AUTHOR

DESCRIPTION

Unicycle stands for Unified Cycle of Earthquakes. It computes fault slip and distributed strain evolution during the seismic cycle using the integral method. The approach combines surface elements and volume elements to incorporate the effect of localized and distributed deformation. In the case of brittle deformation, the method simplifies to the boundary integral method. Slip evolution is controlled by a rate- and state-dependent friction law within the radiation damping approximation. Viscoelastic flow is controlled by a nonlinear rheology for plastic flow that include transient creep and steady-state creep. The coupling between localized and distributed deformation is based on Green’s functions for the deformation induced by uniform plastic strain in volume elements and uniform slip in surface elements. Distributed deformation is captured by cuboid and tetrahedron volume elements.

APPLICATIONS

The method targets the simulation of earthquake ruptures, afterslip, slow-slip events, and viscoelastic relaxation during the seismic cycle to model geodetic data and explore the mechanics of the lithosphere-asthenosphere system. The code for numerical simulations of seismic cycles is written in Fortran90 with MPI parallelism.

The codes are derived in the two-dimensional anti-plane and in-plane strain approximation with and without viscoelastic effects:

unicycle-0d-ratestate computes simulations of seismic cycles for a spring-slider assembly for educational purposes.
unicycle-ap-ratestate computes simulations of seismic cycles on semi-infinite faults within the anti-plane strain approximation.
unicycle-ap-ratestate-serial serial implementation (no parallelism) of unicycle-ap-ratestate for educational purposes.
unicycle-ap-viscouscycles computes simulations of seismic cycles on semi-infinite faults in a viscoelastic half-space using rectangle volumes.
unicycle-ps-ratestate computes simulations of seismic cycles in a brittle elastic half-space within the two-dimensional in-plane strain approximation.
unicycle-ps-viscouscycles computes simulations of seismic cycles in a viscoelastic half-space within the in-plane strain approximation.
unicycle-2d-ratestate computes simulations of seismic cycles in a two-dimensional half-space allowing anti-plane and plane-strain displacements with strike-slip and dip-fault slip.

Simulations of seismic cycles with finite faults in a three-dimensional half-space are possible with

unicycle-3d-ratestate computes simulations of seismic cycles on finite faults in an elastic half-space.
unicycle-3d-viscouscycles computes simulations of seismic cycles on finite faults in a viscoelastic half-space.

SOURCE

The code is organized in the following directory tree structure

    README
+---tex/
+---fortran/
    +---0d/
        +---src/
        +---build/
        +---examples/
    +---2d/
        +---antiplane-serial/
            |   makefile
            +---src/
            +---build/
            +---examples/
               +---tutorials/
        +---antiplane/
            |   makefile
            +---src/
            +---build/
            +---examples/
               +---tutorials/
        +---planestrain/
            |   makefile
            +---src/
            +---build/
            +---examples/
                +---tutorials/
    +---2.5d/
        +---src/
        +---build/
        +---examples/
    +---3d/
        makefile
        +---src/
        +---build/
        +---examples/
            +---tutorials/
    +---docs/
    +---man/
+---matlab/
    +---docs
    +---+unicycle/
    +---examples/

The src directories contain the Fortran code. Running the corresponding makefile places the binaries in the build directory. Example input files are in the tutorials directories. All other examples are for development, test, and research purposes and are not guaranteed to work well. Matlab functions are available in the matlab folder for testing, verification, and development purposes. Codes for educational purposes can be found in fortran/0d, fortran/2d/antiplane-serial, and matlab/docs.

The code documentation is available as a manpage when PATH_TO_UNICYCLE/fortran/man is in the MANPATH environment variable. Load it with

man unicycle-ap-ratestate
man unicycle-ap-viscouscycles
man unicycle-ps-ratestate
man unicycle-ps-viscouscycles
man unicycle-3d-ratestate
man unicycle-3d-viscouscycles

A markdown documentation is in the docs directory. Code documentation is available with doxygen and the HTML version can be generated with

doxygen .doxygen-ratestate
doxygen .doxygen-viscouscycles

Description of the modeling assumptions can be found by compiling the documentation/unicycle.tex into a .pdf file.

SYSTEM REQUIREMENTS

The compilation of Fortran codes requires

fortran compiler (gcc-9 and above)
netcdf and netcdff libraries
lapack and blas libraries
openmpi library

Example compilation and linking can be found in the makefiles. Barebone versions of the codes can be compiled without netcdf support for expediency.

COMMUNITY GUIDELINES

Contribute to the software by reporting issues, requesting new features, or suggesting improvements at https://bitbucket.org/sbarbot/unicycle/issues. For support and third parties wishing to contribute to software development, contact Sylvain Barbot at sbarbot@usc.edu.

VISUALIZATION

The simulations produce output files that can be visualized in Paraview (https://www.paraview.org/) or the Generic Mapping Tools (http://gmt.soest.hawaii.edu/doc/5.3.3/project.html). Simple ASCII files can be visualized efficiently with gnuplot (http://www.gnuplot.info/).

REFERENCES

Wang, B. and Barbot, S., Pulse-like ruptures, seismic swarms, and tremorgenic slow-slip events with thermally activated friction. Earth and Planetary Science Letters, https://dx.doi.org/10.1016/j.epsl.2022.117983, 2023.

Barbot, S., Frictional and structural controls of seismic super-cycles at the Japan trench. Earth, Planets and Space, https://doi.org/10.1186/s40623-020-01185-3, 2020.

Shi, Q., Barbot, S., Wei, S., Tapponnier, P., Matsuzawa, T. and Shibazaki, B., Structural control and system-level behavior of the seismic cycle at the Nankai Trough. Earth, Planets and Space, https://doi.org/10.1186/s40623-020-1145-0, 2020.

Barbot S., Slow-slip, slow earthquakes, period-two cycles, full and partial ruptures, and deterministic chaos in a single asperity fault. Tectonophysics, https://doi.org/10.1016/j.tecto.2019.228171, 2019.

Barbot S., Modulation of fault strength during the seismic cycle by grain-size evolution around contact junctions. Tectonophysics, https://doi.org/10.1016/j.tecto.2019.05.004, 2019.

Barbot S., Asthenosphere flow modulated by megathrust earthquake cycles, Geophys. Res. Lett., https://doi.org/10.1029/2018GL078197, 2018.

Barbot S., Deformation of a half-space from anelastic strain confined in a tetrahedral volume, Bull. Seism. Soc. Am., http://dx.doi.org/10.1785/0120180058, 2018.

Barbot S., J. D. P. Moore and V. Lambert, Displacement and stress associated with distributed anelastic deformation in a half space, Bull. Seism. Soc. Am., 107(2), http://dx.doi.org/10.1785/0120160237, 2017.

Lambert V. and S. Barbot, Contribution of viscoelastic flow in earthquake cycles within the lithosphere-asthenosphere system, Geophys. Res. Lett., https://doi.org/10.1002/2016GL070345, 2016.

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BENCHMARKS

Erickson, B.A., Jiang, J., Lambert, V., Barbot, S.D., Abdelmeguid, M., Almquist, M., Ampuero, J.P., Ando, R., Cattania, C., Chen, A. and Dal Zilio, L., Incorporating full elastodynamic effects and dipping fault geometries in community code verification exercises for simulations of earthquake sequences and aseismic slip (SEAS). Bulletin of the Seismological Society of America, https://dx.doi.org/10.1785/0120220066, 2023.

Jiang J., Erickson B.A., Lambert V.R., Ampuero J.P., Ando R., Barbot S.D., Cattania C., Zilio L.D., Duan B., Dunham E.M. and Gabriel A.A., “Community‐driven code comparisons for three‐dimensional dynamic modeling of sequences of earthquakes and aseismic slip”. J. Geophys. Res., https://dx.doi.org/10.1029/2021JB023519, 2022.

Erickson, B.A., Jiang, J., Barall, M., Lapusta, N., Dunham, E.M., Harris, R., Abrahams, L.S., Allison, K.L., Ampuero, J.P., Barbot, S. and Cattania, C., The community code verification exercise for simulating sequences of earthquakes and aseismic slip (SEAS). Seismological Research Letters, https://dx.doi.org/10.1785/0220190248, 2020.

COPYRIGHT

UNICYCLE is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

UNICYCLE is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with UNICYCLE. If not, see <http://www.gnu.org/licenses/\>.