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Estimation of Kappa (κ_0) and Associated Uncertainties in Iran Using Broadband Inversion Method

Description: 

Abstract
kappa (κ) (Anderson and Hough, 1984), and its site-specific component (κ₀) at a given location, is an important spectral parameter for the characterization of the high-frequency shape of the Fourier acceleration spectrum, predicting and simulating high-frequency ground motion and is usually modeled in log-linear space. For our analysis, we use 2798 acceleration time histories from 325 earthquakes (between 1976 and 2020) in the moment magnitude range M3.5–7.4 and at Epicentral distances (Repi) up to 100 km. Using the broadband inversion approach, we study the spectral decay parameter κ using S-wave recordings at 285 stations in Iran. Here, the κ estimated by Davatgari Tafreshi et al. (2022) using Anderson and Hough's (1984) high-frequency linear fit method is compared with our κ estimation using the FAS broadband inversion approach as described in Edwards and Fäh (2013a); Bora et al. (2015) and Bora et al. (2017) for three major seismotectonic regimes in Iran, namely northern Iran, Zagros, and central-east Iran. In the broadband approach, the FAS at all frequencies is fit to a point-source model using a least-squares fit. For site-specific seismic hazard analyses, κ₀ should be estimated at locations away from an accelerogram location. For this purpose, for site-specific seismic hazard analyses, κ₀ can be inferred from the correlations with V_S30. We correlate the site component of κ (κ₀) with V_S30 and f₀ of the site. Our findings show a weak but negative correlation between κ₀ and V_S30 for three subregions under study. Researchers have studied site-to-site (between-station variability) and model-to-model variability of κ. Still, the uncertainties in κ estimation at a selected site associated with various events (within-station variability) remain uncharacterized. We have estimated a mean κ₀ and its uncertainty for stations with at least 5 records in our dataset, which may be useful for future site-specific seismic hazard analyses.
Keywords: Kappa; Site effects; Attenuation; Broadband Inversion Method

Session: High-frequency Ground Motion Measurements, Assessments and Predictions [Poster]

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Shahram Pezeshk

Student Presenter: No

Invited Presentation: 

Authors