December 2, 2002 GreatCircle.exe, version 1.0.0.4 This utility program calculates the great circle bearing and distance from point 1 to point 2, and the estimated time of arrival of P and S waves from shallow events, if the great circle angular separation is 106 degrees or less. By clicking on the desired data input box, the user can use the mouse, and keyboard number and edit keys to enter or paste in latitude or longitude and time of the event. The user's own coordinates can be stored in a text file named "GreatCircle.ini", which contains one line showing user's latitude and longitude. These numbers must be separated by a comma. The time of the event can be similarly entered in the event time input box. Clicking on "Run" initiates the computation. The results appear on the output screen. line 1: Station coordinates. line 2: Event coordinates. line 3: Azimuth angle from station to event, in degrees, clockwise from north. line 4: Azimuth angle from event to site, clockwise from north. line 5: Angular separation of station and event, Delta, in degrees. line 6: Distance in kilometers or miles. line 7: Event time, estimated P arrival time, and estimated S arrival time (only if Delta is less than 106 degrees). This output can be copied to the clipboard by using the mouse to highlight it and pressing Ctrl+C, and pasted from there to any document. New inputs can be entered, and results calculated by clicking on "Run" again. The output is appended to the results of previous calculations. Third-order least squares fits to the Jeffreys-Bullen travel time tables for shallow focus (1) are used to compute P and S arrival times. The coefficients for P are: 8.70844809507551 14.7631938595216 -9.80722842589179E-02 3.26151740896659E-04 The coefficients for S are: 15.7750490313662 26.2175611081234 -0.166923190615349 5.55023097819056E-04 The curve fit is not exact. Do not expect the displayed arrival times to be accurate to better than a few seconds, especially if the event is deeper than 33 kilometers. The radius of the earth is assumed to be 6371 kilometers, which is the average radius as taken from the Encyclopedia Brittanica. --------- (1) Jeffreys, H. and Bullen, K.E., 1940, Seismological Tables, British Association for the Advancement of Science, Gray Milne Trust. Reprinted 1970. ----------------------------------------------------------- This program was prepared using Visual Basic for Windows 6.0. It should run on any Windows PC if the system file contains "MSVBVM60.DLL". My current email address is bobhelenmcclure@aol.com. Contact me if you have any questions or suggestions. Bob McClure 90 Maple Avenue Locust Valley, NY 11560 Telephone 516/671-4758