01/17/01 Manhattan Earthquake
by John Armbruster, Seismology, Lamont-Doherty Earth Observatory
Manhattan and Queens, NY experienced a minor earthquake at 7:34 A.M. Wednesday January 17, 2001. The magnitude was 2.4, the instrumental location of the earthquake was the upper east side of Manhattan at a depth of approximately 7 kilometers (4.3 miles). The earthquake was located near to the 125th Street fault and it is possible that this fault was the source of the earthquake.
to Seismogram of 01/17/01 earthquake recorded at Lamont-Doherty Earth Observatory
The previous earthquake of this size in the area occurred near Carmel in Putnam County, NY last August (see 08/22/00 article). Earthquakes of this size occur on average once or twice per year in the New York City area. The last earthquake widely felt here occurred in southern Westchester on Oct 19, 1985 and was of magnitude 4. In New York's 300 year history, the largest earthquakes were of magnitude ~5 and they occurred in 1737, 1783, and 1884. These three earthquakes each threw down chimneys and were felt from Maine to Virginia.
Wednesday's quake was minor and did no damage; but if an earthquake of magnitude 5 were to occur within New York City, it is expected that serious damage would result. The 117 years since 1884 is the longest period without such a magnitude 5 earthquake. In a geologic sense it is inevitable that such an earthquake will occur again. But it is not possible to predict earthquakes and we don't know when the next magnitude 5 earthquake will come.
A previous earthquake similar in size and location to that of Wednesday occurred in 1937 centered somewhat to the east in Queens. It was of magnitude ~3.5 and was felt from New Haven, CT to Trenton, NJ. It did not do any serious damage according to "United States Earthquakes 1928-40".
Many people who felt this earthquake thought that there had been an explosion. The loud noise, which they heard, impressed them much more than the shaking they felt. In the eastern U.S., the rocks are old and strong; they transmit the vibrations from the earthquake very efficiently, including the sound of the earthquake. In California, where the rocks are younger and less strong, earthquakes are felt at shorter distances and with less noise. Here in the northeast, an earthquake itself is in stronger rock, so there is a higher "stress drop" -- the movement is a larger, more sudden jump. Noise and shaking are both vibrations. If you think of the vibrations of a musical instrument, a big instrument makes deep notes at low frequency, and a smaller instrument makes higher notes with high frequency. The stronger eastern rock can generate the same amount of energy or sound with a smaller source than a California quake from a larger source. Here shaking is a low note and noise is a high note, so the sound is more impressive than what is felt.
USGS Community Internet Intensity Maps (CIIM)
or "Did You Feel it?"
Aftershock Update 01/19/01
An aftershock was experienced in Queens shortly after 10 a.m. on Friday. No injuries or damage were reported.
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