Auxiliary Materials for
The 2011 Tohoku Tsunami observed by an array of ocean bottom
electro-magnetometers
Luolei Zhang1, Kiyoshi Baba1, Pengfei Liang1, Hisayoshi Shimizu1, Hisashi Utada1
1. Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo
113-0032, Japan
Geophysical Research Letters
Introduction
1. The auxiliary material textS1.docx describes the supplementary methods and text.
The text includes three sections: Section S1 explains the theory of electromagnetic field
simulation. Section S2 is the application of the components of EM field (By, Ex) for
wave height estimation. Section S3 is the estimation of tsunami propagation direction
by using simulated data.
2. Total 10 supplementary figures are provided in auxiliary materials. The content of
these 10 figures are as follows:
fs01.jpg: (Figure S1) The amplitude (left) and phase (right) of the ordinary (red) and
motional (black) impedance Zxy at four sites (NM01, NM02, NM04, and NM05)
obtained from the observed EM fields. The ordinary impedance is obtained by using the
same equation but using electromagnetic data without tsunami-induced signals [Baba et
al., 2013]. The amplitude of 240 m/s (approximate long wave velocity) and the phase of
90° are given by the dashed lines.
fs02.jpg: (Figure S2) The amplitude (left) and phase (right) of motional tipper Mzy at
four sites (NM01,NM02, NM04 and NM05) obtained from observations. The amplitude
of 240 m/s (approximate long wave velocity) and the phase of 90° are given by the
dashed lines.
fs03.jpg: (Figure S3) The seismograms at three sites (NM02, NM04 and NM05)
obtained by broad-band ocean bottom seismometers. Red line is the arrival time of
tsunami at each site.
fs04.jpg: (Figure S4) The tilt data including pitching angle (left) and rolling angle
(right) of OBEM at four sites (NM01, NM02, NM04 and NM05). Red line is the arrival
time of tsunami at each site.
fs05.jpg: (Figure S5) Comparison of the estimated tsunami wave heights  (black) and
' (cyan) based on the vertical component of the observed magnetic fields at the four
seafloor sites, NM01, NM02, NM04 and NM05.
fs06.jpg: (Figure S6) Left: The tsunami wave heights estimated from the major
components of EM fields Bz (green line), By (blue line) and Ex (orange line) at the four
seafloor sites, NM01, NM02, NM04 and NM05. Center: The differences between the
estimations from Bz and By. Right: The differences between the estimations from Bz and
Ex .
fs07.jpg: (Figure S7) Relation between the corrected Akaike information criterion (AICc)
and filter length 0 for each observation site. Red dot denotes the optimum 0
determined by the minimum AICc..
fs08.jpg: (Figure S8) The simulated tsunami wave heights ref and the differences
between ref and the estimations by the three approaches η1, η2, and η3 at the three
observation sites, NM01, NM02 and NM05.
fs09.jpg: (Figure S9) Tsunami propagation directions estimated from the simulation
results: (a) The frequency dependent azimuths θ1(ω) from the array analysis by
assuming a plane wave. Green, blue, orange and black lines are obtained from the
simulated Bz, By, and Ex, and from the simulated wave height η, respectively. The
weighted average azimuths 1 are shown as the dashed lines of corresponding color. (b)
The frequency dependent azimuths θ3(ω) from the magnetic field (blue line), the
tsunami velocity (black line), and the electrical field (orange line). The weighted
average azimuths  3 are shown as the dashed lines of corresponding color.
fs10.jpg: (Figure S10) Black lines indicate the trajectory of the simulated tsunami
velocity (left), magnetic (center) and electric (right) field in x-y plane. Red arrows show
the weighted average azimuth  3 estimated from the single site analysis.