Extracting dips and slope geometry data from the maps

[geotechniqa]

I have the topographic map showing the slope geometry and couple of intersecting faults existing in the slope region.
In order to perform failure potential for wedge and planner assessment. I only have topographic map showing the slope on which the faults are plotted and rock strength data;
Plesae verify the following:
I need to extrat from the map the following
-Slope face Dip : this is I beleive the slope angle with the horizontal (I can easily get from the map)
-Slope face dip direction: how I get this from the topographic map: Should I measure the angle of the line representing the slope crest (on the topographic map) with the north and add 90 degree to it, as geologically defined.
-Fault dip direction: should I measure the angle of the fault with the north and add 90 degreeas as geologically defined
-Fault dip: how can I get that from the map.

 

[moe333]

The dip directions are perpendicular to the strike of the slope face and fault. These may be + or - 90 degrees from the strikes of these orientations. Fault dip should be shown on the map next to the strike.

 

[geotechniqa]

Hello moe 333
let us forget about the fault dip.
Now If you have the fault inclined to the north direction(horizontal in this case toward the left, as shown below) . What is the fault strike here.
Also how you get the strike of the slope face from the topographic map.

Plesae see attachement and comment on it if possibel..?

 

[moe333]

I'm a little confused by your description and picture. If you say the fault is inclined (or dipping) to the top left (approximately 345 degrees), then the strike is perpindicular to this; N75E, or 75 degrees azimuth.

The picture below the fault appears to be slope face contours. The contours are striking about 330 degrees azimuth, so the dip direction would be perpindicular to the contours.

Google strike and dip and you will find a lot of information. Basically, the strike is the horizontal projection of a linear vertical or inclined plane, and the dip direction is the direction of maximum dip. This is perpindicular to the strike. A vertical fault has no dip and therefore no dip direction.

Hope this helps

 

[moe333]

Just to clarify, the the strike of the slope face is parallel to the contours; NNW in your case

 

[fattdad]

A vertical fault has no dip and therefore no dip direction.

This is not fundamentally correct. A vertical fault has a dip of 90 degrees and the dip direction is perpendicular to the strike, but as it's vertical there are two dip directions.

A horizontal fault has neither a strike nor a dip direction, however.

p.s., you should familarize yourself sterographic projections.

f-d


¡papá gordo ain’t no madre flaca!

 

[geotechniqa]

Sorry moe and thanks for reply.
I just have the long line (fault) on the geologic map and I want to get its dip direction angle.
The same think I have the slope coutors and I want to get the dip direction Angle of the slope. I am reaaly confused how to measure these to values from the geologic map.
I plot the long line and the slope contours and I also showed the North direction on my attachment plesae guide me how I measure these quantities for my rock slope stability software .

 

[geotechniqa]

Sorry fattdad. thanks for reply and plesae consider replying to my latest question above

 

[epongra2]

As an engineering geologist, frankly I'm reading some of these questions and cringing. It's pretty obvious you should get some input from a geologist, preferrably the one that put the geologic map together. If you are using a regional geologic map for your geology information, this data is often not at a sufficient scale when you begin to focus on site-specific (i.e. large scale) slope stability analysis.

Sorry to sound harsh, but you are performing a slope stability study after all.

 

[geotechniqa]

Well this is initial study.. after all we have to live with the situation. It should not be that complicated. Just I am asking how you measure (rule: clock wise.. anticlickwise) the strike angle of the slope face and the on the map. Plesae see the attachment