Although earthquakes are not as common in Ohio as some other states, they do occur with some frequency. The Ohio Department of Natural Resources operates an earthquake information network (OhioSeis) across the state, including one at The College of Wooster. Karrie McAllister, who oversees the Wooster station, explains how it works and answers other questions about the likelihood of earthquakes occurring in Ohio.

Q. How common are earthquakes in Ohio?

A. People would be surprised to know that since 1776 more than 160 earthquakes have been felt in Ohio. Some of these have even caused minor to moderate damage. Most earthquakes in Ohio are shallow events. They occur in the upper portion of the crust at depths of three to six miles along pre-existing zones of weakness in basement rocks. While some of these zones of weakness have been mapped out, it is difficult to tell when they will become active or what causes the activity, although most activity is very mild.

Q. Have there been any significant earthquakes in Ohio?

A. Of the significant earthquakes felt in Ohio, not all had their epicenter within the state boundary. The New Madrid earthquakes of 1811 and 1812 (epicentered in Missouri) were felt throughout Ohio and reportedly toppled chimneys in Cincinnati. Anna, a community in Shelby County in western Ohio is a very active zone and has felt many significant earthquakes, some of which even twisted organ pipes at the local church. In January of 1986, a magnitude 5.0 earthquake centered in Lake County shook northeastern Ohio, cracking plaster and breaking windows. Another magnitude 5.0 earthquake in September of 1998 was felt throughout northeast Ohio but was epicentered just over the border in Pennsylvania.

Q. Living in Ohio, is there a serious seismic risk?

A. Seismic risk in Ohio is hard to determine because of the infrequency of earthquake occurrence. Also, because the zones of weakness along which these earthquakes originate do not extend to the surface, they cannot be monitored. Historically, we have not felt any major earthquakes in the past 300 years, but 300 years is an instant in geological time. It is not known whether or not larger earthquakes have occurred here in the past and at what frequency. The Ohio Geological Survey suggests that, according to the records, the western, northeastern, and southeastern parts of the state have a risk of moderately damaging earthquakes.

Q. What is OhioSeis and how does it work?

A. OhioSeis is a network of 23 stations distributed throughout the state, each equipped with a seismometer and a link to the Internet. Earthquake activity is continuously recorded, and all of the data is available online, including the software to read and interpret the data. Each station also has a connection to a GPS (Global Positioning System) unit so all stations are running at the exact same time, which is essential for working with the data. The network is coordinated by the Division of Geological Survey of the Ohio Department of Natural Resources and provides detailed information on small local earthquakes because of the many stations around the state. The station at The College of Wooster is located on the lower level of Scovel Hall (944 College Mall). To learn more, visit our Web site at: http://www.wooster.edu/seismic/seismic.html

Q. What type of instrument is used to measure earthquakes and how does it measure seismic activity halfway around the globe?

A. Our seismometer, a Model S102, is specially designed for education as a research tool. Instead of needing to be buried deep below the surface, it is visible and has been calibrated to remove local movements at ground level, such as a group of students changing classes or walking by the instrument. By filtering out these small waves it is sufficiently sensitive to detect the larger-scale waves from earthquakes around the world. Our station is able to record earthquakes with magnitudes 6.0 and above from almost any location on Earth. Regional earthquakes, however, can be detected at much lower magnitudes.

Q. What does a seismogram of an earthquake reveal?

A. A seismogram can tell us the location of the epicenter of the earthquake and how large the earthquake is. Of the information that can be pulled from a seismogram, the most important measurements are the arrival times of both the P-wave and S-wave, and the amplitude of the surface waves. P-waves, or primary waves, are the fastest moving type of wave. They reach the seismometer before the S-wave, or secondary wave, which gets slowed down as it moves through the liquid core of our Earth. The arrival times of these waves help us pinpoint the location of the epicenter with a complicated distance, rate, and time formula. The amplitude, or how large the surface waves are, coupled with the known distance from the epicenter can give us the magnitude of the earthquake.