Introduction to TISC

Visit also the website https://sites.google.com/site/daniggcc/software/tisc/

TISC is a program simulating 4 processes related to orogenesis and sedimentary basin formation:

1. crustal tectonic deformation (approached by vertical shear, i.e., preserving the vertical thickness of moving tectonic bodies),

2. lithospheric vertical movements (assuming the lithosphere behaves as an elastic or viscoelastic flexural plate),

3. climate (assuming a certain set of climatic parameters such as precipitation, evaporation or humidity), and

4. erosion/sediment transport carried out by surface processes including the river network (transport capacity proportional to water discharge and slope).

The most complex among these is the surface transport, which incorporates the calculation of the river network, a simplified hydrological balance, and the extension of possible lakes. TISC is a pseudo-3D (planform) version of the code tAo, which works in cross-section.

Look at the bibliography (in particular the papers by Garcia-Castellanos et al. [2002] [2003]) referred in the documentation attached to learn more about the fundamentals of the calculations.

THIS PROGRAM IS PARTICULARLY DESIGNED TO:

.To calculate lithospheric flexural isostasy. It can be used externally (from a unix script) as a flexure calculator, as part of a shell script (see option -Q).

.To calculate erosion, fluvial transport, and sedimentation. .To parameterise drainage changes.

.To model foreland basin formation and large-scale sedimentary infill geometries.

CONCEPTUAL MODEL:

The conceptual model implicit in TISC assumes that a thin, flat lithospheric plate floating on the asthenosphere supports isostatically the mass movements at the surface. These are related to erosion/deposition and tectonic movements. Erosion/deposition can be calculated as related to diffusion (hill-slope), river transport and landsliding. Tectonic deformation is calculated by defining faults and shortening/thinning velocities and assuming a vertical shear model.

*Tectonics:

Vertical shear approach for the deformation of user-defined moving blocks (see *.UNIT input files). Sediment is automatically deformed in the same way, assuming the sediment layer deforms at the same speed as the closer lower user-defined body and propagating the deformation forward with an angle of 30 degrees.

*Isostasy:

The flexural deflection of the lithosphere allows for lateral variations of elastic thickness using the input file '.EET' and accounts for a horizontal force P (defined in the '.PRM' file. To rotate the force tensor P an angle beta to obtain P': Px' = Pxc2 + Pys2 + Pxy * 2sc; Py' = Pxs2 + Pyc2 - Pxy * 2sc; Pxy'= (Py-Px)sc + Pxy(c2-s2); Where c2 = cos(beta)cos(beta); s2 = sin(beta)sin(beta); sc = sin(beta)cos(beta); Use this command #nawk 'BEGIN{beta=-22.5/1803.1415927; Px=0;Py=25e12;Pxy=0; c2 = cos(beta)cos(beta); s2 = sin(beta)sin(beta); sc = sin(beta)cos(beta); print "Px= " Pxc2 + Pys2 + Pxy * 2sc, "Py= " Pxs2 + Pyc2 - Pxy * 2*sc, "Pxy= " (Py-Px)sc + Pxy(c2-s2);}'

*Surface processes:

See different available models in the template.PRM file. Main surface processes modify the topography in this model: 1.- Diffusive (flux proportional to slope) for short range scale. 2.- Fluvial (sediment carrying capacity proportional to slope and water discharge) for large scale erosion in channels. Sea&lake sedimentation are included. 3.- Landsliding: imposing a maximum slope to the topography. Fluvial transport can be calcualted following a number of authors.
Use this command to convert from shear stress erodability (model 6) to K in model 3 awk 'BEGIN{print 1.3e-4exp(1.5log(101000))exp(31.5/5log(.05/1.1))}'

*Climate:

Climate can be treated via preimposed rates of precipitation/evaporation (dependent on elevation, latitude, longitude) or via an orographic precipitation model (check the 'hydro_model' parameter in template.PRM).