Faults


Online Metadata

Faults: ArcAtlas: Our Earth (ESRI)

Introduction
Author: E. A. Finko
Editor: A. A. Liouty

A fault, also known as a disjunctive dislocation, is a break in the continuity of a geological
formation. Faults can be formed when the earth's crust is compressed or stretched. They
vary greatly in size, both in length and depth. Faults are classified according to the type
and direction of movement of the rocks on either side of the fault. For example, a fault
along which no appreciable movement has occurred is called a joint. Faults with
appreciable movement include vertical faults, thrust faults, transcurrent faults, and
displacements.

A thrust fault usually has a gently sloping shift (45 to 60 degrees). A very gently sloping
thrust with overlap of tens or hundreds of kilometers is called a tectonic or overthrust sheet.
Faults caused by stretching of the earth's crust frequently result in the subsidence of one
block and the uplift of another block along the plane of fracture. These are called vertical
or inclined faults. Large linear tectonic structures formed by horizontal stretching are called
rifts. They usually form in association with vast, arched uplifting. Rifts can be thousands of
kilometers long and hundreds of kilometers wide. A very large rift is called a rift belt or zone,
such as the east African rift zone or the Baykal rift zone.

Some faults incise the earth's crust and reach the earth's upper mantle. These are called
deep faults and are typically hundreds or thousands of kilometers long, as much as 700
kilometers deep, and from several hundred meters to tens of kilometers wide. Deep faults are
ancient. They bound large blocks of the earth's crust and have different structures and
developments.

Two types of faults are shown on the maps. They are (1) faults created by the dislocation of
rocks that define the geological structures of the continents and (2) faults created by the
morphology of the present-day relief and morphostructure. The first ones include tectonic
contacts and thrust-faults; they are displyaed and interpreted with the Structural Geology.
The second ones include steps and rifts: they are displayed and interpreted with
Morphostructure maps. As a rule, the first type of faults are ancient structures, while those
revealed by relief are comparatively young structures that appeared during the neotectonic
stage of the earth's evolution (mostly in the Neogene and Quaternary periods).

Faults -- Worldwide distribution pattern

The highest density of faults revealed by relief is found in the zones where the lithospheric
plates meet. The zones are called suture zones and are zones of active mountain folding.
Rift faults are found in divergence zones. On the continents, these zones include the east
African rift zone where the African plate is separating from the Somali plate, the Baykal rift
zone that divides the Eurasian plate and the Amur plate, and the Mom rift zone that divides
the Eurasian plate and the North American plate. A high density of deep faults revealed by
present-day relief is found in the collision zone between the Eurasian plate and the African and
Indo-Australian plates. Most faults are deep and seismic. They are related to the complex mountain
relief of the African-Eurasian belt extending from Gibraltar to southeast Asia, sometimes called
the Thetys Belt. The density of faults within the continental plates is much higher on shields and
lower in areas with platformian mantles.

Faults -- Data sets, feature classes, and fields
Data source names:
  AFFALSDD - Africa
  ASFALSDD - Asia
  AUFALSDD - Australia
  EUFALSDD - Europe
  NAFALSDD - North America
  SAFALSDD - South America
Data source type:
  ARC/INFO line coverages

Feature class:
  Line -- Faults
  1 descriptive field.

  Type -- The type of the fault. Contains one of the following phrases:
  tectonic contact
  thrust-fault
  step
  rift

Faults -- Method

The fault maps in this atlas show the relatively large faults that reveal the geological
structure of the continents, mainly fold or block structures. The location of faults
corresponds to the strike of shifted rocks. Information on two types of tectonic dislocations is
also given. The two types are (1) tectonic contacts with dominant vertical dislocations of
rocks (mainly faults, upthrust faults, etc.) and (2) tectonic contacts with dominant horizontal
dislocations of rocks (thrusts).

The morphostructure maps show the largest faults differently revealed by present-day relief.
They are borders of mountains and platformian plains, ranges and depressions, various
pronounced parts of river valleys, chains of lake depressions, and so on.
The attributes on the faults were acquired from the survey maps and regional geological
and geomorphological maps that were used to compile the geological and
geomorphological maps. The maps were of various scales.


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