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Journal: |
Journal of Geophysical Research 2018 No.11
clicks:222 |
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Title:
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Author:
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Satoshi Katakami1 , Yoshihiro Ito2 , Kazuaki Ohta2 , Ryota Hino3 , Syuichi Suzuki3 , and Masanao Shinohara4 |
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Adress: |
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Abstract:
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A slow slip event (SSE) and tectonic tremors occurred approximately 1.5 month prior to the
occurrence of the 2011 Tohoku-Oki earthquake near the Japan Trench. Although we cannot completely
rule out other sources of noise near the observation site, slow earthquakes would demonstrate the
nucleation of a fast slip event from prior slow earthquake activity. Here we report on tectonic tremor activity
detected from short-period ocean-bottom seismometer (OBS) data with a modified frequency scanning
method that allows robust tectonic tremor detection by incorporating information from multiple
frequency passbands in order to suppress false detections. We have identified at least five tectonic tremor
sequences on the OBS records from the end of January 2011 to just before the occurrence of the Tohoku-Oki
earthquake in March 2011. To reveal the spatial distributions of tectonic tremors before the Tohoku-Oki
earthquake, we then calculated tremor energy, with corrected site amplification, from the identified tectonic
tremor time window at each OBS that detected tremors. Possible sources of tremors were distributed in
trenchward side of the SSE fault prior to the main shock. These tremors could be modulated by SSE to take
into account consistent timing between tremor and SSE term, and consistency of spatial locations between
estimated tremor sources and SSE faults. This spatiotemporal pattern in tectonic tremor activity
demonstrates a significant separation of occurrence sources between tectonic tremors and
regular earthquakes. |
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