Determination of earthquake magnitudes using duration of high-frequency energy radiation and maximum displacement amplitudes: application to the April 16, Iran-Pakistan border region earthquake
We applied the magnitude determination method of Hara (2007a, b) to the April 16, Iran-Pakistan border region earthquake (the origin time: 10:44:20 UTC; the location 28.107N 62.053E depth=82km 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 38.5 sec. The estimated magnitude using the above formula is 7.72, which is consistent with Mww 7.7 from USGS WPhase Moment Tensor Solution, and Mw 7.7 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. gAh and gFh in the lower trace denote the arrival of P-wave and estimated end of high frequency energy radiation, respectively.
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.
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: 2013/04/17