Axitra Force & Moment versions
Should you encounter any problem using the program, please feel free to contact me at: Olivier Coutant: olivier.coutant@univ-grenoble-alpes.fr
Thank you to cite the following paper if you publish results obtained with axitra: F. Cotton and Coutant O., 1997, Dynamic stress variations due to shear faults in a plane-layered medium, GEOPHYSICAL JOURNAL INTERNATIONAL,Vol 128, 676-688
DOI: 10.5281/zenodo.4603722
In the Makefile
- select the appropriate options for the compiler (FC) and its options (FFLAGS)
- the code uses openmp parallelization
- then make clean #clean the object, modules make axitra #compile the greeen's function program make convms #compile the convolution program make python #compile python3.7 wrappers
To run 4) edit the "
.data" and ".hist" files according to your needs is either 'axi' or 'axi_suffix' where suffix is an optional parameters passed as positional argument to the two programs 5) run the codes: ./axitra [suffix] ./convms [suffix] 6) the seismograms are written as sac filesTo run under python, see "example.py" or jupyter notebook "example.ipynb" examples under EXAMPLE directory
This "new" version includes the following changes
- a python interface and wrappers to the code
- all input/output files can be given a "suffix" in order to have several configurations in the same directory axitra and convms are then run with the suffix as argument
- the namelist is reduced to a few parameters, nr,ns and nc are dynamically counted
- The duration (tl) and periodicity (xl) can be automatically computed if needed when the values are set to (<=0) in the axi.data namelist
and previous changes
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porting to fortran95 allows for dynamic allocations
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openMP directives for use on shared memory multicore computer
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force sources and moment sources versions are now available in two separate programs (and directories) with almost the same functionnalities: multiple source; multiple receiver; same convolution process
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possibility to enter position in lat,lon coordinates when latlon variable is set to .true., the program will output coordinates in cartesian coordinates in .xyz files. The origin is arbibrary, these cartesian coordinates can then be used as input to the program after setting latlon variable to .false.
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possibility to enter an "axi.date" file that gives an origin date for synthetic when wrinting in sac format
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attenuation formulation follows Martin Galis iand Emmanuel Chaljub suggestion. 2 mechanisms Futterman and Kjartansson.
The reflectivity code consist of 2 executables: (1) axitra computes the Green's function in the frequency domain for
- 5 double couples + isotropic source, at each receiver and for each source (MOMENT VERSION)
- 3 unidirectionanal forces (FORCE VERSION)
(2) convms convolves these Green's function by the appropriate source time function's, and for the chosen mechanism. The output are the seismograms in the time domain in sac format.
In this last version, preprocessing has been removed. axitra now by default
- run in double precision
- uses geographical XYZ axes (No radial, tranverse,...)
- uses harwell routine to compute bessel functions
axitra is then ready to run. The different data files are: (1) input for axitra:
- "axi[.suffix].data" + file giving station coordinates + file giving sources coordinates (2) output from axitra:
- axi[.suffix].head (information about convergence)
- axi[.suffix].res (binary transfert function) (3) input for the convolution program convms
- axi[.suffix].hist
- nkmax= If you have chose to store the bessel functions (which do not depend upon the frequency), nkmax values will be stored for the first nkmax radial wavenumber, if the number of iteration is larger than nkmax, the bessel functions are recomputed each time for those nkmax+... iterations. This value depends on the available memory and the convergence rate. You can try to run the null frequency only to have a rough idea of how long it takes. Set nkmax to 3/2*number_of_iteration_for_freq=0 should be ok if you don't compute too high frequencies (the higher the frequency, the slower the convergence). (ps: You really save a lot of time by storing the bessel functions)
- nkmin= minimum number fo iteration for the wavenumber summation
The parameters defined in "axi.data" are: (1) in the namelist:
- nfreq=number of frequency to compute
- tl=time length of the seismogram (sec), if set to <=0, tl is computed by axitra to contain all arrivals
- aw=coefficient for frequency imaginary part, omega=(2pifreq, aw*pi/tl)
- xl=medium periodicity (m or km, be consistent with the other variables), if set to <=0, automatically computed
- ikmax=max number of iteration, generate an error message if overpassed
- latlon=coordinates given in (lat,lon) (.true.) or in m/km (.false.) when latlon is true, distance unit is set to meter (depth). velocities are in m/s and density in kg/m^3
- freesurface= free surface is set at Z=0 (.true.) or upper space is infinite (.false.)
- sourcefile=source description file
- statfile=receiver description file
(2) in free format and for each layer:
- thickness (or depth of the upper interface), vp, vs, rho, qp,qs Units are [m, m/s and Kg/m^3], or [km, km/s and Kg/km^3] If you specify the upper interface depth, it must be set to 0. for the free surface. !!!! rho unit must be consistent with the length unit (m or km) !!!!
in free format,
I) For the receivers: receiver_index,x,y,z or receiver_index,lat,lon,z
II) For the sources: source_index, x, y, z or source_index, lat, lon, z
III) For the file AXI.HIST
MOMENT VERSION: 2 possibilities depending on the data you chose to give: moment or displacement+width+length: source_index, moment, strike, dip, rake, 0., 0., t0 or source_index, disp , strike, dip, rake, width, length, t0
If you want a null contribution for a given source, just set the corresponding moment (resp disp) to zero
You can compute seismograms generated by an explosive source by setting a negative surface equal to -1 (either negative width or length). The explosion moment is then read as the given displacement ('disp' variable)
FORCE VERSION: source_index, fx_amplitude, fy_amplitude, fz_amplitude, total_amplitude, time_delay
The convention for the axis is: x=north, y=east, z=upward. !!!!!!!! Warling !!!!!!! This convention is different in the computation where the vertical axis is positive downward.
When given in geographical coordinates, axitra read x=latitude then y=longitude
-Since the programs uses an horizontal wavenumber decomposition, the only geometry not allowed is to put the receivers and the sources at the same depth. -The convergence rate depends in part on the depth difference between source and receiver, the closer they are, the longer the convergence is.
- In some (rare) cases, the program may generate an underflow error when computing the term "exp(-igamma(z-zref)) where z may be the receiver or source depth, zref the source or layer depth. This may occurs when you compute very high frequencies (KHz). A solution in that case is to incorporate a new artificial layer between z and zref to reduce the (z-zref) term.
- An artificial vertical plane wave may be (rarely) seen when the source is close to the free surface and when you look at regional distances. This wave is seen only on the terms involving the J0 bessel function. It decreases very quickly as a function of the source depth but has no geometrical spreading (it is a plane wave) and may be visible at the beginning of the seismogram. There is nothing yet to do to remove it completly. Using a recipy given by Bob Herrmann, the horizontal wavenumbers are given a small fractional part, this reduces greatly the effet of this spurious plane wave.
At this time and after several years, we do not know of any injuries due to the use of this program, anyway use it at your own risk...