Earthquake

Description:

A sudden motion of the ground which may result in surface faulting (ground rupture), ground shaking, and ground failure.

This complex motion is caused by a sudden shifting or breaking of subsurface rock to relieve built up stress. The energy released at the center produces a variety of seismic waves that travel out in all directions through the surrounding rock. Some of these waves make their way to the surface and travel out across the countryside.

Secondary Effects:

The effects of earthquakes are largely dependent on the strength of the earthquake as measured by the Richter or other magnitude scales, the concentration of population and extent of development in the impacted area. Slight earthquakes do little damage. As the strengths increase, damage increases from minor glassware breakage through to total devastation. Utility services could be interrupted, transportation routes cut off in places, the chance of fires could increase with gas lines rupturing, live power lines could break and emergency responders could be unable to reach scenes of incidents. Economic impact could be severe due to closed businesses. Marginally profitable businesses may not be restarted resulting in lost jobs. Psychological effects will be significant especially if aftershocks occur. Personal injury caused by falling debris is also a consideration.

Vulnerability:

While Maine has experienced numerous measurable earthquakes in the last 100 years, none have caused substantial damage. However, their distribution throughout the State indicates vulnerability is statewide. Metropolitan areas are subjected to far more structural damage than rural areas because of the density and design of urban buildings, especially multistory structures.

The largest recorded earthquake in Maine from 1747 to the present was estimated to be a 5.9 magnitude that occurred near Eastport in 1904. Record keeping prior to the mid 1800s is sparse and of uneven quality. Between 1747 and 1992 there were 507 earthquakes, some which were too small to be felt. Instrumental monitoring of Maine seismicity began in 1975.

The most seismically active regions of Maine are the area along the eastern side of Passamaquoddy Bay, the Dover-Foxcroft/Milo area, southwestern Maine, especially the Portland/Lewiston region. There is also strong seismic activity that occurs in New Hampshire that can affect people living in western Maine. The same is true of seismic activity that occurs in Quebec along the Saint Lawrence which can affect northwestern Maine.

All of the earthquakes that occur in Maine and New England are intra plate earthquakes. Maine is far inland of the boundaries of the North American plate. The North American plate extends from the Mid-Atlantic Ridge on the east to the western boundary of the U.S. So Maine is near the middle of this plate. Therefore, Maine is not subject to the frequent, deep, and large earthquakes that are generated by the edges of tectonic plates bumping into each other. While the probability of a strong earthquake occurring in Maine is small, it is still a possibility. FEMA has previously said a 7.0 magnitude earthquake could occur anywhere along the east coast. There are hundreds of old faults in New England. However, seismologists have not been able to find any correlation between these fault lines and the location or frequency of New England earthquakes. So in Maine a person could live near a fault and not experience any ground shaking and a person living far away from a fault could experience significant seismic effects.

The Maine Geological Survey says all of Maine has a moderate risk for earthquake.

Mitigation:

Buildings constructed in high risk areas should conform to standards of safety for earthquakes. Emergency planning for earthquakes should include search and rescue, medical assistance, crisis counseling, evacuation, sheltering and mass care, and reduction of the potential problems caused by falling debris, fire, utilities, and hazardous materials. The Maine Geological Survey maps, interprets, and publishes geologic information, and provides advisory and interpretive information for planning and regulatory agencies.

Maine has no statewide building code so most existing buildings and those now being built, do not incorporate seismic mitigation in their construction. It is difficult to sell costly voluntary mitigation measures for low occurrence events even when they have high potential impact. Hospitals, fire and police departments, and EMAs provide services that would be essential in a seismic event yet most of these are housed in buildings that have no seismic mitigation. In a large earthquake it could be difficult to find an adequate undamaged alternate work site. There is no warning that allows for hasty preparations.

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Earthquake

Description:

Secondary Effects:

Vulnerability:

Mitigation:

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