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Rumble, rumble...

The chimney of the historic United Methodist Church in Au Sable that was built of stone in 1925 was also a casualty of the quake. Part of the roof caved in as well.

Commercial items at stores throughout the region littered the aisles. Some experienced broken windows. Power was briefly disrupted to about 3,500 residents in Peru because of a damaged substation.

While we are somewhat isolated from many of the natural disasters that plague other portions of the country, earthquakes are are actually quite common here, as was evidenced by the one that occurred near Tupper Lake last week.

Each year approximately 450 earthquakes occur in the Adirondacks and southeastern Canada, according to the National Earthquake Information Center (NEIC). The major difference between those that occur here and those in the western part of the country, is not surprisingly, magnitude.

An earthquake is measured in both magnitude (M) and intensity. Magnitude is a measured value of its size and is the same no matter where you are, or how strong or weak the shaking was in different locations. Intensity is a measure of the shaking it creates, and varies with location.

A magnitude of 8 or higher defines a "great" earthquake; 7 to 7.9 is considered "major"; 6 to 6.9 is "strong"; 5 to 5.9 is "moderate"; 4 to 4.9 is "light"; 3 to 3.9 is "minor"; and less than 3 is "micro."

Of the 450 or so quakes that rumble through the region every year, perhaps 4 will exceed magnitude 4, 30 will exceed magnitude 3, and about 25 events will actually be reported as having been felt.

A decade will, on average, include three events greater than magnitude 5. A magnitude 3 eventlike the one that recently shook Tupper Lake is sufficiently strong to be felt in the immediate area, and a magnitude 5 event is generally the threshold where damages begins to occur. That means a vast majority of North Country earthquakes go completely unnoticed.

Besides the one I experienced on April 20, 2002, other prominent quakes in the last 100 years include the Timiskaming, Ontario M 6.2 in 1935; the Cornwall, Ontario M 5.6 in 1944; and the Goodnow or Blue Mountain Lake M 5.1 earthquake in 1983.

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