Japan Geoscience Union Meeting 2019

Presentation information

[E] Poster

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG48] Science of slow earthquakes: Toward unified understandings of whole earthquake process

Wed. May 29, 2019 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Satoshi Ide(Department of Earth an Planetary Science, University of Tokyo), Hitoshi Hirose(Research Center for Urban Safety and Security, Kobe University), Kohtaro Ujiie(Graduate School of Life and Environmental Sciences, University of Tsukuba), Takahiro Hatano(Earthquake Research Institute, University of Tokyo)

[SCG48-P38] Possible tectonic tremor activities near the VLFE epicenters in the Sanriku-Oki region in 2011

*Hidenobu Takahashi1, Ryota Hino1, Yusaku Ohta1, Naoki Uchida1, Syuichi Suzuki1, Masanao Shinohara2, Takanori Matsuzawa3 (1.Graduate school of Science Tohoku University , 2.Earthquake Research Institute, University of Tokyo, 3.National Research Institute for Earth Science and Disaster Resilience)

Keywords:tectonic tremor, Sanriku–oki

Recently various kind of slow earthquakes have been discovered along the Japan Trench subduction zone. Prior to the occurrence of the 2011 Tohoku-oki earthquake, occurrence of slow slip events associated with migration of small earthquake epicenters and tectonic tremors was reported near the hypocenter of the Tohoku-Oki earthquake (e.g. Kato et al., 2012; Ito et al., 2015; Katakami et al., 2018). As a different type of a slow-earthquake family, Very Low Frequency Earthquakes (VLFEs) have been detected in more broad areas (Matsuzawa et al., 2015). Takahashi et al. (in prep.) detected the seismic signals from the VLFEs by short-period ocean bottom seismograms (OBS) deployed in the vicinity of the VLFE epicenters in the Sanriku-Oki region, just after the Tohoku-Oki earthquake. They further identified a number of VLFE-like events, not recognized by the onshore data. Here, we report on possible tectonic tremor activities in the same area based on the OBS data after the 2011 Tohoku-oki earthquake.
We detected four sequences of continuous rises of amplitudes on the OBS records. Each of the sequence has a duration of ~ half a day. The sequences were composed of numerous wave trains with good correlations in their growths and decays in observed amplitudes among the stations, but no distinct P- or S-wave onsets were identified for individual wave trains. Interestingly, the spatial variation of the wave trains amplitudes is similar to those of the previously identified VLFEs. These observations suggest that the sequences were composed of small seismic events closely located each other and to the known VLFEs. It is also notable that some of the VLFE-like events discovered by the OBS data were contained in the sequences. We regard the discovered sequence as a kind of tectonic tremor activity and will inspect their characteristics, such as frequency content and its variability, to clarify their nature and discuss their relevance to slow slip events along the shallow subduction interface, which might promote the activities.