Fallas direccionales: Introducción

Fallas que no crecen libremente, pero acomodan desplazamientos de fallas limitantes:

Fallas de transferencia

Fallas que crecen libremente:

Fallas de transcurrencia

Fallas de transferencia ligadas a una tectónica de piel delgada

Falla de transferencia entre dos fallas normales de polaridad opuesta

Fallas de transferencia entre dos fallas de una misma polaridad: Rampas laterales

Fallas de transferencia ligadas a límites de placa: Fallas de transformación

Complicaciones estructurales relacionadas a saltos o terminaciones de una falla direccional (1)

Flexión relajante o constriccional (restraining / releasing bend)

Generación de desplazamiento en el bloque SW de una falla del

Valle Muerto

Complicaciones estructurales relacionadas a saltos o terminaciones de una falla direccional (2)

Regional-scale structures along a strike-slip fault. These structures can include restraining bends associated with thrusts and mountain building, releasing bends associated with basin development and rapid subsidence, and horsetail splays of either normal or reverse faults where deformation is spread over a broader zone. Right-stepping step-overs in a dextral shear zone (as shown here) create pull-apart basins as the fault tips curve toward the continuing fault trace and generate normal slip. Modified after

Block diagrams showing negative and positive flower structures typical of large fault zones that are caused by transtension and transpression, respectively.

Positive flower structure related to upthrown side (or restraining bend).

Negative flower structure related to downthrown side (or releasing bend).

Planos y pliegues secundarios que afectan una zona de “daño” o los alrededores de una falla direccional

A strain model explaining the subsidiary structures along a strike-slip fault.

(a) A map view of dextral simple shear. A square becomes a parallelogram, and a circle in the square becomes an ellipse.

(b) A detail of the strain ellipse showing that folds and thrusts form perpendicular to the shortening direction, while normal faults and veins form perpendicular to the extension direction. R and R shears form at an acute angle to the shortening ′direction.

(c) Note that R and R are similar to conjugate shear fractures formed in rock cylinder ′subjected to an axial stress.

Portrayal of the difference between bends and step-overs, both in right- and left-handed strike-slip systems (releasing and restraining bends).

Mechanisms of block rotation in a right-lateral strike-slip zone. (a) A map view of a grid being subjected to dextral simple shear. (b) The grid lines rotate. Further, fault-bounded blocks may rotate intact as slip on

bounding faults increases (bookshelf model). (c) Alternatively, the fault zone may break into smaller blocks that rotate by different

amounts. In this case, large rotations may occur locally. The amount of rotation is tracked by the paleomagnetic declination in each block (solid arrows) relative to a reference direction (dashed line).

Fracture patterns in wrench zones.A. Part of Dasht-e Bayaz (Iran)

earthquake fracture zone along left-lateral wrench. Western part shows development of synthetic en echelon faults; eastern end shows both antithetic and synthetic en echelon faults.

B. Synthetic and antithetic en eche C. lon fractures (enlargement of east

end of wrench zone in A above). D. Lake Basin fault zone, Montana,

showing en echelon normal faults along indicated wrench zone.

E. Cottage Grove fault zone, Illinois; note en echelon normal faults, parallel mafic dikes, and reversal of vertical separation sense on through-going strike-slip fault. Vertical components indicated in feet.

Ejemplos y ejercicios

Map-view models of fault bends along strike-slip faults. The “edges” of the crustal blocks are provided for reference. (a)Releasing bend at which

normal faults and a pull-apart basin have formed.

(b)Restraining bend at which thrust faults have formed.

(c)Application of this model to the San Andreas Fault north of Los Angeles (LA). The dashed lines outline imaginary reference blocks. The San Andreas Fault bends along the margin of the Mojave Desert.

La Falla Alpina de Nueva Zelandia

The transform system of the Alpine Fault, New Zealand, connects thewest-dipping Tonga-Kermadec subduction zone to the east dippingMacquarie subduction zone. Note the tremendous displacement of major rock units on the Alpine Fault. The northern subduction zone dips east and the southern subduction zone dips west, as shown by the pattern of progressively deeper earthquakes.

La Falla Alpina de Nueva Zelandia: Transferencia entre dos zonas de

subducción

The Alpine Fault in New Zealand is a dextraltransform fault that connects two subducting plate boundaries (see insert for larger field of view). Along this fault the geological units (various colored symbols) are displaced by several hundred kilometers.

The dextral North Anatolian Fault forms the plate boundary between the Anatolian and Eurasian plates; stars show epicenters of large earthquakes between 1939 and 1999. The numbers in brackets indicate the moment magnitudes of the earthquakes. The conjugated East Anatolian Fault has opposite sense of movement (sinistral). In the wedge between both faults the Anatolian Plate is pushed westwards (“tectonic escape”).

Fallas direccionales en los bordes de la Placa del Caribe

Marco tectónico de las fallas direccionales en los límites de la

Placa del Caribe

La falla de Motagua-Polochic

La falla de Boconó

La falla de Bucaramanga - Santa Marta

Paleogene and earlier

Convergence between Nazca-Sam:• Highly oblique for the Pg and Ku• Perpendicular for the Oligocene

La Falla Palestina: Marco tectónico

Strain partitioning at a restraining bend of the Northandean block

Pales

tina fau

lt

Romeral fault

Antioquia batholith

La Falla Palestina: Marco cinemático

D’

DC’

C

B’

BA’

A

50 km

N

4,2 km

26,4 km

27,3 km

26,0 km

Cretaceous sediments

Marble

Diorite

Gneiss

Metamorphic basement

Structural markers along the southern segment of the Palestina fault illustrate

an increase in displacement from 4 km to 26 km.

SAN LUIS