STATISTICAL SIGNIFICANCE OF THE SEISMIC COUPLING COEFFICIENT

Variations in the seismic coupling coefficient (X), the ratio of the o bserved to expected seismic moment release rates,at subduction zones a re commonly used to make inferences about the physics of subduction. T aking into account the power-law form of the earthquake frequency-mome nt relation, it is shown that the observed distribution of X at the wo rld's subduction zones based on the twentieth century's earthquakes ca n be matched by a single value of X approximate to 0.3 if, as is likel y the case, the 90-yr observation time is less than or comparable to t he repeat time of the largest possible earthquake. It is shown that be cause our reliable earthquake record is short, global variations in X based on seismicity alone, are poorly resolved and cannot be used to d istinguish among subduction models.