Tsunami source of the 2011 Tohoku earthquake detected by an ocean-bottom magnetometer

Ichihara, Hiroshi; Hamano, Yozo; Baba, Kiyoshi; Kasaya, Takafumi

doi:10.1016/j.epsl.2013.09.015

Cited by 25 publications

(41 citation statements)

References 24 publications

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“…Recently, reports on the observed circularly polarized coseismic electric field [ Honkura et al ., ; Kuriki et al ., ; Matsushima et al ., ] provided evidences for the role of the Earth's magnetic field in generating EM disturbances. Moreover, observations of the tsunami‐induced magnetic variations [ Manoj et al ., ; Toh et al ., ; Utada et al ., ; Ichihara et al ., ] were further evidences which indicate that the conductive seawater moving across the Earth's magnetic field can also generate observable variations in the magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Induced electromagnetic field by seismic waves in Earth's magnetic field

Gao

Chen

et al. 2014

JGR Solid Earth

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Studied in this article are the properties of the electromagnetic (EM) fields generated by an earthquake due to the motional induction effect, which arises from the motion of the conducting crust across the Earth's magnetic field. By solving the governing equations that couple the elastodynamic equations with Maxwell equations, we derive the seismoelectromagnetic wavefields excited by a single-point force and a double-couple source in a full space. Two types of EM disturbances can be generated, i.e., the coseismic EM field accompanying the seismic wave and the independently propagating EM wave which arrives much earlier than the seismic wave. Simulation of an M w 6.1 earthquake shows that at a receiving location where the seismic acceleration is on the order of 0.1 m/s 2 , the coseismic electric and magnetic fields are on the orders of 1 μV/m and 0.1 nT, respectively, agreeing with the EM data observed in 2008 M w 6.1 Qingchuan earthquake, China, and indicating that the motional induction effect is effective enough to generate observable EM signal. We also simulated the EM signals observed by Haines et al. (2007) which were called the Lorentz fields and cannot be explained by the electrokinetic effect. The result shows that the EM wave generated by a horizontal force can explain the data well, suggesting that the motional induction effect is responsible for the Lorentz fields. The motional induction effect is compared with the electrokinetic effect, showing the overall conclusion that the former dominates the mechanoelectric conversion under low-frequency and high-conductivity conditions while the latter dominates under high-frequency and low-conductivity conditions.

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Section: Introductionmentioning

confidence: 99%

Induced electromagnetic field by seismic waves in Earth's magnetic field

Gao

Chen

et al. 2014

JGR Solid Earth

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“…These are roughly defined as dynamic range of ± 60,000 nT, accuracy of ~ 0.1 nT, and sampling frequency of > 2 Hz. The sampling frequency of > 2 Hz is somewhat over specification for natural source marine electromagnetic sounding methods (e.g., Baba et al 2017), but we chose it for possible applications of electromagnetic sounding on land and of future control source marine electromagnetic sounding, and for possible observation of tsunami induced magnetic field (e.g., Ichihara et al 2013). Temperature measurements are also necessary to correct temperature-dependent drifts of fluxgate magnetometer outputs.…”

Section: System Requirements For Observing Temporal Geomagnetic Fieldmentioning

confidence: 99%

A new miniaturized magnetometer system for long-term distributed observation on the seafloor

Ogawa

Matsuno

Ichihara

et al. 2018

Earth Planets Space

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We have developed a new magnetometer system specialized to multipoint and long-term observations on the seafloor to promote marine or ocean-bottom experiments mainly for the electromagnetic sounding of the Earth's interior. In situ magnetic field observation on the seafloor is an essential geophysical technique to investigate structures of the oceanic crust and the upper mantle, many of which are still frontier as to observational evidences. The in situ and long-term observations require long-term-operable and small-size magnetometer systems, which are placed on the seafloor over a year in pressure-resistant cases without external power supply and communication.We have designed and developed a new electric circuit board of small size and lower power consumption for the magnetometer system. Our new magnetometer system, what we call "DOKODEMO MAG, " is suitable to be installed in a pressure-resistant cylinder of 36 mm diameter and can operate independently over 2 years with a smaller amount of batteries than the conventional system because its power consumption was saved to ~ 33 mW. This magnetometer system is capable of observing orthogonal three-axis magnetic fields continuously with sampling frequency of 5 Hz at maximum and an accuracy of ~ 0.1 nT. The system also records tilt and temperature of the system and voltage of the batteries. Prototype models of this magnetometer system were tested for in situ operation for 5 months on the seafloor around the Kikai caldera in the south of the Kyusyu Island, SW Japan. The results of the test showed sufficient performance of our new magnetometer system and its potential of future usage for every type of marine or oceanbottom operations.

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“…With the advancement of observational devices, tsunami-induced dynamo effects have recently been observed on the seafloor (Toh et al 2011;Ichihara et al 2013;Sugioka et al 2014;Zhang et al 2014a). A few instances of these effects have been documented on land.…”

Section: Introductionmentioning

confidence: 99%

“…We computed the induced electric currents using the previously computed seawater flow. Ichihara et al (2013) provided the theoretical details behind this computation.…”

Section: Induced Electric Current and Magnetic Fieldmentioning

confidence: 99%

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Tsunami-induced magnetic fields detected at Chichijima Island before the arrival of the 2011 Tohoku earthquake tsunami

2015

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Magnetic field disturbances associated with the tsunami caused by the 2011 Tohoku earthquake were observed at Chichijima Island, 1200 km south of the epicenter. The vertical component of the magnetic field showed a periodic signal at approximately 20 min before the tsunami arrived. This study investigated the mechanism of the magnetic field signal using simulation studies. First, we derived a tsunami source model that explained the tide gauge records and sea-level changes at Chichijima Island. Using this model, we then computed the electric current induced by the tsunami and the resulting secondary magnetic field. The computed changes in sea level and magnetic field are consistent with their respective observed waveforms, including the timing of the magnetic field signals. In our interpretation, the tsunami flow induced an electric current along the tsunami wave front, which in turn generated a secondary induced magnetic field ahead of the tsunami wave. Hence, magnetic variations preceding the tsunami were observed at Chichijima Island. This suggests that imminent arrivals of tsunamis can be detected by observations of the magnetic field.

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Tsunami source of the 2011 Tohoku earthquake detected by an ocean-bottom magnetometer

Cited by 25 publications

References 24 publications

Induced electromagnetic field by seismic waves in Earth's magnetic field

Induced electromagnetic field by seismic waves in Earth's magnetic field

A new miniaturized magnetometer system for long-term distributed observation on the seafloor

Tsunami-induced magnetic fields detected at Chichijima Island before the arrival of the 2011 Tohoku earthquake tsunami

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