Conclusions from IRS poster on OSN-1
Some Dogma Debunked
- Previously: Seafloor stations should always be much noisier than island stations,
particularly at short periods because of ocean wave noise.
- The OSNPE has shown that this is not true between OSN and Kipapa, above 0.03Hz.
- Previously: Short period teleseismic body waves should be very difficult to see
in the Pacific. Prior to the OSNPE there were only two.
- The OSNPE observed short period body waves from over ten earthquakes, including
mb's less than 5.
- Previously: Short period horizontal noise at seafloor stations is always much
greater than vertical noise.
- For the borehole sensor in the basement at OSN-1, the short period horizontal
components were consistently quieter than the vertical components.
- Previously: A borehole station should give at most 10dB improvement over a seafloor
or shallow buried sensor.
- On the OSNPE, at short periods, the borehole sensor was quieter than the shallow
buried sensor by up to 20dB on verticals and up to 30dB on horizontals.
- - The above results are based on preliminary observations from a few selected days.
The ambient noise field on all sensors has a strong time dependence which has not been
- - These results will also be site dependent.
- - The performance of the borehole sensor at very low frequencies (below about 0.02Hz)
appears to be contaminated by installation noise, which was observed during testing on
land, and which could be ameliorated by packing the borehole with sand or glass beads.