Hayakawa, M., Y. Hobara, Y. Yasuda, H. Yamaguchi, K. Ohta, J. Izutsu, and T. Nakamura. “Possible Precursor to the March 11, 2011, Japan Earthquake: Ionospheric Perturbations As Seen by Subionospheric Very Low frequency/Low Frequency Propagation”. Annals of Geophysics, vol. 55, no. 1, Apr. 2012, doi:10.4401/ag-5357.