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Automatic computation of moment magnitudes for small earthquakes and the scaling of local to moment magnitude

Edwards, Benjamin ; Allmann, Bettina ; Fäh, Donat ; Clinton, John

In: Geophysical Journal International, 2010, vol. 183, no. 1, p. 407-420

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    Titre
    • Automatic computation of moment magnitudes for small earthquakes and the scaling of local to moment magnitude
    Auteur
    • Edwards, Benjamin. Schweiz. Erdbebendienst, Sonneggstrasse 5, 8092 Zürich, Switzerland. E-mail: edwards@sed.ethz.ch
    • Allmann, Bettina. Schweiz. Erdbebendienst, Sonneggstrasse 5, 8092 Zürich, Switzerland. E-mail: edwards@sed.ethz.ch
    • Fäh, Donat. Schweiz. Erdbebendienst, Sonneggstrasse 5, 8092 Zürich, Switzerland. E-mail: edwards@sed.ethz.ch
    • Clinton, John. Schweiz. Erdbebendienst, Sonneggstrasse 5, 8092 Zürich, Switzerland. E-mail: edwards@sed.ethz.ch
    Type de document
    • Postprint
    Identifiant OAI-PMH
    • oai:doc.rero.ch:300009
    Summary
    Moment magnitudes (MW) are computed for small and moderate earthquakes using a spectral fitting method. 40 of the resulting values are compared with those from broadband moment tensor solutions and found to match with negligible offset and scatter for available MW values of between 2.8 and 5.0. Using the presented method, MW are computed for 679 earthquakes in Switzerland with a minimum ML= 1.3. A combined bootstrap and orthogonal L1 minimization is then used to produce a scaling relation between ML and MW. The scaling relation has a polynomial form and is shown to reduce the dependence of the predicted MW residual on magnitude relative to an existing linear scaling relation. The computation of MW using the presented spectral technique is fully automated at the Swiss Seismological Service, providing real-time solutions within 10 minutes of an event through a web-based XML database. The scaling between ML and MW is explored using synthetic data computed with a stochastic simulation method. It is shown that the scaling relation can be explained by the interaction of attenuation, the stress-drop and the Wood-Anderson filter. For instance, it is shown that the stress-drop controls the saturation of the ML scale, with low-stress drops (e.g. 0.1-1.0 MPa) leading to saturation at magnitudes as low as ML= 4