In model 1, the overburden contains two flat layers with constant elastic properties on each layer, whereas model 2 includes a zone of complex velocity anomalies in the overburden. The rock properties for the model were taken from real well logs of a North Sea field. Typical values for different lithologies at this field are listed in Table 1.
|1|c|Lithology||1|c|Vp (km/s)||1|c|Vs (km/s)||1|c| (g/cm3)|
|Cemented brine sands||3.1||1.55||2.15|
|Uncemented brine sands||2.6||1.3||2.1|
|Cemented oil sands||2.9||1.6||2.05|
|Uncemented oil sands||2.35||1.33||2|
|Volcanic ash (tuff)||2.75||1.23||2.2|
Table 1. Typical rock properties for different lithologies at the North Sea.
Average values for overburden properties in the field are Vp=2.2 km/s, Vs=0.75 km/s, (g/cm3).
In model 1, overburden properties above the flat interface were taken to be the average values indicated above; overburden properties below the interface were the average values with a increase. For model 2, we introduced lateral velocity anomalies by including a smoothed sinusoidal interface between the two layers.