Here’s why Putnam County had a 3.6 magnitude earthquake

The Illinois Valley area was rattled Wednesday with a low-magnitude earthquake with an epicenter near Standard in Putnam County. How common is that? Could it happen again?

Mike Phillips, geology professor at Illinois Valley Community College, answered these and other questions.

People don’t think of the Midwest as earthquake territory, explain why we experienced a tremor today.

Phillips: There are several possibilities. The first is the result of pressure on our tectonic plate. The Earth’s surface is made of plates that move and interact with each other. That interaction results in earthquakes where the plates are touching, but some of that stress can result in the occasional earthquake in the middle of the plate where we are located. A second possibility related to the glaciers that left our area around 12-15,000 years ago. When they melted back, the loss of weight allowed our part of the crust to rise very slowly (about 1 mm/year) which can also result in the occasional earthquake.

This is the third reported earthquake since 2000. The others were in 2004 and 2008. Does this indicate an increase in frequency?

Phillips: No, this is a normal experience for our area. We experience an earthquake about once every five or 10 years.

(Wednesday’s) event and the past two all occurred during the pre-dawn hours. Is this expected or is this coincidental?

Phillips: Yes, just a coincidence. It is expected in the sense that it is more likely people will feel a light earthquake like this one if they are lying still and on an upper floor of their home.

There are places in the world, such as Iceland, where seismic activity is increasing. Are there indications we can expect another earthquake in the years ahead?

Phillips: The Earth is a very active planet with earthquakes occurring all the time. They tend to make the news when they occur where people live. So, yes, we can expect more earthquakes in the future (every five or 10 years for our area), but they are not any more or less frequent that in the past.

The reported magnitude of today’s event was 3.6, which is lower than in the 2004 and 2008 quakes. Can we expect lower-magnitude earthquakes or is there potential for a more damaging event?

Phillips: In our area, the earthquakes are usually small. There was a 3.5 near Dixon in 1999. The largest on record was a 5.1 in eastern Ogle county (west of DeKalb) in 1909.

What should people do to prepare for any future event?

Phillips: Not much. It is always a good idea to have fragile, important items attached to something so they do not fall and break, and you probably shouldn’t have a shelf with things that could fall off directly over your bed. But other than that, our experience with earthquakes are relatively minor.

Phillips encouraged anyone who experienced the earthquake or would like to know more about it to visit earthquake.usgs.gov to learn more. Follow the links to share what you experienced, as ground-level observations are an important data source for researchers.