The Nature of Ambient Noise over a Field in Western Junggar Basin near Karamay, China

摘要

The characteristics of ambient noise over a field in western Junggar Basin near Karamay,China,have been investigated using two arrays of 35 three-component broadband seismometers by means of spectral amplitude and array beamforming analysis within a frequency range of 0.1-10Hz.The aim of this experiment is to understand the characteristics and origins of the secondary microseism (0.1-0.4 Hz) and microtremor (about 2.0-3.0 Hz) signals in a region that is far away from ocean.The results of spectral amplitude analysis show that a secondary microseism peak at 0.22 Hz and a distinct microtremor peak at about 2.5 Hz dominate the noise spectrum.On some occasions,the secondary microseisms can be split into long-period (0.14-0.16 Hz) and short-period (0.185-0.235 Hz) bands.The spectral amplitude of microtremor signals exhibit distinctive cyclical day-to-night variations and the secondary microseisms signals remain stable,relatively.Beamforming analysis results show that the noise energy of microtremor signals mainly comes from the azimuth of 40°-70° pointing towards the city of Karamay,and displays almost no variation over time.Our results indicate that,(1) the secondary microseism signals are mainly generated by ocean waves and can be affected by meteorological activities from different source distances; (2) the microtremor signals consists predominantly of surface waves,originating from the production facility,human activities in the Karamay city.The characteristics of spectral amplitude can help us to better understand noise energy distribution of different frequency band and have guiding significances for further analysis.The predominated azimuth of microtremor signals can be an important factor that biases the estimation of surface wave dispersion information extracted from seismic interferometry.