Shinobu Kurihara
Type of contribution: invited
Session: 5

The impact of the 2011 off the Pacific coast of Tohoku Earthquake on Tsukuba 32-m VLBI station

Shinobu Kurihara, Geospatial Information Authority of Japan Kensuke Kokado, Geospatial Information Authority of Japan Jiro Kuroda, Geospatial Information Authority of Japan Misao Ishihara, Geospatial Information Authority of Japan Ryoji Kawabata, Geospatial Information Authority of Japan

A 9.0-magnitude earthquake named "the 2011 off the Pacific coast of Tohoku Earthquake" hit eastern areas of Japan on March 11. The earthquake measured a lower 6 on the seven-point JMA seismic intensity scale around Tsukuba. The gear wheel for elevation drive of Tsukuba 32-m VLBI antenna was swayed by the earthquake, but there was no critical damage in the antenna and other equipment. Meanwhile, in Tsukuba correlator, several servers and hard-disks fell down from rack and some of them were broken. But the damage was not as serious as our correlator operation couldn't be continued. Many aftershocks measured an intensity of 4 or greater on JMA scale followed over a few weeks after the main shock. We put off restarting VLBI operation due to fear of aftershocks until early April. Tsukuba 32-m returned to the IVS VLBI session from April 4. Following VLBI sessions produced some VLBI positions of Tsukuba, and co-seismic and post-seismic displacement was detected by VLBI. By the way, GSI has installed and maintained over 1,200 of GNSS-based control stations, a large number of triangulation points and benchmarks throughout Japan. Since the crustal displacement was widespread and the magnitude of it was very large, we needed to revise the coordinates of control points. This revision covered the eastern half of Honshu Island; 438 GNSS-based control stations, approx. 43 thousand of triangulation points and approx. 1.9 thousand of benchmarks. All these new coordinates were calculated based on the amount of displacement detected by VLBI observation on May 10. This was because we needed an absolute coordinate based on the international geodetic observation after the earthquake.