Determination of earthquake magnitudes using duration of high-frequency energy radiation and maximum displacement amplitudes: application to the December 21, 2010 Near Chichi-jima Is., Japan earthquake

 

Tatsuhiko Hara

International Institute of Seismology and Earthquake Engineering, Building Research Institute

 

We developed a new method to determine earthquake magnitudes using the following formula (Hara, 2007a, b):

        

where M is an earthquake magnitude,  is the maximum displacement during high-frequency energy radiation from the arrival time of a P-wave,  is the epicentral distance,  is duration of high-frequency energy radiation. The duration of high-frequency energy radiation can be estimated by band-pass filtering of first arriving P-waves (e.g., Hara, 2007a).  are 0.79, 0.83, 0.69, and 6.47, respectively (the units of  were m, km, and s, respectively).

 

   We applied this method to the December 21, 2010 Near Chichi-jima Is., Japan earthquake (the origin time: 17:19:40 UTC; the location 26.892‹N, 143.726‹E after USGS). Figure 1 shows an example of measurements of high-frequency energy radiation. The estimated duration is 32.4 sec. The estimated magnitude using the above formula is 7.61, which agrees with M 7.4 from Japan Meteorological Agency, Mw 7.4 from the Global CMT and 7.5 from USGS WPhase MT.

 

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. gAh and gFh in the lower trace denote the arrival of P-wave and estimated end of high frequency energy radiation, respectively.

 

 

References

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.

 

Last Updated: 2010/12/22