Did you feel the earth move this week? If you were outdoors, or driving chances are you didn't notice. I had just gotten into my vehicle and though for a moment that someone was trying to get my attention by rocking the bumper. The movement was noticeable, but not distinctive - not till I heard the news anyways.
At 1:55 August 24, 2011 an earthquake occurred in the Virginia Seismic Zone, located in the Piedmont region, likely along the Spotsylvania Fault. The Virginia Piedmont area was originally formed as part of a zone of repeated continental collision that created the ancestral Appalachian Mountains. The earthquake's focal mechanism shows reverse slip faulting on a north to northeast striking fault plane, although the actual fault has never been identified. The size of the rupture is likely to be in the range 5–15 km.
Tremors were felt as far south as Georgia; as far north as Quebec and as far west as Illinois, with damage reported as far away as Brooklyn in New York City where several buildings were evacuated and Washington, DC where many monuments remain closed for inspection. According to the USGS, the effects of earthquakes in the eastern United States are able to spread more efficiently than in the western United States because of the goelogical conditions. The relative age of the rock and the fact that this was a shallow earthquake contributed to the widespread effects.
Though NY, NJ and PA all felt the effects, we are please to report that none of our projects were effected - a sign of their quality construction and the incredible ability of stone to withstand movement, from both frost heave and geological upheaval! This sort of activity actually creates the stone we work with or at least similar activity, millions of years ago did!
Rocks are generally classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous, sedimentary, and metamorphic and many subcatergories as they are transformed between one another by the 'rock cycle'.
Igneous rocks are formed when molten magma cools and are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust (example granite), while volcanic or extrusive rocks result from magma reaching the surface (examples pumice and basalt) .
Sedimentary rocks are formed by deposition of either clastic sediments, organic matter, or chemical precipitates, followed by compaction of the particulate matter and cementation during diagenesis. Sedimentary rocks form at or near the Earth's surface. Feildstone, bluestone, Travertine and sandstones are all common sedimentary stones which we work with.
Metamorphic rocks are formed by subjecting any rock type to different temperature and pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the Earth's surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals
This area is particularly rich in stone resources as a result of geologic activity including the Ice Age; when melting glaciers deposited gravel scraped from the northern lands and our rivers; which shape, tumble and deposit a variety of land formations, stone and soils here.
Information gleaned from Wikipedia. Stay tuned for next weeks installation which may (or may not) feature hurricane Irene!
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