3:50 PM - 4:05 PM
[SGD03-07] On application of GNSS-techniques for early tsunami warning in the Sea of Japan
Keywords:tsunami early warning, GNSS
The most of working tsunami early warning systems (TEWS) are based on seismic methods that often cannot provide a reliable and accurate warning due to different reasons. The GNSS-based TEWS recently has been developed and they are free of many shortcomings of seismic methods. Such systems utilize coseismic shifts measured by onshore GNSS-networks for tsunami modeling. The TEWS operating now, for example, REGARD [Kawamoto S. et al., 2017], are mainly focused on detection of huge Mw8-9 class subduction zone earthquakes. They are not designed to process relatively small events, which can produce coseismic displacements less than 10 cm, despite on RTX-techniques or recently developed methods [Fratarcangeli F. et al., 2018], which can detect site position changes of 1-2 cm in horizontal and 3-4 cm in vertical components. However, devastating tsunamis regularly appear in the Japan Sea. They are caused by shallow thrust seismic events with magnitudes Mw6.2-7.8. These quakes generate tsunamis more effectively than Pacific ones with the same magnitude.The epicenters of tsunamigenic earthquakes are distributed along the western coast of Honshu, south-west of Hokkaido and Sakhalin Islands. Nevertheless, tectonics and seismicity of the Japan Seahaven't been sufficiently investigated still and tsunamigenic seismic events can occur along the north-western margin of the sea. For example, the potentially tsunamigenic Mw~6 shallow seismic event occurred near the northeastern coast of Primorye on Nov. 11, 1990.
In this work we explored: 1) the capacity of GNSS-based TEWS application using data about historical Mw 6.2-7.8 Japan Sea crustal seismic events. The appropriate coseismic displacement fields were calculated and analyzed. Possible hypothetic tsunamigenic seismic sources were also considered; 2) the optimal GNSS-site distribution for earthquake source parameters obtaining based on existing and prospective GNSS-networks configuration in the region.
We obtained, that historical tsunamigenic earthquakes occurred along the eastern margin of the Japan Sea induced coseismic displacements ranging from 1 cm to a few decimeters through the northern Honshu and western Hokkaido. Even 1964 Oga-oki, Mw7.0 event caused up to 4 cm surface offsets on the Honshu Island coast. Southwestern Sakhalin Island are also might be affected by centimeter level coseismic movement invoked by the shallow Mw 6.2-7.3 earthquakes appeared in the north of the Sea of Japan and Tatar strait. Hypothetical events with Mw > 7.5 and located in the north-west of the sea may excite displacement varying from 1 to 4 cm in Russian Primorye and Hokkaido Island. A set of inversion tests lead us to a conclusion that GEONET GNSS-network might be used to model tsunamigenic earthquake sources with Mw>7.0-7.8 distributed along the eastern margin of the Japan Sea. Working and prospective GNSS-networks located along the western coast of the sea and Sakhalin Island might be involved into processing of seismic events with Mw ≧ 7.3 appeared in the northern part of the sea.
This work was partially supported by the RFBR grant No. 17-55-53110 and JREX Fellowship.