. Collected reprints, Essa Institute for Oceanography. Oceanography AUTOMATED EPICENTER LOCATIONS 273 1000 1000. time (sec) Fig. 5. Plot of moving cross-correlation between recordings at two of the seismic stations. Maximum positive peak occurs at — second. Azimuth and Distance Once the time delays were obtained for all the station pairs, a least-squares com- puter program was developed to obtain the azimuth and distance from the net stations to the event. The function H which was minimized is given by H = £ {Bk - [DKcos (6 - aK) cos<p]/V}'- K = 1, 6 (1) where: BK is the ob
. Collected reprints, Essa Institute for Oceanography. Oceanography AUTOMATED EPICENTER LOCATIONS 273 1000 1000. time (sec) Fig. 5. Plot of moving cross-correlation between recordings at two of the seismic stations. Maximum positive peak occurs at — second. Azimuth and Distance Once the time delays were obtained for all the station pairs, a least-squares com- puter program was developed to obtain the azimuth and distance from the net stations to the event. The function H which was minimized is given by H = £ {Bk - [DKcos (6 - aK) cos<p]/V}'- K = 1, 6 (1) where: BK is the observed time delay for the Kth station pair DK is the distance between the stations of any Kth station pair d is the azimuth to the event measured clockwise from north at the center of the array aK is the angle measured clockwise between the Kth station pair and the parallel through the station with the highest latitude <P is the emergence angle and V is the assumed velocity oi km/sec. The azimuth obtained from (1) is the result of a scanning process. The scanning- process starts at 0° north and computes the 360° of 6 for each value of <p. <p is limited from 0° to 90°. The incremental steps are F° for both <p and 6. When a minimum of H is found, it steps back F° in both <p and 6 values and then proceeds forward in smaller incremental steps. These steps being G°, where G° < F°. The process stops after a length of 2F° is computed. Incrementation can be made as small as desired. This scanning process is rapid enough so that there would be small gain from a more sophisticated procedure. Figure 6 shows a graph of the least-squares values versus azimuth for <p = 0. This curve is a smooth curve which has, in this case, one maxi- mum and one minimum. Values of H versus <p and 6 yield a smooth surface which leads to no difficulty in obtaining a minimum H value. An attempt was made to ob- tain the minimum value of H by considering the simultaneous
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