LAUSR

We propose an alternative procedure for the capture of the hard‐rock regional kappa ( ). In our approach, we make use of a potential link between the well‐known κ parameter and the properties of coda waves. In our analysis, we consider near‐distance rec‐ ords of four crustal earthquakes of local magnitude 3.7–4.9 that occurred in four regions of France in different geological contexts: the crystalline axial chain of Pyrenees to the southwest, the large sedimentary basin to the southeast, the Alpine range to the east, and the extensional Rhine graben to the northeast. Each earthquake has been recorded at a pair of nearby soft‐ and hard‐rock station sites. The high‐frequency (16–32 Hz) spectral amplitudes of the coda window (carefully selected on the time series of the accelerograms) confirm an exponential decrease, which we quantify by and call “kappa of coda.” It is found that is in‐ dependent of the soil type but shows significant regional variations. measurements (Ander‐ son and Hough, 1984) over the coda window ( ) and full time series ( ) show strong correlation at hard‐rock sites. This suggests that can provide a new proxy to estimate the regional hard rock (Ktenidou et al., 2015). Theoretical analysis is also presented to relate the regional and coda quality factor , which quantifies the average attenuation properties of the crust (both scattering and absorption). It allows interpreting as the time spent by the waves in the medium, weighted by its attenuation properties. This theoret‐ ical analysis also shows that the classical measurement should be frequency dependent; this was confirmed by the spectra of the observed records.