 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
|
What if it happened here?
A short account of what might happen if an earthquake similar to the one in Los Angeles were to occur here—by Dr. Erin Beutel
On Tuesday, July 29th a Magnitude 5.4 earthquake struck the Los Angeles, CA causing minimal damage and no loss of life. Felt over much of the greater Los Angeles area at least 30,000 people have gone online to report the shaking on the USGS website. By going online at http://earthquake.usgs.gov/eqcenter/recenteqsww/ people can click on their area and earthquake and report how much shaking they felt by clicking on the “Did you feel it” button. It also allows people to see how other people in their area experienced the quake as shown in the shake map of yesterdays map of how much shaking was experienced by people on the ground as reported in the “Did you feel it?” portion of the USGS website.
What if it happened here?
What would happen in Charleston if a slightly smaller earthquake than occurred in Los Angeles were to occur along the old Summerville fault? Computer simulations done by Dr. Norm Levine of the College of Charleston Dept. of Geology of a magnitude 5.0 earthquake in the Summerville area indicate that the Tricounty area would be more severely damaged than the L.A. area. Injuries could be as great as 150 persons with possibly more than 20 fatalities. Damage to houses and commercial buildings would be moderate to light, but may result in as many as 300 displaced families and more than $15 million dollars in damage. Overall we could expect more shaking felt over a larger area than was felt in Los Angeles and greater damage to infrastructure such as roads and power lines.
Why would there be more damage?
Much of the TriCounty area is built on filled in marsh and swamp or “fill”. These areas of fill tend to be water saturated and have loose sediment that amplifies the earthquake waves as they pass through (larger or amplified waves cause more damage). Areas that are saturated with water also tend to be less stable foundations for the buildings on top of them. In terms of the USGS “Did you feel it” map as shown above, we might expect a map of a magnitude 5.4 earthquake in the Charleston area to result in a larger area of yellow (light damage) and some areas of orange (moderate damage).
Elsewhere in South Carolina
While magnitude 5.4 earthquakes are not common in the rest of South Carolina, Union County had a magnitude 5 earlier this century and some of the faults near Columbia appear to be moderately active. Earthquakes anywhere in the LowCountry would likely behave similarly to earthquakes in the Charleston area with slightly greater shaking due to the loose sediment and swampy ground. As the ground gets firmer and less saturated with water, the amplification of shaking would likely be less, but the earthquake would be felt over a much larger area than the one in California. For example, the probable magnitude 5.0 earthquake in Union county in 1913 was felt over almost 111,000 square km. In general, earthquakes that occur east of the Rocky Mountains are felt over larger areas than west of the Rocky Mountains because the bedrock in the east is less broken by active faults while west of the Rocky Mountains the ground is broken by tens of thousands of active cracks and faults. Thus, like a solid bell rather than a cracked bell, the more solid bedrock “rings” or shakes more east of the Rocky Mountains.
Curator: hallcr@cofc.edu
