2003 | December 22 | 19:15 | 11:15 | San Simeon | 6.5 | 2 | 35.71°N 121.10°W | 2003 San Simeon earthquake | |
2004 | September 28 | 17:15 | 10:15 | Parkfield | 6.0 | 35.81°N 120.37°W | 2004 Parkfield earthquake | ||
2005 | June 12 | 15:41 | 08:41 | Anza | 5.2 | 33.53°N 116.58°W | 2005 Anza earthquake | [53] | |
2005 | June 16 | 20:53 | 13:53 | Yucaipa | 4.9 | 34.06°N 117.01°W | 2005 Yucaipa earthquake | [54] | |
2007 | October 30 (local) October 31 (UTC) |
03:04 | 20:04 | Alum Rock | 5.6 | 37.43°N 121.78°W | 2007 Alum Rock earthquake | ||
2008 | July 29 | 18:42 | 11:42 | Chino Hills | 5.5 | 33.95°N 117.76°W | 2008 Chino Hills earthquake | ||
2009 | May 17 (PDT) May 18 (UTC) |
03:39 | 20:39 | Inglewood | 4.7 | 33.94°N 118.35°W | 2009 Inglewood earthquake | ||
2010 | January 9 (PST) January 10 (UTC) |
00:27 | 16:27 | offshore Humboldt County | 6.5 | 40.65°N 124.76°W | 2010 Eureka earthquake | [55] | |
2010 | February 4 | 20:20 | 12:20 | offshore Humboldt County | 5.9 | 40.42°N 124.92°W | |||
2010 | March 16 | 11:04 | 4:04 | Pico Rivera | 4.4 | 33.992°N 118.082°W | 2010 Pico Rivera earthquake | [56] | |
2010 | April 4 | 22:40 | 15:40 | northern Baja California | 7.2 | 3 | 32.128°N 115.303°W | 2010 El Mayor-Cucapah earthquake | [57] |
2010 | June 14 (PDT) June 15 (UTC) |
04:26 | 21:26 | Ocotillo | 5.7 | 32.698°N 115.924°W | 2010 El Mayor-Cucapah aftershock | [58] | |
2010 | July 7 | 23:53 | 16:53 | Borrego Springs | 5.4 | 33.417°N 116.483°W | 2010 Borrego Springs earthquake | [59] | |
2011 | January 7 | 23:10 | 16:10 | San Jose California | 4.1 | 37.287°N 121.658°W | 2011 Calaveras earthquake | ||
2011 | January 12 | 23:51 | 08:51 | San Juan Bautista | 4.5 | 36.77°N 121.499°W | 2011 Cox Sleeper earthquake | [60] | |
2012 | August 26 | 19:31 | 12:31 | Brawley | 5.3 | 33.019°N 115.546°W | 2012 Brawley Earthquake Swarm | [61] | |
2012 | December 14 | 10:36 | 02:36 | Off the southwest coast of Catalina Island | 6.3 | 31.2°N 119.6°W | 2012 Avalon Earthquake | [62] | |
2013 | May 23 (PDT) May 24 (UTC) |
03:47 | 20:47 | near Lake Almanor, Greenville | 5.7 | 40.190°N 121.061°W | (swarm) | USGS | |
2013 | October 11 | 23:05 | 16:05 | near Eureka, Humboldt | 4.9 | 40.969°N 124.747°W | [63] |
Preparedness
There are many ways to protect and prepare possible sites of earthquakes from severe damage, through the following processes: Earthquake engineering, Earthquake preparedness, Seismic retrofit (including special fasteners, materials, and techniques), Seismic hazard, Mitigation of seismic motion, and Earthquake prediction.The United States Geological Survey (USGS) and California Institute of Technology (Caltech) provide public education to California. They hope to provide "public education about seismic hazards and methods of reducing or preventing seismic disaster damage." The California Earthquake Authority outlined the risks earthquakes pose to California and measures households can take to "Quake Safe" their house. Putting Down Roots in Earthquake Country and Dare To Prepare are some of the Earthquake Readiness Campaigns.
"Putting Down Roots in Earthquake Country" is a popular 32-page earthquake science and preparedness handbook was first published in 1995 by the SCEC.[64]
end partial quote from:
List of earthquakes in California - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/List_of_earthquakes_in_California
Earthquakes in California are common occurrences since the state is located on the ... The largest recorded earthquake in California was the 1857 Fort Tejon ...
As you can plainly see above there hasn't been anything above about a 6.5 since the 1990s here in California. This is likely why almost no one has died from any earthquake since the 1990s too.
If you add up all the people who died from earthquakes since 1800 in California it is:
3,463 (and this is just the bodies that they could find) since then.
But, the last person to die from an earthquake in California (that anyone knows of) is:
2 people in the San Simeon Earthquake in 2003.
So, so Far we have gone 10 years now with no deaths in California at all from Earthquakes.
My worst experience in an earthquake was coming home from a drive-in movie from Palm Springs up to where I was living with my parents in a friends Desert Cabin temporarily that winter. I woke up suddenly very early in the morning because I was bouncing up and down on my bed from the force of the earthquake. I figured I was less likely to be injured on the bed so I centered myself on the bed as I bounced so I wouldn't be injured or die from edges of the bed or from ramming my head into a wall or ceiling from the force of the earthquake.
The thing is if you have lived in California any length of time 10 to 20 years you have experienced many many earthquakes in the 4.0 to 6.0 range. There are a whole lot of 4.0s and 5.0s but very very few 6.0 or above.
So, as you start to bounce around you look at pictures on the wall moving and chandeliers moving and swaying and if you are in a swimming pool you either want to go to the center of the pool so you don't get a concussion and drown in the pool. If you are inside you want to be in a well built (not old fashioned brick building built before re-bar (reinforcement iron bars were used). Otherwise if the building is too old in a California earthquake you could die from being crushed by bricks. But, most of these buildings have been retrofitted now enforced by law.
As the pictures start falling off the wall and things start to break and fall off shelves like books and trinkets a family might have saved for 50 years or more you start to worry about whether you are going to survive this.
This worst one was the San Fernando Earthquake that I'm talking about in 1971. I was 23 at the time and this was the only earthquake where I thought I was going to die for at least a few minutes. Also, it was so bad at the time that I wasn't sure whether it was a nuclear blast or an Earthquake and this too was pretty terrifying to deal with. And this thing just got bigger and bigger and bigger and never seemed to stop so by the time it finally slowed down and stopped you were pretty messed up because it was sort of like experiencing the END OF THE WORLD (even if it is just the end of your entire family). What is amazing to me is that I was at least 120 miles or more from the epicenter and that it was this bad this far out from it.
Since there also was a joshua tree earthquake eventually I have realized since then our house was very near one of the fault lines that was also moving. So, even though our desert home wasn't torn in two like some were in later quakes we experienced this because of the fault nearby us likely moving too. I realized that they named this later quake the:
Since there also was a joshua tree earthquake eventually I have realized since then our house was very near one of the fault lines that was also moving. So, even though our desert home wasn't torn in two like some were in later quakes we experienced this because of the fault nearby us likely moving too. I realized that they named this later quake the:
-
The 1992 Landers earthquake was a magnitude 7.3 earthquake that occurred on June 28 ... The quake was preceded by the 6.1 magnitude Joshua Tree ...8 KB (1,131 words) - 20:24, 18 November 2013This earthquake even though I didn't live there then IN 1992 (I ONLY LIVED THERE FULL TIME NEAR YUCCA VALLEY IN THE WINTER OF 1970-71), the epicenter was only a few miles (not more than 10) from where we were during the San Fernando Earthquake. So, likely the San Fernando Earthquake set the stage underground for the Landers Earthquake about 20 years later.
Here is THE WORST EARTHQUAKE I EVER HAD TO EXPERIENCE AND LIVE THROUGH: from Wikipedia:
1971 San Fernando earthquake
From Wikipedia, the free encyclopedia
(Redirected from San Fernando Earthquake)
The San Gabriel Mountains with the Veterans Hospital complex in center
|
|
Date | February 9, 1971 |
---|---|
Origin time | 14:00:41 UTC |
Duration | 12 seconds [1] |
Magnitude | 6.6 ML [2] |
Depth | 13 km (8.1 mi) [2] |
Epicenter | 34.41°N 118.40°WCoordinates: 34.41°N 118.40°W [3] |
Type | Thrust |
Countries or regions | Southern California United States |
Total damage | $553 million [4] |
Max. intensity | XI (Extreme) [3] |
Peak acceleration | 1.25g at Pacoima Dam [5] |
Landslides | Yes |
Casualties | 64 killed [4] |
The event impacted a number of health care facilities in the Sylmar, San Fernando, and other densely populated areas north of Los Angeles. The Olive View Medical Center and Veterans Hospital both experienced very heavy damage and buildings collapsed at both sites causing the majority of deaths that occurred. The buildings at both facilities were put together with mixed construction styles, but engineers were unable to thoroughly study the buildings' responses because they were not outfitted with instruments for recording strong ground motion, and this prompted the Veterans Administration to install seismometers at all of its high risk sites. Other sites throughout the Los Angeles area had been instrumented as a result of local ordinances and an extraordinary amount of strong motion data was recorded, more so than any other event up until that time, and the success in this area spurred the initiation of California's Strong Motion Instrumentation Program.
Transportation around the Los Angeles area was severely afflicted with roadway failures and the collapse of several major freeway interchanges. The near total failure of the Van Norman Dam resulted in the evacuation of tens of thousands of downstream residents, though an earlier decision to maintain the water at a lower level may have contributed to saving the dam from being overtopped. Schools were strongly affected, as they had been during a previous earthquake in Long Beach, but this time amended construction styles greatly improved the outcome for the thousands of school buildings in the Los Angeles area. Other aspects of the event included a methane seep that emanated from the floor of the Pacific Ocean near Malibu for several days following the earthquake, and hundreds of various types of landslides that were photographically documented and visually surveyed in the San Gabriel mountains. As had happened following other earthquakes in California, legislation related to building codes were once again revised, with laws that addressed construction (Alquist Priolo Special Studies Zone Act) near or adjacent to active fault zones.
Contents
Earthquake
The magnitude 6.6 San Fernando earthquake occurred on February 9 at 6:00:41 am Pacific Standard Time (14:00:41 UTC) and had a duration of about 12 seconds. The origin of faulting was located five miles north of the San Fernando valley and considerable damage was seen in localized portions of the valley and also in the foothills of the San Gabriel mountains above the fault block. The fault that was responsible for the movement was not one that had been considered a threat, and this highlighted the urgency to identify other similar faults in the Los Angeles metropolitan area. The shaking surpassed building code requirements and exceeded what engineers had prepared for and although most dwellings in the valley were built in the prior two decades, even modern earthquake resistant structures sustained serious damage.[6]Several key attributes of the event were shared with the 1994 Northridge earthquake considering both were brought about by slip of steeply dipping thrust faults in the mountains north of Los Angeles (though no ground rupture occurred in 1994) and the resulting earthquakes were similar in magnitude. Since both occurred in urban and industrial areas and resulted in significant economic impairment, each event has drawn critical observation from planning authorities and has been thoroughly studied in the scientific communities.[7]
Landslides
See also: Landslide classification
Analysis of aerial photographs taken for the USGS by a private company and the United States Air Force
over 250 square kilometers of the mountainous areas north of the San
Fernando Valley revealed that the earthquake triggered over 1,000
landslides. Also documented was the occurrence of highly shattered rock
along the ridge tops, and rockfalls that were the result of both the
initial shock and the aftershocks, which continued for several days, but
few of the slides that were logged from the air were also observed from
the ground. The greatest number of slides were centered to the
southwest of the mainshock epicenter and close to the areas where
surface faulting took place. The extent of the slides ranged from 15–300
meters (49–980 ft) in length, and could be further categorized as rock
falls, soil falls, debris slides, avalanches, and slumps. The most
frequently-encountered type of slide was the surficial (less than one
meter thick) debris slides and were most often encountered on terrain
consisting of sedimentary rock.[8]Aftershocks
Aftershocks | ||
5.8 ML | Feb 9 at 14:01:08 | |
5.8 ML | Feb 9 at 14:02:44 | |
5.3 ML | Feb 9 at 14:10:28 | |
5.2 ML | Feb 9 at 14:43:47 | |
Allen, Hanks & Whitcomb 1975, p. 260 |
Main article: Aftershock
A three week inspection of the aftershock activity was undertaken
that included events that were recorded by an array of permanent
stations that were operated by the California Institute of Technology, a USGS instrument stationed at Point Mugu, and California Department of Water Resources
seismometers at Pyramid Springs and Cedar Springs. Temporary
seismometers that were set up in response to the mainshock were up and
running from as soon as several hours to several days after the main
event and provided data up to March 1. The catalog of items that were
recorded included 200 shocks of magnitude 3.0 or greater and four shocks
of magnitude 5.0 or greater and was mostly complete, with the exception
of the first hour of activity, when the larger aftershocks were
overshadowing the smaller events.[2]The overall pattern of aftershock activity appeared in the shape of a symmetrical inverted "U" but with slightly more concentrated activity on the southwest flank. Several of the smaller shocks approached the area of surface faulting, but for the most part, the area directly under the area of heaviest shaking and damage lacked aftershock activity. The Pacoima Dam, with its unusually high peak ground acceleration reading, laid very close to the center of that aftershock-free zone.[2]
Surface faulting
For more details on this topic, see Fault (geology).
Prominent surface faulting trending N.72°W was observed along the San
Fernando Fault Zone from a point south of Sylmar stretching nearly
continuously for 10 kilometers (6.2 mi) east to the Little Tujunga
Canyon. Additional breaks occurred farther to the east, but were in a
more scattered fashion, while the western portion of the most affected
area saw scarps (especially the detached Mission Wells segment) that
were less pronounced. Although the complete Sierra Madre Fault Zone had
previously been mapped and classified by name into its constituent
faults, the clusters of fault breaks provided a natural way to identify
and refer to the areas. As categorized during the intensive studies
immediately following the earthquake, the sections were labeled the
Mission Wells segment, Sylmar segment, Tujunga segment, Foothills area,
and the Veterans fault.[9][10]All of the segments shared the common elements of thrust faulting with a component of left-lateral slip, a general east-west strike and a northward dip, but they were not unified with regard to their connection to the associated underlying bedrock. The initial surveyors of the extensive faulting in the valley, foothills, and mountains reported only tectonic faulting while excluding fissures and other features that arose from the effects of compaction and landsliding. In the vicinity of the Sylmar fault segment there was a low possibility of landslides due to a lack of elevation change, but in the foothills and mountainous area a large amount of landsliding occurred and more work was necessary to eliminate the possibility of misidentifying a feature. Along the hill fronts of the Tujunga segment some ambiguous formations were present because some scarps may have had influence from downhill motion, but for the most part they were tectonic in nature.[9]
In repeated measurements of the different fault breaks at locations following the earthquake, the results remained consistent, leading to the belief that most of the slip had occurred during the mainshock. While lateral, transverse, and vertical motions were all observed after the earthquake, the largest individual component of movement was 1.6 m (5 ft 3 in) of left lateral slip near the middle of the Sylmar segment. The largest cumulative amount of slip of 2 meters (6 ft 7 in) occurred along the Sylmar and Tujunga segments, and the overall fault displacement was summarized by geologist Barclay Kamb and others as "nearly equal amounts of north-south compression, vertical uplift (north side up), and left lateral slip and hence may be described as a thrusting of a northern block to the southwest over a southern block, along a fault surface dipping about 45° north."[11]
Previous seismicity
See also: Paleoseismology
The San Fernando earthquake was the first in a series (1987 Whittier Narrows,
1991 Sierra Madre) of damaging earthquakes on reverse faults in the Los
Angeles area that culminated with the 1994 Northridge event. The events
triggered discussions concerning the largest magnitude earthquake that
could be generated by one of the faults, especially in the Transverse Ranges, but the focal point of earthquake hazard assessments in California are often the San Andreas Fault and other associated dextral
faults. Although there is a lack of paleoseismic data on reverse faults
in the Los Angeles area, a trench excavation at a site on the Sierra
Madre-Cucamonga fault revealed that two large historic earthquakes
occurred in the last 15,000 years.[12]Situated at the boundary to the San Gabriel Valley and San Fernando Valley, the Sierra Madre-Cucamonga fault runs along the southern edge of the San Gabriel Mountains for a total of 95 kilometers (59 mi) where the northwestern most 19 km (12 mi) comprises the San Fernando fault (the section responsible for the February 9 earthquake). A 1980's fault study including mappings and a trench excavation determined that a major earthquake had most likely not occurred to the east of the San Fernando rupture area for at least the last several thousand, and possibly the last 11,000 years.[12]
The fault was studied again in the late 1990s in the Loma Alta Park near Millard Canyon where a fault scarp larger than 2 m (6 ft 7 in) was accessible along a (late quaternary) elevated stream terrace. The clearly defined fault was exposed in the trench and emerged as a .5 m (1 ft 8 in) band of course gravels lining the hanging wall. By studying the truncated rocks and a wedge-shaped accumulation of gravel and soil, it was possible to visually reconstruct the original geometry of the rock prior to the thrust and eventual and partial collapse of the hanging wall back onto the footwall. It was found that the youngest debris in the colluvium dated to 10,000 ka (giving a rupture date for the most recent earthquake of within the last 10,000 years) and an estimate of the maximum slip given for the event was 3.8–4 meters (12–13 ft).[12]
The evidence found at the Loma Alta trench investigation site brought new information into the deliberation regarding the maximum size of earthquakes near Los Angeles. The large amount of slip observed there did not correspond with a short 15–20 km (9.3–12 mi) rupture length of the Sierra Madre Fault Zone, and instead suggested that the historical thrust earthquakes were much larger in magnitude than what was seen with the 1971 event, given its smaller 2 meters (6 ft 7 in) of maximum observed displacement. Two methods were employed to infer the scope of the events at the site (one regression-based and the other based on the seismic moment) and produced a maximum magnitude of 7.5 or 7.6 for the most recent movement of the fault. The results supported an earlier hypothesis that seismic energy release on the Sierra Madre Fault Zone is characterized by infrequent but large earthquakes. A duplicate event in modern times would rupture to the south towards populated areas and would produce strong ground motion capable of damaging modern buildings and other critical infrastructure.[12]
Ground acceleration
Main article: Peak ground acceleration
In early 1971 the San Fernando Valley was the scene of a congested
network of strong-motion seismometers, which provided a total of 241 seismograms (by comparison, the 1964 Alaska earthquake
did not provide any strong motion records) and this made the earthquake
the most documented event (at the time) in terms of strong-motion seismology. Part of the reason there had been so many stations that recorded the event was due to a 1965 ordinance
that was passed that required newly constructed buildings in Beverly
Hills and Los Angeles over six stories in height to be outfitted with
three of the instruments. This stipulation ultimately found its way into
the Uniform Building Code
as an appendix several years later. One hundred and seventy five of the
recordings came from these buildings, another 30 were on hydraulic structures, and the remainder were from ground-based installations near faults, including an array of the units across the San Andreas Fault.[13]The instrument that was installed at the Pacoima Dam recorded peak acceleration (1.25g) that was twice as large as any previously seen from an earthquake, though the extraordinarily high acceleration was just part one part of the picture, considering that duration and frequency of shaking also play a role in how much damage can occur. The accelerometer at that location was firmly mounted on a concrete platform on a granite ridge just above one of the arch dam's abutments. Cracks formed in the rocks and a rock slide came within 15 feet of the apparatus, and the foundation remained undamaged, but a small (half-degree) tilt of the unit was discovered that was apparently responsible for closing the horizontal pendulum contacts. As a result of what was considered a fortunate accident, the machine kept recording for six minutes (until the unit's paper ran out) and the scientists were left with additional data on 30 of the initial aftershocks.[13]
Natural gas emission
See also: Petroleum seep and Sedimentary organic matter
At eight o'clock on the morning of February 9 eyewitnesses noticed
abundant natural gas escaping the ocean surface near Malibu Point, which
is situated about 50 km (31 mi) to the southwest from the earthquake's
epicenter, and where some homes suffered minor structural damage. The
gas had probably been escaping since the time of the mainshock, but had
not been noticed because fog had reduced the visibility close to the
coast. The seep originated on the ocean floor under 6–8 m (20–26 ft) of
water about 500 m (1,600 ft) from the mouth of Malibu Creek.
The location was within the Malibu Coast deformation zone that is
underlain by a number of north-dipping faults. Samples of the gas were
obtained by teams from the USGS as well as from Los Angeles County from
near the sea floor, where the stratum consists of marine shale,
mudstone, siltstone, and sandstone.[14]The bubbles rose from an area on the sea floor that contained profuse organic material and were found to contain mostly methane, with smaller portions of nitrogen, carbon dioxide, oxygen, and argon. The bubbles escaped the ocean's surface over an area that covered 120 m (390 ft) by 12 m (39 ft) at a rate of one to five per second on February 11, but two days earlier they were emanating at a higher rate, and this is also when an additional zone of bubbles was seen closer to the shore. The gas was coming from small holes and craters on the sea floor that were several millimeters to as large as 40 centimeters (16 in) in diameter. The craters contained abundant grass and other organic debris, and the greatest concentration of gas appeared to be coming from the areas with the most organic material and from the larger craters, which were arranged in groups that were several centimeters to several meters apart and were somewhat aligned with the N.78°E orientation of the emanation at the surface.[14]
No ruptures were seen on the sea floor during the exploration dives, and because the cohesive nature of the sediment inhibited its movement on the sea floor, any scarps or fissures that were generated at the time of the earthquake would still have been present since the earthquake had occurred two days prior. It was determined that the composition of the gas had characteristics of marsh gas and had been released after having been formed in the decaying material in the sediment or having been trapped in the bedrock, but neither proposal could be eliminated at the time of the analysis.[14]
Damage
The areas that were affected by the strongest shaking were the outlying communities north of Los Angeles bounded by the northern edge of the San Fernando Valley at the base of the San Gabriel Mountains, with the exception of the unincorporated districts of Newhall, Saugus, and Solemint Junction, where moderate damage was also present, even to newer buildings. The area where the heaviest effects were present was limited by geographical features on the three remaining margins, with the Santa Susana Mountains on the west, the Santa Monica Mountains and the Los Angeles River to the south, and along the Verdugo Mountains to the east. Loss of life that was directly attributable to the earthquake amounted to 58, but a number of heart attack and other health-related deaths were not included in this figure. Most deaths occurred at the Veterans and Olive View hospital complexes, and the rest were spread between private residences, the highway overpass collapses, and a ceiling collapse at the Midnight Mission in downtown Los Angeles.[15]The damage was greatest both near and well north of the surface faulting as well as at the foot of the mountains. The hospital buildings, the freeway overpasses, and the Sylmar Juvenile Hall facility were situated on course alluvium that overlaid thousands of feet of loosely consolidated sedimentary material. Underground water, sewer, and gas systems did not fare well in the city of San Fernando where the breaks were too numerous to count and some sections were so badly damaged that they were abandoned. Ground displacement damaged sidewalks and roadways with cracks in the more rigid asphalt and concrete often exceeding the width of the shift in the underlying soil. Accentuated damage near alluvium had been documented previously during the investigation of the effects of the 1969 Santa Rosa earthquakes. A band of similarly intense damage further away near Ventura Boulevard at the southern end of the valley was also identified as having been related to the soil type.[16]
A number of federal, county, and private hospitals suffered varying degrees of damage, with four major facilities in the San Fernando valley experiencing structural damage and two of those experiencing collapse. The Indian Hills Medical Center, Foothill Medical Building, and the Pacoima Lutheran Professional building were all heavily damaged, but nursing homes were also affected. One facility in particular, the one-story Foothill Nursing Home, sat very close to a section of the fault that broke the surface and was raised up three feet relative to the street where surface faulting ran along the sidewalk and across the property, but the building was not in use at the time and remained standing. Though the reinforced concrete block structure was afflicted by the shock and uplift, the relatively good performance was in stark contrast to the Olive View and Veterans Hospital complexes.[17]
Olive View Hospital
Main article: Olive View – UCLA Medical Center
The majority of the buildings at the Los Angeles County-owned,
880 bed hospital complex had been built prior to the adoption of new
construction techniques that had been put in place following the 1933 Long Beach earthquake.
Some of the buildings at the large facility escaped damage, like the
set of one-story structures 300 feet west of the new facility, but those
that did have damage consisted of either wood frame or masonry
structures. The five story reinforced concrete Medical Treatment and
Care Building was one of three new additions to the complex (all three
sustained damage) and was assembled with earthquake-resistant construction
techniques and was completed in 1970. The hospital was staffed with 98
employees and had 606 patients at the time of the earthquake and all
three of the deaths that occurred at the Olive View complex were in this
building. Two were due to power failure of life support systems and
one, an employee who was struck by a portion of the collapsing building
as they attempted to exit the building, was a direct result of the
destruction.[17]The Medical Care building building included a basement level that was exposed (above grade) on the east and south sides, mixed (above and below grade) on the west side, and below grade on the north side of the building, due to the shallow slope at the site. The complete structure, including the four external stairways, could be considered five separate buildings, since the stair towers were detached from the main building by about four inches. Earthquake bracing used in the building's second through fifth floors consisted of shear walls, but a rarely used slip joint technique used with the concrete walls at the first floor level excluded them from being used as shear walls. Damage to the building was described as excessive at the basement and first floor levels (including ceiling tiles, telephone equipment, and elevator doors) with little damage further up, and the difference in rigidity at the second floor was proposed as a cause of the considerable damage to the lower levels. As a result of the first floor nearly collapsing, the building was leaning to the north by nearly two feet, and three of the four concrete stair towers fell away from the main building.[17]
On the grounds of the facility, cracks in the pavement and soil were present (though no surface faulting was present) plus power and communications failures affected the hospital at the time of the earthquake. In addition to the collapse of the stairways, the elevators were out of commission. Very few people occupied the lower floors of the building and the stairways at the early hour and casualties in these highly affected areas may have increased had the shock occurred later in the day. The duration of strong ground motion was probably similar to the 12 seconds that was observed at the Pacoima dam and an additional length of shaking may have been enough to bring the building to collapse.[17]
Veterans Hospital
The Veterans Hospital entered into service as a tuberculosis hospital in 1926 and became a general hospital in the 1960s. By 1971 the facility comprised 45 individual buildings, all lying within 5 km (3.1 mi) of the fault rupture in Sylmar, but the structural damage was found to have occurred as a result of the shaking and not from ground displacement or faulting. Twenty six buildings that were built prior to 1933 had been constructed following the local building codes and did not require seismic-resistant designs. These buildings suffered the most damage, with 4 buildings totally collapsing, and resulted in a large loss of life at the facility. Most of the masonry and reinforced concrete buildings constructed after 1933 withstood the shaking and most did not collapse, but in 1972 a resolution came forth to abandon the site and since that time the remaining structures were demolished.[18]Few strong motion seismometer installations were present outside of the western United States prior to the San Fernando earthquake but, upon a recommendation by the Earthquake and Wind Forces Committee, the Veterans Administration entered into an agreement with the Seismological Field Service (then associated with NOAA) to install the instruments at all VA sites in Uniform Building Code zones two and three. It had been established that these zones had a higher likelihood of experiencing strong ground acceleration and the plan was made to furnish the selected VA hospitals with two instruments where one unit would be installed within the structure and the second would be set up as a free-field unit located a short distance away from the facility. As of 1973 a few of the highest risk (26 were completed in zone 3 alone) sites that had been completed were in Seattle, Memphis, Charleston, and Boston.[18]
Van Norman dam
See also: Baldwin Hills Reservoir and Bull Creek (Los Angeles County)
Both the Upper and Lower Van Norman Dam were severely damaged as a
result of the earthquake. The lower dam was very close to overflowing
and approximately 80,000 people were evacuated for four days while the
water height in the reservoir was lowered. This was done as a precaution
to accommodate further collapse due to a strong aftershock. Some canals
in the area of the dams were damaged and not usable, and dikes
experienced slumping but these did not present a hazard. The damage at
the lower dam consisted of a landslide that dislocated a section of the
embankment. The earthen lip of the dam fell into the reservoir and
brought with it the concrete lining while what remained of the dam was
just 1.5 meters (4 ft 11 in) above the water level. The upper lake subsided
.9 m (2 ft 11 in) and was displaced about 1.5 m (4 ft 11 in) as a
result of the ground movement and the dam's concrete lining cracked and
slumped.[19]The upper dam was constructed in 1921 with the hydraulic fill process, three years after the larger lower dam, which was fabricated the same way. An inspection of the lower dam in 1964 paved the way towards an arrangement between the State of California and the Los Angeles Department of Water and Power that would maintain the reservoir's water level that was reduced 10 feet lower than was typical. Since the collapse of the dam lowered its overall height the decision to reduce its capacity proved to be a valuable bit of insurance.[19]
Differential ground motion and strong shaking (MM VIII) was responsible for severe damage to the Sylmar Juvenile Hall facility and the Sylmar Converter Station (both located close to the Upper Van Norman lake). The Los Angeles Department of Water and Power as well as the County of Los Angeles investigated and verified that local soil conditions were the cause of the ground displacement and resulting destruction. The area of surface breaks on the ground at the site was 900 ft (270 m) (at its widest) and stretched 4,000 ft (1,200 m) down a 1% grade slope towards the southwest. As much as 5 ft (1.5 m) of lateral motion was observed on either end of the slide, and trenches that were excavated during the examination at the site revealed that some of the cracks were found as deep as 15 ft (4.6 m). The two facilities, located near Grapevine and Weldon canyons that channel water and debris off the Sierra Madre mountains, are lined by steep ridges and have formed alluvial fans at their mouths. The narrow band of ground disturbances were found to have been the result of settling of the soft soil in a downhill motion. Soil liquefaction played a role within confined areas of the slide, but it could not be responsible for all of the motion at the site, and tectonic slip of faults in the area was also excluded as a cause.[20]
Transportation
See also: Southern California freeways
Substantial disruption to about 10 miles of the freeways in the
northern San Fernando Valley took place with most of the damage
occurring at the Foothill Freeway / Golden State Freeway interchange and
along a five mile stretch of Interstate 210. On Interstate 5, the most
significant damage was between the Newhall Pass interchange on the north
end and the I-5 / I-405
interchange in the south, where subsidence at the bridge approaches and
cracking and buckling of the roadway made it unusable. Several
landslides occurred between Balboa Boulevard and California State Route 14,
but the most significant damage occurred at the two major interchanges.
The Antelope Valley Freeway had damage from Newhall Pass to the
northeast, primarily with settling and alignment issues, and splintering
and cracking at the Santa Clara River and Solemint bridges.[21]- Golden State Freeway - Antelope Valley Freeway Interchange
Main article: Newhall Pass interchange
While the Newhall Pass interchange was still under construction at
the time of the earthquake, the requisite components of the overpass
were complete. Two of the bridge's 191-foot sections fell from a maximum
height of 140 ft (43 m) at the site, along with one of the supporting
pillars, when vibration caused the spans to slip off of their supports
at either end due to lack of proper ties and insufficient space (a 14 in
(360 mm) seat was provided) on the support columns. Ground displacement
at the site was ruled out as a major cause of the failure and in
addition to the fallen sections and a crane that was struck during the
collapse, other portions of the overpass were also damaged. Shear
cracking occurred at the column closest to the western abutment, and the
ground at the same column's base exhibited evidence of rotation.[22]- Golden State Freeway - Foothill Freeway Interchange
Main articles: Interstate 5 in California and Interstate 210 and State Route 210 (California)
This interchange is a broad complex of overpasses and bridges that
was nearly complete at the time of the earthquake and not all portions
were open to traffic. Several instances of failure or collapse at the
site took place and two men were killed while driving in a pickup truck
as a result. The westbound I-210 to southbound I-5, which was complete
with the exception of paving at the ramp section, collapsed to the
north, likely because of vibration that moved the overpass off its
supports due to a seat that was too short. Unlike the situation at the
Antelope Valley Interchange, permanent ground movement (defined as
several inches of left-lateral displacement with possibly an element of
thrusting) was observed in the area. The movement contributed to heavy
damage at the Sylmar Juvenile Hall facility, Sylmar Converter Station,
and the Metropolitan Water District Treatment Plant, but its effects on
the interchange was not completely understood as of a 1971 report from
the California Institute of Technology.[22]Schools
See also: Atwater Avenue Elementary School (Los Angeles), Bishop Alemany High School, John Marshall High School (Los Angeles, California), and Patrick Henry Middle School (Los Angeles, California)
The large number of public school buildings in the Los Angeles area
displayed mixed responses, and those that were built after the
enforcement of the Field Act
clearly showed the results of the reformed construction styles. The
Field Act was put into effect just one month following the destructive
March 1933 Long Beach earthquake that heavily damaged many public school
buildings in Long Beach, Compton, and Whittier. The Los Angeles Unified School District had 660 schools consisting of 9,200 buildings at the time of the earthquake with 110 masonry buildings that had not been reinforced to meet the new standards. Also in use were more than 400 portables and 53 wood frame
pre-Field Act buildings. All of these buildings had been previously
inspected with regard to the requirements of the Act, and many were
reinforced or rebuilt at that time, but earthquake engineering experts
recommended further immediate demolition or refurbishment after a
separate evaluation was done after the February 1971 earthquake and
within a year and a half the district followed through with the
direction with regard to about 100 structures.[23]At Los Angeles High School (20 mi (32 km) from Pacoima Dam) where the exterior walls of the main pre-Field Act building (constructed 1917) were unreinforced brick masonry, long portions of the parapet and the associated brick veneer broke off and some of the fragments fell through the roof to a lower floor, while other material landed on an exit stariway and into a courtyard area. The main building was demolished at a cost of $127,000, and none of the various post-Field Act buildings were damaged at the site. With the exception of the concrete gymnasium, all of the buildings at Sylmar High School (3.75 mi (6.04 km) from Pacoima Dam) were post-Field Act, one-story, wood construction. Abundant cracks formed in the ground at the site, and some foundations and many sidewalks were also cracked. The estimate for repairs at the site was $485,000. At 2 mi (3.2 km), Hubbard Street Elementary School was the closest school to Pacoima dam, and was also less than a mile from the Veterans Hospital complex. The wood frame buildings (classrooms, a multipurpose building, and some bungalows) were built after the Field Act, and damage and cleanup costs there totaled $42,000. Gas lines were broken and separation of the buildings' porches was due to lateral displacement of up to six inches.[23]
Aftermath
Following many of California's major earthquakes, lawmakers have acted quickly to develop legislation that has been focused on public outreach and funding research, but some of the directives that related to seismic retrofits were left incomplete, partly due to the passage of time following the disasters, when the drive to follow through with improvements to regulation often subsided. Legislation was drafted following other damaging California earthquakes including the 1933 Long Beach earthquake (Field Act, Garrison Act) and the 1984 Morgan Hill earthquake (Unreinforced Masonry Building Law). One of the laws that arose after the San Fernando earthquake that focused on health care facilities was The Hospital Seismic Safety Act that called for the application of medical facility safety standards to all new hospital construction.[24]- California Strong Motion Instrumentation Program
See also: 1940 El Centro earthquake
Earthquake engineers in Southern California
were exposed to a small number of compelling seismograms in the 1930s
and 1940s, but strong-motion seismology was not specifically sought by
seismologists until later events occurred. The San Fernando earthquake
made evident the need for strong-motion data for improvements in
earthquake engineering applications and the California Strong Motion
Instrumentation Program originated with the goal of maximizing the
volume of data by furnishing and maintaining instruments at selected
buildings, structures, and ground response stations.[25][26]- Alquist Priolo Special Studies Zone Act
See also: Al Alquist
Introduced as Senate Bill 520 and signed into law in December 1972,
the AP Act was originally known as the Alquist-Priolo Geologic Hazard
Zones Act, and the legislation has the goal of reducing damage and
losses due to surface fault ruptures. The act restricts construction of
buildings designed for human occupancy across a fault that is known to
be active. The state geologist is responsible for mapping well-defined
faults that have evidence of surface faulting within the last 11,000
years and creating regulatory zones with relation to the potentially
active faults. The State Mining and Geology Board then holds public
hearings concerning the worthiness of the zone in the wake of a 90 day
review period. State, county, and city agencies are then responsible for
enforcing the building restrictions within their jurisdiction.[27]See also
- California State Route 126
- Earthquake (film)
- Interstate 105 (California)
- Long Beach Search and Rescue
- San Gabriel Fault
- Wadsworth Chapel
References
- Jump up ^ Maley, R. P.; Cloud, W. K. (1971), "Preliminary strong-motion results from the San Fernando earthquake of February 9, 1971", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, p. 163
- ^ Jump up to: a b c d Allen, C.R.; Engren, G.R.; Hanks, T.C.; Nordquist, J.M.; Thatcher, W.R. (1971), "Main shock and larger aftershocks of the San Fernando earthquake, February 9 through March 1, 1971", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, pp. 17–19
- ^ Jump up to: a b Stover, C. W.; Coffman, J. L. (1993), Seismicity of the United States, 1568-1989 (Revised) – U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, p. 92
- ^ Jump up to: a b Reich, Kenneth (February 4, 1996). "'71 Valley Quake a Brush With Catastrophe". Los Angeles Times.
- Jump up ^ Cloud & Hudson 1975, pp. 278, 287
- Jump up ^ Steinbrugge, K. V.; Schader, E. E.; Bigglestone, H. C.; Weers, C. A. (1971). San Fernando Earthquake: February 9, 1971. Pacific Fire Rating Bureau. p. vii.
- Jump up ^ Bolt, B. (2005), Earthquakes: 2006 Centennial Update – The 1906 Big One (Fifth ed.), W. H. Freeman and Company, pp. 106–107, ISBN 978-0716775485
- Jump up ^ Morton, D. M. (1971b), "Seismically triggered landslides in the area above the San Fernando Valley", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, p. 99
- ^ Jump up to: a b Kamb et al. 1971, pp. 41–43
- Jump up ^ U.S Geological Survey Staff (1971), "Surface faulting", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, p. 57
- Jump up ^ Kamb et al. 1971, p. 44
- ^ Jump up to: a b c d Rubin, C. M.; Lindvall, S. C.; Rockwell, T. K. (1998). "Evidence for Large Earthquakes in Metropolitan Los Angeles". Science (American Association for the Advancement of Science) 281 (5375): 398–402. doi:10.1126/science.281.5375.398.
- ^ Jump up to: a b Cloud & Hudson 1975, pp. 273, 277, 287
- ^ Jump up to: a b c Clifton, H. E.; Greene, H. G.; Moore, G. W.; Phillips, R. Lawrence (1971), "Methane seep off Malibu Point following the San Fernando earthquake", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, pp. 112–116
- Jump up ^ Steinbrugge, Schader & Moran 1975, pp. 323–325
- Jump up ^ Steinbrugge, Schader & Moran 1975, pp. 350–353
- ^ Jump up to: a b c d Steinbrugge, Schader & Moran 1975, pp. 341–346
- ^ Jump up to: a b Bolt, B.; Johnston, R. G.; Lefter, J.; Sozen, M. A. (1975), "The study of earthquake questions related to Veterans Administration hospital facilities", Bulletin of the Seismological Society of America (Seismological Society of America) 65 (4): 937, 938, 943–945
- ^ Jump up to: a b Youd, T. L.; Olsen, H. W. (1971), "Damage to constructed works, associated with soil movements and foundation failures", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, pp. 126–129
- Jump up ^ Smith, J. L.; Fallgren, R. B. (1975), "Ground displacement at San Fernando Valley Juvenile Hall and the Sylmar Converter Station", San Fernando, California, earthquake of 9 February 1971, Bulletin 196, California Division of Mines and Geology, pp. 157–158, 163
- Jump up ^ California Division of Highways (1975), "Highway damage in the San Fernando earthquake", San Fernando, California, earthquake of 9 February 1971, Bulletin 196, California Division of Mines and Geology, p. 369
- ^ Jump up to: a b Jennings, P. C.; Wood, J. H. (1971), "Earthquake damage to freeway structures", Engineering features of the San Fernando earthquake of February 9, 1971, California Institute of Technology, pp. 366–385
- ^ Jump up to: a b Meehan, J. F. (1975), "Performance of public school buildings", San Fernando, California, earthquake of 9 February 1971, Bulletin 196, California Division of Mines and Geology, pp. 355, 356, 359–364
- Jump up ^ Scott, Julia (April 14, 2006). "Some state earthquake safety laws underfunded, unenforced". Oakland Tribune. (subscription required)
- Jump up ^ Lee, W. H. K. (2002), "Challenges in observational seismology", International Handbook of Earthquake & Engineering Seismology, Part A, Volume 81A (First ed.), Academic Press, p. 273, ISBN 978-0124406520
- Jump up ^ Shakal, A. F.; Huang, M.; Ventura, C. E. (1988). "The California Strong Motion Instrumentation Program: Objectives, Status, and Recent Data". from the 9th World Conference on Earthquake Engineering, Tokoyo, Japan, August 2–9, 1988.
- Jump up ^ Bryant, W. A. (2010). "History of the Alquist-Priolo Earthquake Fault Zoning Act, California, USA". Environmental & Engineering Geoscience (Geological Society of America) XVI (1): 7–18.
- Sources
- Allen, C.; Hanks, T. C.; Whitcomb, J. H. (1975), "Seismological studies of the San Fernando earthquake and their tectonic implications", San Fernando, California, earthquake of 9 February 1971, Bulletin 196, California Division of Mines and Geology, pp. 257–262
- Cloud, W.K.; Hudson, D. E. (1975), "Strong motion data from the San Fernando, California, earthquake of February 9, 1971", San Fernando, California, earthquake of 9 February 1971, Bulletin 196, California Division of Mines and Geology, pp. 273–303
- Kamb, B.; Silver, L.T.; Abrams, M.J.; Carter, B.A.; Jordan, T.H.; Minister, J.B. (1971), "Pattern of faulting and nature of fault movement in the San Fernando earthquake", The San Fernando, California, earthquake of February 9, 1971; a preliminary report published jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, Geological Survey Professional Paper 733, United States Government Printing Office, pp. 41–54
- Steinbrugge, K. V.; Schader, E. E.; Moran, D. F. (1975), "Building damage in the San Fernando Valley", San Fernando, California, earthquake of 9 February 1971, Bulletin 196, California Division of Mines and Geology, pp. 323–353
External links
- San Fernando Earthquake — Southern California Earthquake Center
- Historic Earthquakes - San Fernando, California — United States Geological Survey
- California Geological Survey - About CSMIP — California Department of Conservation
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end quote from:
1971 San Fernando earthquake - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/1971_San_Fernando_earthquakeThe 1971 San Fernando earthquake (also known as the Sylmar earthquake) occurred in the early morning of February 9 in the foothills of the San Gabriel ...
1971 02 09 - San Fernando, California - Earthquake Hazards Program
earthquake.usgs.gov/earthquakes/states/events/1971_02_09.phpFeb 9, 1971 - This destructive earthquake occurred in a sparsely populated area of the San Gabriel Mountains, near San Fernando. It lasted about 60 ...Images for 1971 San Fernando earthquake
youtube:- www.youtube.com/watch?v=D5fA7bEyyCsNov 19, 2010 - Uploaded by thomas crenshawOld footage of some of the destruction resulting from the 1971 San Fernando earthquake. My dad rushed us ...
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