Seismic moment assessment of earthquakes in stable continental regions-I. Instrumental seismicity

This Part I study, in conjunction with Part II, develops a method to determine, within specified uncertainty bounds, the seismic moment, and thus moment magnitude, of all earthquakes of stable continental regions (SCR) for which instrumental or intensity data exist. Its basis is polynomial regression analysis using a database of SCR earthquakes with direct seismic moment determination. The independent variables include modern teleseismic magnitudes and regional magnitudes (Part I), and isoseismal areas or number of recording stations (Part II). Part III is an application of the methodology of Parts I and II to several major historical earthquakes. All data used in the regressions are assigned individual uncertainties estimated from the literature or from experience; formal confidence limits (68 per cent or 95 per cent) on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis. The most complete development is for the teleseismic magnitudes Ms and mb. For both, the final regression for log(Mo) is a quadratic formula that closely emulates the relationship between amplitude magnitudes and Mo expected from dislocation theory and source-scaling arguments. Regressions are also derived for the regional magnitudes mLg and ML, because there are many SCR events, mainly pre-1964, that have no teleseismic magnitudes. Prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ± 0.18.–0.28 range, and from regional magnitudes in the ±0.23–0.38 range over a wide magnitude band. Finally, the methodology developed here is generic, even though the database is specific. Application to plate-boundary, oceanic intraplate, or active continental intraplate regions should be straightforward.