Book Description

Spectral density estimates, depicting seismic noise recorded in Australia by temporary networks of the Earthquake Mechanism Laboratory, range from 5 to 20 dB higher (at 1.0 Hz) than similar estimates made from seismic noise recorded at Uinta Basin Observatory, Vernal, Utah. Amplitudes of microseisms recorded at network stations show similar time-varying trends which seem correlated to meteorological conditions. In the band about 1.0 Hz, the estimated coherence of microseisms approaches that for unrelated samples when sensors are separated by approximately 2 km. Studies of 178 teleseisms suggest a detection threshold of mb = 4.6 for shallow teleseisms occurring as far as 90 degrees from network stations. Many of the teleseismic recordings show anomalous short-period P waves. Visual estimates of the coherence of P waves, recorded at network stations, range from almost coherent to almost incoherent. (Author).