Seismic Response to Ocean Waves: Microseisms and Plate Waves

• Main Author: Chen, Zhao
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: eScholarship, University of California 2019
• Subjects: Geophysics; Beamforming; Cross-correlation; Icequake; Ice shelf; Microseism; Plate wave; Antarctic; Pine Island Glacier; Ross Ice Shelf; Southern Ocean; Antarc*; Ice Shelf; Ice Shelves; Iceberg*
• Online Access: http://www.escholarship.org/uc/item/4kd733km

Microseisms and plate waves are two types of seismic waves that are generated by the interaction between the ocean surface gravity waves and the solid Earth, providing the primary seismic noise source on the Earth.The source distribution of microseisms is important to study their generation mechanisms and in imaging Earth structures. Comparisons between different preprocessing methods to identify microseism source areas were made using Cascadia Initiative ocean bottom seismometer array data, where it was found that the total energy arriving from pelagic and coastal areas is similar. Moreover, pelagic-generated signals tend to be weaker but have a longer duration, in contrast to coastal-generated signals that tend to be stronger but have a shorter duration.Ocean surface gravity waves interacting with Antarctic ice shelves affect their integrity and likely play a role in their evolution, critical for assessing long-term changes that will affect the rate of sea level rise. Long-period gravity-wave impacts excite plate waves in the ice shelves, which can expand pre-existing fractures and trigger iceberg calving. Flexural-gravity waves (<20 mHz) and extensional Lamb waves (20-100 mHz) were identified on both the Ross Ice Shelf and the Pine Island Glacier ice shelf. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the Ross Ice Shelf and the Pine Island Glacier ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity-wave excitation. The transfer of ocean wave energy to ice shelves was determined from the comparison of gravity wave forcing of the Ross Ice Shelf measured by an ocean bottom hydrophone near the ice shelf front with nearby broadband on-ice seismic observations. The relative impact of gravity wave forcing on the Ross Ice Shelf integrity is inferred from comparison of the Ross Ice Shelf response amplitudes in 0.001-0.04 Hz band and from the association of icequake activity with very-long-period (0.001-0.003 Hz) and swell (0.03-0.1 Hz) band responses.