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Rapid determination of the energy magnitude Me

Rapid determination of the energy magnitude Me. D. Di Giacomo , S. Parolai, H. Grosser, P. Bormann, R. Wang, and J. Zschau. SAFER Final Meeting Potsdam, 3 June 2009. Me and Mw : example from a simplified source model. M 0 calculated from displacement amplitudes at f << f 0. f 0. 10 MPa.

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Rapid determination of the energy magnitude Me

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  1. Rapid determination of the energy magnitude Me D. Di Giacomo, S. Parolai, H. Grosser, P. Bormann, R. Wang, and J. Zschau SAFER Final Meeting Potsdam, 3 June 2009

  2. Me and Mw : example from a simplified source model M0 calculated from displacement amplitudes at f << f0 f0 10 MPa 100 MPa ER calculated from squared velocity amplitudes around f0 f0 The form of the moment spectra is calculated from an ω2 model according to Aki (1967) and Brune (1970): f0 is calculated assuming a Brune (1970) source model: where β = 3.75 km/s, c = 0.49, ∆σ is referred to as “stress parameter”.

  3. Correction for wave propagation effects Single station approach to determine ER e.g. Venkataraman and Kanamori (2004): AK135Q • P-wave signals in the distance range 20°-98°. • Moderate/Strong to Great earthquakes. • Global Earth model AK135Q. • Numerical simulations of Green’s functions.

  4. Spectral amplitude decay functions Spectral amplitude decay functions for periods between 1 s and 16 s in steps of one octave. The solid lines represent the median spectral amplitude decay function for a given period, the shaded areas represent the 25th and 75th percentile. SinglestationES determinations by:

  5. ER and Me for cumulative P-wave windows Velocity seismogram at the station KMBO and normalized high frequency envelope (Bormann and Saul, 2008) for the Wenchuan earthquake According to the new IASPEI standard: with ES given in Joule.

  6. The case of the Wenchuan earthquake A stable Me(GFZ) = 8.0 determination obtained using 180 s P-wave time windows could have been provided about 10-12 min after OT.

  7. The case of the great Sumatra earthquake Me(GFZ) determination using (S-P) time windows for the 26-12-2004 Sumatra earthquake. Already about 15 min after OT our procedure could have provided a stable Me determination.

  8. Importance of comparing Mw and Me The locations differ by about 100 km and the moment magnitudes Mw are very similar. However, the differences in the high frequency content observed in the seismograms cannot be explained by the small difference in Mw.

  9. Importance of comparing Mw and Me However, the high frequency content observed in the seismograms is significantly different and cannot be explained by Mw only. Mw(GCMT) = 7.0 Me(GFZ) = 7.1 Mw(GCMT) = 6.8 Me(GFZ) = 6.4 The locations differ by about 250 km and the moment magnitudes Mw and the fault plane solutions are very similar.

  10. Summary • Me and Mw measure two different aspects of the seismic source, therefore they should be used together in order to better evaluate and discriminate between the tsunami and the shaking potential of strong and great earthquakes. • Spectral amplitude decay functions for different frequencies have been computed given the reference Earth model AK135Q in order to accomplish in a rapid and robust way the correction for the wave propagation effects. • Our procedure calculates ER, and hence Me, for cumulative P-wave windows up to the S-wave arrival in case of very long rupture time duration, so that the problem of the time window saturation effect is avoided. • Once implemented in a near- or real-time procedure a stable Me determination could be provided within 10 min after OT, even for great earthquakes.

  11. Thank You!

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