Time-Reverse imaging of the tsunami source (Hossen, Cummins, Roberts and Allgeyer)

Time-Reverse imaging of the tsunami source

Many tsunami source inversion techniques have already been developed to derive source models with the assumption that tsunami generation is due to slip on a single large fault. Therefore, these inversion techniques cannot determine to what extent subsidiary phenomena - such as submarine landslides, block movement, or slip on splay faults - have contributed to the tsunami generation. We are proposing a new method that can be used to derive source models without requiring the assumption of slip on a fault of pre-determined geometry or even knowing the earthquake source area, but inverts directly for sea surface displacement without regard to faulting or source complexity. The proposed method is based on ”Time Reverse Imaging (TRI)” technique, which has been used in underwater acoustic and medical imaging. We have applied TRI to recover the initial sea surface displacement associated with the tsunami source. To show the application of this method we have chosen the tsunami triggered by the March 11, 2011 Tohoku earthquake, for which an unprecedented number of high-quality observations are available. We compare the findings of the TRI result with other more conventional methods of source inversion.

Refocused source

Refocused source (left) obtained by using real observations which are retransmitted through the medium simultaneously. The height of the refocused source is determined by the uniform scaling approach. The heavy, red curve denotes the axis of the Japan Trench. The maximum height in the refocussed image is located between the epicenter (red star) and the Trench axis. (right) Agreement of tsunami waveforms calculated using this source (green) are compared with observed tusnami waveforms (red). (From Hossen J., Cummins P.R., Roberts S.G., Allgeyer, S. (2014) Time-reverse imaging of the tsunami source, accepted by Pure and Applied Geophysics).

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