Northridge earthquake 1994
The Northridge earthquake occurred on 17th January 1994 at 04:30 local time (12:30 UTC ) in Reseda in the city of Los Angeles . The earthquake had a high magnitude of 6.7 M w and reached level IX (devastating) on the Mercalli scale . The peak of the surface acceleration (peak ground acceleration) was the highest ever measured in an urban environment value in North America. 57 people died and more than 9,000 were injured. The damage was 20 billion dollars estimated there was thus one of the most expensive natural disasters in the United States. The quake affected almost the same region as the 1971 San Fernando earthquake (Sylmar Earthquake) which has a thickness of 6.6 M W reached.
The earthquake
The earthquake struck in the San Fernando Valley about 19 miles northwest of downtown Los Angeles near the Northridge community . The epicenter of the quake was in the Reseda district , near the intersection of Reseda Boulevard and Saticoy Street. The exact determination of the location of the epicenter took a few days, so that in the meantime the name "Northridge earthquake", which was coined by the media, became common. The name held up, in part because of the extensive damage and casualties in Northridge.
The National Geophysical Data Center determined the depth of the hypocenter to be 17 km. Despite the proximity of the region to the San Andreas Fault , the quake did not occur on this fault , but on a previously undiscovered, (blind) thrust which was not visible on the surface .
Damage and sacrifice
Damage occurred up to a distance of 125 km. Most of them were registered in the west of the San Fernando Valley, as well as in the cities of Santa Monica , Simi Valley and Santa Clarita . At least 57 people were killed in the earthquake and more than 9,000 were injured, 1,600 of whom were hospitalized.
At the Northridge Meadows apartment complex , 16 people were killed in the building collapse. The Northridge Fashion Center was also badly damaged, mostly from the collapse of parking garages.
Major damage to highways occurred up to a distance of 32 km from the epicenter. Parts of Interstate 10 (Santa Monica Freeway) , Interstate 5 (Golden State Freeway) and California State Route 14 (Antelope Valley Freeway) collapsed and had to be rebuilt. The Newhall Pass Interchange , the junction of Interstate 5 and California State Route 14, collapsed, as had happened 23 years earlier in the 1971 San Fernando earthquake, even though the interchange had been rebuilt with reinforced components.
When the intersection collapsed, LAPD policeman Clarence W. Dean was killed while on motorcycle patrol south. In the early morning darkness he overlooked the collapsed section when changing from I-14 to I-5, fell twelve meters and was instantly dead. When the intersection was rebuilt a year later, it was in his honor Clarence Wayne Called Dean Memorial Interchange .
Several commercial buildings collapsed, and other damage included the collapse of the Anaheim Stadium scoreboard, which collapsed over several hundred (fortunately empty) spectator seats. In addition, there was damage to quite a few buildings, which only became apparent after a while and then led to a total write-off.
Type of damage
The peculiarity of this earthquake consisted of the pronounced shaking movements and the strong acceleration of the ground, which reached values up to the height of the acceleration due to gravity . In addition, damage was caused by landslides and fire. Most of the deaths and damage occurred in multi-storey buildings, especially those with a wooden structure, due to the special features of the earthquake. The buildings whose ground floor were structurally weak compared to the floors above were particularly hard hit, such as those with open parking spaces on the ground floor below the building (see picture). As is common with earthquakes, unreinforced brick structures and buildings on steep slopes have often been damaged. Most school buildings, however, withstood the earthquake well. Overall, the number of victims remained low as it occurred not only early in the day, but also on a national holiday, Martin Luther King Day .
Numerous fires were caused by gas pipes that tore off their foundations when houses slipped, and by gas-powered hot water devices that were not adequately secured against the movements that occurred and fell from the wall. In the San Fernando Valley, main gas and water lines were severed on various occasions, causing flames to burst through the water in some streets.
The building regulations, which, due to the well-known frequency of earthquakes in California, stipulate special construction methods and building reinforcements so that buildings can withstand most earthquakes largely without damage, had a decisive influence on the relatively minor damage in relation to the strength of the quake. However, it turned out that some details of the regulations were not so well adapted to the forces occurring in the Northridge earthquake, so the building regulations were revised after the quake.
Aftermath of the quake
Valley fever
One unusual effect of the earthquake was an outbreak of valley fever ( coccidioidomycosis ), a respiratory disease caused by breathing in airborne spores . In the eight weeks following the earthquake, the number of cases of illness (203) was almost ten times higher than usual, and three people died from the disease. The increase in cases of illness is explained by the raising of dust by landslides triggered by the quake. Most cases of illness occurred directly in the downdraft of landslides.
Effects on earthquake protection devices
Before the Northridge earthquake, it was assumed that an appropriately designed damping mechanism, which is built into devices for the vibration control of buildings, effectively suppressed vibrations and fluctuations in the building and thus contributed to the earthquake safety of the building. Comparisons of the earthquake safety theoretically existing on the basis of such devices with the behavior of buildings equipped with them observed in reality during the Northridge earthquake showed that, however, precisely the forces arising due to the damping were one of the main causes of the damage found. The investigations made it clear that theoretical considerations are insufficient to reliably describe the effects of earthquakes on buildings.
Aftermath of the quake in legislation
The Northridge earthquake resulted in a number of legislative changes.
Eleven hospitals were damaged by the earthquake or were even unusable afterwards. The affected hospitals could not only guarantee the supply of the area, their patients also had to be transferred to other, still functioning hospitals. Because of this, a law was passed by the California government that all facilities associated with the emergency room had to be converted to earthquake-proof by January 1, 2005.
Because of the numerous fires caused by demolished hot water gas heating systems, a law was passed in 1995 that required such systems to be secured against earthquakes. Furthermore, great efforts have been made to reinforce road overpasses against shaking movements.
Due to the heavy losses suffered by various insurance companies as a result of the earthquake, insurance against earthquake damage in California was severely restricted or completely abandoned. For this reason, the state government created the California Earthquake Authority , a privately financed and publicly administered organization that guarantees at least basic protection against such damage.
See also
Individual evidence
- ↑ Northridge Earthquake ( Memento of the original from September 4, 2004 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Southern California Earthquake Data Center. Retrieved November 17, 2008
- ^ Northridge Earthquake . Earthquake Engineering Research Center (EERC), University of California, Berkeley. 2005. Archived from the original on July 12, 2006. Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved November 17, 2008.
- ^ A b Preparing for the "Big One" - Saving Lives Through Earthquake Mitigation in Los Angeles, CA: Executive Summary. ( Memento of the original from April 15, 2013 in the web archive archive.today ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Office of Policy Development and Research, US Department of Housing and Urban Development
- ↑ James D. Cooper et al .: Public Roads On-Line (Summer 1994): The Northridge Earthquake: Progress Made, Lessons learned in Seismic-Resistant bridge Design. United States Department of Transportation - Federal Highway Administration
- ↑ Secure Your Stuff: Water Heater. ( Memento of the original from May 3, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Instructions for securing hot water devices against earthquakes
- ↑ Coccidioid mycosis outbreak. ( Memento of the original from February 2, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Landslide Hazards Program, United States Geological Survey
- ↑ Valentin Shustov: Hot Topic # 2: The 1994 Northridge Earthquake: Seismic Base Isolation. College of Engineering and Computer Science, California State University, Northridge
- ^ About the CEA. ( Memento of the original from December 16, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. California Earthquake Authority (CEA) homepage
Web links
- Northridge Earthquake. The Northridge quake at the Southern California Earthquake Data Center
- The Northridge Earthquake. Detailed information on the earthquake at the United States Geological Survey (English)
- Selected Activities in Response to the 1994 Northridge Earthquake. Research activities after the Northridge earthquake, Earthquake Engineering-Strong Motion Group, University of Southern California (English)
Coordinates: 34 ° 12 ′ 47 " N , 118 ° 32 ′ 13" W.