For South Carolina Mapping from USGS see:
                             http://geology.com/state-map/south-carolina.shtml

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Historic Earthquakes

THE CHARLESTON EATHQUAKE of 1886:

Charleston, South Carolina
1886 September 01 02:51 UTC
 (local August 31)
Magnitude 7.3
Intensity X

Largest Earthquake in South Carolina

 This is the most damaging earthquake to occur in the Southeast United States and one of the largest historic shocks in Eastern North America. It damaged or destroyed many buildings in the old city of Charleston and killed 60 people. Hardly a structure there was undamaged, and only a few escaped serious damage. Property damage was estimated at $5-$6 million. Structural damage was reported several hundred kilometers from Charleston (including central Alabama, central Ohio, eastern Kentucky, southern Virginia, and western West Virginia), and long-period effects were observed at distances exceeding 1,000 kilometers.

Effects in the epicentral region included about 80 kilometers of severely damaged railroad track and more than 1,300 square kilometers of extensive cratering and fissuring. Damage to railroad tracks, about 6 kilometers northwest of Charleston, included lateral and vertical displacement of tracks, formation of S-shaped curves and longitudinal movement.

The formation of sand craterlets and the ejection of sand were widespread in the epicentral area, but surface faulting was not observed. Many acres of ground were overflowed with sand, and craterlets as much as 6.4 meters across were formed. In a few locations, water from the craterlets spouted to heights of about 4.5 to 6 meters. Fissures 1 meter wide extended parallel to canal and stream banks. A series of wide cracks opened parallel to the Ashley River, and several large trees were uprooted when the bank slid into the river.

 At Summerville, a small town of 2,000 population, 25 kilometers northwest of Charleston, many houses settled in an inclined position or were displaced as much as 5 centimeters. Chimneys constructed independently of the houses commonly had the part above the roofline thrown to the ground. Many chimneys were crushed at their bases, allowing the whole chimney to sink down through the floors. The absence of overturning in piered structures and the nature of the damage to chimneys have been interpreted as evidence that the predominant motion was vertical.

The meizoseismal area of MM intensity X effects is an elliptical area, roughly 35 by 50 kilometers, trending northeast between Charleston and Jedburg and including Summerville. Middleton Place, about in the center of this ellipse, is at the southeast end of a zone (perhaps 15 kilometers long) of microearthquake activity that still continues today. This seismic activity may be a continuation of the 1886 aftershock series.

The intraplate epicenter of this major shock is not unique for large earthquakes in the Eastern and Central United States. Other intraplate earthquakes include those at Cape Ann, Massachusetts (1755), and New Madrid, Missouri (1811-1812). Earthquakes occurring along boundaries of plates (e.g., San Francisco, 1906) are well understood in terms of plate tectonics, but those occurring within plates are not similarly understood. This problem still is being studied more than 100 years after the earthquake.

This earthquake was reported from distant places such as Boston, Massachusetts; Milwaukee, Wisconsin, Chicago, Illinois; Cuba and Bermuda.

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S.C. First to Create Detailed Seismic/Wind Maps

      SEE www.llr.state.sc.us for more information:   

         South Carolina has been impacted by quite a few hurricanes recently.With all of the nasty weather, it was easy to miss three tiny earthquakes in August, all striking the Low Country within one week. South Carolina annually experiences an average of 10 to 20 quakes per year. So far this year, 17 have been detected. The three most recent shakers all registered below 3 on the Richter scale, meaning they were hardly felt. Each came nowhere near the 7.6 magnitude quake that rocked Charleston more than a century ago. The 1886 quake was felt from Cuba to Chicago.

         LLR’s Gary Wiggins, Building Codes Council Administrator, has been hard at work in updating seismic and wind speed maps to aid architects, engineers and contractors in designing and constructing buildings that can withstand extreme forces of nature in the areas of the state most at risk.

          In the past, local building officials have had to rely upon tiny maps found in the International Building Codes to make key safety decisions affecting construction projects. For coastal counties like Berkeley, the maps show as many as three wind speed zones ranging from 100 miles per hour to 120 miles per hour. As a result, officials have required contractors to erect buildings to higher standards than required in some areas of the counties and lower standards than required in other areas.

He began the difficult and tedious project in May of this year.

First, Wiggins obtained the original seismic and wind speed maps for South Carolina from the U.S. Geological Survey Office (USGS) in Colorado. He then persuaded the S.C. Department of Commerce to grant him access to a computer in their building that had the GIS software for map design. After teaching himself GIS software, he spent eight hours a day three days a week for six weeks at the computer studying maps of the state, county by county. He prepared detailed and specific maps of the state and for each of the state’s 29 counties that are affected by multi wind zones or seismic design categories. As a quality control check, the local building officials for the jurisdictions affected were invited into the office to review his work for accuracy.

“They travel the highways of their counties every day,” Wiggins said. “They were able to identify landmarks I might have missed or pointed out a rural road that no longer existed.”

“South Carolina is the only state in the country to define to the degree by physical elements to where the lines precisely fall,” he said. “I’ve used streets, lakes, riverbanks, etc. – clearly visible known geographic features or landmarks.”

On Aug. 25, 2004, the Building Codes Council reviewed Wiggin’s work and gave the newly drawn maps their seal of approval. Building officials were given until Nov. 4, 2004 to make any additional comments. Once final, the maps will be made available on disk to anyone desiring a copy, or they can download a copy from a link on LLR’s Web site.

Wiggins is understandably proud of the final work product.

“The savings in construction costs for builders, and ultimately consumers, will be significant,” he said. “Builders will be able to build to the exact safety level for a county. Anyone will be able to physically identify where the exact seismic and wind speed lines are in the state. And the local building official will no longer have to make a difficult and controversial decision.”