Statistical properties of seismic noise measured in underground spaces during seismic swarm

Abstract

The results of seismic noise analysis during West Bohemia seismic swarm (Sep- tember 2011) are presented. The continuous measurements of seismic noise were performed at the seismic station located in underground space. The main purpose of the investigation is the estimating of parameters of seismic noise at the time fragments including the swarm and after its finishing. Eight characteristics of the noise were used which include mutlifractal parameters and wavelet-based entropy. Noise characteristics were calculated within adjacent time windows of the length 1 min with further averaging of 1 min estimates within adjacent 1 h fragments. The main peculiarity of the resulting time series of mean values of seis- mic noise parameters with time step 1 h is their daily periodicity. Besides that some statistics extractperiodicityof1week.Awavelet-basedmultiplecorrelationmeasureestimatedwithin weekly moving time window was applied to variations of 8 mean daily seismic noise para- meters. The seismic swarm manifests in non-stationary behaviour of the noise parameters which includes breaking the daily periodic structure and existing of irregular spikes. In spite of existing spikes and irregular components the swarm is characterized by relatively high values of multiple correlations.