Velocity Model Database Extension Tables

Genloc uses two extension tables of the css3.0 schema to define  velocity models called mod1d and ttcalc .  The contents of each of these tables is described in detail here.

ttcalc table

Each travel time calculator that expect to access the velocity model database is expected to register it's existence in this table.  Consequently this table is normally only edited by a developer who wants to add a new travel time calculator to the generic tt interface.  Here is the current table viewed with dbe:

The algorithm name is used to reference a travel time method by name.  The libname attribute defines the name of the shared library used by the generic tt interface.    The actual name is generated by prepending a "lib" prefix to the libname attribute.  For example, for libname=tttaup the shared object tt actually search for will be called

ttentry and uentry give the actual entry point names for the travel time and slowness vector calculators in this shared object.

mod1d table

The mod1d table is designed to hold data that defines any earth model that can be specified as a function of depth alone.  Here  is a dbe view of a sample mod1d table.

Models are given a name defined by the modname attribute that should be used by travel time calculators to match the model name input to the generic travel time calculator interface (see tt(3)).  paramname refers to the physical property being defined for this model name and units give the physical units of that quantity.  The actual values assigned to the model at a given depth are determined from the depth, paramval, and grad attributes.  The depth attribute defines the depth (in km) in the earth at which the property paramname takes on the value paramval.  The grad attribute defines the gradient in units/km of this property below the grid point depth.  This can be used to define models made up of piecewise linear segments or with constant velocity layers by setting grad=0 everywhere.

regmodel and regions tables

These two tables are interlinked and between themselves and with the mod1d calculator.  They are used by the ttregions calculator to allow the use of different models and different travel time calculators in different locations within a network.  Here are examples of both viewd by dbe:

The regmodel table defines which travel time calculator and velocity model are to be used for a given region name (attribute regname).  The regions table defines polygonal regions as a series of latitude-longitude pairs that define polygonal regions (in clockwise order).