Noise from Arctic Ocean Earthquakes

• 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

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.