Earthquake

Total Score=64


Definition

A shaking or trembling of the crust of the earth, caused by underground volcanic forces or by breaking and shifting of rock beneath the surface registering 5.5 or more on the Richter Scale producing casualties and considerable property damage.

Background

Earthquakes rank as one of nature's most violent events. The energy released by an earthquake that is 8.5 on the Richter Scale is roughly equal to 12 times the energy released by the Hiroshima atomic bomb. How is this determined? Earthquakes are measured using sensitive monitoring equipment called seismographs. Using several seismograph locations, seismologists can pinpoint the location and depth of an earthquake. They can usually locate an earthquake within one tenth of a degree latitude or longitude. In addition to determining location, the seismologists can also determine the strength of the earthquake. Two main scales are used to show the strength: the Richter Scale and the Modified Mercalli Intensity Scale.

The Richter Scale is probably the most well known by the public and is usually given in news reports. This scale is an logarithmic scale which shows the magnitude of an earthquake. This is determined from seismograph readings rather than from actual reports of shaking. Contrary to popular belief, the Richter Scale goes on indefinitely with each increase of one indicating 10 times the strength of the previous number. For example; a 3 on the Richter Scale would be 10 times stronger than a 2, and 100 times stronger than a 1.

The Modified Mercalli Intensity Scale was developed to show the intensity of an earthquake without using measuring devices. This scale ranges from 1 to 12 and is used to describe the effects on people and property. This scale works well for earthquakes that occurred before seismographs were developed.

The northeastern part of the State is classified as a minor risk zone, a small portion of the Northwest and Southeast are classified as major risk zones and the remainder of the State is a moderate risk zone. Poland lies within the moderate risk zone, which means that moderate damages can be expected from an earthquake. The classifications given are due to the presence of geologic fault lines in the St. Lawrence Valley and the Laurentian Trough in Canada.

Since 1766, Maine has experienced 446 minor earthquakes ranging in intensity from feeling minor vibrations to destroying brick chimneys.

Seismic stations, locations that measure earthquakes are located at Whiteface Mountain in New Hampshire, and Waterville Maine as well as another near Caribou in Northern Maine.

The map below shows the level of risk of an earthquake across the country

Source USGS

Below is a map of the current seismic activity across the New England region for the past 6 months:

Source: http://www.ldeo.columbia.edu/LCSN/recenteqs/

History

During the last 100 years, Poland has experienced the effects of numerous earth tremors with epicenters within 25 miles of the town. The following epicenters were recorded by the USGS:

2/5/1929

Auburn

10/8/1929

Lewiston

1/15/1935

Lewiston

3/8/1942

Lewiston

10/30/1945

Lewiston

2/5/1976

Lewiston

2/15/1976

North of Lewiston

1/4/1978

Otisfield

1/4/1978

Otisfield

2/21/1979

Lewiston

7/12/1980

West of Auburn

9/18/1983

Northeast of Lewiston

9/18/1983

Northeast of Lewiston

3/13/1984

12 Km South of Auburn

10/7/1985

3 Km North of Auburn

11/26/8?

5.3 Km Southeast of Auburn

2/12/1995

5.3 Km Southeast of Lewiston

2/17/1995

6 Km South of Lewiston

7/30/1996

4.2 Km SE of Raymond

Here is a list of New England Earthquakes compiled from data provided by the Weston Observatory of Boston College.

Time of Year

The earthquake probability period is year-round

Speed of Onset

The occurrence of an earthquake is of rapid onset, which does not permit citizens in area of impact to initiate preparedness actions.

Duration of Event

The duration of this violent event is generally less than one minute. Several tremors may be felt up to several days following a major earthquake.

Area of Impact

The effects of an earthquake may be experienced throughout the town.

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Copyright 2004, Wayne Cotterly

Revised 4/1204