Determination of earthquake magnitudes using duration of high-frequency energy radiation and maximum displacement amplitudes: application to the July 17 2006 Java Tsunami earthquake

Tatsuhiko Hara

International Institute of Seismology and Earthquake Engineering, Building Research Institute

Recently, we developed a new method to determine earthquake magnitudes using the following formula (Hara, 2006):

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 (Lomax, 2005; Park et al., 2005; Ni et al., 2005; Hara, 2006). are 0.79, 0.87, 0.68, and 6.38, respectively (the units of were M, km, and sec, respectively).

We applied this method to the July 17, 2006 Java Tsunami earthquake. Figure 1 shows an example of measurements of high-frequency energy radiation. The estimated duration is 155.6 sec. This is consistent with the centroid time shift (69.1 sec) of the Harvard CMT solution, and some rupture models (Ji, http://neic.usgs.gov/neis/eq_depot/2006/eq_060717_qgaf/neic_qgaf_ff.html; Yagi, http://www.geo.tsukuba.ac.jp/press_HP/yagi/EQ/20060717Jawa/). The estimated magnitude using the above formula is 7.7, which well agrees with Mw of the Harvard CMT solution (7.7).

This result suggests that our method is useful for rapid magnitude determination of large shallow earthquakes including tsunami earthquake, since it is possible to determine magnitudes by processing of first arriving P-waves.

Fig. 1. An example of measurements of high frequency energy radiation. The upper and lower traces are an observed seismogram and its smoothed time series of squares of band-pass (2-4 Hz) filtered seismogram (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.

References

Hara, T., Measurement of duration of high-frequency energy radiation and its application to determination of magnitudes of large shallow earthquakes, submitted to Earth Planets Space, 2006.

Lomax, A., Rapid estimation of rupture extent for large earthquakes: Application to the 2004, M9 Sumatra-Andaman mega-thrust, Geophys. Res. Lett., 32, L10314, doi:10.1029/2005GL022437, 2005.

Ni, S., H. Kanamori, and D. Helmberger, Energy radiation from the Sumatra earthquake, Nature, 434, 582, 2005.

Park, J., K. Anderson, R. Aster, R. Butler, T. Lay, and D. Simpson, Global seismographic network records the great Sumatra-Andaman earthquake, Eos Trans. AGU, 86(6), 57, 2005.

Last Updated: 2006/07/21