Name of program: FLTSLP

Type of program (eg quake model, mesh generator, strain calculator, visualizer, etc): INVERTS GROUPS OF FOCAL MECHANISM SOLUTIONS FOR ORIENTATION AND RELATIVE MAGNITUDES OF PRINCIPAL STRAIN RATES AND FOR RELATIVE MICROPOLAR VORTICITY

Author: R.J. TWISS & L.D. GUENTHER -- Robert J. Twiss <twiss@geology.ucdavis.edu>

Institution: GEOLOGY DEPARTMENT, UNIV. OF CALIF. AT DAVIS

Program's heritage (ie name and author of predecessor code if any):

Actively being further developed (y/n): Y

Language: FORTRAN

2d (y/n):

3d (y/n):

Elastic full space (y/n):

Elastic half space (y/n):

Layered elastic (y/n):

Viscoelastic half space (y/n):

Layered viscoelastic (y/n):

Maximum number of faults:

Forward model (y/n):

Inversion capability (y/n):

Type of inversion:

Finite element ability (y/n):

Boundary constraints:

Automatic mesh generation:

Includes self gravitation (y/n):

Quasi-static failure criteria (y/n):

User defined failure criteria (y/n):

Hardwired failure criteria (eg Coulomb):

Dynamic solution (y/n):

Includes waves (y/n):

Highest resolved frequency:

Includes inertia (y/n):

Are there accompanying utilities (y/n):

Is it one main program or several programs that communicate via scripts, files, and pipes? ONE MAIN PROGRAM

If it is several programs, please give a 1 line description of the major players.

Input format description: Pre-processing program reads Hypo71 format seismic data. FLTSLP reads a variety of data formats for seismic P and T axes and shear-plane/slickenline data.

Output format description:

Is this code available to interested researchers (y/n):

Executable available (y/n): Y (to be available shortly.)

Type of machine: DEC Alpha, SUN SPARC

Source available (y/n): N

Please describe what you consider to be the important features of this code in a paragraph or two.

The program inverts groups of focal mechanism solutions or shear-plane/slickenline data for the orientation and relative magnitudes of the principal strain rate axes and for the magnitude of the relative micropolar vorticity. The inversion is based on micropolar kinematic theory (see references below).

We have used the inversions to map the geometry and distribution of principal strain rate axes with depth and horizontal location within aftershock sequences of major earthquakes to define the characteristics of post-main-shock deformation, as well as within regions of distributed seismicity and areas where abundant shear-plane/slickenline data are available to define the geometry and distribution of tectonic deformation.

The program uses a downhill simplex method with random restart to find the best-fit model to the data, and provides a capability for bootstrap statistical evaluation of the resulting model parameters.

References describing the algorithms or results from use:

THEORY:

Twiss, R. J., G.M. Protzman, S.D. Hurst; 1991. Theory of slickenline patterns based on the velocity gradient tensor and microrotation; Tectonophysics, 186, 215-239.

Twiss, R.J., B.J. Souter, and J. R. Unruh; 1993. The effect of block rotations on the global seismic moment tensor and the patterns of seismic P and T axes; Jour. Geophys. Res. 98(B1): 645-674.

Twiss, R.J. and J.R. Unruh. 1998. Analysis of Fault-Slip Inversions: Do They Constrain Stress or Strain Rate? Jour. Geophys. Res., 103(B6): 12205-12222.

APPLICATIONS:

Unruh, J.R., R.J. Twiss, and E. Hauksson. 1996. Seismogenic deformation field in the Mojave block and implications for tectonics of the eastern California shear zone. Jour. Geophys. Res., 101(B4): 8335-8361.

Unruh, J.R., R.J. Twiss, and E. Hauksson. 1997. Kinematics of postseismic relaxation from aftershock focal mechanisms of the 1994 Northridge, California, earthquake. Jour Geophys. Res. 102(B11):24,589 - 24,603.