Earthquakes in Maryland - Do They Really Happen?

Every month or two, I tease a friend of mine named Barb, and a cousin Pam, who both live in California about their earthquakes. Whenever a new earthquake happens in that area, there is always talk about the "Big One" that may one day come and, perhaps, even sooner than anyone believes. Even Yellowstone National Park has recorded over 500 earthquake swarms in the last two years, leading many researchers to believe these are forerunners of a much larger earthquake. The largest one (so far) measured at 4.1 magnitude occurred on March 25, 2008, although as of January 8 2009, the activity has decreased - for now.

It is a standing joke among many that California and other closely related areas will some day slide into the Pacific Ocean, never to be seen again. In order to honor my missing friend, I will have to take a trip to Las Vegas, Nevada, where the new coastline of the Pacific will be located. As I told her, it will probably shorten my driving time and distance by a couple of hours, at the very least. The truth is that the Pacific and North American Plates are moving horizontally past one another, so California is not going to fall into the ocean; however, it is possible that Los Angeles and San Francisco will one day be neighboring cities - quite literally.

However, the fact is, I may have a very good chance of experiencing an earthquake although I am in the eastern portion of the United States. Recently, on December 26 2008, a 3.4 magnitude earthquake was recorded a few miles from where I live and the epicenter was located near Lancaster, PA. A few days later on December 30 2008, another one at 2.4 magnitude occurred. On December 9, 2003, my brother felt a 4.5 magnitude earthquake near his home below Fredericksburg, VA.

All these earthquakes lend credence to an event that happened to me a few years ago when, while walking through my dining room, I literally missed a step as though the ground had moved away from beneath me. It was as though the earth had shifted. When I told others about what happened, I was invariably laughed at; fortunately, the facts alone are vindication that something did happen, as there are at least 61 known and recorded earthquake events within the confines of Maryland and not counting those felt where the epicenters were in another part of the country.

History also bears this out since Maryland is not immune to earthquake activity or the aftereffects of other earthquakes, even when the epicenter was hundreds of miles away. One of the earliest recorded earthquakes was felt in Annapolis, Maryland from an earthquake in Massachusetts, on November 18 1755. Maryland has felt earthquakes from as far away as Missouri and Canada. Yet earthquakes even closer happen quite often as Virginia has had several in the past few years.

When faults exist, they are usually miles below in bedrock and a quake may not even rattle a dish in the cabinet. However, in the eastern part of the United States and east of the Rockies, earthquakes may be felt from miles away due to the plates being located in the Atlantic Ocean and the Caribbean Sea and thus further away, whereas California is relatively close to the plates. Faults east of the Rockies are also harder to find and the best proof is the occurrence of an earthquake in a specific area.

The closest known fault I can find to my area is in the Blue Ridge-South Mountain Anticlinorium (BR-SMA), called the Short Hill Fault (SHF), which is a younger-over-older thrust fault that has been folded within the rocks as contractional motion was underway. Even so, this includes the North Mountain Fault in Washington County, MD and the Bull Run Mountain Fault in the Frederick County, MD to the Adams County PA area. These faults are not known to be active, yet they do exist and many more faults are believed to be undetected at this time.

It is interesting to note that on September 9, 1962 and on April 26 1978, an earthquake occurred within 15 miles of my home with a magnitude of 3.3 and 3.10, respectively. These earthquakes were two of the largest in the state (even if considered minor), though I find no record of damage caused by them. Although there is little fear that even a major earthquake would cause this area to slide into the Atlantic Ocean, there is a possibility that old mountains could disappear and new ones take their place, creating new valleys and lakes.

Earthquakes happen every day all over the world. Most earthquakes may not be felt and a few have caused significant and catastrophic damage in both life and property as has happened in California. Therefore, the next time you think the earth moved, it probably did.

Sources:

U.S. Geological Survey Earthquake Hazards Program

Kinematics of the Short Hill Fault

Earthquakes and Maryland