface faulting is offshore between Newport Beach and Laguna Beach. Because only minor vertical displacements are expected, the potential is small for generating a seismic sea wave or tsunami from this 7-mile-long offshore segment, and is not considered in this scenario. Oscillatory waves in enclosed water bodies (seiches) occur in the local harbors.
Photo 3. This wood frame house in the Long Beach-Compton area was thrown off its foundation in the March 1933 earthquake. Photo by Olaf P. Jenkins, DMG photo file.
The scenario earthquake is consistent with the judgment ". . . that earthquakes of M 6.5 to 7, accompanied by as much as 6 feet of surface displacement, are appropriate design earthquakes for ordinary planning purposes for most faults in the Los Angeles region" (Ziony and Yerkes, 1985).
The degree of ground shaking resulting from the scenario earthquake will depend on (1) the distance from the causative fault and (2) variations in the geologic materials.
In preparing a regional intensity map for assessing lifeline damage, Reichle and Kahle (1986) developed a computational procedure based on the Evernden seismic intensity model (Evernden and others, 1973, 1981; Evernden, 1975; and Evernden and Thomson, 1985). This computer model calculates the ground shaking acceleration on a grid of reference points throughout a region employing equations that account for the influence of distance from the fault source, attenuation, and the surface geology. The intensities are calculated by using an empirical relationship between acceleration and the intensity scale.
Reichle and Kahle's model is used in this scenario, and differs from that of Evernden and others (1981) in that it assumes that shaking intensity does not depend on depth to water table. Also, it predicts intensities for bedrock sites within 3 miles of the fault and at distances greater than 25 miles on unsaturated alluvium that are approximately one unit higher than Evernden's. The model was guided by the areal extent of intensity VII and VIII shaking for earthquakes of magnitude about 7 on other California faults, notably the 1868 Hayward and the 1952 Kern County earthquakes.
Development of the seismic intensity distribution map begins with attenuation versus distance calculations plotted as concentric ellipses centered on the fault zone. With distance from the fault, each successive ellipse is an intensity unit less than the previous one. On well consolidated bedrock within a distance of 5 miles of the fault the ellipses denote Modified Mercalli intensities of VII; within 22 miles they are VI or greater; within 50 miles they are V or greater. In areas of less-consolidated ground, seismic intensities due to shaking can be up to 2 units higher. Therefore, within 5 miles of the fault, the softest ground, Quaternary sedimentary deposits, would have predicted intensities of IX. In the same area, bedrock of intermediate consolidation would have predicted intensities of VIII.
Intensities higher than IX are not shown because intensities X through XII are generally attributed to the secondary effects of ground breakage. Intensities X through XII may occur in the areas of potential ground breakage (faulting, liquefaction, landslides).
The intensities are generally highest at the fault and decrease with distance from the fault. The concentric pattern is modified by the areal distribution of geologic materials that respond differently to shaking. This difference accounts for the intensity being VIII nearest the fault in the uplifted area of consolidated rock, and for intensity IX occurring 3 miles away from the fault in unconsolidated alluvium.
The area within 25 miles of the fault will be subjected to shaking of Modified Mercalli intensity VIII or greater, strong enough to cause considerable damage in ordinary substantial buildings; great damage in poorly built structures). MM intensity VIII or greater shaking effects extend throughout the alluvial sections of the Los Angeles basin, to the vicinity of Monrovia and West Covina, including the San Fernando Valley and virtually all of the populated alluvial areas of coastal Orange County south to San Juan Capistrano.
Intensity VII and lesser shaking occur in the consolidated rocks in the hilly areas, including the Santa Monica Mountains, Verdugo Mountains, Puente Hills, and the mountainous areas of Orange County.
Within the planning area, there are local zones where intensities greater than MM IX could result from faulting, liquefaction, or landslides.
The liquefaction potential in Holocene sediments is high where the depth to the water table is less than 10 feet. The liquefaction potential is medium where the depth to the water table is between 10 and 30 feet. Areas subject to liquefaction include Los Angeles and Long Beach harbors, Marina del Rey, Newport Bay, Balboa, and areas in urban Orange County.
Figure 5. Modified Mercalli intensities estimated for the scenario earthquake of M 7 on the Newport-Inglewood fault zone. southern California.
Areas subject to seismically induced landsliding include the Palos Verdes Hills, Santa Monica bluffs, and some potentially unstable slopes in eastern Orange County.
COMPARISON TO M 8 EARTHQUAKE
ON THE SAN ANDREAS FAULT
The Newport-Inglewood fault zone is located within the Los Angeles metropolitan area, whereas the San Andreas fault is more than 30 miles distant. Therefore, in the Los Angeles metropolitan area, the impact of an earthquake of M 7 on the Newport-Inglewood fault zone (Figure 5) would be stronger than the impact of a M 8 earthquake on the San Andreas fault (Figure 6).
Figure 6. Modified Mercalli intensities for a M 8 earthquake on the San Andreas fault, southern California. Modified from Davis and others, 1982b.
In 1857 an earthquake of magnitude about 8 occurred on the San Andreas segment nearest Los Angeles. That earthquake resulted from a nearly 200 mile rupture of the San Andreas fault, from Cholame Valley in central California to Cajon Pass near San Bernardino; maximum displacement was 27 feet. A scenario of the impact of a repeat of the 1857 earthquake on existing lifelines was published by the Division of Mines and Geology (Davis and others, 1982b). The earthquake postulated in the present scenario is of magnitude about 7, resulting from subsurface rupture of 45 miles of the Newport-Inglewood fault zone, and the maximum surface displacement is 6 feet.
The M 8 earthquake on the San Andreas fault damages a larger area, including parts of San Bernardino, Kern, and Ventura counties, than does the M 7 event on the Newport-Inglewood fault zone. Within the Los Angeles metropolitan area, the impact of the M 7 event on the Newport-Inglewood fault zone (Figure 5) is greater than that of the M 8 event on the San Andreas fault (Figure 6). In the Los Angeles-Long Beach area the shaking intensity is mostly MM VII from the M 8 earthquake on the San Andreas fault (Figure 6) (Davis and others, 1982b), and is MM VIII to MM IX from the M 7 event on the Newport-Inglewood fault zone (Figure 5). This is a significant difference in the intensity of shaking and occurs in the heart of the Los Angeles metropolitan area. Faulting and ground deformation from the Newport-Inglewood fault zone event also directly impact many more lifelines, critical structures, and industrial facilities, than do faulting and ground deformation from the San Andreas fault event. Lifelines in the Los Angeles metropolitan area, such as highways, petroleum, and waste water, will be more severely damaged by the Newport-Inglewood fault zone event than by the San Andreas fault event.
IMPACT OF POSTULATED EARTHQUAKE
Maps portraying the impacts of the scenario earthquake upon the lifelines are presented in Special Publication 99.
There are about 155 acute-care hospitals with a total bed count of 43,000 beds located in the zone of potentially damaging ground shaking within 25 miles of the fault zone. Approximately 55 hospitals are within 5 miles of the fault zone and 4 hospitals are within the mile-wide fault zone.
For planning purposes, it is estimated that 14,439 beds (34 percent) of the 43,000 total will not be available for use.
There are nine major corridors for traffic in the area of the Newport-Inglewood fault zone: five major north-south routes (1, 110, 405, 710 and 605) and four major east-west routes (10, 22, 42, and 91).
Routes 1 and 405 lead into the area from both the north and south, and about 30 miles of each route is exposed to intensity IX shaking. The other three north-south routes traverse the area diagonally and each has about 8 miles exposed to intensity IX shaking.
The major east-west routes traverse the area diagonally and each has about 8 miles exposed to intensity IX shaking.
Route 5 provides an alternative north-south corridor east of the zone of high intensity shaking. There are numerous alternative surface streets which can be used to bypass damaged portions of freeways.
Over 130 miles of state highways and over 350 state bridges in the Los Angeles area will be shaken at intensity IX or greater resulting from the scenario event on the Newport-Inglewood fault. Intensity IX is considered to be the threshold of critical damage to highways.
For planning purposes alternate emergency routes that are at grade (not elevated) and not likely to be affected by fallen power lines or close to heavily damaged buildings should be identified. Alternate routes are especially important along 405 north and south of Long Beach and along 710 leading into Long Beach, where significant damage may occur.
Highway emergency response plans should be coordinated with those developed for air, rail, and marine transport in order to optimize plans for integrated transportation capability. Access to and travel within the stricken area will be difficult and should be limited to the highest emergency priorities.
There are five major airports in the Los Angeles basin (Los Angeles International, Burbank, Ontario International, John Wayne, and Long Beach International). Los Angeles International alone has a passenger/personnel use of about 250,000 people per day. There are four major military airports in the area. Many small airports in the area could be used in post-earthquake response and recovery operations.
Control towers, fuel tanks, and other structures will be damaged. Runway damage due to liquefaction occurs at John Wayne and Los Alamitos (military) airports, but will be repaired within 24 hours to two days. Freeway damage will impair access to airports and damage to electrical and petroleum facilities will limit usage of airports that are operating.
Ground and rail failures occur in the Wilmington, Long Beach, and Seal Beach areas. The rail bridge to Terminal Island is closed.
The Los Angeles to Santa Monica line is closed by faulting at the bridge over Ballona Creek. The lines from Los Angeles and from Watts to El Segundo are closed due to faulting and shaking damage to bridges.
Faulting closes the line from Compton to east Long Beach. The bridge at the Route 710 crossing just west of the Los Angeles River is damaged.
The line into Seal Beach Naval Weapons Station is closed by faulting and liquefaction. The Orange to San Diego line is closed due to liquefaction.
Port Facilities at Los Angeles ---Long Beach Harbor
Access to Terminal Island is limited to Ocean Boulevard across Gerald Desmond Bridge, because of approach failures at Vincent Thomas and Schuyler Heim bridges. In Long Beach, Route 710 is closed due to liquefaction and access to the southeast basin is limited to Queensway Bridge. Liquefaction and settlement severely restrict rail access, and damage many rail-mounted gravity cranes.
Utility lines, oil pipelines, and waste water lines are extensively damaged, reducing the harbor operations to 25 percent for one week. Fires occur in the harbor area; these and ruptured oil storage facilities pose the threat of a major fire.
Oscillatory water waves in enclosed bodies of water (seiches) have damaged ships and moorings in the harbor areas from Santa Monica to Newport Beach.
SCENARIO MAPS AND DAMAGE
ASSESSMENTS ARE INTENDED FOR
EMERGENCY PLANNING PURPOSES ONLY
They are based upon the following hypothetical chain of events:
1. A particular earthquake occurs;
2. Various localities in the planning area experience
a specific type of shaking or ground failure;
3. Certain critical facilities undergo
damage and others do not.
The conclusions regarding the performance of facilities are hypothetical and not to be construed as site-specific engineering evaluations. For the most part, damage assessments are strongly influenced by the seismic intensity distribution map developed for this particular scenario earthquake. There is disagreement among investigators as to the most realistic model for predicting seismic intensity distribution. None have been fully tested and each would yield a different earthquake planning scenario. Facilities that are particularly sensitive to emergency response will require a detailed geotechnical study.
The damage assessments are based upon this specific scenario. An earthquake of significantly different magnitude on this or any one of many other faults in the planning area will result in a markedly different pattern of damage.
Photo 4. Settling cracks on Pacific Coast Highway, 1.4 miles southeast of Huntington Beach Pier, 1933 Long Beach earthquake. Photo from Long Beach Public Library collection.
Within 25 miles of the fault zone, telephone lines designated for essential services are 25 percent usable in the first day, 50 percent usable in the second day, and 75 percent usable at the end of the third day. The availability of telephone communications for the public is significantly lower.
Electric Power Facilities
Five power plants --- Harbor, Long Beach, Alamitos, Haynes, and Huntington Beach --- are shut down for more than 3 days. A post-earthquake inspection at the San Onofre nuclear power plant indicates no damage.
Five major transmission substations in the Culver City-Compton area are out of service for more than 3 days, making it difficult to re-route power into the area.
The 3 major substations serving coastal Orange County are out of service for more than 3 days, making it difficult to re-route power into the area.
The flow of water in primary transmission lines crossing or within the fault zone is reduced by half for the first day and will return to normal in a week. Areas southwest of the fault zone from Huntington Beach to Inglewood must rely on local storage or tank trucks for drinking water.
The principal treatment plants in Los Angeles County, at El Segundo and Carson, are damaged and operate at less than 50 percent capacity. The main Orange County plant is in the fault zone north of Newport Beach and is severely damaged; it will be inoperable for several months.
Main waste water lines into the Carson treatment plant from the north (San Gabriel Valley) and the east (Long Beach) are heavily damaged at the fault crossing between Compton and Long Beach.
Damage and lack of fresh water for treatment and of electrical power for pumping, result in sewage flowing into soils, channels, and streets, contaminating the ground water and the coastline.
Along the fault zone there are thousands of damaged natural gas mains, valves, and service connections. There are numerous fires in streets at broken gas lines, and in structures at broken house-line connections. Faulting causes breaks in major transmission pipelines at three locations: Slauson Avenue, 104th Street, and along the Los Angeles River.
Ground failures cause breaks in transmission lines in Sepulveda Canyon and Marina del Rey. In Long Beach Harbor the trunk line crossing at the Heim Bridge is broken due to ground failure. The high pressure gas line to the Huntington Beach power plant breaks where it crosses the marshlands east of Bolsa Chica State Park.
A major fire rages for several days at one of the refineries in the Carson-Wilmington area.
Many fuel lines rupture at the fault crossings between Baldwin Hills and Huntington Beach.
In Los Angeles Harbor, ground failures rupture oil pipelines and storage facilities, discharging oil into the channel. A fire on Mormon Island poses the threat of a major conflagration.
The fuel line to the Los Angeles Department of Water and Power power plant in east Long Beach is ruptured by faulting.
In Seal Beach, ground failures have damaged storage facilities and piping, with consequent fuel spillage into Alamitos Bay. The fuel line to Huntington Beach power plant is damaged by faulting. Facilities utilized for the manufacture, processing, and storage of various petrochemicals warrant special attention to reduce the risk of a potentially widespread release of toxic emissions.
APPLICATION OF SCENARIO
The Earthquake Planning Scenario maps and related damage assessments illustrate a regional damage pattern that is likely to occur in this specific scenario earthquake of magnitude about 7 resulting from subsurface rupture of a 45-mile length of the Newport-Inglewood fault zone. Recognition of the possible impacts will allow informed planning by state and local officials concerned with emergency preparedness and response.
This study was funded in part by the U. S. Geological Survey under the Earthquake Hazards Reduction Program.
Photo 5. Collapsed single story business building of unreinforced masonry, 1933 earthquake. Photo by Olaf P. Jenkins, DMG photo file.
Photo 6. Northwestward view along Newport-Inglewood fault zone (1941). The San Gabriel River (on right) flows into Alamitos Bay (left). Photo from Spence Collection, University of California, Los Angeles.
SELECTED BACKGROUND REFERENCES
Barrows, A. G., 1974, A review of the geology and earthquake history of the Newport-Inglewood structural zone, southern California: California Division of Mines and Geology Special Report 114, 115 p.
Bonilla, M. F., Mark, R. K., and Lienkaemper J. J., 1984, Statistical surface fault displacement: Bulletin of the Seismological Society of America, v. 74, no. 6, p. 2379-2411.
Bryant, W. A., 1985a, Fault Evaluation Report FER-172 southern Newport-Inglewood fault zone, southern Los Angeles and northern Orange Counties: California Division of Mines and Geology, 7 maps, scale 1:24,000.
Bryant, W. A., 1985b, Fault Evaluation Report FER-172 northern Newport-Inglewood fault zone, Los Angeles County, California: California Division of Mines and Geology, 12 maps, scale 1:24,000.
Bryant, W. A., 1988, Recently active traces of the Newport-Inglewood fault zone, Los Angeles and Orange counties, California: California Division of Mines and Geology, Open File Report 88-14, 15 p., 1 plate.
Davis, J. F., Bennett, J. H., Borchardt, G. A., Kahle, J. E., Rice, S. J., and Silva, M. A., 1982a, Earthquake planning scenario for a magnitude 8.3 earthquake an the San Andreas fault in the San Francisco Bay area: California Division of Mines and Geology, Special Publication 61, 160p.
Davis, J. F., Bennett, J. H., Borchardt, G. A., Kahle, J. E., Rice, S. J., and Silva, M. A., 1982b, Earthquake planning scenario for a magnitude 8.3 earthquake on the San Andreas fault in southern California: California Division of Mines and Geology, Special Publication 60, 128p.
Evernden, J. F., 1975, Seismic intensities, "size" of earthquakes, and related phenomena: Bulletin of the Seismological Society of America, v. 65, p. 1287-1315.
Evernden, J. F., and Thomson, J. M., 1985, Predicting seismic intensities in Ziony, J. I., editor, Evaluating earthquake hazards in the Los Angeles region --- an earth-science perspective: U. S. Geological Survey Professional Paper 1360, p. 151-202.
Evernden, J. F., Kohler W M., and Clow, G. D., 1981, Seismic intensities of earthquakes of conterminous United States --- their prediction and interpretation: U. S. Geological Survey Professional Paper 1223, 50 p.
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