GTL Model Details
Details about adding GTL to seismic velocity models vary significantly depending on the velocity models being used.
The CVM-S4 model provides a rule-based GTL for regions in Los Angeles Basin, and in the Salton Sea region of southern California that was derived from various data sources including borehole and oil well-logs. When you query cvm-s4, the GTL information is added to the returned data by the underlying model. It provides Vs values below 200m/s in some regions. There is no way to remove the GTL without modifying the underlying CVM-S4 software.
CVM-H model can deliver a GTL. The GTL is controlled by the USE_GTL flag in the conf/ucvm.conf file. Set this flag to true, and the model will return material properties in the top 350m based on the Ely-Jordan method.
CVM-S4.26 model can deliver a GTL. The GTL is controlled by a flag in the model/cvms5/data/config file. By default, this flag is set to off, in which case the lowest Vs values the model will return are about 850m/s.
Users can edit this flag, set it to gtl=on, and the model will return lower velocities based on the Ely-Jordan method.
When the model returns low Vs values, the combined_data columns of ucvm_query are no different from the model data columns. This is true for both the CVM-S4.26 and CVM-H models. If the user configures these models to return a GTL, UCVM treats the GTL values as native model values, and the model columns, and combined_data columns are identical.
However, when the user specifies that UCVM should add a GTL, the native model values are returned in the model_values colums, and the combined_model plus GTL values are returned in the combined_data columns.
The GTL works if you explicitly specify where the GTL starts and ends (which for all practical purposes is 0m depth start and 350m depth end for Ely). You have to specify both the GTL and the interpolation scheme, which for the Ely GTL is “ely”.
Therefore, the command to query the 1d model with the Ely GTL using the Ely interpolation function from 0m to 350m depth is:
