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Measuring the Background Open-Ocean Tsunami Spectrum Using the Pacific Basin Dart Array

Session: Advances in the Science and Observation of Tsunamis

Type: Oral

Date: 4/22/2021

Presentation Time: 10:15 AM Pacific

Description: 

The background open-ocean tsunami spectrum (BOOTS) is an under-studied topic. It describes the spectrum of oscillations that occur out in the open-ocean in the tsunami band (~1 min-2 hrs).It is important because it plays a key role in understanding the local site response at a tide gauge, and it can be extended to show the tsunami site response at locations with no tide gauges. The objective of this study is to measure the BOOTS and its associated noise using long time series of noise from DART deployments in the Pacific Basin.

In order to accomplish do these calculations, data is used from the recovered bottom pressure recorders of the DART buoys which has a time-spacing of 15 seconds. As a consequence of this sampling rate, it is possible to measure the BOOTS over the full tsunami band. The quality-controlled de-tided pressure is used in the calculation of the spectra. These are computed every two weeks for each DART buoy for as long as fidelity data is available. Tsunami events anywhere in the Pacific Basin over the time frame of 2000-2018 are filtered out to ensure that the spectra are mainly that of the background oscillations. Spectra generally have a simple log-linear decay, so a least-squares inversion is done for every spectrum in order to compute the slope and intercept. From this we obtain time-series of each of the set wo parameters to study the temporal variation of the BOOTS for each DART.

Preliminary results show that the BOOTS is neither simple nor constant for each DART. Some DARTs, like those in the Aleutians and Cascadia, experience seasonal fluctuations in both the slope and intercept. Meanwhile, other regions, like the SE Pacific and the NE Pacific, have little seasonal variability in slope and noise. Ongoing work is being done to understand the physical mechanism behind this result. Overall, the study will provide much needed insights into the behavior of the BOOTS in the Pacific Basin. The broader impact of this being that understanding it can be used to study the tsunami site effect in areas with or without tide gauges.

Presenting Author: Sean Santellanes

Student Presenter: Yes

Authors