Tuesday, July 2, 2013

Data on Monday's offshore Fairport Harbor earthquake gets tweaked

Tweaking the data on Monday's small earthquake off Fairport Harbor Village is placing the event a tad closer to the shoreline but at the same relative depth as first determined.

The 3.2-magnitude temblor occurred at 3:48 a.m. with its epicenter located 3 kilometers – or 1.86 miles – due north of the village at a depth of 5 kilometers, or slightly more than 3 miles, says state geologist Mike Hansen.

Hansen is in charge of the Ohio Department of Natural Resources' Division of Geological Survey's Ohio Seismic Network.

This network consists of 29 automated seismic detection units maintained by a corps of volunteers.
Area installations include units at Lake Erie College in Painesville, Lakeland Community College in Kirtland, the Geauga Park District's Observatory Park in Montville Township, the Cleveland Museum of Natural History in Cleveland, and the Ashtabula County Emergency Management Agency in Jefferson Village.

Hansen said the U.S. Geological Survey took note of 18 felt reports from Northeast Ohio residents who said they were aware of the incident.

That is a rather large number given the early morning hour of the event, Hansen said also.

“As earthquakes go it was a pretty small event,” Hansen said. “And it's been pretty quiet up there, too.”

Which has not always been the case, however.

A look at the Geological Survey Division's earthquake data demonstrates the region underneath Lake Erie and offshore from Cleveland to Conneaut Harbor has encountered a goodly number of similar-size minor tremors in recent years.

From 2002 to the present this just-described region has experienced 42 or 43 minor earthquakes, the bulk of them close to Monday's event.

Nor was Monday's earthquake the only one recorded from this area within the past few months.

A 2.7-magnitude earthquake was detected on March 8 from very near Monday's earthquake.

Yet scientists are unsure why this zone has experienced so much seismic activity over the past decade or so, says Hansen.

“That's one of the mysteries we'd like to see answered,” Hansen says. “There are obviously some fault lines out there.”

Of course, Hansen also says, a good part of the challenge is that the events are happening offshore and underneath Lake Erie. Such a remote and challenging location makes it difficult to conduct good research the way scientists can when dealing with a land-based event.

Hansen does offer assurances that all of the events happened well below the active rock salt mining operations on-going underneath the lake.

In no way did this mining cause the events anymore than the salt dome is in danger of being compromised, Hansen says.

Also, these underneath Lake Erie earthquakes excludes those that have occurred inland in Northeast Ohio. Among them was the 5.0-magnitude (4.96-magnitude in actuality) that was keenly felt in many locations on Jan. 31, 1986 and resulted in two minor injuries.

Its epicenter was on the Leroy Township-Montville Township line near Rt. 86. This was the state's third strongest-ever earthquake.

A total of 13 aftershocks were detected following the Jan. 31 event as well.

- Jeffrey L. Frischkorn

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