Charleston Rocks!!! The Earthquake of 1886 EarthCache
Charleston Rocks!!! The Earthquake of 1886
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Welcome to the beautiful historic area of Charleston.
Most of us, when we think of catastrophic earthquakes in the US, we automatically think about the west coast and cities like LA and San Francisco and the San Andreas Fault. But, on August 31st of 1886, the area right below your feet experienced the most destructive earthquake ever recorded in the Eastern half of North America.
Today you see the historic area much as it was at the time of the quake. Many more areas in the city also show damage and hopefully this earthcache will make you aware of just how extensive the damage was.
The above co-ordinates are for a small parking lot with metered spaces that will enable you to not only get the information you need for logging this cache but also can be a great starting point for just walking around the historic area and also finding some other caches. If parking is unavailable at this location, you can park elsewhere and then navigate on foot to this area.
To log this cache you will need to take a short walk on Bay Street from the Battery (the waterfront) up to the Old Exchange Building at Broad and email me your observations and answers. What evidence do you see that this area was damaged in the earthquake? (See examples in photos) Does it appear that the buildings would be able to better withstand another magnitude 7 earthquake today? Only 124 known deaths occurred in 1886. How do you think that would compare if the same magnitude quake occurred today? Before now were you aware of the earthquake potential here?
In the summer of 1885, Charleston was hit by an intense hurricane and many homes and businesses had just barely recovered from those damages when the earthquake occurred. In the aftermath of the earthquake's almost total devastation, decisions had to be made about what to do to best restore the city. Some felt everything that was damaged should just be torn down and start over from the ground up. Others could not bear the thought of totally losing all the beautiful old homes, churches and buildings that already made Charleston unique. In the end, it came down to money and the availability of raw materials so in a way both points of view prevailed. Since FEMA didn’t exist, it was all up to the towns to manage on their own. Nearby states assisted with raising money and supplying building materials. Any building that could possibly be repaired and made safely usable was rebuilt even if it meant bolting it back together using long threaded rods which came to be known as earthquake bolts. Decorative plates were placed on the ends of the bolts. Brickwork was re-laid and the cracks were covered over with smooth plaster and the city has carried on mostly unchanged, especially in the historic district, until the present.
The Charleston quake consisted of two main shocks---eight minutes apart on an otherwise quiet evening. Although reports of numerous small shocks occurring 5-10 days before in the town of Summerville some 15 miles away were received, they mostly went unheeded. The shocks were felt over a 2.5 million square mile area--from Cuba to Toronto and Bermuda to the Mississippi. Nearly two-thirds of the US population at the time felt the shocks. Only the New Madrid, MO quake of 1811 was more intense but because of the small population in that area at the time of the quake, comparatively little structural damage occurred.
Although no means of measuring earthquake magnitude existed in 1886, seismologists and geologists since then have determined that the quake measured 7.3 to 7.6 on the Richter Scale and a X on the modified Mercalli Scale--a scale of earthquake intensity based on observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction). Ninety percent of the buildings in Charleston were damaged. Trains were derailed and tracks were buckled and distorted. The area where you are along the Battery and the wharves suffered the greatest damage since this area was built on “made” land (areas of filled in marshes) that comprised a large portion of Charleston. The destruction of life and property was staggering and the fire stations, water supplies and hospitals were all but totally wiped out.
Immediately afterwards, several geologists from the USGS were given the task of determining the “where" and the “why”. By early 1887 the following conclusions had been reached by this commission. The earthquake originated in an oval area about 18 miles wide and 26 miles long running on a northeast to southwest axis centered approximately on Middleton Place on the Ashley River about 15 miles northwest of Charleston. The earthquake had at least 2 and possibly 3 epicenters. The first shock had two separate components occurring 33 seconds apart with each emanating from a different epicenter. The shock waves traveled through the earth at about 3.5 miles a second. No tidal waves or tsunamis were generated because the source of the shocks was onshore. The rupture occurred at a depth of at least 7.5 miles with an average slip (or displacement) of about 6 feet.
Geologically, Charleston is in one of the most seismically active areas in the Eastern US. Today, this fault area is known to geologists as the Middleton Place-Summerville Seismic Zone (MPSSZ). The MPSSZ appears to have two steeply dipping faults: the deeper northeast-trending Woodstock Fault and the shallower northwest-trending Ashley River Fault. The Woodstock Fault is split into 2 sections, the North and South sections offset laterally by a short distance. These two sections are crossed and connected together by the Ashley River Fault and lock together directly under the town of Summerville resulting in a permanent zone of stress where destructive earthquakes can be expected to occur in the future.
Even though geologists were able to determine the epicenters of the quake and the underlying geology fairly quickly, it wasn’t for another 60 to 70 years and the advent of plate tectonics theories that the final questions about “why” were answered.
Although earthquakes can occur anywhere on earth, most occur at the boundaries of the tectonic plates—those eight large and several smaller separate masses of firmament that float on the earth’s molten mantle. They continue to constantly move, slipping and sliding against each other, sometimes subducting or sliding under each other. The history of the earth’s continents is all about these plates moving around creating and destroying new land mass configurations. Earthquakes occurring along the edges of the plates, known as interplate earthquakes, are fairly easy to explain. On the other hand, little is known about why intraplate quakes or earthquakes within a plate occur. Although South Carolina is now located well within the interior of the North American plate far from any plate boundary, at one point it may not have been.
Some geologists today feel that the seismicity of the Charleston area stems from its position on top of an ancient rift zone which formed as the North American plate moved away from the African plate beginning in the Late Triassic period(about 200 million years ago) as the super continent of Pangaea was breaking apart. Africa left behind land that became permanently attached to the North American continent including most of Florida and parts of southern Georgia and Alabama. Parts of the North American plate attached to the African and European plates as well. South Carolina was left with a faulted, broken surface. As the plates were pulling apart, the upper crust thinned out (much like chewing gum or silly putty does as it stretches) and started sinking forming valleys called grabens along the edge of the continent. These grabens filled with hundreds of feet of sediments and are now located far under the South Carolina Coastal Plain at a depth of at least 7 miles. As the land bent, sagged and fractured it created the Middleton Place-Summerville Seismic Zone. This severely fractured subsurface and underground faults left by the collision and retreat of the African and North American plates as well as the continuing generalized continental pressure as the North American plate moves ever so slowly may well be the ultimate explanation for the seismic activity in this area. It is thought that this zone has been active for at least 48 million years and there is evidence of a number of previously massive quakes. It is estimated that over the last 5000 years the area has had 5 large earthquakes and that a large quake occurred about 1100 years prior to the 1886 quake.
There is no reason to believe that another quake just as devastating will not occur at some point in the future. Currently there is a monitoring network established with seven stations near the 1886 epicenters. Data is fed 24/7 from the monitoring center at Charleston Southern University to the US Geological Survey offices in Colorado. Eighty-two small quakes in the 2.8 to 3.1 magnitude range were reported between 2001 and 2004 within the MPSSZ although occasionally they occur outside of this area. Two quakes were recorded in 2002 about 15 miles off the coast of Charleston that measured 4.3 and 3.8 in magnitude. Although the earthquake potential here in this area is high, the focus of emergency preparedness has mostly been on hurricanes which also present an obvious risk. Just ask anyone who was here in Charleston when Hugo hit in 1989---but that's another story!!
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