Erhard Wielandt

Crust and upper mantle structure of the Bohemian Massif from the dispersion of seismic surface waves

SummaryThe phase velocity dispersion of Rayleigh waves for the Moxa-Vienna (MOX-VIE) and Moxa-Kašperské Hory (MOX-KHC) profiles, and of both Rayleigh and Love waves for the Kašperské Hory-Ksiąź (KHC-KSP) profile have been measured and inverted into models of shearwave velocity vs. depth. The three paths cross, respectively, the central part of the Bohemian Massif, its western margin, and the Bohemian Pluton and Cretaceous. For the MOX-VIE profile mean and lower crustal shear wave velocities of 3.7 and 3.9 km/s, respectively, a mean Moho depth of 34 km, and no existence of a low-velocity layer in the lower crust were found. The model obtained for the MOX-KHC profile is characterized by a slightly lower velocity in the lower crust (3.8 km/s), by a slightly lower Moho depth (32 km), and by the appearance of a weak low-velocity channel between 55 and 140 km. The crustal section of the final model for the KHC-KSP profile agrees well with the KHKS82 model derived by Novotný from results of DSS along international profile VII. Our final Rayleigh-wave model has significantly lower shear-wave velocities down to 215 km in the mantle. A systematic difference of 0.18 km/s between the average velocities of Rayleigh and Love waves has been revealed for the depth range from 30 to 215 km. Since almost no contamination of the fundamental Love mode with higher modes has been observed, and since the investigated structure hardly contains an unresolved system of thin, alternately low- and high-velocity layers, the cause of the difference is evidently polarization anisotropy of the upper mantle beneath the Bohemian Massif. It is recommended that the discussed investigations should be supplemented with data from the fan of KSP-GRF (Gräfenberg Array, Germany) paths and from the KHC-BRG (Berggiesshübel, Germany) profile.

85.18 – Software for Seismometer Calibration and Signal Analysis

This chapter discusses the software for seismometer calibration and signal analysis. The chapter includes the various programs, which include: CALEX, DISPCAL, NOISECON, SINFIT, TILTCAL, and UNICROSP. CALEX determines parameters of the transfer function of a seismometer from the response to an arbitrary input signal (which must be recorded together with the output signal). DISPCAL determines the generator constant of a horizontal or vertical seismometer from an experiment where the seismometer is moved stepwise on the table of a machine tool or a mechanical balance. NOISECON converts noise specifications into several sets of standard and nonstandard units and compares them to the USGS New Low Noise Model. SINFIT fits a sinewave to two signals (normally input and output signals of an amplifier, filter, or seismometer). The first signal is supposed to be an undisturbed reference signal, and the frequency of the sinewave is determined from the first signal alone. TILTCAL determines the generator constant of a horizontal seismometer from an experiment in which the seismometer is tilted stepwise.