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By Sylvain Barbot (primary-developer)

University of Southern California

Published on


Relax implements a semi-analytic Fourier-domain solver and equivalent body forces to compute quasi-static relaxation of stress perturbation.

It is not an acronym, it's a motto!

The open-source program Relax evaluates the displacement and stress in a half space with gravity due to dislocations, Mogi sources, and surface tractions; and the nonlinear time-dependent deformation that follows due to power-law rheology materials in the bulk and/or rate-strengthening friction faults. The numerical method is based on a Fourier-domain elastic Green's function (Barbot & Fialko, 2010a2010b) and an equivalent body-force representation of co-seismic and post-seismic deformation processes (Barbot et al., 2009b). Application of the method for the 2004 Mw 6 Parkfield earthquake can be found in the work of Barbot et al. (2009b) and Bruhat et al. (2011). A coupled model of afterslip and laterally-heterogeneous viscoelastic flow following the 1999 Mw 7.6 Chi-Chi earthquake using relax is described by Rousset et al. (2012).

The possible applications for the earthquake-cycle modeling include: i) co-seismic displacement and Coulomb stress calculation, ii) quasi-static stress transfer between earthquakes due to a postseismic transient, iii) modeling of postseismic transients including nonlinear rheologies and multiple mechanisms, iv) cycle of multiple earthquakes and spin-up models, v) loading cycle of lakes or the monsoon. The distribution includes various examples for published coseismic slip distributions.

Release Notes

Relax-1_0_7.tgz [2014-09-30] 

Source code, documentation and examples.

Binaries are available. Binaries are suitable for use on single core/processor computers as well as multi-core or multi-processor computers. They can only be used on a single compute node of a cluster.


We are thankful for the support of Yuri Fialko during the early development of the methodology at the Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography. We acknowledge the contribution of Walter Landry, who ensured the portability of the code and streamlined its installation process. We appreciate the efforts of Lucile Bruhat, Yaru Hsu, Mikhail Kogan, Zhen Liu and Baptiste Rousset for testing an earlier version of the code. We are grateful to the work of Sagar Masuti, at the Earth Observatory of Singapore, who ported the code to CUDA. The support of the Computational Infrastructure for Geodynamics is greatly appreciated. Feedback from many users around the world contributed to improving the quality of the software and documentation.