On the relation between P-wave travel time residuals and the age of continental plates

Abstract

A new set of P-station anomalies has been computed for 583 seismological observatories which sent their arrival times to the International Seismological Centre between 1964 and 1974. These P-residuals are used as a marker of the variations of the properties of the uppermost mantle. Important changes of P-residuals are observed within continents and particularly within Precambrian shields. It is shown that residuals tend to increase outwards from the centers of the North American and Scandinavian shields. As a first approximation, the P-residuals are a linear function of the root square of the age of the basement inside stable continental plates. For these stable plates, a P-residual is an indirect measurement of lithospheric thickness. The lithospheric thickness Z (in km) is related to its age t (in 10 9 years) by: z ≃ 10 + 140 t We then speculate on a possible use of P-residuals in the search of Archean nuclei inside Precambrian shields. Tiksi, in northern Siberia, is the “fastest” station on continents and could be the location of a very old continental nucleus.