Nairwita Mazumder, Rich Abbott
A few days back Jim noticed (alog ) that the "Bumbling line" which varies over a large frequency range is again back on ETMX seismic channels . This was first noticed on March and disappeared before ER7 and again was seen from 4th August. One can see the lines at all the horizontal and vertical sensors on ETMX.
I have attached a pdf containing some follow up work done during Rich's recent visit to LHO. The first plot in the pdf is the spectrogram of ETMX GS13 on 26th August. It can be seen that there are multiple wandering lines having a fixed offset. We were suspecting that some magnetometers at the End X might be the culprit (as we could not find any correlation between temperature fluctuation with the line ).
The second and third plots are the spectrum of H1:PEM-EX_MAG_EBAY_SEIRACK_Z_DQ and H1:ISI-ETMX_ST2_BLND_Z_GS13_CUR_IN1_DQ for 2nd August and 26th August respectively. The red one is for 2nd August when the bumbling line could not be found and the blue one is the recent data (26th August). It is clear that the peaks appearing on ISI-ETMX_ST2_BLND_Z_GS13 after 3rd August are correlated with the peaks of the spectrum (which also appeared around the same time) of SEIRACK magnetometer .
The plots on the second page shows the coherence between GS13 and the magnetometers in the VEA and SEIRACK. It looks like the magnetometer on the SEI rack has stronger coherence with GS13 sensors than the magnetometer located at VEA . I have marked two points (blue and red cross) in the coherence plots to highlight two of the many peaks.