Tsunami Case Study Of Tsunami

968 Words4 Pages
The giant tsunami by the 2011 Tohoku earthquake (M9.0) caused destructive damages along the coastal areas in the northeastern Japan with over 20,000 victims. The tsunami was developed with two-step increasing of sea level: a broad wave associated with uplift of the whole source area and a unipolar impulsive wave (Fig. 1)1-3. Because the latter impulsive wave is considered as a main cause of the tsunami damages, understanding of its origin is quite important to reducetsunami damage in future times.However, the source area has not been well constrained due to the lack of tsunamiobservatories especially in the seaside area of the Japan Trench. In this letter, we report the first reliable estimate of the source location of the impulsive tsunami by using the novel data set: magnetic field variationscollected byan ocean bottom electromagnetometer (OBEM) settled about 50 km east of the trench axis. The geomagnetic data from the OBEM indicates thatthe source area is close to the trench axis, and includes latitude 39.0N that is about 100 km north of the seismic epicentral region.Construction of the back propagation curves from the…show more content…
Motion of conductive seawater relative to ambient geomagnetic field generates electromagnetic fields5. Observations of tsunami-induced electromagnetic field were recently made based on ocean bottom and island observatories6,7.As shown in the supplemental Information, the vertical component of the tsunami-induced magnetic field at the bottom of the seawater (bZ) is proportional to the sea level change ( ). Moreover, the horizontal component of the induced magnetic field (bH) is in the direction of the tsunami propergation, and the temporal variation of the horizontal component is delayed by 90 degrees to that of the sealevel change. These relations can be approximatealy expressed
Open Document