This number may be larger than Nph if arrival times are rejected because the distance to a seismic station exceeds the maximum allowable distance or because the arrival-time observation is inconsistent with the solution. Nph Number of P and S arrival-time observations used to compute the hypocenter location. Increased numbers of arrival-time observations generally result in improved earthquake locations. In general, the smaller this number, the more reliable is the calculated depth of the earthquake. This parameter provides a measure of the fit of the observed arrival times to the predicted arrival times for this location.
Smaller numbers reflect a better fit of the data.
The value is dependent on the accuracy of the velocity model used to compute the earthquake location, the quality weights assigned to the arrival time data, and the procedure used to locate the earthquake. The horizontal location error, in km, defined as the length of the largest projection of the three principal errors on a horizontal plane. The principal errors are the major axes of the error ellipsoid, and are mutually perpendicular. Erho thus approximates the major axis of the epicenter's error ellipse. The depth error, in km, defined as the largest projection of the three principal errors on a vertical line.