Site attenuation and source parameters on the North Anatolian Fault zone, eastern Turkey estimated from the aftershocks of 13 March 1992 Erzincan earthquake

Site attenuation and source characteristics of 45 aftershocks of the 13 March 1992 Erzincan, eastern Turkey earthquake have been determined from SH-wave spectra using a least-squares best-fit method. Although the most of the seismograms were recorded on the ophiolitic rock sites and the average regional attenuation correction of Q(f) = 35 f^0.83 was applied, the high fall-off rates ranging between 3.0 and 4.5 beyond the corner frequencies of 8–13 Hz were observed on the SH spectra. The site attenuation value, , has been calculated from the slope of the high frequency part of the SH spectra. It was found that varied in the range of 0.0124–0.0364 s and the average was 0.0246 s with a standard deviation of 0.0047 s. The high fall-off rates of observed spectra have decreased considerably as a result of site attenuation corrections and converged to an average value of 2.3. We concluded that the high fall-off rates of SH wave spectra are mainly controlled by highly deformed Miocene ophiolitic formations which covers a wide area in the North Anatolian Fault zone in the vicinity of Erzincan region. Using the spectra that were corrected for regional and site attenuation, and assuming a Brune's source model; seismic moment, source radius, and stress-drops of the aftershocks were computed. We found that stress-drops for some of the aftershocks in Erzincan area have slightly decreased after removal of site attenuation over SH wave observed spectra.     

Ground-Motion Scaling in the Western Alps

In order to empirically obtain the scaling relationships for the high-frequency ground motion in the Western Alps (NW Italy), regressions are carried out on more than 7500 seismograms from 957 regional earthquakes. The waveforms were selected from the database of 6 three-component stations of the RSNI (Regional Seismic network of Northwestern Italy). The events, M _W ranging between 1.2 and 4.8, were recorded within a hypocentral distance of 200 km during the time period: 1996–2001. The peak ground velocities are measured in selected narrow-frequency bands, between 0.5 and 14 Hz. Results are presented in terms of a regional attenuation function for the vertical ground motion, a set of vertical excitation terms at the reference station STV2 (hard-rock), and a set of site terms (vertical and horizontal), all relative to the vertical component of station STV2.The regional propagation of the ground motion is modeled after quantifying the expected duration of the seismic motion as a function of frequency and hypocentral distance. A simple functional form is used to take into account both the geometrical and the anelastic attenuation: a multi-variable grid search yielded a quality factor Q(f) = 310f ^0.20, together with a quadri-linear geometrical spreading at low frequency. A simpler, bi-linear geometrical spreading seems to be more appropriate at higher frequencies (f > 1.0 Hz). Excitation terms are matched by using a Brune spectral model with variable, magnitude-dependent stress drop: at M _w 4.8, we used Δσ = 50 MPa. A regional distance-independent attenuation parameter is obtained (κ₀ = 0.012 s) by modelling the average spectral decay at high frequency of small earthquakes.In order to predict the absolute levels of ground shaking in the region, the excitation/attenuation model is used through the Random Vibration Theory (RVT) with a stochastic point-source model. The expected peak-ground accelerations (PGA) are compared with the ones derived by Ambraseys et al. (1996) for the Mediterranean region and by Sabetta and Pugliese (1996) for the Italian territory.     

Comparing classical statistic and machine learning models in landslide susceptibility mapping in Ardanuc (Artvin), Turkey

Natural Hazards - Landslide susceptibility maps provide crucial information that helps local authorities, public institutions, and land-use planners make the correct decisions when they are...