** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its 50 society members.
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Research
Solid earth sciences
202212202212
Tectonic tremors immediately after the 2011 Tohoku-Oki earthquake detected by near-trench seafloor seismic observations
Takahashi H, Hino R, Uchida N, Matsuzawa T, Ohta Y, Suzuki S, Shinohara M
Tectonic tremor, Ocean bottom seismometer, The 2011 off the Pacific coast of Tohoku earthquake, slow earthquake, aseismic slip
(a) The number of tectonic tremors detected in this study every 15 days (b) Model of the amount of slip on the plate interface around the tremor sources considered to have affected the tremor activity. Black and red lines indicate quasi-periodic slow slip and afterslip by the Tohoku-Oki earthquake, respectively.
Temporal seismic observations from pop-up type ocean-bottom seismometers were used to detect tectonic tremors immediately following the 2011 Tohoku-Oki earthquake in the northern periphery of the aftershock area. Near-field observations clearly distinguished tremors from regular earthquakes based on their spectral shape in the frequency band of 1–4 Hz. In addition to tremors accompanied by very low-frequency earthquakes (VLFEs), we detected 130 tremors without known VLFE activity during April–October 2011. The newly detected tremors were in the vicinity of a sequence of small repeating earthquakes, indicating a mixed distribution of tremors and regular interplate earthquakes in the region. Tremor activity was high immediately after the deployment of seismometers and gradually decreased. In addition, the tremor activity fluctuated with two activations with an interval of approximately 90 days, similar to the intervals between tremor bursts after 2016. The results of the study suggest that the observed tremors occurred under the influence of aseismic slip caused by the decaying afterslip of the preceding Tohoku-Oki and Mw 7.4 interplate earthquakes and episodic accelerations with a quasi-periodicity unique to the area.
