- Request #146 (s. Zuzlewski):
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In Northern California, we have a plan to recompute depths for all the
quakes in our catalog using the tools that Fred Klein has programmed.
They will then be relative to the geoid. But, we also want to retain
the information about the original depth calculated relative to the
model. And, we want to define how the depths are defined (and include
information about the velocity models used to calculate the hypocenter).

For this purpose, we are proposing a change to the structure of the origin
table in AQMS.

1.- New field Origin.crust_type:
    Definition: The type of crust model used for travel time
        calculations: each type has its own geometry of
        velocity layers or gradients within layers, tied
        to the options of the location program.
    Datatype:    VARCHAR2(1)
    Constraints: crust_type IN ('H','T','E','L','V')
                 H - Homogeneous layers, all stations at top
                     (hypoinverse CRH model)
                 T - Travel time table with linear gradient, all
                     stations at top (hypoinverse CRT model)
                 E - Hypoellipse layer model, using station elevations
                     (hypoinverse CRE model)
                 L - Hypoellipse single gradient model, using station
                     elevations (CRL)
                 V - Hypoellipse single gradient over halfspace model,
                     using station elevations (CRV)

2.- New field Origin.crust_model:
    Definition: The code for the regional (geographic) crust model that
        is dominant in the travel time calculations. The crust
        model depends on the location of the earthquake origin
        and not on the recording station. The code is for the
        highest weighted model if more than one is used.
    Datatype:    VARCHAR2(3)
    Constraints: Any free-format string up to 3 characters

3.- New field Origin.depth_type:
    Definition: The earthquake depth is referred to some depth datum,
        and the choices are to the geoid (GD), or to a
        "floating" datum which is the top of the crust model
        (MD). For MD, all the recording stations are located at
        top of the model and their elevations are not used.
        Station corrections can incorporate the effects of
        elevation.
    Datatype:    VARCHAR2(2)
    Constraints: depth_type IN ('GD','MD')
                 GD - Geoid depth (Hypoinverse model types E, L or V
                      are always geoid depths)
                 MD - Model depth (model types T or H if uncorrected by
                      depth datum are always MD)

4.- New field Origin.depth_datum:
    Definition: The depth datum value is the model depth - (minus) the
        geoid depth. The depth datum value is comparable to the
        elevations above the geoid of nearby seismic stations
        assumed to be at the top of the model. For geoid depth
        crust models, the depth datum value is 0.
    Datatype:   NUMBER(7,3)

5.- Update existing field Origin.depth:
    Definition: The depth is distance in km of the earthquake source
        below the depth datum, which is either the geoid or the
        model surface. 

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==> Discussed.
All those parameters are on the hypoinvserse (v1.40) summary line.
PH, DN & SZ to discuss the request some more.
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