Determination of earthquake magnitudes using duration of high-frequency energy radiation and maximum displacement amplitudes: application to the April 20, Sichuan, China earthquake

We applied the magnitude determination method of Hara (2007a, b) to the April 20, Sichuan, China earthquake (the origin time: 00:02:47 UTC; the location 30.284°N 102.956°E depth= 12.3 km after USGS). In this method, an earthquake magnitude, M, is calculated by the following formula:

where is the maximum displacement (m) during high-frequency energy radiation from the arrival time of a P-wave, is the epicentral distance (km), is duration (s) of high-frequency energy radiation. The duration of high-frequency energy radiation is estimated by band-pass filtering of first arriving P-waves.

Figure 1 shows an example of measurements of high-frequency energy radiation. The estimated duration is 20.5 sec. The estimated magnitude using the above formula is 6.87, which is a little larger than M_ww 6.6 from USGS WPhase Moment Tensor Solution, and M_w 6.6 from the Global CMT solution.

Fig. 1. An example of measurements of high frequency energy radiation. 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 energy radiation, respectively.

Acknowledgements

We retrieved BHZ channel waveform data, recorded at the Global Seismograph Network (GSN) stations, from IRIS DMC (Incorporated Research Institutions for Seismology, Data Management Center). We used SAC (Seismic Analysis Code) (Goldstein et al., 2007) for seismic waveform data analyses.

References

Goldstein, P., D. Dodge, M. Firpo, L. Minner, J. E. Tull, D. Harris, and W. C. Tapley, SAC - Seismic Analysis Code, http://www.iris.edu/manuals/sac/manual.html, 2007.

Hara, T., Measurement of duration of high-frequency energy radiation and its application to determination of magnitudes of large shallow earthquakes, Earth Planets Space, 59, 227–231, 2007a.

Hara, T., Magnitude determination using duration of high frequency energy radiation and displacement amplitude: application to tsunami earthquakes, Earth Planets Space, 59, 561–565, 2007b.

This analysis was done by Tatsuhiko Hara.

Last Updated: 2013/04/23