SEISMIC MOMENT ASSESSMENT OF EARTHQUAKES IN STABLE CONTINENTAL REGIONS .1. INSTRUMENTAL SEISMICITY

This Part I study, in conjunction with Part II, develops a method to d etermine, within specified uncertainty bounds, the seismic moment, and thus moment magnitude, of all earthquakes of stable continental regio ns (SCR) for which instrumental or intensity data exist. Its basis is polynomial regression analysis using a database of SCR earthquakes wit h direct seismic moment determination. The independent variables inclu de 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 majo r historical earthquakes. All data used in the regressions are assigne d individual uncertainties estimated from the literature or from exper ience; formal confidence limits (68 per cent or 95 per cent) on both t he regression formulas and the predicted seismic moment values are the n possible via error propagation analysis. The most complete developme nt is for the teleseismic magnitudes M(s) and m(b). For both, the fina l regression for log(M(0)) is a quadratic formula that closely emulate s the relationship between amplitude magnitudes and log(M(0)) expected from dislocation theory and source-scaling arguments. Regressions are also derived for the regional magnitudes M(Lg) and M(L), because ther e are many SCR events, mainly pre-1964, that have no teleseismic magni tudes. Prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the +/-0.18-0.28 range, and from regional magni tudes in the +/-0.23-0.38 range over a wide magnitude band. Finally, t he 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.