Interesting Info on Earthquakes in the Southeast U.S.

[njc]

I didn’t want to take over Libster’s thread checking in on those living in California, but I just love earthquakes and volcanoes and all the stuff that goes along with it. I was obsessed when I was in school studying this stuff, and I guess I still am!

I wrote in the previously mentioned thread about an earthquake that occurred in Virginia in 2003, the first one I have ever experienced. I had no clue what was going on, because as with most, I never thought about earthquakes occurring in the east, I always think of Cali and other locations along the “Ring of Fire”. Even with all my research in school, I always focused out there.

So I was looking around the internet trying to find a story about the earthquake in VA to post (http://fredericksburg.com/News/FLS/2003/122003/12092003/1193995) and came across some other things of interest about earthquakes and the southeast US…

Virginia, like most states on the eastern seaboard, has a moderate level of risk from earthquakes (see attached drawing). The largest earthquake known to have occurred in the region was the 1886 Charleston, South Carolina, earthquake (estimated magnitude 6.6-6.9). That quake was felt as far north as Canada, as far west as Missouri, and as far south as Cuba.

Since 1774, the year of the earliest documented Virginia earthquake, there have been over 300 earthquakes in or near the Commonwealth. The largest earthquake in Virginia was the 1897 Giles County shock (near Virginia Tech). The maximum intensity was VIII (Mercalli scale) in Giles County, and it was felt over 11 states (approximately 280,000 square miles). The estimated magnitude for this event was 5.8, making it the third largest earthquake in the eastern United States in the last 200 years (second largest in the southeastern U.S.).

Taken from http://www.mme.state.va.us/DMR/PUB/Brochures/quake.html

In 1897, an earthquake with an estimated magnitude of 6.0 rocked Virginia Tech in the southwestern area of the state, Chapman said. The shock was centered in neighboring Giles County and was felt from Pennsylvania to Georgia. And although we tend to think of Alaska and California as the typical sites of seismic activity in the United States, eastern Tennessee is one of the most active areas in the nation in terms of the number of earthquakes recorded.
The most damaging seismic event in the U.S. prior to the 1906 earthquake and fire that destroyed San Francisco occurred in coastal South Carolina in 1886, Chapman said. The "Charleston earthquake," which caused structural damage as far away as Richmond and Atlanta, reached an estimated magnitude of 7.3 on the Richter scale -- essentially the same magnitude as the shock that killed more than 17,000 people in northwestern Turkey in August 1999.

"Recent seismological studies suggest that the southern Appalachian highlands have the potential for even larger earthquakes than have occurred in the past," Martin said. "But now those events would take place in much more highly populated areas. Felt earthquakes don't occur as often in the Southeast as in California, because the tectonic strain rates are different. Our region tends to experience large earthquakes isolated by long periods of quiet."

"However," James Martin warned, "we are under a significant threat of large, damaging earthquakes. In terms of seismic vulnerability, many buildings in the southeastern U.S. today are similar to those in Turkey. In neither place is there adequate structural protection of buildings. If another 7.3 magnitude earthquake hit Charleston today, the city would suffer much the same damage as cities in Turkey."

There's another difference between California and the Southeast as seismic zones. "The earth's crust is stronger here," Chapman explained. "So shock waves moving from the epicenter of an earthquake don't lose as much energy as during quakes in California. When a magnitude 7.0 earthquake occurs in the Southeast, the waves affect a larger area and can cause more damage at a greater distance than when a similar shock hits California."

Taken from http://www.sciencedaily.com/releases/2003/12/031212080152.htm

So anyways… thanks for letting me share this long post. I just find it so interesting!

 

[Momoftwo]

I live in No VA now, but used to live in Columbia, MD. Around 1990 we had a 2.7 that really made more of a whooshing sound than any movement. There was a quick shake and the whooshing sound and that was it. The funny thing is a couple of days later we had about a 2.3 at 1130 at night that woke me up and then a day or so after that there was a 1.5 or so that people actually called the fire dept about. They called to say their lamps were swaying. The reality is, you can''t even feel a 1.5. There is a fault line that runs up in Maryland and into PA. The biggest earthquakes in the US haven''t been in CA. Just more happen there.

 

[njc]

Date: 6/17/2005 2:29:11 PM
Author: Momoftwo
There is a fault line that runs up in Maryland and into PA.

I actually tried a little bit to find a fault map for the US, but was unsuccessful.

The biggest earthquakes in the US haven't been in CA. Just more happen there.

This is pulled from what i posted before:

And although we tend to think of Alaska and California as the typical sites of seismic activity in the United States, eastern Tennessee is one of the most active areas in the nation in terms of the number of earthquakes recorded.

And the image i attached, which i now realize i never explained, shows the epi-centers of 2,460 earthquakes, occuring i guess since theyve recorded this kind of stuff. Eastern Tennessee is totally black. I just find that so interesting. And the whole thing about the ground being harder here causing the "waves" to travel farther. I really want to find a fault map....

ETA: This may be the best i can find:

Virginia is located in the middle of the North American plate, rather than along the edges of two plates, so there is much less quake activity. In California, quakes occur on fault lines closer to the surface. In Virginia, quakes occur along faults at depths of three to 15 miles. The December 9 quake occurred at the three-mile depth.

 

[movie zombie]

me too! i''ve always loved reading about volcanos and earthquakes....it was so tempting to get in the car and drive up to mt st helens when she was doing her thing.

flying from the bay area in california to seattle one can see the string of volcanos starting with lassen...and flying south one can see the ancient cones left down around san luis obispo. the san andreas fault from a plane is impossible to miss. oh, and if you ever fly from reno to the bay area, i hope you get that view of yosemite valley....

the idea that the earth is a living and always evolving entity in and of itself makes so much sense to me.

can you imagine the power it takes to pick up the mississippi river and move it?!

peace, movie zombie

 

[fire&ice]

As Lop noted in the other thread, I did OBSESS about earthquakes after quaking in my boots a couple of years ago. The fault we live on is called the Columbian Fault. I think someone just made it up as the fault runs along the tiny hamlet of Columbia. Our carpenter was driving out to our house on the highway. He felt nothing as many other drivers experienced. Wonder why? I guess the tires, motion & the road is always meant to move a bit. No damage other than a couple of pictures falling. The dogs ran to me - confused and kinda like wow - this is fun. No advanced warning. Though, I wonder if that is because they aren''t seasoned. But, just before the quake, "the boys" (cat brothers) DARTED under the porch. I don''t know if they knew something was up or after prey. I know when a tornadoe is about to hit - the animals really tell you. Must be some type of pressure change. You know to be scared when things are erily silent including the birds.

NJC, that earthquake near Tech in 1897 was said to be bigger than reported. At the time, the epi-center happened in such a remote area. But, who knows?

The North Carolina Natural History Museum has one of those "earthquake activity" interplays. It''s cool. We saw ours on there.

With all this chat about Southeast earthquakes - kinda makes me nervous.

On a serious note, the SE doesn''t build to earthquake standards. So, a smaller EQ could cause damage. I know some foundations were ruined. We have trusses & they just went with the flow. And, in CA, many people I know have that putty put on the bottom of breakables.