Presentation on theme: "D. Di Giacomo, S. Parolai, H. Grosser, P. Bormann, R. Wang, and J. Zschau Rapid determination of the energy magnitude Me SAFER Final Meeting Potsdam, 3."— Presentation transcript:
D. Di Giacomo, S. Parolai, H. Grosser, P. Bormann, R. Wang, and J. Zschau Rapid determination of the energy magnitude Me SAFER Final Meeting Potsdam, 3 June 2009
The form of the moment spectra is calculated from an ω 2 model according to Aki (1967) and Brune (1970): f 0 is calculated assuming a Brune (1970) source model: where β = 3.75 km/s, c = 0.49, σ is referred to as stress parameter. Me and Mw : example from a simplified source model f0f0f0f0 around f 0 E R calculated from squared velocity amplitudes around f 0 f << f 0 M 0 calculated from displacement amplitudes at f << f 0 f0f0f0f0 10 MPa 100 MPa
Correction for wave propagation effects P-wave signals in the distance range 20°-98°. Moderate/Strong to Great earthquakes. Global Earth model AK135Q. Numerical simulations of Greens functions. AK135Q Single station approach to determine E R e.g. Venkataraman and Kanamori (2004):
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 25 th and 75 th percentile. Single station E S determinations by:
E R 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 E S given in Joule.
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.
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.
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.
Importance of comparing Mw and Me Mw(GCMT) = 7.0 Me(GFZ) = 7.1 The locations differ by about 250 km and the moment magnitudes Mw and the fault plane solutions are very similar. Mw(GCMT) = 6.8 Me(GFZ) = 6.4 However, the high frequency content observed in the seismograms is significantly different and cannot be explained by Mw only.
Summary 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 E R, 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. 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.
The radiated seismic energy E R From Venkataraman and Kanamori (2004) Sensible to the dynamic characteristics and complexities of the earthquake rupture process E G = Fracture Energy E H = Heat Energy E R = Radiated Seismic Energy The energy released as elastic waves is proportional to the square of the ground motion velocity: e.g. Haskell (1964) Single station approach to determine E R, e.g. Venkataraman and Kanamori (2004) going into the seismic waves E R represents the fraction of the energy balance involved in the earthquake process going into the seismic waves
Importance of comparing Mw and Me The differences in the high frequency content observed in the seismograms can be attributed to different source characteristics (not evident by considering Mw alone). Mw(GCMT) = 7.6 Me(GFZ) = 7.19 Mw(GCMT) = 7.6 Me(GFZ) = 6.75 The locations differ by about 500 km and the moment magnitudes Mw are nearly identical.