By Mary Bodel
When most people in the U.S. think about earthquakes, the San Adreas fault comes to mind. A few may also remember the New Madrid fault in Mississippi, but the rest of the country thinks it's pretty safe. Is it?
Not really. The Cascadia subduction zone is off the Washington (state) coast and is capable of bigger earthquakes than those mentioned above. While it is difficult to pin down exact locations of faults east of the Mississippi, there are quite a few locations capable of experiencing an earthquake.
Three of the major types of earthquakes are subduction, strike slip and blind thrust. There are of course, many others...including those caused by volcanoes. The San Andreas is a strike slip fault line. That means it moves horizontally passed each other. A subduction zone is where one continental plate is diving under another one. These tend to have massive quakes. The 2004 Indonesia quake that caused the devastating tsunamis was a subduction zone. Blind thrust are a fault line that moves upward from the rocks below.
Another problem with some areas is the type of ground and the depth of the water table. When the table is high and buildings are on soil rather than bedrock, a process called liquifaction is possible. If you are unfamiliar with the term, let me point out an experiment that will show it to you. You may even want to use this experiment to talk to your kids.
Get a cake mix (any kind as long as it's powdered). Pour the liquid ingredients in, but don't stir. You will see some of the dry mix floating on top of the liquid. That's an example of liquifaction. If your house or other building is built on this type of soil, you will probably have more damage than someone who built on rock or has a lower water table.
In areas that are known to have earthquakes on a regular basis, there are building codes that are designed to reduce damage and loss of life. Masonry must be reinforced, bridges and roadways must be built to code, and various other factors are taken into consideration. Even with these precautions, earthquakes can and do still kill and destroy.
While none of us were around for the 1811 and 1812 New Madrid quakes, the people living there kept an accounting of some of the events. New Madrid, by the way, appears to be a rift fault. The area had sand blows (sand came shooting out of the ground like a geyser), noxious vapors were emitted and after the quake, the Mississippi river flowed backwards for three days.
There weren't many people there at the time, but there are now. A repeat performance without proper preparations could be *really* bad.
The Loma Prieta quake came on a branch of the San Andeas. As prepared as people thought they were, things failed on a massive scale...especially interstate 880, the double decker freeway.
Northridge, in 1994 was a blind thrust earthquake. It was also one of the most frightening experiences in my life. California had made changes to its codes following the 880 collapse, but it wasn't enough. Several major freeway bridges failed, houses slipped off their foundations and both gas and water mains ruptured.
Despite repeated warnings, people were unprepared. My next article will discuss preparation. Most people I have met here in Southern California are still not really prepared for the next quake, in hopes it won't happen if they don't think about it. Please, think about it.
Not really. The Cascadia subduction zone is off the Washington (state) coast and is capable of bigger earthquakes than those mentioned above. While it is difficult to pin down exact locations of faults east of the Mississippi, there are quite a few locations capable of experiencing an earthquake.
Three of the major types of earthquakes are subduction, strike slip and blind thrust. There are of course, many others...including those caused by volcanoes. The San Andreas is a strike slip fault line. That means it moves horizontally passed each other. A subduction zone is where one continental plate is diving under another one. These tend to have massive quakes. The 2004 Indonesia quake that caused the devastating tsunamis was a subduction zone. Blind thrust are a fault line that moves upward from the rocks below.
Another problem with some areas is the type of ground and the depth of the water table. When the table is high and buildings are on soil rather than bedrock, a process called liquifaction is possible. If you are unfamiliar with the term, let me point out an experiment that will show it to you. You may even want to use this experiment to talk to your kids.
Get a cake mix (any kind as long as it's powdered). Pour the liquid ingredients in, but don't stir. You will see some of the dry mix floating on top of the liquid. That's an example of liquifaction. If your house or other building is built on this type of soil, you will probably have more damage than someone who built on rock or has a lower water table.
In areas that are known to have earthquakes on a regular basis, there are building codes that are designed to reduce damage and loss of life. Masonry must be reinforced, bridges and roadways must be built to code, and various other factors are taken into consideration. Even with these precautions, earthquakes can and do still kill and destroy.
While none of us were around for the 1811 and 1812 New Madrid quakes, the people living there kept an accounting of some of the events. New Madrid, by the way, appears to be a rift fault. The area had sand blows (sand came shooting out of the ground like a geyser), noxious vapors were emitted and after the quake, the Mississippi river flowed backwards for three days.
There weren't many people there at the time, but there are now. A repeat performance without proper preparations could be *really* bad.
The Loma Prieta quake came on a branch of the San Andeas. As prepared as people thought they were, things failed on a massive scale...especially interstate 880, the double decker freeway.
Northridge, in 1994 was a blind thrust earthquake. It was also one of the most frightening experiences in my life. California had made changes to its codes following the 880 collapse, but it wasn't enough. Several major freeway bridges failed, houses slipped off their foundations and both gas and water mains ruptured.
Despite repeated warnings, people were unprepared. My next article will discuss preparation. Most people I have met here in Southern California are still not really prepared for the next quake, in hopes it won't happen if they don't think about it. Please, think about it.
