Earthquake Country
We've had four earthquakes in the last week or so. While I am not prone to panic during these episodes, it does give one cause to think. And prepare. I spent about 30 minutes looking for an earthquake kit on the internet this afternoon. They can be expensive. I also looked up what items should be included in an earthquake kit, and I have about 75% of the items, so I guess I will drag out one of my plastic bins and place all of the necessary items in one place. I paid $300 for an emergency kit about 10 or 11 years ago and now I can't find it. I bought it just before the Northridge earthquake and fortunately, I didn't need it.
My home at the time was built on rock and sustained only 1 superficial crack on a wall. Most of the homes on my street fared fairly well. When I drove down Ventura Boulevard later that morning to see what the damages were, it was absolutely astounding. On one side of the street, the buildings were normal. On the other side, whole facades of buildings had fallen. Some buildings needed to be propped up. Driving down Ventura Boulevard was like driving down a street in a war-torn, bombed-out country. And this was only 1/2 mile from my house.
Days later, I drove by Ground Zero of the Northridge quake. One apartment house had fallen flat like a pancake. The first floor was totally squashed. It looked like it had never existed. The second floor was now the first floor, and so on. I saw pictures of the cars in the carports and they looked like the Wicked Witch's shoes peeking out from Dorothy's house in the Wizard of Oz. A nearby park became a tent city for all of the people who had been displaced, not only from this particular apartment building, but also from other buildings throughout the Valley that had been condemned because of the damange.
Am I scared? Not really. I have complete faith in our emergency system here in Los Angeles. Am I nervous? A little. If an earthquake happens, I hope that it happens at night, when people are sleeping and not too many people are up and about. If an earthquake happens, I hope that my children and my father and brothers will be safe. I hope that we will be able to communicate with each other and assure each other that we are safe and sound.
When the Northridge quake hit, the people of Los Angeles really pulled together. I am confident that this will happen again. Los Angeles is such a blessed city--a truly wonderful place to live--that earthquakes, landslides, runaway fires, tsunami warnings, riots, drive-by shootings, and wife-killers/child-molesters-that-get-exonerated-by-crazy-juries are a small price to pay for living here. I wish these things didn't happen, of course, but because Los Angeles is such a wonderful city, I cannot imagine not living here and will gladly put up with such natural and unnatural disasters.
And apparently, a lot of other people feel the same way.....according to U.S. Census data, about ONE MILLION people have moved to the LOS ANGELES/LONG BEACH metro area in the last 10 years.
Here are some links/interesting info about living in Southern California:
http://interactive2.usgs.gov/learningweb/students/landpeople_s_la_hazards.htm
Living in Earthquake Country Southern California is home to more than 20 million people and is vital to the Nation's economy. Unfortunately, the region is also laced with many active faults that can produce strong earthquakes. The San Andreas Fault is the best known. It runs almost the entire length of California and generates shocks as large as magnitude 8. In Southern California the last magnitude 8 earthquake was in 1857. But smaller temblors, like the 1971 San Fernando and 1994 Northridge earthquakes, occur more frequently. Both of these magnitude 6.7 quakes were very damaging.
An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth's surface. This shaking can cause buildings and bridges to collapse; disrupt gas, electric, and phone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis).
More Earthquakes to Come
Southern California has a problem with earthquakes - it hasn't been having enough of them. After the 1994 magnitude 6.7 earthquake in Northridge (northwest of La Crescenta), scientists used new techniques to study seismic activity. They have discovered that Southern California has not had enough large earthquakes to release all the pressure building up underground.
When the tectonic plates under the Earth's crust grind against each other, energy builds. In Southern California, the stresses are distributed along the San Andreas Fault and other smaller faults. When too much stress builds up along a fault, the earth's crust cracks and earthquakes occur. Quakes must occur to relieve the pressure along the faults.
But a look back at the earthquake history of the last two centuries suggests that Southern California should have had seven times as many Northridge-sized earthquakes as it has had. The scientists' conclusion: in Southern California, the probability of a magnitude 7 or greater earthquake by the year 2024 is as high as 80 to 90 percent.
http://gis.esri.com/library/userconf/proc02/pap0535/p0535.htm
Liquefaction-related ground failure historically has caused extensive structural and lifeline damage in urbanized areas around the world. Recent examples of these effects include damage produced during the 1989 Loma Prieta, 1994 Northridge, 1995 Kobe, and 1999 Turkey earthquakes. These and other historical earthquakes show that the distribution of liquefaction-related damage is not random, but generally is restricted to recently alluviated areas that contain low-density, saturated, granular sediments. Extensive young gravel, sand, and silt deposits in the Oxnard Plain and along the Santa Clara River, shallow groundwater, and the presence of nearby potentially active faults, indicate that parts of Ventura County are particularly susceptible to liquefaction-related hazards. During the Northridge earthquake, liquefaction occurred at the mouth of the Santa Clara River in Oxnard/Ventura, in Simi Valley, and along the Santa Clara River between Fillmore and Newhall (Barrows et al., 1995). Settlement and lateral spreading caused by the earthquake resulted in rupture of an oil pipeline near the I-5 crossing of the river, directly east of Ventura County, and initiated an oil spill that contaminated large portions of the river downstream.
The potential for liquefaction depends on both the susceptibility of a deposit to liquefy and the opportunity for ground shaking to exceed a specified threshold level required for liquefaction to occur. Liquefaction susceptibility is the relative resistance of a deposit to loss of strength when subjected to strong ground shaking. Loss of soil strength as a result of liquefaction during an earthquake can result in ground failures at the earth's surface. These failures, including localized ground settlement and lateral spreading, can cause significant property damage. Physical properties of surficial deposits govern the degree of resistance to liquefaction during an earthquake. These properties include sediment grain-size distribution, density, cementation, saturation, and depth. Sediments that lack resistance (susceptible deposits) commonly include saturated, sandy young deposits. Sediments resistant to liquefaction include older deposits that are dry or sufficiently dense.
My home at the time was built on rock and sustained only 1 superficial crack on a wall. Most of the homes on my street fared fairly well. When I drove down Ventura Boulevard later that morning to see what the damages were, it was absolutely astounding. On one side of the street, the buildings were normal. On the other side, whole facades of buildings had fallen. Some buildings needed to be propped up. Driving down Ventura Boulevard was like driving down a street in a war-torn, bombed-out country. And this was only 1/2 mile from my house.
Days later, I drove by Ground Zero of the Northridge quake. One apartment house had fallen flat like a pancake. The first floor was totally squashed. It looked like it had never existed. The second floor was now the first floor, and so on. I saw pictures of the cars in the carports and they looked like the Wicked Witch's shoes peeking out from Dorothy's house in the Wizard of Oz. A nearby park became a tent city for all of the people who had been displaced, not only from this particular apartment building, but also from other buildings throughout the Valley that had been condemned because of the damange.
Am I scared? Not really. I have complete faith in our emergency system here in Los Angeles. Am I nervous? A little. If an earthquake happens, I hope that it happens at night, when people are sleeping and not too many people are up and about. If an earthquake happens, I hope that my children and my father and brothers will be safe. I hope that we will be able to communicate with each other and assure each other that we are safe and sound.
When the Northridge quake hit, the people of Los Angeles really pulled together. I am confident that this will happen again. Los Angeles is such a blessed city--a truly wonderful place to live--that earthquakes, landslides, runaway fires, tsunami warnings, riots, drive-by shootings, and wife-killers/child-molesters-that-get-exonerated-by-crazy-juries are a small price to pay for living here. I wish these things didn't happen, of course, but because Los Angeles is such a wonderful city, I cannot imagine not living here and will gladly put up with such natural and unnatural disasters.
And apparently, a lot of other people feel the same way.....according to U.S. Census data, about ONE MILLION people have moved to the LOS ANGELES/LONG BEACH metro area in the last 10 years.
Here are some links/interesting info about living in Southern California:
http://interactive2.usgs.gov/learningweb/students/landpeople_s_la_hazards.htm
Living in Earthquake Country Southern California is home to more than 20 million people and is vital to the Nation's economy. Unfortunately, the region is also laced with many active faults that can produce strong earthquakes. The San Andreas Fault is the best known. It runs almost the entire length of California and generates shocks as large as magnitude 8. In Southern California the last magnitude 8 earthquake was in 1857. But smaller temblors, like the 1971 San Fernando and 1994 Northridge earthquakes, occur more frequently. Both of these magnitude 6.7 quakes were very damaging.
An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth's surface. This shaking can cause buildings and bridges to collapse; disrupt gas, electric, and phone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis).
More Earthquakes to Come
Southern California has a problem with earthquakes - it hasn't been having enough of them. After the 1994 magnitude 6.7 earthquake in Northridge (northwest of La Crescenta), scientists used new techniques to study seismic activity. They have discovered that Southern California has not had enough large earthquakes to release all the pressure building up underground.
When the tectonic plates under the Earth's crust grind against each other, energy builds. In Southern California, the stresses are distributed along the San Andreas Fault and other smaller faults. When too much stress builds up along a fault, the earth's crust cracks and earthquakes occur. Quakes must occur to relieve the pressure along the faults.
But a look back at the earthquake history of the last two centuries suggests that Southern California should have had seven times as many Northridge-sized earthquakes as it has had. The scientists' conclusion: in Southern California, the probability of a magnitude 7 or greater earthquake by the year 2024 is as high as 80 to 90 percent.
http://gis.esri.com/library/userconf/proc02/pap0535/p0535.htm
Liquefaction-related ground failure historically has caused extensive structural and lifeline damage in urbanized areas around the world. Recent examples of these effects include damage produced during the 1989 Loma Prieta, 1994 Northridge, 1995 Kobe, and 1999 Turkey earthquakes. These and other historical earthquakes show that the distribution of liquefaction-related damage is not random, but generally is restricted to recently alluviated areas that contain low-density, saturated, granular sediments. Extensive young gravel, sand, and silt deposits in the Oxnard Plain and along the Santa Clara River, shallow groundwater, and the presence of nearby potentially active faults, indicate that parts of Ventura County are particularly susceptible to liquefaction-related hazards. During the Northridge earthquake, liquefaction occurred at the mouth of the Santa Clara River in Oxnard/Ventura, in Simi Valley, and along the Santa Clara River between Fillmore and Newhall (Barrows et al., 1995). Settlement and lateral spreading caused by the earthquake resulted in rupture of an oil pipeline near the I-5 crossing of the river, directly east of Ventura County, and initiated an oil spill that contaminated large portions of the river downstream.
The potential for liquefaction depends on both the susceptibility of a deposit to liquefy and the opportunity for ground shaking to exceed a specified threshold level required for liquefaction to occur. Liquefaction susceptibility is the relative resistance of a deposit to loss of strength when subjected to strong ground shaking. Loss of soil strength as a result of liquefaction during an earthquake can result in ground failures at the earth's surface. These failures, including localized ground settlement and lateral spreading, can cause significant property damage. Physical properties of surficial deposits govern the degree of resistance to liquefaction during an earthquake. These properties include sediment grain-size distribution, density, cementation, saturation, and depth. Sediments that lack resistance (susceptible deposits) commonly include saturated, sandy young deposits. Sediments resistant to liquefaction include older deposits that are dry or sufficiently dense.
posted by knutty4knitting @ 6:31 PM
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