Abstract
Tsunami flow across the geomagnetic field induces electric currents in both the ocean and the ionosphere. These currents generate secondary magnetic fields, observable at the seafloor and on land. Magnetic field disturbances during two Chilean tsunamis (2010 and 2015) were recorded at Easter Island Observatory. These tsunamis were produced after the earthquakes in Chile on February 27, 2010, at 06:34 UTC, and September 16, 2015, at 22:55 UTC, respectively. Differences between existing studies regarding the origin of the tsunamigenic disturbances, and the lack of studies using a numerical model for both the water velocity and the induced magnetic field, motivated us to compare magnetic records with computed magnetic fields for the two events. Modeled disturbances were calculated by applying the Biot–Savart law to tsunami simulations. Our model can calculate tsunami-induced perturbations in the vertical component of the geomagnetic field, obtaining a good agreement with the observations. We hypothesize that the magnetic measurements may be produced by a combination of oceanic and ionospheric electric currents. Our analysis further reveals that even a relatively small tsunami, such as the one produced by the 2015 \(M_\text {w}\) 8.2 earthquake, induces an observable magnetic perturbation due to the water movement. Future improvements to our model may allow us to identify situations in which magnetic variations precede the tsunami arrival, thereby allowing early tsunami detection.
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Acknowledgements
C. Torres would like to thank Programa Formación de Capital Humano Avanzado (PFCHA) of the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), Chile, for the financial support of his PhD (CONICYT PFCHA/DOCTORADO NACIONAL/2015—21150632). The authors would like to thank the International Real-time Magnetic Observatory Network (INTERMAGNET) for the dataset used in this work, Chambon-La-Forêt Observatory and Institut de Physique du Globe de Paris (IPGP) as creators of the Easter Island Observatory (with funding from National Aeronautics and Space Administration, NASA), the Hydrographic and Oceanographic Service of the Chilean Navy (SHOA) for the bathymetry data, Departamento de Ingeniería Matemática of Universidad de Concepción for computational support regarding data processing, and M. Miller for his assistance with the production of figures and the improvement of the manuscript. The DART records are available from NOAA’s National Data Buoy Center at http://www.ndbc.noaa.gov/dart.shtml. Wavelet software was provided by C. Torrence and G. Compo, and is available at URL: http://atoc.colorado.edu/research/wavelets/. Figures in this study are produced using Matlab R2017b and the Generic Mapping Toolkit of Wessel et al. (2013). Finally, the authors thank the Editor and the two anonymous reviewers for their constructive comments and suggestions.
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Torres, C.E., Calisto, I. & Figueroa, D. Magnetic Signals at Easter Island During the 2010 and 2015 Chilean Tsunamis Compared with Numerical Models. Pure Appl. Geophys. 176, 3167–3183 (2019). https://doi.org/10.1007/s00024-018-2047-y
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DOI: https://doi.org/10.1007/s00024-018-2047-y