Development of an on-site Data Processing System-and-Application Soft for Reconnaissance Survey to Estimate Deep Geological Structure Using Microtremors

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The fundamental programs and system-and-application softs have been developed for easy and quick data-processing for a new exploration technique which makes use of microtremors observable at any time in any place with a fairly stable spectrum. The technique can estimate geologic structure in a form of S-wave velocity distribution down to a depth of about 3km from measuring phase velocities of surface waves (Rayleigh waves) in microtremors with periods longer than Is, by observing with a seismic array consisting of 7 to l0 seismometers.The data processing in the technique includes estimating power spectra and cross spectra. For the measurement of phase velocities of surface waves, frequency-wavenumber power spectral densities (F-K spectra) for the F-K method, and spatial autocorrelation coefficients (SPAC coefficients) for the SPAC method are calculated from microtremor data observed. The phase velocities of surface waves are then inverted to an S-wave velocity distribution by an inversion technique.All the fundamental programs and application softs required with these data processing are included in the newly developed application soft 'BIDOU', in which the theoretical phase velocities of either Rayleigh or Love waves for a structure model are also available.A cross section of profile withspatially placed sites where seismometer arrays are deployed and geologic structures are determined is also given by S-wave velocity versus depth distribution, for which the soft program 'DANMEN' has been developed. The program 'DANMEN' can link with respective layrs for S-wave velocities determined under the sites where arrays are deployed.These developed programs and softs are fully integrated data acquisition and processing for a new exploration technique using microtremors, operating in Widows 3.1 on PC.These powerful programs and softs have been tested at more than 50 sites where good results have been obtained.