My first thought was of disappointment. I have yet to feel an earthquake up close and personal and as a geologist I find this depressing. I felt the Hector Mine earthquake (M7.1) back in 1999. It woke me up all the way in UT. We drove out to CA to observe the fault rupture. It was awesome. I felt a M3.1 earthquake that occurred in San Juan Bautista, CA when we lived in Monterey, CA. These were either at a distance or tiny, they just aren't what I am looking for in an earthquake. I want the personal touch.
Since earthquakes are a personal passion of mine, I thought I would answer some questions and discuss some thoughts I have heard today from friends of mine who are not geologists.
1) Are there faults everywhere? I thought there were only faults in places like CA.
While I cannot reliably say there is a fault under every person's feet in America or the rest of the world, the truth is faults are common just about everywhere. Faults are created when the Earth's crust experiences such substantial force (either tensional, compressional or shear) that the rocks can no longer bend to accommodate the stress they are placed under. A fault differs from a fracture in that there is movement (displacement) across a fault.
The Earth is broken up into plates that facilitate motion relative to one another. Plate tectonics, which encompasses both the rifting and collision/subduction of the Earth's crust, has both moved and built the continents through geologic time . Each time the crust rifts apart or moves back together, faults partially facilitate this motion. These faults remain even after the cessation of major activity along them.
These faults are preexisting zones of weakness in the Earth's crust and when placed under stress, they may "reactivate" or experience movement again. Depending on the type of stress they experience they may be more or less likely to reactivate and they may experience a different type of motion than they had the last time they were active.
In the case of VA, the area in question lies between the Appalachians and the Mid-Atlantic Ridge. Both of these geographic features are the result of faulting (and magmatism). The Spotsylvania Fault has existed since the Paleozoic Era when the Appalachians were built and was later remobilized during the rifting that formed the Atlantic Ocean. A magnitude 4.5 earthquake on the nearby Lakeside fault occurred in December 2003, which suggests that while earthquakes are not an everyday occurrence in the area, they are by no means unexpected.
2) Earthquake Prediction, or "Isn't it eerie?"
Because the dynamics of faulting are so complex (see discussion above), it is IMPOSSIBLE for geologists/seismologists to predict earthquakes. We give estimates. These estimates have been frequently taken out of context by the media. For example, geologists in CA have been mocked for saying a major earthquake is due to strike California for as long as I can remember. This has become a source of mockery for many. It is only within the past three years that we have been able to reduce the estimate of "due" to an actual number for the San Andreas fault system, even then it is stated in probabilistic terms. In the case of the article cited by Army Wife 101, that says that New York City is "overdue" for a major earthquake, it is possible that the city is due, however, the data is based on 2 earthquakes that occurred in 1783 and 1884. It is equally possible that the timeline between major earthquakes is longer or shorter, because we simply don't have enough data to accurately project just how frequent significant earthquakes (magnitude 5 or greater) occur there. It is possible these guys are right on the money, but it is also possible that it will be a while. Either way, it was a specific study of the faults in and around New York and this area may have completely different probabilities than the fault system in the Virginia Piedmont.
An earthquake anywhere is a concern, but if you look at the map, you can see that while it is foolish to ignore the risk earthquakes pose, VA and NY are reasonably safe compared to many other places, like the New Madrid Fault Zone I am sitting next to right now or the Cascadia Subduction Zone which underlies the Oregon and Washington coastlines is of far greater concern.
3) The "Big One"
Size is only part of the equation when it comes to earthquakes, but size does matter. The most devastating and largest earthquakes occur along locked faults and usually associated with subduction zones. For example, the 1964 Alaska Earthquake or "Good Friday Earthquake" was the largest earthquake in recorded history to hit the US at a magnitude 9.2. This earthquake collapsed buildings, caused a tsunami that inundated forests and dropped a ship on a inland. Nothing that occurred today is on par with this historic quake.
 |
| Image Courtesy of: http://bit.ly/qgbjQE |
4) So if faults are just about everywhere and there is some risk associated with all of them, should I be worried?
Well, the answer is: it depends. Your risk in an earthquake is not simply a measure of the magnitude of the quake, as today's earthquake demonstrates. It is also related to the type of material the fault runs through, the type of fault it is, the depth below ground surface where the earthquake originates, the type of structure you are in, your distance to the epicenter, etc. This is why the earthquake hazard maps were developed. They take each of these factors into account. For example a magnitude 5.9 earthquake in Ankara, Turkey demolished some buildings, killing people in part because the fault runs right under the city and in part because the concrete buildings in that area of the world are particularly prone to earthquake damage.
Depending on where you live in the country, you are more prone to certain types of natural hazards than others. For example, if I were to rank the immediate risks to myself, given my knowledge of the area, I would rank them as follows: tornado >flood >fire >earthquake >pandemic/zombies >volcano >hurricane >tsunami. This is why I keep a weather radio.
The good news is that the general preparation for natural hazards is basically similar. The CDC has an excellent resource that can help your family plan for any hazards you might face. These are things every military family should be familiar with, because the rule of thumb in hazard preparedness (according to FEMA) is that it takes at least 72 hours to mobilize an effective emergency response. By being prepared, you put yourself and your family in a position of relative safety and security, no matter what happens.
I know today was exciting, perhaps even scary, but the good news is that very little damage was done. If it reminds you to take a moment and take stock of how prepared your family is if something serious happens, then that is a positive outcome.
If you have any questions about earthquakes or other geologic hazards, I am more than happy to entertain them. I love geology. That's why I get up everyday and work on it.
6 comments:
it was exciting... and the animals in the house had such different reactions, it was interesting
This was informative -- thank you!
Another thing for military families to consider is whether the active-duty member will be pressed into service during the disaster. When we lived in coastal Georgia, my sweetie told me I'd have to evacuate myself in a hurricane because he'd be called into work.
That is a really great point. I made the assumption, because my experience was like yours, that spouses are going to have to respond to the disaster (whatever it may be) w/o their significant other.
If small children are involved (or pets in my case), this becomes more complicated. Planning for all of ones family members needs to happen too.
This is really interesting! I have always loved learning about natural disasters.
And to add to what Bette said, same goes for Guard families. It is the mission of the Guard to get called out in the case of natural disasters. I've always had to make sure we have supplies for storms because my husband was always one of the first called in for duty be it blizzard, hurricane, etc. (we've had it all in PA and MD).
Good Point!
Post a Comment