6:15 PM - 7:30 PM
[STT53-P04] Construction of the seismic observation network around Shimokita Peninsula (2)
Keywords:Seismic observation network, Shimokita Peninsula
We have completed the installation of AS-net which consists of 36 observation sites at August 2014, in addition to 20 stations already installed in 2013. Seismic data recorded by AS-net are distributed at the nation-wide real-time distribution network for seismic data, JDX-net. From January 2015, it became able to download the seismic data by AS-net via continuous seismic data download web service managed by NIED. It would contribute to enhance the precision of seismic monitoring and any other researches for seismology.
We estimated the level of background noise for each AS-net station. As a noise level, we calculated the root-mean-square (RMS) value for the amplitude of 1 hour ambient noise waveform. As a result, the noise level in daytime exceeds 50 micro-cm/s at 11 stations. On the other hand, the noise level in daytime was around 10 micro-cm/s or less at 14 stations. At the stations with higher noise level, the ambient noise were dominant at 0.5-1 Hz. The measured average S-wave velocity (Vs) for soil layer between the seismometer at borehole bottom (~20 m depth) and ground surface was related to the noise level for each station; the stations with averaged Vs of 300 m/s or less tended to show higher noise level. It indicates that the noise level at each station depends on the soil condition.
Then we relocated earthquakes around Shimokita region during 2014 automatically using AS-net data in addition to the other stations nearby. Up to 4616 events were determined by our relocation, which are 2.5 times as many as JMA hypocenter catalogue (1846 events). Of course, our result contains some artificial events; blasts, seismic exploration and so on. For natural earthquake, we caught 375 events during a swarm around Towada from 20 to 31 January 2014 (287 events in JMA catalogue). To distinguish these various events we got, we will check them in detail with manual measurement. Frequency-magnitude diagram for our catalogue peaks out at around M0.6 while that for JMA catalogue peaks out at around M1. It implies that the AS-net enhanced earthquake detection capability around Shimokita region.
Sekine, S., S. Sawada, K. Kasahara, S. Sasaki, Y. Tazawa, H. Yajima, 2014, Construction of the seismic observation network around Shimokita Peninsula, Jaman Geoscience Union Meeting 2014, Yokohama, STT57-P09, April 2014.