d. di giacomo, s. parolai, h. grosser, p. bormann, r. wang, and j. zschau rapid determination of the...
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D. Di Giacomo, S. Parolai, H. Grosser, P. Bormann,
R. Wang, and J. Zschau
Rapid determination of the
energy magnitude Me
SAFER Final MeetingSAFER Final Meeting
Potsdam, 3 June 2009Potsdam, 3 June 2009
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”.
20
2
200)(ff
fMfM
3/1
00
Mcf
Me and Mw : example from a simplified source modelMe and Mw : example from a simplified source model
ff00
ER calculated from squared velocity
amplitudes around faround f00
M0 calculated from displacement
amplitudes at f << ff << f00
ff00
10 MPa
100 MPa
Correction for wave propagation effectsCorrection 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 Green’s functions.
AK135Q Single station approach to determine ERe.g. Venkataraman and Kanamori (2004):
Spectral amplitude decay functionsSpectral 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.
Single station ES determinations by:
EERR and Me for cumulative P-wave windows 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.
The case of the Wenchuan earthquakeThe 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 earthquakeThe 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 MeImportance 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 MeImportance of comparing Mw and Me
Mw(GCMT) = 7.0Me(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) = 6.8Me(GFZ) = 6.4
However, the high frequency content observed in the
seismograms is significantly different and cannot be explained by Mw only.
SummarySummary
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.
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.
Thank You!Thank You!