Using DART-recorded Rayleigh waves for rapid CMT and finite fault analyses of large megathrust earthquakes.

Abstract:

We study the use of long-period Rayleigh waves recorded by the DART-type ocean bottom pressure sensors. The determination of accurate moment and slip distribution after a megathrust subduction zone earthquake is essential for tsunami early warning. The two main reasons why the DART data are o interest to this problem are; 1 – contrary to the broadband data used in the early stages of earthquake analysis, the DART data do not saturate for large magnitude earthquakes, and 2 – DART stations are located offshore and thus often fill gaps in the instrumental coverage at local and regional distances. Thus, by including DART recorded Rayleigh waves into the rapid response systems we may be able to gain valuable time in determining accurate moment estimates and slip distributions needed for tsunami warning and other rapid response products.

Large megathrust earthquakes are among the most destructive natural disasters in history but also pose a significant challenge real-time analysis. The scales involved in such large earthquakes, with ruptures as long as a thousand kilometers and durations of several minutes are formidable. There are still issues with rapid analysis at the short timescales, such as minutes after the event since many of the nearby seismic stations will saturate due to the large ground motions. Also, on the seaward side of megathrust earthquakes, the nearest seismic stations are often thousands of kilometers away on oceanic islands. The deployment of DART buoys can fill this gap, since these instruments do not saturate and are located close in on the seaward side of the megathrusts.

We are evaluating the use of DART-recorded Rayleigh waves, by including them in the dataset used for Centroid Moment Tensor analyses, and by using the near-field DART stations to constrain source finiteness for megathrust earthquakes such as the recent Tohoku, Haida Gwaii and Chile earthquakes.