HR: 17:00h
AN: S34B-05 INVITED     [Abstracts]
TI: Observations of Infragravity Waves at the Monterey Ocean Bottom Broadband Station (MOBB)
AU: * Dolenc, D
EM: dolenc@seismo.berkeley.edu
AF: Seismological Laboratory, University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720 United States
AU: Romanowicz, B
S34B-05 AF: Seismological Laboratory, University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720 United States
AU: Stakes, D
S34B-05 AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: McGill, P
S34B-05 AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: Neuhauser, D
S34B-05 AF: Seismological Laboratory, University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720 United States
AB: The primary reason for installing ocean bottom broadband seismic stations is to record earthquakes. At the same time observations of non-seismic signals, like infragravity waves, can help us learn more about their generation and propagation. Such observations can also enable us to better understand the coupling between the ocean and the solid earth and learn more about the earth structure using non-seismic sources. MOBB was installed 40 km offshore in the Monterey Bay at a water depth of 1000 m in April 2002 in collaboration between Berkeley Seismological Laboratory and Monterey Bay Aquarium Research Institute (McGill et al., 2002). It comprises a three-component broadband seismometer with a temperature sensor, a water current meter measuring current speed and direction, and a differential pressure gauge (DPG). The station is continuously recording data which are retrieved, on average, every three months. Infragravity waves can be observed at MOBB on stormy as well as quiet days. When compared to the energy of the short-period ocean waves recorded at the local buoys, infragravity waves in the longer than 20 s period band are found to be mainly locally generated from shorter period waves. Two types of modulation of the infragravity signal are observed. First, the entire infragravity band signal is modulated in-phase with tides, possibly as a result of the nonlinear exchange of energy between the short-period waves and tidal currents. Second, a longer-period modulation of the infragravity signal is observed and is best correlated with the energy of the 14 s period ocean waves. This correlation indicates that the mechanism of generation of double frequency microseisms and infragravity waves are likely strongly related. Analysis of the previously recorded data during the Oregon ULF/VLF experiment at 600 m water depth also indicates that infragravity waves are primarily locally generated. Preliminary analysis of the data recorded at the station KEBB located further north, about 330 km offshore Washington at 2376 m water depth (Keck experiment, courtesy of Will Wilcock), also suggests that the low frequency seismic noise is generated primarily when storms reach the coast.
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: Fall Meeting 2005