Noise excess can be seen in a wide frequency range (around 1-500Hz) not as a narrow peak.
Fig.1 and Fig.2 show the spectra in various time of IN1_DQ and OUT_DQ, respectively.
Red curve shows the quite situation as a reference.
Blue, green, brown, and magenta curve indicate the spectra at the time of the 1st, 2nd, 5th, and 6th noise excesses in Fig.3.
These noise excess seems to appear at the same time with the excess on the RMS (3-10 and 10-30Hz) of seismometer signal at IXV as shown in Fig.4
Because Seismometer at IXV is connected to IXV rack and power supply is shared with VIS signals, we cannot reject the possibility of electrical coupling.
So I tried to check another PEM sensors. But unfortunately, there is no alive PEM sensor around IXC and seismometers at MCF and BS don't also seem to be alive.
What is the permanent sensor...?
