thompson geologic process id through landform analysis
TRANSCRIPT
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Geologic Process Identification through Landform Analysis
Ian Thomsen
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Topographic Position Index
From Jenness 2006
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Inherently Scalable Adjusts to capture features of different scales
• Quickly
• Easily
• Repeatable
Jenness, 2006
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• Comparing elevation of each cell to the mean of all cells in an annulus of radius 100 cells (3000 meters) around it.
• Only interested in large, regional-scale features
Raster Calculator
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Slope Tool
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TPI < -6 = Canyon bottom
-4 < TPI < 3 , Slope < 12° = Gentle Slope
-4 < TPI < 3 ; Slope > 12° = Steep Slope
3 < TPI < 6 = Steep Slope
6 < TPI = Ridge top
Raster Calculator
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Focal Statistics Operations
Areas of statistical operation can be customized to the scale of interest
For example: • 4500m square window
discards signal from smaller features
• 19500m window only captures largest features
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Identify all points which are classed as Steep Slope or Ridge Top at 4500x4500m scale but only class as Shallow Slope at 19500x19500m scale • Filters out all features too large to be fault generated • Removes smaller topographic relief
Raster Calculator
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Pamir
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Results
• Method successfully marks landforms which match characteristics of fault scarp structures
• Successfully removes other topography from consideration
But…
• Issues of scale
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Results
• Defines SOME topographic relief as fault related, but not all
• MORE problems of scale
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Results Obvious problems:
• Where are the faults?! They SHOULD be around here!
Two possibilities:
• There is no fault here
Or
• The scale of features of interest is lost in more recent features
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Problems identifying fault features with TPI
Extremely scale dependent
Scale must be uniform
Difficult to detect topography of interest within other geologic/erosional features
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Implications of work
Check the accuracy of map data
Identify sites where fault-generated features are more and less likely to be found
Can be applied to any geological features whose scale can be isolated from “background” topography
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Future work
Develop statistical methods to quickly combine
TPI
Lithologic changes
Seismic activity
Test method accuracy in the field
Refine algorithm
Apply TPI analysis to other geologic mapping projects