The VELMOD-2 seismic velocity model of the Netherlands on- and offshore
TNO
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Advisory Group for the Ministry of Economic Affairs
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TNO Built Environment and Geosciences Geological Survey of the Netherlands PO box 80015
3508 TA Utrecht The Netherlands
VELMOD-2 is a layer cake model, with seismic velocities modeled per lithostratigraphic layer (Figure 1).
Figure 1. Lithostratigraphic layers of VELMOD-2
Main data sources for the model are lithostratigraphic depth data in DINO, the National Geo-data Centre of the Netherlands, and sonic logs of some 1300 boreholes (Figure 2).
Figure 3 Linear least squares relations between Vintand zmidfor the main compacting layers of VELMOD-2
The position dependent parameter V0was determined at borehole locations and then kriged on a grid with cells of 1 km x 1 km. Determination of V0at borehole locations was effected by calibrating model traveltime through a layer to the traveltime according to the sonic data.
The velocity model for the non-compacting layer of the Zechstein Group consists of a grid of interval velocities, based on sonic data and seismic traveltime data.
Figure 5 shows the V0-distribution for the layer of the Upper and Lower Germanic Trias groups, whereas the kriging standard deviation of this distribution is shown in Figure 6.
51°N 52°N 53°N 54°N 55°N
7°E 6°E 5°E 4°E 3°E
Region 1a Region 1b
Region 1cPresence of only Late Jurassic deposits
Region 2 Platform or halfgraben
0 50 km
Scale 1 : 2 500 000 Projection UTM31 Ellipsoid ED50
Region 2 High
Broad Fourteens Basin
Central Netherlands Basin Dutch
Central Graben
Lower Saxony Basin Step
Graben
Terschelling Basin
Vlieland Basin
Roer Valley Graben West
Netherlands Basin
Jurassic basins
Present-day absence of Jurassic deposits
S R
Q P
O
M N L K J
H G F E
D B A
Figure 4. Regional subdivision of K for layers of Jurassic age
Figure 5. V0-distribution (VELMOD-2) for the layer of the Upper and Lower Germanic Trias groups
Figure 6 Kriging standard deviation of V0for the layer of the Upper and Lower Germanic Trias groups
Figure 2. Borehole locations with sonic data available to VELMOD-2
K-values are regionally constant for the layers of Jurassic age (Figure 4), or constant for the entire Dutch on- and offshore.
For information on Exploration and Production issues and E&P data see the Netherlands Oil and Gas Portal www.nlog.nl
All layers, except that of the Zechstein Group, are compacting layers. Their model velocities are assumed to increase linearly with depth:
V(x,y) = V0(x,y) + K•z
The model parameters K were derived from linear least squares relations between interval velocity Vint
and mid-depth zmidper layer (Figure 3).
