Koseki, Kiwamu,

Looking into the seismic trend, we indeed see high seismicity in the mid seismic band (a few 10 mHz - a few 100 mHz) in the past five days.

However, the IM motion of PR3 had became larger before the seismicity elevated. So we are concluding that the PR3 motion can not entirely be explained by the seismic activity.

The first attachment shows the spectra of all of the IM degrees of freedom. The solid traces are those from the last night while the dashed lines are for the same data but from the 22nd of this October. The peak at 0.45 Hz existed from the past and its height used to be lower by a factor of five-ish in all the degrees of freedom.

Also, the second attachment shows the mid-band seismic trend for this past three weeks. Interestingly, there seems to be some kind of seismic waves going along the North-South direction which are visible in IXV, EXV and the center areas. It kept decaying in the past few days. Comparing this against the spectra shown above, we found that the timing for the elevation of the seismic activity didn't coincide with the time when the 0.45 Hz peak in the PR3 IM increased. The 0.45 Hz peak in the PR3 IM had increased something like two days before the mid-band seismicity elevated. So for the reason, it is hard to say that the 0.45 Hz is entirely driven by seismic noise.