The San Andreas Fault

SAF: Earthquakes 1

Earthquakes take place along the San Andreas Fault System on a daily basis, most of which we never feel.

Resulting Landforms: Sag Ponds

Example: Lost Lake in the Cajon Pass Sag Ponds result from fault movement that has caused sunken ground from crushed rocks, etc. Runoff and/or springs cause water to collect in the depression. On the southwest side of Lost Lake there is an active trace of the San Andreas Fault You can see Lost Lake in the upper left half of the photograph, with the red arrows indicating the direction of SAF movement.

Resulting Landforms: Off-set Streams

Example: Wallace Creek in the Carrizo Plain Offset by 430 feet as a result of the moving San Andreas Fault Offsetting occurs in rupture events (earthquakes) In the 1857 Great Fort Tejon earthquake the creek moved 31 feet!

SAF: Earthquakes 2

Some of California's most notorious earthquakes have taken place along the SAF 1857 Great Fort Tejon Earthquake (magnitude about 7.8) 1906 San Francisco Earthquake (magnitude 7.7-8.3) 1989 Loma Prieta Earthquake (magnitude 6.9)

3 Segments of the SAF

Southern Segment (Mojave) Runs along the southern base of the San Bernardino Mountains, through the Cajon Pass (under I-15!) and along the Northern base of the San Gabriel Mountains

What is the San Andreas Fault?

A Strike-Slip Fault Displacement is lateral along fault.

Resulting Landforms: Scarps

A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other.[1] It is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault (a sort of old rupture), or by a movement on a recent active fault. Example: Elkhorn Scarp

What is the San Andreas Fault?

A transform boundary 810 miles of transform boundary in California Where the North American Plate and Pacific Plate slide past each other

3 Segments of the SAF

Central Segment Known not for earthquakes, but aseismic creep, a slow movement of the plates past each other

The San Andreas Fault System

Locally includes the San Jacinto, Banning & Elsinore Faults

3 Segments of the SAF

Northern Segment Runs north from Hollister, at times off the coastline and into the Pacific Ocean, then back, ending at the Mendocino Triple Junction (where the Pacific, North America and Gorda Plates all meet).

Landforms Resulting from the San Andreas Fault

Off-set streams and channels Sag ponds Different rocks on either side of the SAF Scarps Pressure ridges

Resulting Landforms: Pressure Ridges

Pressure Ridges result where tectonic forces push rock upward