Magnitude scaling relationships using P waves for earthquake early warning in South Korea

The scaling relationships of the peak displacement, Pd, and the maximum predominant period, τpmax, of P waves were investigated to estimate magnitudes for earthquake early warning in South Korea. Pd and τpmax were measured for 504 vertical records from 70 earthquakes at distances of 20 to 100 km. The earthquakes occurred between 2001 and 2011 and ranged from ML = 3.0 to 5.2. Since the events were generally low to moderate in magnitude, the parameter for a real-time high-pass filter was adjusted and the first 3 seconds of the P-waves were processed. The scaling relationships of Pd and τpmax obtained from iterative regressions were M = 1.17 log(Pd) + 0.87 log(R) + 6.57 and M = 3.30 log(τpmax) + 5.75, respectively, where R is the epicentral distance in kilometers, Pd is in centimeters, and τpmax is in seconds. The average errors of the magnitude estimates obtained from the mean of the Pd magnitude and τpmax were 0.06 magnitude units for the calibration data but 0.37 for a recent magnitude 3.9 event, which implies that the scaling relationships can be used in these forms but the relationships still need to be improved with more data to be useful for mitigating damage from future earthquakes around the Korean Peninsula.