Noise from Arctic Ocean Earthquakes

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...

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Bibliographic Details
Main Authors: Keenan, Ruth E., Dyer, Ira
Other Authors: MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF OCEAN ENGINEERING
Format: Text
Language:English
Published: 1984
Subjects:
Seismology
Snow
Ice and Permafrost
Acoustics
*ACOUSTIC CHANNELS
*GEOACOUSTICS
*ACOUSTIC WAVES
*UNDERICE
*EARTHQUAKES
ARRAYS
DEPTH
SHORT RANGE(TIME)
SPECTRA
ICE
VERTICAL ORIENTATION
SEISMIC WAVES
CANOPIES
HORIZONTAL ORIENTATION
ACOUSTIC SCATTERING
ARCTIC REGIONS
ELASTIC WAVES
NOISE(SOUND)
DIRECTIONAL
LOW FREQUENCIES
ARCTIC OCEAN
TIME SERIES ANALYSIS
TWO DIMENSIONAL
PEAK VALUES
REPRINTS
SHEAR PROPERTIES
SOURCES
Arctic
Arctic Ocean
Haystack
Ice
permafrost
Online Access:http://www.dtic.mil/docs/citations/ADA196337
http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA196337
Description
Summary: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 energetic(up to 400kJ), are of surprisingly long duration(up to 72s at its 8-dB down levels), have low-frequency content(peaks in the 5-15-Hz region), and have haystack spectra(4th 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. Pub. in Jnl. of the Acoustic Society of America, v75 n3 p819-825 Mar 1984. No copies furnished by DTIC/NTIS.

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