Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1999
Description:
In this thesis the analysis of natural ice events is carried out based on direct measurements of ice-borne seismo-acoustic waves generated by ice fracturing processes. A
major reason for studying this phenomenon is that this acoustic emission is a significant contributor to Arctic ocean ambient noise. Also the Arctic contains rich mineral
and oil resources and in order to design mining facilities able to withstand the harsh
environmental conditions, we need to have a better understanding of the processes
of sea ice mechanics. The data analyzed in this thesis were collected during the Sea
Ice Mechanics Initiative SIMI’94 experiment which was carried out in the spring of
1994 in the Central Arctic.
One of the contributions of this thesis was the determination of the polarization
characteristics of elastic waves using multicomponent geophone data. Polarization
methods are well known in seismology, but they have never been used for ice event
data processing. In this work one of the polarization methods so called Motion Product Detector method has been successfully applied for localization of ice events and
determination of polarization characteristics of elastic waves generated by fracturing events. This application demonstrates the feasibility of the polarization method
for ice event data processing because it allows one to identify areas of high stress
concentration and "hot spots" in ridge building process.
The identification of source mechanisms is based on the radiation patterns of the
events. This identification was carried out through the analysis of the seismo-acoustic
emission of natural ice events in the ice sheet. Previous work on natural ice event
identification was done indirectly by analyzing the acoustic energy radiated into the
water through coupling from elastic energy in the ice sheet.
After identification of the events, the estimation of the parameters of fault processes in Arctic ice is carried out. Stress drop, seismic moment and the type of ice
fracture are determined using direct near-field measurements of seismo-acoustic signals generated by ice events. Estimated values of fracture parameters were in good
agreement with previous work for marginal ice zone.
During data processing the new phenomenon was discovered: "edge waves", which
are waves propagating back and forth along a newly opened ice lead. These waves
exhibit a quasi-periodic behavior suggesting some kind of stick-slip generation mechanism somewhere along the length of the lead. The propagation characteristics of these
waves were determined using seismic wavenumber estimation techniques. In the low
frequency limit the dispersion can be modeled approximately by an interaction at the
lead edges of the lowest order, antisymmetric modes of the infinite plate.
Description:
Support for this thesis was provided by Office of Naval Research.
Keywords:
Microseisms
;
Seismology
;
Underwater acoustics
;
Remote sensing
;
Sea ice
;
Ice
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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