## FMTT Overview

Teleseismic tomography uses relative arrival time residuals from distant earthquakes to image wavespeed variations in the upper mantle beneath a seismic array. The code distributed here is unique in that it uses the Fast Marching Method (FMM) to compute traveltimes and paths through the 3-D model. FMM is a grid based eikonal solver that combines computational speed and robustness. The inverse problem is solved using a subspace inversion method which is also fast and robust. The forward and inverse steps can be used iteratively in order to address the non-linear nature of the tomographic inverse problem. Spherical coordinates are used to account for the curvature of the Earth. Like most teleseismic tomography codes, traveltimes from the distant source to the edge of the 3-D model are computed using a global reference model. In our case, we use ak135, although other models could be substituted.

A detailed instruction manual is supplied with the distribution, and can also be downloaded here in PDF format:

instructions.pdf (2.8 MB)

### Code

The teleseismic tomography code is written mainly in Fortran 90,
although some Fortran 77 code is used for computing ak135 traveltimes. The
code has been tested on a number of platforms, and should work on most
computers that have acces to compilers distributed by the likes of GNU,
NAG, Portland, Pathscale, Intel, Fujitsu and Sun. The complete source code,
a detailed manual and example input files, can be downloaded here. Enquires should be directed to the author Nick Rawlinson. You will need to register with iEarth prior to download.

To unpack the contents of this file, type something like:

`gunzip -c fmtt_v1.0.tar.gz | tar xvof -`

in an empty directory. A number of new sub-directories will be created.
Instructions on how to use the code can be found in the sub-directory
`docs`.

### Papers

Rawlinson, N. and Sambridge M., 2005. "The fast marching method: An
effective tool for tomographic imaging and tracking multiple phases in
complex layered media", *Explor. Geophys.*, **36**,
341-350.