abstract

A vertical component seismograph with a magnification of about 8 million at 20 cps was operated cps was operated 1780 feet below the surface at the Sterling mine of the New Jersey Zinc Company in Ogdensburg, New Jersey. Background noise, local earthquakes and teleseismic body phases were recorded. For frequencies greater than 2 cps, the continuous part of the background noise was fairly stationary during nighttime recording intervals and at a level lower than that at all but 9 of the 54 sites surveyed by Frantti (1963).

During 730 hours of recording at quiet background noise levels, 8 local earthquakes were detected. Six local shocks were recorded during an additional 2160 hours by conventional short period instrumentation located at Ogdensburg and Sterling Forest, New York. These data, combined with historical data on the occurrence of 22 larger shocks local to the area, are consistent with a linear relation between the logarithm of earthquake number and magnitude. This relation is given by log N = 2.6−0.9M, where N is the annual number of earthquakes which occur within 300 km of Ogdensburg and which have magnitudes greater than or equal to M. On this basis the seismicity of the area, which lies within a region of Paleozoic and early Mesozoic diastrophism, is about 2 orders of magnitude less than that of Southern California, 3 orders of magnitude less than that of the Garm region in Central Asia, and 4 orders of magnitude less than that of the Kwanto region in Japan.

Phases from 18 distant earthquakes were recorded by the high gain instrument. Only P and S phases from West Indies shocks, 20 degrees distant, exhibited motion with frequencies greater than 3 cps.

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