Abstract
P-wave arrival-time data from earthquakes in the Zagros Fold Belt area of western Iran, recorded at as many as 20 local stations temporarily in operation during September 1976, are used to find errors in epicentre locations issued by the International Seismological Centre (ISC). Assuming that Zagros earthquakes are generally confined to the crust (Jackson and Fitch 1981), it was possible to obtain accurate epicentres for these earthquakes, and to conclude that they are mislocated towards the northeast by the ISC and that the ISC P n velocity is inappropriate for Zagros. It is shown that when inaccurate velocity models are used in earthquake locations, the geometry of the network of stations used induces a new type of travel-time residuals, called “geometrical residuals” here, which will disappear if the velocity models are corrected. The geometrical residuals contain information about the correct velocity structure and appear in the routine epicentre locations issued by the ISC. Identification of these residuals can lead to a wealth of new data for accurate velocity determinations.
Published Version
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