Program to calculate travel times for given stations and hypocenter location at local distances. The program uses the HYPOCENTER travel time calculations. By default, the model used is from STATION0.HYP, unless another model is selected in the s-file.
The program operates in two modes:
If iasp.inp is present, and there are no arguments, arrival times for stations in iasp.inp are calculated and put in file iasp.out to be used with MULPLT. The iasp.inp contains the stations in the waveform file. It is thus possible to calculate theoretical arrival times without any picks in the S-file. The iasp.inp is generated by MULPLT when the user asks for synthetic phases (MULPLT IASP option). The phases calculated are first and possibly second arrivals. For short distances there would only be first arrivals like Pg. Although refracted arrivals might be present, they are not calculated since they are unlikely to be seen. For larger distances both refracted P and PG are calculated like PN3 and PG. PN and PB are not specifically calculated but will appear as one of the PNX. When running the program, an output is also give on the text screen:
1 FNA 230.977905 N4 35.8533058 1 FNA 230.977905 G 38.0395508 2 IGT 308.198364 N4 45.9507637 2 IGT 308.198364 G 50.4460907 3 MRVN 293.900574 N4 44.1098595 3 MRVN 293.900574 G 48.1656075 4 PUK 46.8152657 G 8.61053467 5 SCTE 248.730225 N4 38.1072121 5 SCTE 248.730225 G 40.8507156 6 TIR 104.178276 G 17.6073112 7 KBN 212.190460 N4 33.3805771 7 KBN 212.190460 G 35.0128403 8 PHP 106.046379 G 17.9404621 9 SGRT 303.668915 N4 45.3243828 9 SGRT 303.668915 G 49.6978455
This gives the station, epicentral distance, type of phase and travel time for the P-phase. The travel times for the S-phases are calculated using the Vp/VS ratio given in the station file and NOT by using a possible S-velocity model in the station file.
Free standing program for calculation of theoretical arrival times for station given in an S-file To operate in this mode, the command ttlocal sfile is given. The program calculates theoretical arrivals for the phases given in the s-file and write the output file with the original arrival times replaced by the theoretical times. All weights etc are kept. N and B-phases are used if given in S-file and specified in station file. A possible S-velocity model is ignored. Relocating the output file should give same locations as given in input file with zero residuals. In this mode there can be many events in the input s-file. The station file used is the one from the first event. Optionally the arrival times can be have added noise if a second argument is used like e.g. ttlocal collect.out 2.0 where input file is collect out and random noise is added. The noise generator is the Fortran RAND function which gives random numbers from 0-1 so in the example we would get random numbers between 0 and 2. The nose added to the arrival times for P is then between -1 and 1. The noise added to the S is multiplied with Vp/Vs.
The output file is ttlocal.out
Peter Voss : Fri Nov 12 10:33:10 UTC 2021