4.2 Dipping stratigraphy

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4.2 Dipping stratigraphy

In this model an East-West trending valley dissects a simple tilted stratigraphy, so that the outcrop pattern curves around the topography (the model geometry is also that of a dipping dyke). The results are compared for a barometric survey, where the survey locations are at a constant height above sea level (in this case 400 m above the top of the block), and a draped survey where the locations maintain a constant height above the local land surface (in this case 400 m above the land surface).

Click on the images to launch Noddy. A legend is provided at the end of this page.


	Block model showing topography dissecting a dipping three layer stratigraphy LOAD JPEG IMAGE

In order to use these history files you will also need to download the following file! topofile.top

	Barometric Survey	Draped Survey
Link
Gravity	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Gravity	In this image the distance to the top of the body controls the local strength of the anomaly, with the hill outcrops dominating the survey.	With a draped survey the anomaly strength actually peaks at the base of the valley.
Magnetics	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Magnetics	As with the gravity image, the magnetic survey mainly reflects the variable distance between the outcrop and sensor.	In this model the geometry of the body is more clearly defined, however there is a distinct asymmetry between North- and South-facing slopes, with the high susceptibility layer significantly weaker on the South-facing slope.
Magnetics	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Magnetics	As with the gravity image, the magnetic survey mainly reflects the variable distance between the outcrop and sensor.	In this model the geometry of the body is more clearly defined, however there is a distinct asymmetry between North- and South-facing slopes, with the high susceptibility layer significantly weaker on the South-facing slope.
Magnetics at Pole	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Magnetics at Pole	As with the -50° inclination model, the magnetic survey mainly reflects the variable distance between the outcrop and sensor.	In this model the geometry of the body is still more clearly defined, and the anomaly strength is more uniform along strike. The local fluctuations in anomaly strength along the length of the body reflect the discretisation of the land surface into cubes.
Magnetics at Pole 1VD	LOAD TIFF IMAGE	LOAD TIFF IMAGE
Magnetics at Pole 1VD	As with the pole image, the magnetic survey mainly reflects the variable distance between the outcrop and sensor.	In this model the geometry of the body is more clearly defined as a linear dipole anomaly. The local fluctuations in anomaly strength along the length of the body reflect the discretisation of the land surface into cubes. (The look up table of this image has been clipped to show more detail.)

Key Survey Specifications Scales

green

k = 0 r = 3

green layer

k = 10^-2

purple

k = 10^-2 r = 0

purple layer

k = 0

image width

10,000 m

inclination

-50° or -90°

intensity

50,000 or 70,000 gamma

flying height

400 m

max

min

max

min

WWW conversion by Ian Brayshaw