Teleseismic P residuals have been monitored as a function of time at 13 stations in southern California during the 5-year period 1972 to 1976. These residuals, when normalized to minimize common path and source effects, and corrected for the marked azimuthal dependence of residuals in southern California, show no significant variation. This indicates that no detectable velocity changes have occurred during this time in the vicinity of the stations monitored. It is estimated that a velocity change of ∼9 per cent occurring over a path length of 10 km and lasting for at least 6 months should be resolvable. Either such changes have not taken place in the region monitored, or any velocity anomalies are confined to a small depth range in the crust, and are poorly sampled by teleseismic waves.

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