Broadband seismic. noise analysis of the Himalayan Nepal Tibet Seismic Experiment

We analyze background noise to assess the effects of experimental temporary seismic vault construction and to determine the time needed for noise at sites to stabilize after deployment noise as part of the Himalayan Nepal Tibet Seismic Experiment (HIMNT). We calculated power spectral densities of background noise for each component of each broadband seismometer deployed in Nepal and Tibet and then compared them with the high-noise model and low-noise Model of Peterson (1993). All segments from day and night local time windows were included in the calculation without parsing out earthquakes. Noise levels were considerably higher for the Nepal stations than the Tibet stations, in particular, in the high frequencies. The most northern of the stations in Tibet show unexpected day/night differences of similar to 10-20 dB for the vertical components, which is significantly greater than the day/night differences of the horizontal components. However, all the stations show noise levels concordant with microseism peak levels. Power spectral density estimates show moderate noise levels with all stations falling within the high and low bounds of Peterson (1993), except for the southern Nepal stations, which were built above ground and exceed the high-noise model at frequencies > 1.0 Hz. The time needed for noise at a site to stabilize was similar to 1-5 days after deployment.