Determination of earthquake magnitudes using duration of high-frequency seismic signal andmaximum displacement amplitudes: application to the February 6, M7.8 and M7.5 Turkey
earthquakes
We applied the magnitude determination method of Hara (2007) to the February 6, M7.8 Turkey
earthquake (the origin time: 01:17:35 UTC; the location 37.174°N 37.032°E depth 17.9 km after USGS) andthe February 6, M7.5 Turkey earthquake (the origin time: 10:24:49 UTC; the location 38.024°N 37.203°E
depth 10.0 km after USGS). In this method, an earthquake magnitude is calculated using high-frequency
seismic signal duration, the maximum displacement during high-frequency seismic signal from the arrival
time of a P-wave, and the epicentral distance. The duration of high-frequency seismic signal is estimatedthrough band-pass filtering of first arriving P-waves.
Figure 1 shows an example of measurements of high-frequency seismic signal duration for theM7.8 event. The median of the measured durations is 151.6 sec. The estimated magnitude is 7.87, which isconsistent with Mww 7.8 from USGS W-Phase Moment Tensor solution and Mw 7.8 from the Global CMTsolution.
Figure 2 shows an example of measurements of high-frequency seismic signal duration for theM7.5 event. The median of the measured durations is 25.5 sec. The estimated magnitude is 7.44, which isconsistent with Mww 7.5 from USGS W-Phase Moment Tensor solution, and a little smaller than Mw 7.7 fromthe Global CMT solution.

Fig. 1. An example of measurements of high frequency seismic signal duration for the February 6, M7.8
Turkey earthquake. The upper, middle and lower traces are an observed seismogram, the squares of theband-pass (2-4 Hz) filtered seismogram, and its smoothed time series (normalized by the maximum value),respectively. “A” and “F” in the lower trace denote the arrival of P-wave and estimated end of highfrequency seismic signal, respectively.

Fig. 2. An example of measurements of high frequency seismic signal duration the February 6, M7.5 Turkey
earthquake. The upper, middle and lower traces are an observed seismogram, the squares of the band-pass(2-4 Hz) filtered seismogram, and its smoothed time series (normalized by the maximum value), respectively.
“A” and “F” in the lower trace denote the arrival of P-wave and estimated end of high frequency seismicsignal, respectively.
Acknowledgements
We analyzed BHZ channel waveform data recorded at stations of HK (Hong Kong Seismograph Network), GT (Albuquerque Seismological Laboratory(ASL)/USGS, 1993), IC (Albuquerque Seismological Laboratory (ASL)/USGS, 1992), and IU (Albuquerque Seismological Laboratory/USGS, 2014). We
retrieved the data from the IRIS DMC (Incorporated Research Institutions for Seismology, Data Management Center). We used SAC (Seismic Analysis Code)(Goldstein et al., 2003; Goldstein and Snoke, 2005) for some parts of the data analyses.

References
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This analysis was done by Tatsuhiko Hara (Last Updated: 2023/02/07)