Special Reports
Regional Location:

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Greenwich Mean Date:
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Mb 5.1 (NEIC), Mw 5.0 (Harvard)

5.0 km
(Fixed for quick analysis)

Upstate New York shaken by a M 5.1 temblor

Seismo-Watch More Special Earthquake Reports

April 20, 2002

An earthquake measuring M 5.1 occurred early this morning in Upstate New York, shaking a wide area, breaking windows, cracking plaster and foundations, and tossing items from tables and shelves, but there have been no reports of injuries at this time. New York Governor George Pataki declared a state of emergency in Essex and Clinton counties near the Vermont and Canadian Borders.

Seismo-Watch EQ Flash! Alert Bulletins notified subscribers of this earthquake within minutes after it happened. You should subscribe to the service too! It's FREE and Fast! NOW! Wireless EQ Flash! via pager, cell phone or PDA's! More info.

According to the National Earthquake Information Center (NEIC) the earthquake measured a body wave magnitude (Mb) of 5.1 and a local body wave magnitude (mblg) of 5.1 and occurred at 6:50 a.m. EST, April 20, about 15 miles southwest of Plattsburgh and a mile north of Mill Village, along the southern flank of Crossways and Hogback Mountains, just a little west of the Little AuSable River. See a Topozone topographic map or a MapQuest road map. See USGS Special Earthquake Report.

The Natural Earthquake Hazards Program (NEHP) of the Geological Survey of Canada (GSC) recorded a local body wave magnitude (mblg) of 5.1 and a Moment magnitude (Mw) of 5.0. See GSC Special Report.

The focal depth was relatively shallow and the NEIC automatic processors placed fixed the depth at 5.0 km beneath the surface. NEIC explains that these are preliminary results and further analysis may modify the location, depth and magnitude of this event.

Harvard Geophysical Laboratory (HRV) obtained a Moment magnitude (Mw) of 5.0 using a depth of 8.9 km and their fault plane solution suggested high angle reverse (up and over) motion along a north-south trending plane. The Geological Survey of Canada obtained a similar result using a depth of 10 km. The Lamont-Doherty Cooperative Seismographic Network (LCSN) also obtained a Moment magnitude of (Mw) 5.0 using a depth of 11 km and their focal mechanism was similar to Harvard's and the Geological Survey of Canada's results.

Foreshocks and Aftershocks
There were no foreshocks and five aftershocks have been recorded by the Lamont-Doherty Cooperative Seismographic Network (LCSN) thus far, a

Many local residents said they felt both aftershocks, the largest of which help topple additional items. See an excellent seismogram of the main shock and three aftershocks on April 20 recorded by LCSN Station ACCN (Adirondacks Community College, Glen Falls, NY).

Lamont-Doherty Cooperative Seismographic Network (LCSN) will deploy a series of portable seismographs to monitor the region for aftershocks. This will help define the characteristics of the fault that caused the rupture.

Background Information
This earthquake occurred in the southernmost extent of the Western Quebec Seismic Belt -- a zone defined by a northwest-trending belt of historic earthquakes located north of the Ottawa River and south to New York State. The belt becomes more northerly as it crosses south of the St. Lawrence River and into the Adirondacks. Prominent earthquakes along this trend in the last 100 years include the Timiskaming 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.

The largest historic earthquake in the Northeastern United States and Southeastern Canada measured about M 7 and occurred in the Charlevoix Seismic Zone in 1663 about 425 km to the northeast of this latest event. That zone is quite active, producing up to a couple dozen quakes a month, and has released five quakes registering M 6.0+ in the last 340 years.

Other seismic belts in the region include the Lower St. Lawrence River, the Northern Appalachians (Maine and New Brunswick) and the Northern New England Coast. [Side Bar -- Seismo-Watch covered these seismic belts from 1995 - 1997 in their Seismo-Watch Newsletter. It was a popular feature but was discontinued when the Newsletter was canceled. .]

Damage Reports
The quake was strongly felt in the epicentral region and as far away as Southern Quebec and Ontario, Ohio, Pennsylvania, New Jersey, Maryland and throughout much of the upper New England coast. Did you feel this quake?

New York Governor George Pataki declared a state of emergency in Essex and Clinton counties near the Vermont and Canadian borders. New York State Emergency Management Office has asked property owners to report their earthquake damage to their respective local offices (See list of contact numbers). According to the Post-Standard Newspaper in Syracuse, most of the damage, was confined to an 11-mile stretch from Jay to Keesville along the Essex-Clinton County line.

There were no immediate reports of injuries, but the Vermont State Police received calls about cracked foundations and broken windows, and sections of at least two roads collapsed near the epicenter in upstate New York. Road crews are currently out looking for additional damage and inspecting bridges for possible structural damage.

Department of Environmental Conservation inspected all dams in the area but found no damage. State Troopers were also dispatched to assist local law enforcement and emergency services.

In the town of AuSable Forks, 15 miles south of Plattsburgh, the quake caused three sections of state Route 9N to crumble into swamps by the AuSable River (enlarge photo at right). The Post-Standard reported that a flood in summer 1998 had weakened the road. Scattered water main breaks and collapsed culverts were also reported in AuSable Forks. State Route 22 bridge near Plattsburgh was closed briefly for inspection.

The quake jolted many people from sleep, caused buildings to sway and walls to vibrate. Pictures were knocked from walls, hanging plants swung and items on tables and shelves were thrown to the floor.

Many first thought it was a terrorist strike, as the federal government had issued a warning of a possible attack to financial centers just the day before. Yet it was fairly clear it was an earthquake after a few moments of shaking.

Many said the shaking lasted for as long as 15-20 seconds and some close to the epicenter heard a loud noise like a heavy truck or fright train passing by. Some reported their animals were skittish prior to the quake, then scattered once the shaking started. Common descriptions included doors shaking, walls vibrating, windows rattling.

Several chimneys collapsed, including the one from the United Methodist Church in AuSable that was built of stone in 1925. Part of the roof caved in as well.

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

Damage assessment is still going on and more information will be added as it becomes available.

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Report update: 3:20:11 PM, Wednesday, April 24, 2002

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