Spectra of seismic noise at selected Indian stations

India Meteorological Department (IMD) is operating five digital seismograph systems at New Delhi (NDI),.Shillong (SHL), Pune (POO), Kodaikanal (KDK) and Dhamlsala (DHM) since last few years. The details pertaining to instrumental characteristics and software for data retrieval and processing are presented in this paper, Through PC based algorithms. noise pectra are computed and interpreted for these five stations. It is found that the maximum peak occurs at about 6Hz for Pune. Shillong and Kodaikanal while at New Delhi and Dharmsala, it is noted at about 2 Hz. The spectral peak at Shillong as deduced from the SRO system shifts to about I Hz which is in agreement with a similar observation reported at Gauribidanur seismic array.

Application of Seismic Interferometry by Multidimensional Deconvolution to Earthquake Data Recorded in Malargüe, Argentina

Seismic interferometry (SI) refers to the principle of generating new seismic responses using crosscorrelations of existing wavefield recordings. In this study, we report on the use of a specific interferometric approach, called seismic interferometry by multidimensional deconvolution (SI by MDD), for the purpose of retrieving surface-wave responses. In theory, SI by MDD suffers less from irregularities in the distribution of (passive) sources than conventional SI. Here, we confirm this advantage for the application to surface waves originating from regional earthquakes close to Central Chile. For that purpose, we use the Malargüe seismic array in Argentina. This T-shaped array consists of two perpendicular lines of stations, which makes it rather suitable for the application of SI by MDD. Comparing the responses retrieved through SI by MDD to the responses retrieved using conventional SI, we find that the application of SI by MDD results in surface-wave responses that are both more accurate and more stable than surface-wave responses that are retrieved using conventional SI. That is, our results demonstrate that SI by MDD suffers less from non-uniformly distributed earthquakes and differences in the power spectra of earthquake responses. In addition, we show that SI by MDD mitigates the effect of site amplification on the retrieved surface waves.