Early Tuesday morning, an earthquake was reported along the West Virginia/Virginia border, about 30 minutes from Roanoke, V.A. The quake registered as a 1.9 on the Modified Mercalli Intensity Scale. Very few people would have felt any shaking at this intensity, but it was enough to be recorded.
Earthquakes in West Virginia
West Virginia doesn’t have many earthquakes, and they are not as strong as ones felt on the west coast. This is because West Virginia is in the middle of a tectonic plate. They are so rare in West Virginia that over the past 40 years, there have only been 25 earthquakes with a magnitude greater than 2.5. Some of the bigger quakes felt in W.Va. over the years were manmade. An injection well was used to get rid of brine from a gas field, which caused disruptions underground.
Earthquakes along the east coast are different in terms of damage and intensity. An east coast earthquake with a high magnitude will be felt further away than a similar one on the west coast. The North American tectonic plate is denser than the Pacific plate. This causes the energy to travel further along the east coast. In contrast, the Pacific plate is less solid, which breaks up the energy before traveling far. Earthquakes on the west coast often stay within the area because of this.
The Modified Mercalli Intensity Scale and the Richter Scale
We’re all probably used to hearing earthquakes described with the Richter Scale, but how is the Modified Mercalli Intensity Scale different? The Modified Mercalli Intensity Scale measures the effect of a quake on people and the environment. The Richter Scale measures the energy released by the tectonic plates.
The Modified Mercalli Intensity Scale makes more sense in terms of damage. The scale ranks from 1-10, with a 1 being “not felt” and a 10 being “extreme.” When using the MMI scale, some criteria are more reliable than others. The MMI scale changes over the years as we develop and understand the Earth more, but it is not scientific. It’s only useful to areas where people live, as the scale uses witnesses to evaluate the intensity and the damage. The scales are comparable but don’t often match.
Scientists use the Richter Scale to judge magnitude. We like to think of the Richter Scale as a range, usually between 1-10, but there are no limits. However, we’ve never experienced an earthquake that reaches a 10 on the Richter Scale. A 10 on the Richter Scale would undoubtedly be a 10 on the MMI scale.
Earlier this year, Alaska experienced an 8.2 magnitude earthquake, the strongest in decades. The city of Kodiak had to evacuate to higher ground as the quake triggered warnings for tsunamis. The warnings included the states of California, Oregon, Washington, and Hawaii. These warnings were later canceled. Aftershocks were felt months later in Alaska.