Observation and Inversion of Seismo-Acoustic Waves in a Complex Arctic Ice Environment

• Main Author: Miller, Bruce E.
• Other Authors: MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF OCEAN ENGINEERING
• Format: Text
• Language: English
• Published: 1990
• Subjects: Seismology; Snow; Ice and Permafrost; Acoustics; *SEISMIC WAVES; UNDERICE; FACILITIES; ELASTIC PROPERTIES; PATHS; TIME SERIES ANALYSIS; EXPLOSIVES; ICE; STATIONARY; CANOPIES; TRAVEL; INVERSION; HORIZONTAL ORIENTATION; HYDROPHONES; AMPLITUDE; ACOUSTIC DATA; FLEXURAL PROPERTIES; LOW FREQUENCY; DETONATIONS; ARCTIC REGIONS; RIDGES; BEAUFORT SEA; WATERBORNE; ARCTIC OCEAN; GEOPHONES; DATA BASES; PARAMETERS; *SEA ICE; *ACOUSTIC WAVES; SAFARI NUMERICAL MODELING; ICE MECHANICS; PLANE WAVES; DATA PROCESSING; SEISMIC DATA; SEISMIC REFRACTION; ACOUSTIC REFRACTION; THESES; SEISMOACOUSTIC WAVES; Arctic; Arctic Ocean; Beaufort Sea; Ice; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA226652; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA226652

Propagation of low frequency seismo-acoustic waves in the Arctic Ocean ice canopy is examined through analysis of hydrophone and geophone data sets collected in 1987 at an ice camp designated PRUDEX in the Beaufort Sea. Study of the geophone time series generated by under-ice explosive detonations reveals not only the expected longitudinal and flexural waves in the ice plate, but also an unexpected horizontally-polarized transverse (SH) wave arriving at a higher amplitude than other wave types. The travel paths of all three observed wave types are found to be refracted in the horizontal plane along a line coincident with a known ridge separating the ice canopy locally into two distinct half-plates, the first of thin first year ice and the second of thicker multi-year ice. The origin of the SH wave appears to be near the detonation and not associated with the interaction of longitudinal, flexural or waterborne waves with the ridge line. The need to determine the exact location of each detonation from the received time series highlights the dramatic superiority of geophones over hydrophones in this application, as does the ability to detect the anomalous SH waves and the refracted ray paths, neither of which is visible in the hydrophone data. Inversion of the geophone data sets for the low frequency elastic parameters of the ice is conducted initially by treating the ice as a single homogeneous isotropic plate of demonstrate the power of SAFARI numerical modeling in this application. A modified stationary phase approach is then used to extend SAFARI modeling to invert the data sets for the elastic parameters of the two ice half-plates simultaneously. (rwj)