Upper limit to earthquake size

Abstract

CHINNERY and North¹ have used data relating surface wave magnitude to seismic moment, M₀, to convert magnitude-frequency statistics for the Earth into a seismic moment distribution. For M₀ values ranging from about 2 × 10²⁵ to 2 × 10³⁰ dyne cm they found that their data could be represented by where N is the number of shallow earthquakes (depth < 70 km) each year with seismic moment greater than or equal to M₀. On the basis of the remarkably good fit of equation (1) to their data, they argued that seismic moments considerably in excess of 2 × 10³⁰ dyne cm were likely to occur as they did not consider it probable that the linear trend stopped immediately beyond the last data point. I have used recent results on the movement of lithospheric plates in conjunction with equation(1) to estimate an upper limit for M₀. It turns out that this upper limit is probably not much in excess of the moment of the Chile earthquake of 1960 ( ∼ 2 × 10³⁰ dyne cm) (ref. 2).