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Earthquake Hazard

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Submitted By caltx13
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The city I chose for my hazard analysis is Los Angeles CA and the hazard that is the highest risk to the city is an earthquake. L.A. is the second largest city in the United States; it encompasses over 498 square miles and is surrounded by mountains and ocean. L.A. is a very urban environment, its high concentration of infrastructure makes it vulnerable to earthquakes, but at the same time it also gives it the resources it needs to respond to earthquakes or any other hazards. L.A. has had a few large scale earthquakes in the last decades and some geological experts predict it will suffer a major quake in the near future. How it has responded to those disasters in the past is what has laid the foundation as to how the city will deal with future earthquakes or other hazards and attempt to minimize their impact on the city. Los Angeles lies around 60 miles from the San Andreas Fault. This fault line is one the most active fault lines in the world and as such is capable of producing severe earthquakes. And even though Los Angeles doesn’t lie directly underneath it like the city of San Francisco, the fault line does pose a great danger to the city. But even more of a threat to the city is the many unknown smaller fault lines that run beneath it. With a population of over 4 million people, a large size earth quake would cause substantial damage and injure or kill a large number of people. L.A. has had around six major earthquakes that were 6.0 or stronger in the last hundred years. It does also have thousands of small ones throughout the year that people don’t even feel. The last major earthquake that struck the city was in 1994. This earthquake which has been dubbed the Northridge quake was one of the worst the city ever experienced. It caused the deaths of over 60 its citizens and caused damaged in the millions. But that quake brought forth many changes in the way the city prepares for natural disasters. Earthquakes are not the only disasters that can strike the city. It has also suffered from large scale civil unrests, storms, floods, wildfires, and even some tornadoes in the 1980’s. But the major threat to the city is and will always be the big earthquake that every geologist predicts will strike. They say it’s not a matter of if but a matter of when. It could strike tomorrow or in 30 years. And it won’t be just the city of Los Angeles itself that will be affected. It will affect all of the surrounding areas as well, like Orange County just to the south of it. It too is densely populated and a large earthquake there would also be devastating. Then there’s also the city of Long Beach, a fairly large city itself. It too would suffer severely. The city of Los Angeles as well as the state of California in general have a good hazard mitigation plan in place in the event of an earthquake, large or small. I remember when I was growing up in the central coast of California. We would do earthquake drills at least once a week in school. The sirens would sound and everyone would get under their desks. In all the time I lived in California I only experienced an earthquake once and it was definitely a scary feeling. I’ve been in tornadoes, riots, war zone, and even a hurricane in Louisiana. But that earthquake that happened when I was 9 years old still scares me till this day. As far as what resources city of Los Angeles has available and ready to dispatch in case an earthquake strikes is very impressive. But no matter how much planning is done or how many resources are available, there is always going to be unavoidable damage and casualties. All that can be done is to try minimize them. The L.A. mitigation plan is extensive; it follows an all hazards approach. The city’s main focus in its mitigation efforts besides saving as many lives as possible is to protect its critical infrastructure. This would include its city hall, its major hospitals and of course its bridges and freeways which are very important to the city. The city also has an Emergency Operations Plan. This EOP identifies in detail the sixteen major hazards that the city leaders believe can strike the city. The plan also identifies each specific hazard, their threat, their potential for destruction, and it addresses how the city will respond to and recover from any of these hazards. The EOP also specifies the roles and responsibility of all its departments that will be participating in response and recovery operations after a disaster such as an earthquake. The city of Los Angeles is committed in protecting its vast infrastructure. The city has identified its major areas that it deems critical when an earthquake occurs. These infrastructures are its water treatment facilities, dams, and reservoirs. Also its electric power system and its communication system. All these systems have taken a big hit when an earthquake has struck the L.A. area. For example the Northridge quake made the city experience its first blackout in its history. The cost to the electrical power system was in the hundreds of millions. Los Angeles has been able to implement better ways to lessen the damage caused by earthquakes that have occurred in the past. Better building methods have saved many structures and lives. One example is the Los Angeles Dam. It suffered major damage in the 1971 San Fernando earthquake that it could have collapsed and brought millions of gallons of water rushing into the city. The dam was built in the early 1900’s when there were no construction methods that provided resistance to earthquake shaking. But after 1971 L.A. repaired the dam using more modern construction techniques. The 1994 Northridge Earthquake put the Los Angeles Dam to the test. The Northridge Earthquake was almost equal in magnitude to the 1971 San Fernando Earthquake. Ground shaking was very intense. Yet the dam showed only minor deformation and minor cracking. Despite the intense shaking, the crest of the dam had only moved slightly. These modern construction methods have not only been applied to dams but to just about every type of building and even freeways that have been constructed in L.A. area for the last couple of decades. These new construction methods have proven effective against earthquake shaking and have minimized damage to infrastructures and in turn saved lives. This new modern method of building has been the biggest mitigation measure that the city has implemented. The map below shows the major and minor fault lines in the Los Angeles area. It’s clear that the San Andreas Fault line is not the only threat; any one of these fault lines at any given time can cause a major earthquake.

The Los Angeles area has had over 23 major earthquakes since 1933. They are shown in the map below. These 23 have caused significant damage and loss of life not just to Los Angeles but to all of Southern California. References used: United States Geological Survey City of Los Angeles Hazard Mitigation Plan California Geological Survey

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