| Strike and Dip Symbols |
| Strike and dip are a way of representing the three-dimensional orientation of a planar surface on a two-dimensional map. The
strike is the compass direction of a horizontal line on the plane. All the horizontal lines on a plane are parallel, so they
all have the same characteristic compass direction. The dip is the angle at which the plane slopes downhill from the horizontal,
at its maximum slope, which is at right angles (90�) from strike.
|
| Map Symbol |
Definition |
Explanation of symbol |
 |
strike and dip of beds other than horizontal or vertical |
- strike (longer line) is horizontal line on bedding plane
- strike parallels nearby contacts between stratified rocks
- dip shows which way beds run downhill
- dip angle, number at end of dip symbol, is how much beds tilt down from horizontal
|
 |
horizontal beds |
- because the bed is horizontal it strikes in all directions
- because the bed is horizontal, the dip is 0%
|
 |
strike and dip of vertical beds |
- strike (longer line) is horizontal line on bedding plane
- because the bed dips vertically (has a 90% dip), it dips equally in either direction at right angles to strike,
so the dip line is shown extending in both directions
|
| Geologic Fault Symbols |
| Type of Fault |
Map Symbol |
Definition |
Type of Regional Stress |
Geologic Associations |
| normal |
 |
hanging wall down, footwall up |
tension |
- zones of crustal extension
- divergent plate boundaries
- edges of horsts and grabens
- Basin and Range region
|
| detachment |
 |
low-angle normal fault, footwall - gneiss, hanging wall - shallow-crust rocks |
tension |
- boundaries of metamorphic core complexes
|
| thrust |
 |
hanging wall up, footwall down |
compression |
- zones of crustal compression
- convergent plate boundaries
|
| reverse |
 |
high-angle (45° or more dip) thrust fault |
compression |
- zones of crustal compression
- convergent plate boundaries
|
| strike-slip |
 |
rocks on either side move horizontally in opposite directions |
shear |
- continental margins undergoing oblique (not straight on) plate convergence
- transform plate boundaries
|
| oblique-slip |
 |
combines horizontal and vertical motion |
combination |
- orogenic mountain belts
- continental margins undergoing oblique (not straight on) plate convergence
|
| Geologic Fold Symbols |
| Type of Fold |
Map Symbol |
Definition |
Appearance of Beds in Map View |
| anticline |
 |
up fold |
- roughly parallel stripes
- dip away from center (away from axis)
- oldest at center (along axis)
- youngest farthest from center
|
| plunging anticline |
 |
up fold with tilted axis |
- roughly a U-shaped pattern
- plunges in direction U points
- oldest at center (along axis)
- youngest farthest from center
|
| syncline |
 |
down fold |
- roughly parallel stripes
- dip toward center (toward axis)
- oldest farthest from center
- youngest at center (along axis)
|
| plunging syncline |
 |
down fold with tilted axis |
- roughly a U-shaped pattern
- plunges in direction U opens
- oldest farthest from center
- youngest at center (along axis)
|
| monocline |
 |
strata tilted in one direction |
- all dip in same direction
|
| structural dome |
 |
upward bulge in layered rocks |
- roughly a bull's eye pattern
- dip away from center
- oldest in center
- youngest farthest from center
|
| structural basin |
 |
downward bulge in layered rocks |
- roughly a bull's eye pattern
- dip toward center
- youngest in center
- oldest farthest from center
|
« Back to TOP
Geology 101 - Introduction to Physical Geology
Basics Table--
Geologic Map Symbols
Created by Ralph L. Dawes, Ph.D. and Cheryl D. Dawes, including figures unless otherwise noted
updated: 7/10/11
Unless otherwise specified, this work by
Washington State Colleges
is licensed under a Creative Commons
Attribution 3.0 United States License.
