In the first attached file is it shown where we performed the various injections. From the analysis we can assert that:

• We couldn't pinpoint the scatterer to a specified location, but we could localize it to the east flange of the IB tower. In fact, when we did the tapping test on the beam dump and on the flange, both the accelerometer on the beam dump (BD ACC) and the one on the inner side of the flange (IB ACC X) see the same amount of noise. The 101 Hz peak came up, instead the 157 Hz peak was not excited (see plots 2 to 4, along x, y and z directions). Also while doing the injections with the shaker on the beam dump we excited both the beam dump and the flange, as shown on plot 5. To be noticed that this time also the structure at around 157 Hz has grown in Hrec.
• During the broadband injections we also observed an increase of coherence between PRCL and PMC TRA at 101 Hz, which already had been pointed out by the BRUCO even during quiet periods (look at plot 6). This could be explained through the PSTAB loop, which tries to compensate at those frequencies (in fact this increase in the coerence is also visible on the PSTAB error signal). However, we do not see any effect during the injections in the band 150-160 Hz.
• Plot 7 shows the injections of lines at 155, 156, 157 and 158 Hz that had been performed with the shaker installed on the beam dump. Only the 156 and 157 Hz are coupled in PRCL and Hrec.
• Plot 8 shows the tapping performed on the pipes linking SIB1 to SIB2. There is no coupling to Hrec. It is not surprising because there are the bellows to isolate the seismic noise. We should have done it on both sides of the bellows as well in order to verify if it is coming from the viewports.

Another test we could do is to increase the power going to the beam dump by turning the waveplates of the IPC1 (EIB) and 2 (SIB1). This would require a dedicated shift.