Stormquakes: New sources light up North America
Abstract
The ocean is the primary source of the ambient seismic wave field in the solid Earth. The ambient wave field is often categorized as seismic hum (> 50s period), and as primary and secondary microseisms with spectra that peak near 15 and 5 s period. Displacements due to these three processes are ubiquitous. Debate about excitation mechanisms continues but it is generally agreed that the source regions of these three processes are widely distributed along coastlines or across the entire ocean. However, the 20 to 50 s frequency band has received less attention, and sources of the ambient seismic wave field in this band are elusive. We discovered transient waves in this frequency band in seismic data recorded by the USArray Transportable Array. Unlike seismic noise studied in other bands, these 20-50s Rayleigh wave packets produce coherent signals the source of which can be located to within about 25 km using the distant USArray data. The sources consistently lie in regions with steep bathymetry and coincide with large storms located seaward of the North American coastline. These "stormquakes" cause long lasting ground motions over periods of hours to days with isolated surface wave packages that are equivalent to earthquakes of magnitude 3.5 or greater. The sources migrate along the shelf break coincident with the storms. We hypothesize that these waveforms are produced by transient pressure sources on the seafloor that are excited by the interference between ocean waves and steep bathymetry. Often, wavefields of stormquakes can propagate across the entire North American continent. Their discovery provides new insights into the ambient seismic wavefield. Here, we hope to investigate the physical excitation process of stormquakes, and ultimately to use them as new sources to investigate North American crustal structure.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S13C0461F
- Keywords:
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- 7203 Body waves;
- SEISMOLOGYDE: 7255 Surface waves and free oscillations;
- SEISMOLOGYDE: 7260 Theory;
- SEISMOLOGYDE: 7270 Tomography;
- SEISMOLOGY