Temporal variation of noise correlation function (NCF) in Beijing and surroundings: Its relation with climate events and implications

Noise correlation function (NCF) was calculated using the data of the Beijing Capital-Area Telemetered Digital Seismograph Network from June 12 to September 12, 2005. Signal-to-noise ratio (SNR) is used to characterize the quality of NCF at each station pair. The SNR (in dB) is shown to be dependent on the separation distance <i<R</i< of the station pair via SNR = <i<A −B</i<log<i<R</i<. 'Normalized average SNR' for all the station pairs can then be calculated, as represented by the value of SNR taking <i<R</i< = 250 km in the empirical SNR-<i<R</i< relation, to measure the overall quality of the NCF result. The 'normalized average SNR' of the NCF shows temporal variation and is apparently dependent on the root-mean-square (RMS) velocity of the microseism. The result obtained by this experiment provides clues to the explanation of the properties of NCF, such as the dominant mechanism underlying (diffuse wave fields or uncorrelated sources), and the dependence of SNR on the time length of recordings.