GTT91

   Break this file into three parts (gtt91.1, ttimes91.1, and zstp91.1) as indicated and install into your UNIX system to generate three new manual pages. -------- gtt91.1 -------

NAME
gtt91 - construction of computer accessible travel time tables

SYNOPSIS
gtt91

DESCRIPTION
gtt91 comprises a sequence of routines to set up a representation of the travel travel time tables for a given velocity model in terms of the tau-spline procedure of Buland & Chapman (1983), together with routines for user access (interactive and graphical).

  Construction of tau-spline tables:
The two basic stages are:
remodl - construction of partial tau integrals for different segments of a velocity model of the Earth. This requires discretisation of the velocity model at depths corresponding to the slowness employed in the representation of the tables. It is at this point in the process that the velocity model has to be specified and linked in with the rest of the routines - subsequently all necessary information on the model is carried in the direct access table files. The procedure remodl generates two table files:
remodl.hed, remodl.tbl
which are used as the input to the second stage (setbrn)

setbrn - construction of the tau-spline coefficients for different travel time branches corresponding to distinct seismic phases. The tau-splines are generated for each of the depths at which the model was sampled. In addition auxiliary tables are set up to allow interpolation to arbitrary depth. The procedure setbrn generates two direct access table files identified by the name of the velocity model
e.g. iasp91.hed, iasp91.tbl
These tables are used in the routine ttimes91 which returns travel times for seismic phases at specified distance and in other display and location procedures

A Makefile template is provided to allow the construction of the tau-spline tables for different velocity models. The specification of the velocity model used for iasp91 is in terms of polynomials (up to cubic) in normalised radius for different portions of the velocity model. The main body of routines used by the gtt91 system are stored in the
$GTT91/libtau.f
and two include files
$GTT91/limits.inc and $GTT91/ttlim.inc
are needed.

  Access to travel time tables:
The simplest mode of access to the travel time tables is interactive use of the ttimes91 command which allows user specification of phases and returns the travel times for all specified phases at a particular epicentral distance, for a given source depth.

The travel time information can also be accessed in graphical form (Postscript output suitable for Laserwriter II) using the zstp command which allows windowing in range and time. A X-window version (zstx) is under development.

The interface to the tau-spline tables is readily adapted to other computational procedures: Printed travel time tables can be generated in a two stage process:
i) Set up a summary file of travel timesfor many different source depths and distances using the routine
ttable
which allows interactive specification of source depths and distances, and includes all available phases.
ii) Run the table sort routine
wtac
which allows the interrogation of the summary file produced by ttable.
wtac prompts for a phase code and the number of characters to match and also the range of epicentral distances required. Output of travel time tables is to a specified file in tbl format. This tbl file can then be printed using ptroff facilities.

Other facilities (including information on take-off angles for source mechanism studies) are under development.

ENVIRONMENT

GTT91
    Home directory for sources of gtt91 routines access required for constructing modified travel time tables

SEE ALSO
ttimes91, shake91, zstp91, zstx91, syax91

AUTHORS
R. Buland, National Earthquake Information Centre, U.S. Geological Survey Golden, Colorado
TTIMES91

B.L.N. Kennett, Research School of Earth Sciences, Australian National University Canberra, Australia ------- ttimes91.1 -------

NAME:
ttimes91 - travel time table access using tau-splines

SYNOPSIS
ttimes91

DESCRIPTION
ttimes91 is a simple user interface to access the travel times for a wide variety of seismic phases at a given distance for specified source depth, with user control over the selection of phases.

ttimes91 is set up to automatically access the tau-spline tables for the 1991 IASPEI Seismological Tables based on the velocity model iasp91 (direct access files - iasp91.hed, iasp91.tbl). Other sets of tables can be accessed by invoking ttimes91 with an argument e.g.
ttimes91 iasp89
for tables (iasp89.hed, iasp89.tbl).

  Phase specification
The phase specification scheme is briefly described when ttimes91 is run. Initially the specification procedure is set up in query mode and responses need to be made at the star prompt (*), a null response terminates the specification. The selection of phases can be done either by giving a sequence of generic phase names or by specifying keywords. The available keywords are:
P      gives P-up, P, Pdiff, PKP and PKiKP
P+     gives P-up, P, Pdiff, PKP, PKiKP, PcP, pP, pPdiff, pPKP,
             pPKiKP, sP, sPdiff, sPKP, sPKiKP
S      gives S-up, S, Sdiff, SKS
S+     gives S-up, S, Sdiff, SKS, sS, SSdiff, sSKS,
             pS, pSdiff, pSKS
basic  gives P+, S+ and ScP, SKP, PKKP, SKKP, PP and PKPPKP
all    gives all available phases

  Depth specification
Once the choice of phase branches has been made the depth needs to be specified and the specified tau-splines appropriate for that depth are then formed.

  Distance specification
The user is prompted for epicentral distance (delta) and the travel time, slowness, curvature and depth derivative are displayed for each phase.

A new depth can be chosen by setting the distance negative, and the procedure terminated but setting the depth negative as well.

SEE ALSO
gtt91

AUTHORS
R. Buland, National Earthquake Information Centre, U.S. Geological Survey Golden, Colorado
ZSTP91

B.L.N. Kennett, Research School of Earth Sciences, Australian National University Canberra, Australia -------- zstp91.1 --------

NAME:
zstp91 - graphical interface to travel time tables using tau-splines

SYNOPSIS
zstp91 < zst.cmd

DESCRIPTION
zstp91 is a simple user interface to access the travel times for a wide variety of seismic phases and display them in a selected time and distance window.
User control is provided over the selection of phases.

  Running zstp91
zstp91 is run from a command file specifying the parameters for the phase control as well as the features of the distance-time window and frame. The run sequence is
  zstp91 < zst.cmd
where zst.cmd is a command file. For example to produce plots for all available phases over the span from 0 to 180 degrees for travel times up to 30 minutes, and a source depth of 200km.
     iasp91                 Model file
	200.	           <tt> depth
     1.  180.              <tt> delta min,max
        2                  <tt> pen colour
     0.                    <tt> reduction slowness
     FR                    Frame: FR-full frame, NL-no labels
     5.0                   <fr> x-orig
     2.0                   <fr> y-orig
     3                     <fr> font choice
         0.00   180.00     <fr> Dmin, Dmax
        15.00              <fr> length of D-axis
         0.00    40.00     <fr> Trmin,Trmax
        25.00              <fr> length of T-axis
        20.00   10.000     <fr> Large Tic spacing D,T
         5.00    1.000     <fr> Small Tic spacing D,T
         0       0         <fr> # of dec. in label D,T
        0.4300   0.47500   <fr> character size text,title
     Delta  deg                                          X-txt
     Time  min                                           Y-txt
     iasp91   200 km source                              Title

  Phase specification in zstp91:
Groups of seismic phases can be selected via the keywords used for ttimes91 The available keywords are:
P      gives P-up, P, Pdiff, PKP and PKiKP
P+     gives P-up, P, Pdiff, PKP, PKiKP, PcP, pP, pPdiff, pPKP,
             pPKiKP, sP, sPdiff, sPKP, sPKiKP
S      gives S-up, S, Sdiff, SKS
S+     gives S-up, S, Sdiff, SKS, sS, SSdiff, sSKS,
             pS, pSdiff, pSKS
basic  gives P+, S+ and ScP, SKP, PKKP, SKKP, PP and PKPPKP
all    gives all available phases

SEE ALSO
gtt91

AUTHORS
B.L.N. Kennett, Research School of Earth Sciences, Australian National University Canberra, Australia
using the travel time routines developed by:
R. Buland, National Earthquake Information Centre, U.S. Geological Survey Golden, Colorado