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!