Abstract

Spectral parameter kappa κ is used to describe spectral amplitude decay “crash syndrome” at high frequencies. The purpose of this research is to estimate spectral parameter kappa for the first time in Croatia based on small and moderate earthquakes. Recordings of local earthquakes with magnitudes higher than 3, epicentre distances less than 150 km, and focal depths less than 30 km from seismological stations in Croatia are used. The value of kappa was estimated from the acceleration amplitude spectrum of shear waves from the slope of the high-frequency part where the spectrum starts to decay rapidly to a noise floor. Kappa models as a function of a site and distance were derived from a standard linear regression of kappa-distance dependence. Site kappa was determined from the extrapolation of the regression line to a zero distance. The preliminary results of site kappa across Croatia are promising. In this research, these results are compared with local site condition parameters for each station, e.g. shear wave velocity in the upper 30 m from geophysical measurements and with existing global shear wave velocity – site kappa values. Spatial distribution of individual kappa’s is compared with the azimuthal distribution of earthquake epicentres. These results are significant for a couple of reasons: to extend the knowledge of the attenuation of near-surface crust layers of the Dinarides and to provide additional information on the local earthquake parameters for updating seismic hazard maps of studied area. Site kappa can be used in the re-creation, and re-calibration of attenuation of peak horizontal and/or vertical acceleration in the Dinarides area since information on the local site conditions were not included in the previous studies.

Highlights

  • Ground motion at the site is influenced by source, propagation path, and local site conditions, and is described using acceleration Fourier Amplitude Spectrum of shear waves

  • Site kappa can be used in the re-creation, and re-calibration of attenuation of peak horizontal and/or vertical acceleration in the Dinarides area since information on the local site conditions were not included in the previous studies

  • Site kappa (κ0) and VS30 values estimated for each station are comparable with global values, for the VS30 ≥ 1000 m/s

Read more

Summary

Introduction

Ground motion at the site is influenced by source, propagation path, and local site conditions, and is described using acceleration Fourier Amplitude Spectrum of shear waves. Spectral decay parameter kappa (κ) was first introduced by [1] to describe deviation at high frequencies between observed acceleration spectrum of shear waves (S) from seismograms and simple Brune source omega-square model [2]. The objective of this study was to calculate κ from S wave acceleration spectrum using classical AH84 [1] approach for three component recordings of local earthquakes ML ≥ 3, epicentral distances RE ≤ 150 km, and focal depths h < 30 km.

Objectives
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call