Accession Number:

ADA196337

Title:

Noise from Arctic Ocean Earthquakes

Descriptive Note:

Corporate Author:

MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF OCEAN ENGINEERING

Personal Author(s):

Report Date:

1984-03-01

Pagination or Media Count:

7.0

Abstract:

Earthquakes along the mid-Artic ridge radiate earthborne compressional and shear waves, which in turn excite the Artic acoustic channel. These waterborne arrivals, called T waves, have been observed about 300 km from the source and apparently enter the acoustic channel by scattering of vertical rays into nearly horizontal ones by the Arctic ice canopy above the source. The T waves are acoustically energeticup to 400kJ, are of surprisingly long durationup to 72s at its 8-dB down levels, have low-frequency contentpeaks in the 5-15-Hz region, and have haystack spectra4th power positive and negative dependence below and above the peak frequency, respectively. Characteristics of these sporadic noises are displayed for one event in a sonogram, in short time frequency spectra, in a time series, and in directional spectra. Directional analysis was accomplished with use of a large approx. 1 km two-dimensional horizontal array. Speculations on duration of the observed events suggest that source depth, water-column reverberation above the source, and source magnitude, including rapid-fire multiple source excitations, could be the primary causes. Keywords Underice acoustic scattering Seismic waves Acoustic waves. Reprints.

Subject Categories:

  • Seismology
  • Snow, Ice and Permafrost
  • Acoustics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE