Uncertainties in Earthquake Source Spectrum Estimation using Empirical Green Functions

German A. Prieto, Robert L. Parker, Frank L. Vernon, Peter M. Shearer, & David J. Thomson

Published 2006, SCEC Contribution #933

We analyze the problem of reliably estimating uncertainties of the earthquake source spectrum and related source parameters using empirical Green Functions (EGF). We take advantage of the large dataset available from 10 seismic stations at hypocentral distances (10 < d < 50 km) to average spectral ratios of the 2001 M5.1 Anza earthquake and 160 nearby aftershocks. We estimate the uncertainty of the average source spectrum by performing propagation of errors, which, due to the large number of EGFs used, is significantly smaller than that obtained using a single EGF. Our approach provides an estimate of the earthquake source spectrum and its uncertainties, as well as confidence intervals on source parameters such as radiated seismic energy or apparent stress, allowing the assessment of statistical significance. This is of paramount importance when comparing different sized earthquakes and analyzing source scaling of the earthquake rupture process. Our best estimate of radiated energy is 1.24e11 Joules with 95\% confidence intervals (0.73e11, 2.28e11). The value of apparent stress 0.33 (0.19 ,0.59) MPa obtained is relatively low compared to previous estimates from smaller earthquakes in the same region.

Prieto, G. A., Parker, R. L., Vernon, F. L., Shearer, P. M., & Thomson, D. J. (2006). Uncertainties in Earthquake Source Spectrum Estimation using Empirical Green Functions. In Prieto, G. A. (Eds.), Earthquakes: Radiated Energy and the Physics of Faulting, (, pp. 69-74) San Francisco, USA: AGU doi: 10.1029/GM170.