Prediction of Magnitude and Epicentral Distance from a Single Seismic Record: A Case Study of the Ahar-Varzaghan Earthquake
DOI:
https://doi.org/10.15273/ijge.2016.04.019Keywords:
Earthquake Early Warning Systems, B-Δ method, Single Station records, Ahar-Varzaghan Earthquake, Northwestern IranAbstract
Earthquake magnitude and P wave amplitude (Pmax) are important parameters for Earthquake Early Warning Systems (EEWS), yet their dependence on source mechanism, focal depth and epicentral distance (Δ) has not been fully studied. We examined a method to estimate an earthquake‘s magnitude and epicentral distance using the initial part of P-wave data (within 3 s) for application in EEWS. The B-Δ method is used to estimate the epicentral distance from a single station data in a short time. Fitting a simple function with the form of y(t) = Bt à— exp(-At) to the first few seconds of the waveform envelope, coefficients A and B are determined through the least-squares method. LogB is inversely proportional to logΔ, where Δ is the epicentral distance. This relation holds true regardless of earthquake magnitude. B values are calculated on the basis of 48 vertical-component accelerograms of the Ahar-Varzaghan earthquake in a magnitude range Mw4.5-6.4 and epicentral distances less than 100 km. Using this method, we could estimate the epicentral distance by logΔ = -0.69 logB + 2.5 and earthquake magnitude by Mest = 1.89 logPmax - 1.76 logB + 5.52. The greatest advantage of this method is its accuracy and rapidness.
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