What Type of Plate Boundary Is the San Andreas Fault? — Reading Comprehension

Grades

Standards

MS-ESS2-3
RI.6.1
RI.7.4
RI.8.2

About This Reader

This explanatory passage examines the San Andreas Fault as a transform plate boundary where the Pacific and North American plates slide horizontally. It explains earthquake formation through stress buildup and sudden plate movements, referencing the 1906 San Francisco earthquake. The text clarifies that the fault isn't a single crack but a network of smaller faults, with varying movement patterns. Aligns with NGSS MS-ESS2-3 (plate tectonics) and CCSS RI.6.7 (visual/technical information). The content helps students understand fault monitoring for earthquake prediction and connects to real-world seismic safety concerns in California, making plate tectonics tangible through a famous geological feature.

CONTENT PREVIEW

A Famous Fault Line

The San Andreas Fault is one of the most well-known geological features in North America. Stretching about 800 miles through California, it marks the boundary between two major tectonic plates: the Pacific Plate and the North American Plate. But what kind of plate boundary is it?

A Transform Boundary

The San Andreas Fault is a transform plate boundary. Unlike convergent boundaries (where plates collide) or divergent boundaries (where plates pull apart), transform boundaries involve plates sliding horizontally past each other. The Pacific Plate moves northwest, while the North American Plate moves southeast. This side-by-side motion creates enormous stress, leading to earthquakes.

How Earthquakes Happen

Because the plates don’t slide smoothly, friction locks them in place. Over time, stress builds up until the rocks suddenly break, releasing energy as an earthquake. Some of California’s biggest quakes, like the 1906 San Francisco earthquake, were caused by movement along this fault.

Network of Smaller Faults

The San Andreas Fault isn’t just one straight line—it’s a network of smaller faults branching out across the region. Some sections move slowly and steadily, while others stay stuck for years before suddenly shifting. Scientists monitor these movements to predict future quakes.

Why It Matters

Understanding the San Andreas Fault helps prepare for earthquakes that can damage buildings and infrastructure. While it won’t disappear anytime soon, studying it helps keep people safer in earthquake-prone areas.

What is the main idea of the passage?

The history of earthquakes in CaliforniaHow the San Andreas Fault was discoveredThe type of plate boundary and features of the San Andreas FaultWays to prevent earthquakes from happening

What kind of plate boundary is the San Andreas Fault?

Convergent boundaryDivergent boundaryTransform boundarySubduction zone

How do earthquakes occur along the San Andreas Fault?

Plates collide and push mountains upwardPlates pull apart, creating new crustPlates slide past each other, building up stress until they suddenly shiftMagma rises and erupts as volcanoes

Which of these best describes the movement of plates at the San Andreas Fault?

The Pacific Plate moves southeast, and the North American Plate moves northwestBoth plates move in the same directionThe Pacific Plate moves northwest, and the North American Plate moves southeastThe plates move vertically, causing uplift

What was a major earthquake caused by the San Andreas Fault?

The 1989 Loma Prieta earthquakeThe 1906 San Francisco earthquakeThe 1994 Northridge earthquakeThe 2011 Tohoku earthquake

Why is the San Andreas Fault not a single straight crack?

It is made of many small branching faultsIt is slowly disappearing over timeIt only exists underwaterIt was formed by volcanic activity

What does the word "transform" mean in this passage?

Plates colliding to form mountainsPlates sliding horizontally past each otherPlates separating to create new crustPlates melting under extreme heat

Why do scientists study the San Andreas Fault?

To predict earthquakes and improve safetyTo find new sources of oil undergroundTo stop the plates from movingTo create artificial islands