Contemporary measurements of the background open ocean tsunami spectrum using the Deep-ocean Assessment and Reporting of Tsunami (DART) stations

Abstract. A reference power law of ω², where ω is angular frequency, has been traditionally used to characterize the background open ocean tsunami spectrum (BOOTS) slope from a period of 10 mins to 120 mins. However, this characterization is based on data from temporary deployments of bottom pressure sensors that lasted from several weeks to 11 months and only in scattered areas of the Pacific, leaving its effects on aleatory and epistemic uncertainties of tsunami source models unconstrained. Here we measure the BOOTS slope using 1–15 years of bottom pressure recorder data sampled at 15 s from the Deep-ocean Assessment and Reporting of Tsunamis (DART) stations. We utilize probabilistic power spectral density plots to create background noise models for 34 DART stations across the Pacific basin. We find that often a simple log-linear decay does not correctly characterize the observed background spectrum. We find deviations from the expected –2 behavior with instances of it being larger or greater, with a strong seasonality signal. In addition, we plot the median power for each DART station at the periods of 120 s, 250 s, and 800 s. Lastly, a significant part of the energy in the BOOTS is from infragravity waves, we calculate their heights and their mean values for December, January, and February and June, July, and August. We found that meteorologically induced infragravity wave events are the largest factors in seasonal variations of the BOOTS slope and intercept, especially in the east Pacific. We show the typical meteorological systems that drive these events, and we connected tropical systems from off the coast of Mexico to infragravity wave events in the east and central Pacific. Finally, we found that infragravity wave events may impact small to moderate tsunamis.