Infrasonic and Seismic Signals from Earthquake and Explosions in Arequipa, Peru

This paper reports work in characterization of infrasonic and seismic signals from mining explosions and an earthquake. Wavelet transform together with ampligram and time scale spectrum are used to address characterization issues for both infrasonic and seismic signals. The ampligram may be considered as an analogy to signal decomposition into Fourier components. In that case different components correspond to different frequencies. In the present case different components correspond to different wavelet coefficient magnitudes, being equivalent to spectral densities. The time scale spectrum is a forward wavelet transform of each row (wavelet coefficient magnitude) in the ampligram. The time scale spectrum reveals individual signal components and indicates the statistical properties of each component: deterministic or stochastic. This study focuses on infrasound and seismic data from the earthquake and the following type of mining operation: rock fragmentation for copper recovery (Cerro Verde mine) where moderate sized explosions are designed to break the rock for further processing. Infrasound and seismic signals have been recorded during three weeks at University of San Agustin observatory station (Arequipa, Perú) on January 2006. A single infrasound microphone, seismometers and accelerometers were used. From the recorded data two events were chosen to this study: an earthquake occurred 19th of January measuring 3.8 on the Richter scale and a mining explosion. Infrasonic signals from the mining area show arrivals a few milliseconds before the seismic signals. The infrasonic signal from the earthquake has the appearance of the z-component of seismic signals.