EARTHQUAKE HAZARD
(Source: US Geological Survey)
New York State Geological Survey
Damaging earthquakes have occurred in New York and surely will again. The likelihood of a damaging earthquake in New York is small overall but the possibility is higher in the northern part of the state and in the New York City region.Significant
earthquakes, both located in Rockaway and larger than magnitude 5,
shook New York City in 1737 and 1884. The quakes were 147 years apart
and the most recent was 122 year ago. It is likely that another
earthquake of the same size will occur in that area in the next 25 to 50
years. A magnitude 5.8 earthquake in New York City would probably not
cause great loss of life. However
the damage to infrastructure – buildings, steam and gas lines, water
mains, electric and fiber optic cable – could be extensive.
Earthquake Hazard Map of New York State
Acceleration of the ground during an earthquake is more important than total movement in causing structural damage. This
map shows the two-percent probability of the occurrence of an
earthquake that exceeds the acceleration of earth’s gravity by a certain
percentage in the next fifty years.
If
a person stands on a rug and the rug pulled slowly, the person will
maintain balance and will not fall. But if the rug is jerked quickly,
the person will topple. The same principle is true for building damage
during an earthquake. Structural damage is caused more by the
acceleration of the ground than by the distance the ground moves.
Earthquake
hazard maps show the probability that the ground will move at a certain
rate, measured as a percentage of earth’s gravity, during a particular
time. Motion of one or two percent of gravity will rattle windows,
doors, and dishes. Acceleration of ten to twenty percent of gravity will
cause structural damage to buildings. It takes more than one hundred
percent of gravity to throw objects into the air.
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