A magnetic anomaly was recorded at Easter Island on 27 February 2010 during the Chile tsunami event. The physics of the magnetic anomaly is analyzed using kinematic dynamo theory. Using a single wave model, the space and time behavior of the magnetic field is given. By joint analysis of the magnetic observations, tide gauge data and numerical results of the global tsunami propagation, we show the close resemblance between the predicted spatial and temporal magnetic distributions and the field data, indicating the magnetic anomaly at Easter Island was actually induced by the motion of seawater under tsunami waves. Similarity between the field magnetic data at Easter Island during 2010 Chile tsunami and sea surface level is verified with realistic tsunami propagating model.
Kinematic dynamo problem is studied with tsunami motion in open oceans. Using long wave approximation, a series solution of the dynamo problem is established with fast convergent rate based on a small parameter relating water wave dispersive effects. Taking solitary wave and single wave as typical tsunami wave models, the magnitude of tsunami induced magnetic field is estimated at the order of 10 nano Tesla （nT） just over sea level and 1 nT at altitudes of several hundreds kilometers, respectively, depending on the wave parameters as well as earth magnetic field. The space and time behavior of the magnetic field predicted by present model shows fairly similarity with the field data at Easter Island during 2010 Chile tsunami.
