Influences of azimuth on the local earthquake magnitude measurement

Azimuth is one of the factors that affect the local earthquake magnitude measurement. In this study, we collected the earthquake events from 2007 to 2015 recorded by the Hubei regional seismograph network. Using the digital seismic waveforms, we measured the magnitudes of the local earthquakes in the Hubei area and calculated the magnitude differences from those published by the China Earthquake Networks Center. To deep understand the influences of azimuth on the local earthquake magnitude measurement, the average magnitude deviation and standard deviation in each interval are statistically analyzed. Taking each digital seismic station as the center, the earthquake events recorded by each station are divided into 12 intervals with 30° as an interval. The results show that except the 24 non-earthquake intervals, in the remaining 300 intervals the average magnitude deviation less than 0.3 accounts for 81.7%. Furthermore, deducting the 14 intervals with only one event, in the other 286 intervals, 98.3 percentage of the azimuth standard deviation is less than 0.5. After azimuth corrections, both the average magnitude deviations and the azimuth standard deviations of each interval decrease, indicating the influences of azimuth on the measurement of local earthquake magnitude decreasing. Therefore, it is necessary and meaningful to correct the magnitude deviation caused by different azimuths.