Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

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

[S-CG65] Reducing risks from earthquakes, tsunamis & volcanoes: new applications of realtime geophysical data

Wed. May 23, 2018 9:00 AM - 10:30 AM A10 (Tokyo Bay Makuhari Hall)

convener:Mitsuyuki Hoshiba(Meteorological Research Institute), Satoshi Kawamoto(Geospatial Information Authority of Japan), Naotaka YAMAMOTO CHIKASADA(防災科学技術研究所, 共同), Masashi Ogiso(Meteorological Research Institute, Japan Meteorological Agency), Chairperson:Hoshiba Mitsuyuki(Meteorological Res. Inst., JMA, Japan), Kawamoto Satoshi(Geospatial Information Authority of Japan )

9:30 AM - 9:45 AM

[SCG65-03] Significantly large rotation and tilt motion of cabled seismic stations off Sanriku, northeastern Japan

*Takeshi Nakamura1, Naoki Hayashimoto2 (1.National Research Institute for Earth Science and Disaster Resilience, 2.Japan Meteorological Agency)

Keywords:Earthquake Early Warning, ocean-bottom seismic observation, seismic amplification, acceleration offset

Deployments of cabled stations in ocean-bottom areas enhance the effectiveness of earthquake early warnings for suboceanic earthquakes in terms of early signal detections and improvements of accuracy for hypocenter analyses. We investigated strong-motion data for rapid magnitude estimations at cabled ocean-bottom stations deployed in the source area of the 2011 Tohoku earthquake (M9.0) in the northeastern Japan. We found DC offsets in accelerations due to movements of the cabled stations during strong motions. Our waveform analyses on the offset data showed that the stations are rotated and tilted in proportion to input motions. The analysis results also showed that the orientation angle around the cable direction is more affected by the motion at earthquakes than the angle along the direction, because of the cylindrical shaped station housing in the long cable. At the 2011 Tohoku earthquake (Mw 9.0), the cabled sensor is rotated up to 57.7° around the cable direction and tilted 1.4° along the cable. If we apply double integrations for such data, the large rotation causes anomalous displacement waveforms with significantly large amplitudes in the two components perpendicular to the cable direction, which would contribute to the overestimation of displacement magnitudes.
In this presentation, we show schemes of magnitude estimations that can suppress the anomalous amplifications by using the single component data along the cable or by squared root of sum of squares of three components at ocean-bottom stations. We compare the estimated magnitudes with those listed in a hypocenter catalog which is estimated by using land station data.