RELAX: Time-dependent stress-driven viscoelastic relaxation and afterslip

RELAX: Time-dependent stress-driven viscoelastic relaxation and afterslip

RELAX: its' 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). 

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. 

How to get the software?

The latest version of the RELAX, including the source code, run examples, and binaries for various platforms, is available at the CIG repository

You can get a local copy of the code with the history of changes using the following Mercurial command:

hg clone relax 

Don't hesitate to contact the author if you familiarized yourself with the documentation but still need help installing or using the software. 

Example: Nonlinear postseismic viscoelastic relaxation

The following simulation corresponds to the postseismic relaxation of a nonlinear viscoelastic mantle below a vertical strike slip fault. The computation results from the input script provided as an example in the installation package. The arrows correspond to the instantaneous velocity. The central patch indicates where coseismic slip occurred on the fault before the relaxation. The colors that appear in the middle of the movie are the patterns of vertical velocity at the surface of the lithosphere.