Magnetic Signals at Easter Island During the 2010 and 2015 Chilean Tsunamis Compared with Numerical Models

摘要

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 Mw 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.