|
|
|
|
|
|
|
|
|
|
|
|
On August 31, 1886, 121 years ago, a colossal earthquake shook the city of Charleston with a ferocity that was felt for
several million miles – from Cuba to New York, and Bermuda to the Mississippi River. This earthquake was one of the most damaging earthquakes
in the Eastern United States, with a magnitude of 7.3. The earthquake left ninety percent (90%) of the brick structures in Charleston damaged
and fires subsequently ravaged the city. In honor of this tremendous event in Charleston history, August 31 (today) is Earthquake Memorial Day.Of the destruction that day, most of it was to the building infrastructure. 19% of the buildings within Charleston were made of wood and the remaining of mortar. The wooden structures swayed to and fro as the brick ones, and their chimneys were snapped off; however a well-braced wooden house, with all the parts carefully pinned together, forms a compact and elastic whole, which tends to return to its normal state as soon as the disturbing cause has passed. This is not the case for mortar buildings. Very few of the buildings injured were well built and constructed with the proper materials. For example, the mortar seems to have been made with fine sand mixed, and in some instances, with red clay. This becomes dry and crumbling in the course of time, and makes a very insecure building. As such, the mortar buildings broke apart and fell to the ground, causing additional damage to other structures as well as causing many fatalities.
The type of sediment also affected the degree of damage. Much of Charleston was originally marsh/wetland areas. As population continued to grow, the city had no other choice but to “fill-in” the marsh areas, creating “made ground.” This is problematic because during an earthquake, “made ground” is more susceptible to liquefaction. Liquefaction is a process in which the strength of soil (already saturated with water) is diminished due to extensive shaking, amplified due to the “softness” of the soil. This process results in ground failure and collapse of structures on that surface.
While much of the 1886 earthquake focus is on Charleston, the earthquake caused extensive damage in other areas. The earthquake burst the mill dam at Langley Pond near Aiken, SC causing a four-foot wall of water to spread through the area, knocking a train from its tracks. Craterlets, chasms and trenches were found throughout the region. Additionally fires ravaged much of the area due to broken pipelines.
Earthquake events have been documented in the state since 1698. About seventy percent of these earthquakes are located in the Middleton Place-Summerville Seismic Zone (MPSSZ), 30 kilometers northwest of downtown Charleston. Since 1997, 128 earthquakes have been recorded in the MPSSZ. The risk from a reoccurrence of an earthquake of magnitude 6 or higher within the region is greater now due to changes in land use and population growth. Major hazards due to ground shaking and liquefaction during an 1886 style event could lead to an estimated 14 billion dollars of damage and potentially 900 fatalities with 45,000 injuries. Furthermore, the HAZUS analysis for the region projects extensive infrastructure damage that would complicate relief efforts.
Curator: hallcr@cofc.edu
