Determination of earthquake magnitudes using duration of high-frequency energy radiation and maximum displacement amplitudes: application to the February 6, Santa Crus Islands earthquake
Building Research Institute
We developed a 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 February 6, Santa Crus Islands earthquake (the origin time: 01:12:27 UTC; the location 10.738S 165.138E depth=28.7km after USGS). Figure 1 shows an example of measurements of high-frequency energy radiation. The estimated duration is 90.7 sec. The estimated magnitude using the above formula is 7.74, which is a little smaller than Mww 8.0 from USGS WPhase Moment Tensor 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. gAh and gFh in the lower trace denote the arrival of P-wave and estimated end of high frequency energy radiation, respectively.
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: 2013/02/06