Demo Files

Oasis montaj provides two demo models with this distribution: "Salt" and "Death Valley". These models are installed as sub folders under "C:\Users\Public\Public Documents\Geosoft\Desktop Applications\data\gmsys-3d". We recommend that you copy this data into separate “working project" folders prior to opening and manipulating the models. Thus, you will maintain the clean original copy.

These demo model files are provided when "Geosoft sample data" is selected during the software installation process. To add this data later, from Start, select Control Panel and then go to "Uninstall a program". Select (highlight) "Geosoft Desktop Applications", right click and select Change. In the Change Installation dialog, select Add or Remove Applications and then select "Geosoft sample data". Click Add or Remove.

Salt

"Salt" is a demonstration model that represents a simple offshore salt dome. The model consists of six grids. The files are installed in the "salt_model" subdirectory.

Grid Name Contents
sealevel.grd flat surface at elevation=0
bathy.grd bathymetric surface
top_salt.grd top of salt body
bottom_salt.grd base of salt body
basement.grd basement surface
salt_obsgrav.grd observed gravity

Death Valley

"Death Valley" covers a small area in southern Nevada. The data were provided by the USGS and were taken from OFR-00-189. Just open the “dv_demo” workspace to see the 3D model. The grids in the initial model are:

Grid Name Contents
topo_m_1.grd Topography
c1_m_1.grd 1st subsurface horizon
c2_m_1.grd 2nd subsurface horizon
c3_m_1.grd 3rd subsurface horizon
Basement_m_1.grd Observed Bouguer gravity
dv_calc1.grd Calculated model response
dv_err1.grd Calculated error

The model used a Bouguer density of 2.67, ZREF= 2315 meters, and half-space bottom = -13,000 meters. The layer densities from top to bottom are 2.00, 2.10, 2.30, 2.42, and 2.65 gm/cc.

After calculating the response of the model, thereby refreshing dv_calc1.grd, we performed a structural inversion on the basement horizon, using a “Regional Offset” of 0.0 mGals. (This assumes that you used a “DC-shift” of 18 in the first screen of the “Model Definition”.) Adjusting the Regional Offset moves the average level of the layer being inverted up or down. The resulting basement grid is in Basement_inv_1.grd, the resulting calculated response of the model is in dv_calc2.grd, and the resulting error is in dv_err2.grd.

The inversion modifies the grid in the model and does a simple one-level backup, which can be undone with the "undo" command. Back up grids manually before running multiple inversions if you want to retain the original horizon.