Friday, October 21, 2011

Earthquakes Versus Aftershocks

Not being a geologist or seismologist, I am at a distinct disadvantage in describing some of the phenomena with which we now live in Central Virginia. Since the 5.8 earthquake here (5.9 if you consider the work of foreign sources and a local university) occured in August, there have been many aftershocks. An aftershock is a "smaller earthquake" occuring in response and following a larger magnitude occurance. They may occur for weeks or even months following a larger quake. We have now had 42 aftershocks since the August quake. These range from about 1.6 to 3.5 or so. These aftershocks can also do damage. Some of the homes which were unscathed by the initial quake have been damaged by subsequent aftershocks. North of here, a road which seemed fine following the initial quake, collapsed following a 2.2 aftershock. The low magnitude or low Richter scale assignment of these aftershocks can be misleading. Since the type of shaking and the way an aftershock or quake is experienced by your building varies, depending upon the depth of that particular quake or aftershock in relation to your building,some strange things can occur.Some people had broken concrete pads in garages following a 1.8 aftershock which was fairly superficial, whereas a 3.2 deeper in the ground, caused nothing for them earlier, even when it came from the same general area. Yes, aftershocks are earthquakes too.
In addition, this area has felt what we believe to be 80 plus aftershocks, about half of which are never reported, or never detected on the US Geological Survey site. ( This may be why additional devices are being deployed here.
The concerning thing is that with this many aftershocks we could debate that these may no longer be true aftershocks, but pre-shocks for an event which could be worse than a 5.8 locally, and be a major earthquake for the Eastern Seaboard.
The funny thing is that the aftershocks keep on coming, the animals are still frightened, and most of the time, there is no local news coverage of this. Virginia's nuclear generators are still not up again in the area of the quake. Maybe that's a good thing for awhile.
All I can do is make sure we have disaster supplies, make sure caches of supplies are in several areas of the house. Heavy objects such as mirrors, refrigerators, stoves, pictures, have been well anchored to walls and more importantly to the studs behind those walls. We have locked up fragile glassware, and put some barriers in the pantry so shaken objects wont be thrown across the room again. We try to comfort the animals and give them extra attention when we can. Then, we wait, for all of this to pass.

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