6.3 Examples of major transform fault systems (e.g., San Andreas Fault)

Transform faults are where tectonic plates slide past each other horizontally. The San Andreas Fault in California is a prime example, stretching 1,300 km along the Pacific and North American plate boundary. It's known for major earthquakes and complex fault geometry.

Other notable transform faults include the Alpine Fault in New Zealand and oceanic faults like the Charlie-Gibbs Fracture Zone. These systems shape landscapes, create seismic hazards, and provide insights into plate tectonics and crustal deformation processes.

Transform Fault Systems Worldwide

Major Continental Transform Faults

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• Transform fault systems occur at plate boundaries where two tectonic plates slide past each other horizontally with minimal vertical movement
• San Andreas Fault in California stretches approximately 1,300 km, forming the boundary between the Pacific and North American plates
• Alpine Fault in New Zealand extends for about 600 km along the South Island, accommodating motion between the Pacific and Australian plates
• North Anatolian Fault in Turkey spans roughly 1,500 km, separating the Anatolian and Eurasian plates
• Dead Sea Transform in the Middle East runs for about 1,000 km, marking the boundary between the African and Arabian plates

Oceanic Transform Faults

• Queen Charlotte Fault off the coast of British Columbia and Alaska spans approximately 900 km along the Pacific-North American plate boundary
• Oceanic transform faults along the Mid-Atlantic Ridge offset segments of the spreading center (Charlie-Gibbs Fracture Zone, Romanche Fracture Zone)
• Mendocino Fracture Zone in the northeastern Pacific Ocean extends for about 4,000 km, separating the Pacific and Gorda plates
• Macquarie Fault Zone south of New Zealand stretches for approximately 1,600 km along the Australian-Pacific plate boundary

San Andreas Fault: Tectonic Setting

Fault Characteristics and Geometry

• Right-lateral strike-slip fault forming the transform boundary between Pacific and North American plates
• Extends approximately 1,300 km through California from Salton Sea in the south to Cape Mendocino in the north
• Complex network of parallel and branching fault strands creates a zone of deformation up to several kilometers wide
• Segmented nature of the fault system includes the Carrizo, Mojave, and Coachella segments, each with distinct behavior

Fault Movement and Seismic Activity

• Average movement rate along the fault 20-35 mm per year with variations along different segments
• Responsible for significant seismic activity in California (1906 San Francisco earthquake, 1989 Loma Prieta earthquake)
• Tectonic stress accumulation and release results in both creep (slow, continuous movement) and stick-slip behavior (sudden energy releases in earthquakes)
• Paleoseismic studies reveal recurrence intervals for large earthquakes ranging from 100-300 years on different fault segments

San Andreas Fault vs Other Transform Faults

Comparison with Continental Transform Faults

• San Andreas Fault and North Anatolian Fault both exhibit right-lateral strike-slip motion
• Alpine Fault in New Zealand shows left-lateral movement contrasting with San Andreas Fault's right-lateral motion
• San Andreas Fault system longer and more complex than many continental transform faults with multiple parallel strands and branches
• Dead Sea Transform, similar to San Andreas Fault, created significant topographic features (Dead Sea basin, lowest land-based elevation on Earth)

Contrast with Oceanic Transform Faults

• Oceanic transform faults along mid-ocean ridges differ from continental transform faults like San Andreas in length, depth, and association with seafloor spreading
• San Andreas Fault entirely continental while oceanic transform faults typically connect segments of mid-ocean ridges
• Oceanic transform faults generally have simpler geometries compared to the complex, branching structure of the San Andreas Fault system
• Seismic behavior of oceanic transform faults often characterized by more frequent, smaller magnitude earthquakes compared to the San Andreas Fault

Features of Transform Fault Systems

Geomorphological Indicators

• Linear valleys, ridges, and escarpments form due to horizontal displacement and erosion along fault lines
• Offset streams and rivers common geomorphic indicators of transform fault movement (Wallace Creek along San Andreas Fault)
• Pressure ridges and pull-apart basins develop due to local compression and extension resulting from fault geometry and movement
• Sag ponds, small bodies of water trapped in depressions along fault lines, characteristic of many transform fault systems (Elizabeth Lake along San Andreas Fault)

Geological and Structural Features

• Fault gouge and breccia formed by grinding and crushing of rocks along fault plane serve as important geologic indicators of transform fault activity
• Transform faults juxtapose different rock types and geologic formations, creating abrupt changes in lithology across fault zones
• Geothermal activity and hot springs often associated with transform fault systems due to deep fracturing and fluid circulation along fault planes
• Development of flower structures, positive and negative, in cross-sectional views of transform fault zones due to complex deformation patterns