Analysis of Empirical B–Δ Relationships in the Southern and Southwestern Zagros and Evaluation of Their Applicability in Earthquake Early Warning Systems

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Graduate University of Advanced Technology, Kerman, Iran

Abstract

In this study, the performance of the single-station B–Δ method in Earthquake Early Warning Systems (EEWS) was investigated for the southern and southwestern Zagros regions (Lorestan, Khuzestan, and Bushehr provinces). The goal of this method is to rapidly estimate earthquake magnitude and epicentral distance using only the first few seconds of the P-wave in a single accelerogram. To this end, 72 accelerograms from 16 earthquakes with Mw ≥ 4 were processed. In this method, by fitting an exponential function to the initial portion of the P-wave, two main parameters are calculated: parameter A, which represents the rate of amplitude attenuation over time, and parameter B, which indicates the initial growth rate of the P-wave amplitude. These parameters are determined using the least squares method. Analysis of the resulting plots showed a linear and inverse relationship between log B and log Δ, allowing estimation of the epicentral distance (Δ). To estimate earthquake magnitude, the peak P-wave amplitude is also used. Based on the data studied, the relationships for epicentral distance and magnitude were obtained as log⁡〖∆=-0.1142 log⁡〖B+1.55±0.46 〗 〗 , M_est=0.337 log⁡〖P_max-0.804 log⁡〖B+5.659±0.34 〗 〗respectively, for the study region. Comparison of these estimated values with the observed data indicated satisfactory performance, suggesting that these relationships can be used for rapid estimation of key earthquake parameters in EEWS for the southern and southwestern Zagros. These results demonstrate the capability of the B–Δ method to provide fast and reliable preliminary estimates for earthquake hazard management in the studied areas.

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Articles in Press, Accepted Manuscript
Available Online from 05 October 2025

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