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Geomorphic Evidence of Active Faulting
thumbnail of geomorphic block diagram (Click to enlarge)

The Earth's surface is transformed by movement along active faults, producing features that help us determine the location of the fault and are diagnostic of the fault's level of activity. Examples are provided in the block diagram above. These various features are shown on the map using the codes and abbreviations listed below.


Codes indicating strength of the evidence

G1  - strongly pronounced feature

G2  - distinct feature

G3  - weakly pronounced feature

 ?   -  additional uncertainty in tectonic origin


af -    alignment of multiple features as listed

as -   arcuate scarp

bt  -   downthrown surface tilts back toward fault

df  -   depression formed by some aspect of fault deformation, undifferentiated

dr  -   sag, depression formed in right stepover of                      fault trace

gi  -   linear break (or gradual inflection) in slope

hb   - linear hillside bench

hv -   linear hillside valley

ls  -    fault scarp height enlarged by landsliding

lv  -    linear valley or trough

mp - Youngest traces disturbed by human activities. Mapped trace bisects disturbed zone. Location uncertainty (dash gap in linework) equals half width of disturbed zone.

n   -   notch

pr  -   pressure ridge in left stepover

rr  -    right-laterally offset ridge line

rs  -   right-laterally offset stream or gully

sb  -  broad linear scarp (implies multiple traces)

sc  -   scissor point, sense of vertical separation reverses

se  -   subsoil exposed

sl  -   linear scarp, undifferentiated

sn  - narrow linear scarp (implies dominant trace)

sp  - spring

ss  -  swale in saddle

vl  -  line of vegetation

See Block Diagram of Geomorphic Features
used as Evidence for Active Faulting
geomorphic block diagram

Comments to Jim Lienkaemper (jlienk@usgs.gov)

(Last updated 6 March 2006)