Geology Introduction to Strike-Slip Faults

Levant Strike-Slip Faults Left-lateral strike-slip Levant fault, plate boundary between Arabia and Africa

San Andreas from Space San Francisco Bay, California.  Two northwest-southeast- trending faults are visible.  The Hayward Fault, bordering the urban area east of San Francisco Bay  The San Andreas Fault, crossing the mid-San Francisco Peninsula before dipping beneath the Pacific Ocean and surfacing again northwest of Golden Gate Bridge

San Andreas fault, western North America

Outline Stick-Slip and Creep Andersonian Theory Kinematics Strike-Slip Faults on Continental Margins Strike-Slip Faults on Mid-Ocean Ridges

Stick-Slip: Elastic Rebound Theory 

Elastic Rebound Theory Imagine a fence across an active fault Imagine a fence across an active fault

Elastic Rebound Theory Imagine a fence across an active fault Imagine a fence across an active fault Regional deformation occurs but the fault does not break. The fence becomes curved. Regional deformation occurs but the fault does not break. The fence becomes curved.

Elastic Rebound Theory Imagine a fence across an active fault Imagine a fence across an active fault Regional deformation occurs but the fault does not break (locked fault) Regional deformation occurs but the fault does not break (locked fault) Once the fault breaks, the fence is sheared in half and marks offset Once the fault breaks, the fence is sheared in half and marks offset The far-field strain may limit whether the fault accommodates all the plate motion at its trace The far-field strain may limit whether the fault accommodates all the plate motion at its trace

Elastic Rebound Theory

Creep (Aseismic Slip) Imagine a fence across an active fault Imagine a fence across an active fault Slip occurs slowly on the fault continually over time (fault is not locked) Slip occurs slowly on the fault continually over time (fault is not locked) Creeping faults do not store elastic energy that might be released by a stick-slip event (an earthquake) Creeping faults do not store elastic energy that might be released by a stick-slip event (an earthquake)

Andersonian Theory

Conjugate Strike-Slip Faults

Determining Sense of Slip

Right-Lateral (Dextral)

Left-Lateral (Sinistral)

Arrow Heads ( ) and Tails ( ) Block moving toward you like an arrowhead heading towards you Block moving away from you like seeing the feathers of an arrow

Arrow Heads ( ) and Tails ( ) Right-lateral or left-lateral? Right-lateral or left-lateral?

Arrow Heads ( ) and Tails ( ) Left-lateral Left-lateral

Arrow Heads ( ) and Tails ( ) Sinistral or Dextral? Sinistral or Dextral?

Arrow Heads ( ) and Tails ( ) Dextral Dextral

Strike-Slip Faulting: Shallow Brittle vs Deep Shear

Strike-Slip Faulting: EQ’s = dislocations Landers rupture propagation movies

Strike-Slip Faulting: EQ’s = dislocations

Strike-Slip Faults on Continental Margins What is the sense of slip? What is the sense of slip? N 50 m

Strike-Slip Faults on Continental Margins Right-lateral (dextral) Right-lateral (dextral) N 50 m

Transtension

Development of a Pull-Apart Basin

Pull-Apart Basin

Initial Releasing Bend

Evolution of a Releasing Bend

Normal (-) Flower Structure - Tulip

Transpression

Development of a Restraining Bend

Initial Restraining Bend

Evolution of a Restraining Bend

Reverse (+) Flower Structure - Palm

Summary of Flower Structures - Palms & Tulips

Summary of Step Overs - Strike-Slip Faults

Los Angeles - Pull apart structure Releasing bend

Summary of Flower Structures - Palms & Tulips

Oceanic Strike Slip fault: Transforms

Strike-Slip Faults on Mid-Ocean Ridges What is the sense of slip? What is the sense of slip?

Strike-Slip Faults on Mid-Ocean Ridges Right-lateral (Dextral) Right-lateral (Dextral)

Pacific-Antarctic Ridge Magnetic anomalies from present to 9.9 Ma Magnetic anomalies from present to 9.9 Ma Warm colors indicate positive polarity Warm colors indicate positive polarity Cool colors indicate reverse polarity Cool colors indicate reverse polarity