Abstract
Abstract. Seismically induced ground motion at a site is generally influenced by the seismic source, the propagation path and the local site conditions. Over the last several decades, researchers have consistently asserted that for near-site attenuation, the spectral parameter κ is subject primarily to the site conditions. In this research, we estimated the parameter κ based on the acceleration amplitude spectrum of shear waves from local earthquakes recorded by seismological stations situated in the western part of Croatia from the slope of the high-frequency part. The spatial distribution of κ values is comparable with seismological, geophysical and geological features, with the published coda-Q values for each station as well as with the isoseismal maps for selected stronger earthquakes in the study area. The complex pattern of longitudinal and transversal major late-orogenic fault zones dissecting early-orogenic thin-skinned tectonic cover in the Kvarner area and the shallow depth to the Moho (Mohorovičić discontinuity) in the Adriatic foreland (southern Istria) are probably responsible for a significant part of wave attenuation and for the anisotropy of attenuation. Regional near-surface attenuation distribution and modelled macroseismic fields point to the conclusion that attenuation properties of rocks in the northwestern External Dinarides are far from isotropic, and the most likely anisotropy sources are the preferential orientations of cracks and fractures under the local tectonic stress field, trapping of waves along major faults (waveguides), and/or attenuation within the fault zones. These results are important for gaining further insight into the attenuation of near-surface crust layers in the northwestern External Dinarides and the associated Adriatic foreland as well as in similar geotectonic settings.
Highlights
It is a well-known fact that earthquake shaking at the particular site in terms of observed or recorded strong ground motion is subject to complex source characteristics, attenuation of seismic waves when they propagate through the Earth’s crust and changes resulting from local site conditions (e.g. Reiter, 1990)
Attenuation of seismic waves is a key factor in seismic hazard assessment for earthquake prone regions
This paper presents the calculated values of the highfrequency parameter κ (Anderson and Hough, 1984) and the local site-specific component κ0 in the area of northwestern External Dinarides and the respective Adriatic foreland based on recordings from four Croatian seismological stations
Summary
It is a well-known fact that earthquake shaking at the particular site in terms of observed or recorded strong ground motion is subject to complex source characteristics, attenuation of seismic waves when they propagate through the Earth’s crust and changes resulting from local site conditions (e.g. Reiter, 1990). It is a well-known fact that earthquake shaking at the particular site in terms of observed or recorded strong ground motion is subject to complex source characteristics, attenuation of seismic waves when they propagate through the Earth’s crust and changes resulting from local site conditions This paper presents the calculated values of the highfrequency parameter κ (Anderson and Hough, 1984) and the local site-specific component κ0 ( called near-site or near-surface attenuation) in the area of northwestern External Dinarides and the respective Adriatic foreland based on recordings from four Croatian seismological stations. The κ − Re model is used to estimate the value of the site-specific (near-site) attenuation parameter as a zero-distance κ0 value. Estimated regional and local variations in the spectral parameter κ were compared with the geological characteristics of the investigated area and with macroseismic fields for selected earthquakes
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