[J04-2] Geohazard early warning systems II

[J04-2-05] Prediction of the Magnitude and Epicentral Distance from a Single Seismic Record, a Case Study of Ahar-Varzaghan Earthquake

^○Majid Mahood (Earthquake Prediction Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran)

Magnitude and an amplitude parameter Pmax determined from the very beginning of P wave are important for earthquake early warning systems (EEWS), yet their dependence on source mechanism, focal depth and epicentral distance has not been fully studied. We examined a method to estimate an earthquake's magnitude and epicentral distance using only initial part of P-wave data (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 amount of time. Fitting a simple function with the form of y(t)=Bt*exp(-At) to the first few seconds of the waveform envelope, coefficients A and B are determined through the least-squares method. Log B is inversely proportional to log Δ, 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 Ahar-Varzaghan earthquake with magnitude range Mw 4.5-6.4 and epicentral distances less than 100 km. Using this method, we could estimate the epicentral distance by logΔ=-0.69logB+2.5 and earthquake magnitude by Mest=1.89log Pmax-1.76logB +5.52. The greatest advantage of this method is its accuracy and rapidness.