FMST Overview

FMST is an iterative non-linear traveltime tomography code in 2-D spherical shell coordinates (constant radius, variable latitude and longitude). One possible application of the code is surface wave tomography using, for example, traveltimes of high frequency interstation rayleigh waveforms extracted from the ambient seismic noise field. The forward problem is solved using a grid based eikonal solver known as the fast marching method (FMM), and the inverse problem is solved using a subspace inversion method. Note that the code is not suitable for models which require the Earth's poles or its periodicity to be taken into account.

Figure 1. Example showing distortion of seismic wavefronts (computed with FMM) in the presence of significant variations in wavespeed. The underlying image was obtained by applying the above surface wave tomography code to Rayleigh wave group traveltimes extracted from long term cross-correlations of the ambient seismic noisefield (results courtesy of Erdinc Saygin).

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

instructions.pdf (2.8 MB)

Code

FMST is written in Fortran 90, and uses shell scripts to iteratively apply the various pieces of code in order to solve the complete non-linear tomography problem. The code has been tested on a number of platforms, and should work on most computers that have access 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 fmst_v1.1.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.