HR: 09:50h
AN: S11C-08    [Abstracts]
TI: Observations of Infragravity Waves at the Monterey Ocean Bottom Broadband Station (MOBB)
AU: * Dolenc, D
EM: dolenc@seismo.berkeley.edu
AF: UC Berkeley Seismological Lab, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720 United States
AU: Romanowicz, B
EM: barbara@seismo.berkeley.edu
AF: UC Berkeley Seismological Lab, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720 United States
AB: Ocean bottom broadband seismic observations show increased noise level when compared to land recordings. Infragravity waves are an important source of background noise at periods longer than 20 seconds. Long-period background noise can partially be removed by post-processing (Crawford and Webb, 2000; Stutzmann et al., 2001). At the same time, observations of infragravity waves can help us better understand their generation from short-period waves. We investigated the correlations between the infragravity waves recorded at MOBB and the short-period ocean wave data recorded at nearby ocean buoys. MOBB was installed 40 km offshore in the Monterey Bay at a water depth of 1000 m in April 2002 in collaboration between Berkeley Seismo Lab and Monterey Bay Aquarium Research Institute (MBARI) (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. We calculated power spectral density (PSD) of the MOBB vertical component for 1-hour long periods for all the data recorded until June 2004. The results were compared to the spectral wave density (SWD) of the ocean waves as recorded on the eight regional NOAA buoys located from offshore Southern California to Alaska, and the six local NOAA buoys located offshore Northern California. The results clearly show that the width of the infragravity wave band recorded on MOBB was best correlated with the energy of the ocean waves recorded at the local NOAA buoy, located just 23 km W of MOBB. To further explore observed correlation between the MOBB PSD and the buoy SWD, we focused on several 7-day periods and calculated correlation coefficient between 1-hour long MOBB PSD and buoy SWD values. The highest correlation was observed for the closest buoy located just outside Monterey Bay. The results show that the 7-17 sec ocean waves were best correlated with seismic waves with 30-200 sec period. A weaker correlation was observed with the other two buoys located over the continental shelf to the north. Correlation with the buoys located to the south and those located further offshore was much smaller. We plan to further investigate these observations as well as compare them with the results obtained from island (FARB) and other land BDSN stations. We will also include pressure and tides data to better understand where and how the energy is transferred from the ocean to the seismic waves. We will use the obtained results to remove the long-period noise from the MOBB vertical channel to improve the quality of the seismic data.
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2004 AGU Fall Meeting