Determination of earthquake magnitudes using duration of high-frequency energy radiation and maximum displacement amplitudes: application to the September 16, 2015 Chile earthquake

    We applied the magnitude determination method of Hara (2007) to the September 16, 2015 Chile earthquake (the origin time: 22:54:33 UTC; the location 31.570S 71.654W depth=25 km after USGS). In this method, an earthquake magnitude, M, is calculated by the following formula:

where A is the maximum displacement (m) during high-frequency energy radiation from the arrival time of a P-wave, Δ is the epicentral distance (km), t 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 duration. The estimated duration is 119.1 sec. The estimated magnitude using the above formula is 8.19, which is consistent with Mww 8.3 from USGS WPhase Moment Tensor Solution and Mw 8.2 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.

We analyzed BHZ channel waveform data recorded at the Global Seismograph Network (GSN) stations. We retrieved the data from the IRIS DMC (Incorporated Research Institutions for Seismology, Data Management Center). We used SAC (Seismic Analysis Code) (Goldstein et al., 2003; Goldstein and Snoke, 2005) for seismic waveform data analyses.


This analysis was done by Tatsuhiko Hara.
Last Updated: 2015/9/18