# Faults, Plate Tectonics, and Earthquake Hazards

Rocks that make up Earth's thin outer shell are under constant stress. We know this because of faults, which are fractures in Earth’s crust where movement occurs. Faults can be small and hard to see contacts between adjacent rocks or they can be hundreds of miles long. For instance, the San Andreas Fault in California is visible from space! Faults bound the sides of tectonic plates, the huge chunks or pieces of the Earth's crust.

In this module, you can learn about the reasons why earthquakes occur. You will also investigate the different types of faults and plate tectonic boundaries. You will explore these concepts in context of Washington, Oregon, and California, the three main ShakeAlert states. We also include information about the Basin and Range (Nevada) and Alaska.

#### Key Points:

Learners will be able to:

• Understand the forces, stress and strain that result in particular fault motions and their geometry
• Relate these geologic structures to different types of plate motions (divergent, convergent, and transform)
• Describe the different types of faults and plate motion in the ShakeAlert states, such as the Cascadia Subduction Zone and the San Andreas fault

• 23 Number of Resources

These resources provide an introduction to concepts and terms that will be used throughout the modules.

### Take 2: Plate vs. Crust Time: 2m / Level: Novice

People often use the terms crust and tectonic plates interchangeably. It can be confusing because they are paired, and yet they are distinct from each other.

### Take 2: Epicenter vs. Hypocenter (Yep, there is a difference) Time: 2m / Level: Novice

The epicenter is the map location on Earth’s surface, above where earthquake began. An earthquake actually begins inside the earth at the hypocenter. Learn more!

### Take 2: Hazard vs. Risk Time: 2m / Level: Novice

A seismic hazard is the probability that earthquake shaking of a certain intensity will occur in a given geographic area, within a given window of time.  From that, risks can be assessed and included in mitigation efforts. Let's compare them.

### Impacts of Geodesy in Science and Life Time: 5m 2s / Level: Novice

How do scientists study millimeter scale movements of earth’s surface over time? How do we keep all of our clocks synchronized around the world? With geodesy!

The cool, rigid outer layer of Earth is highly fractured. In most places, huge chunks or pieces of this rigid outer layer, called plates, are in continuous motion. Plates can range from 50 km to 200km thick. Continental plates are thicker and less dense than oceanic plates that are formed at spreading ridges.

### Mapping Worldwide Earthquake Epicenters Time: / Level: Novice

Computer-based visualizations and/or current earthquake reports are used to determine worldwide patterns of earthquake magnitude, depth, and location. These activities use the IRIS Earthquake Browser (IEB; ds.iris.edu/ieb) and are designed to stimulate interest in global earthquake patterns and their causes. This activity provides a natural transition to teaching plate tectonics.

### Introduction to Faults and Plate Tectonics Time: / Level: Novice

This interactive activity provides three options to demonstrate the geometry of faults (normal, reverse, and strike-slip) and fault displacements with 3-D models. Fault models aid in the visualization and understanding of how faults are created and move because the instructor and their learners can manipulate a 3-D model for a hands-on experience.

### Faults, Plate Boundaries, & Stress—How are they related? Time: 8m 43s / Level: Novice

[updated 2021] Earth-science educators, do you ever get asked, "What is stress? Why do faults form in Earth’s crust? or How are faults related to plate boundaries?"  This animation describes stress in Earth's outer layer and how it leads to both faults and tectonic plate boundaries.

### Plate Tectonic Boundaries: Three types differentiated Time: 6m 40s / Level: Novice

This intermediate-level animation describes what the tectonic (lithospheric) plates are and how they interact. It differentiates between continental and oceanic plates, and between the three major types of boundaries.

### Plate Tectonics—What Are the Forces that Drive Plate Tectonics? Time: 7m 30s / Level: Novice

UPDATED (Jan, 2022) - New Ending On Convection
Lithospheric plates are part of a planetary scale thermal convection system. The energy source for plate tectonics is Earth’s internal heat while the forces moving the plates are the “ridge push” and “slab pull” gravity forces.

### Measuring Plate Tectonic Motions with GPS Time: / Level: Novice

This animation shows how high-precision GPS networks help us understand plate tectonic motions and earthquake hazards around the world, with a focus on the Western United States. Developed for the Geodesy Tools for Societal Issues (GETSI) project with funding from the National Science Foundation.

The Pacific Northwest of the United States is home to several different types of faults that can create small to very large earthquakes. Learn about the three different types of earthquakes, to include an M9 earthquake that occurred along the Cascadia Subduction Zone on January 26, 1700.

### Earthquake Alert Times in the Pacific Northwest (ShakeAlert system) Time: / Level: Novice

What would you do with seconds to prepare for earthquake shaking? With even a few seconds, ShakeAlert© earthquake early warning can save lives and reduce injuries by alerting people that an earthquake may cause shaking near you as it triggers automated actions.

### Earthquake Early Warning System for the Pacific Northwest Time: / Level: Novice

On March 11, 2011, a devastating magnitude-9 earthquake struck off the coast of Tohoku, Japan, where the Pacific Plate dives beneath the Okhotsk Plate. On January 26th, 1700, the West Coast of the United States experienced a similar tsunami-generating megathrust earthquake. An earthquake like this will strike the Cascadia subduction zone again. How can we protect ourselves?

### Pacific Northwest: Three types of tectonic earthquakes Time: 4m 13s / Level: Novice

It is common knowledge that the Pacific Northwest can expect a subduction-zone megathrust earthquake in the future.  But did you know that there are other types of damaging earthquakes.  This animation uses analogies and cartoon block diagrams to teach about the three types of earthquakes.

### Pacific NW—The Cascadia Subduction Zone (geomorphology) Time: 2m 41s / Level: Novice

The Cascadia Subduction Zone of the Pacific Northwest is comprised of a collection of major geographic features, including the subducting plate, the subduction plate boundary, the Coast Range, the Puget-Willamette lowlands, and the Cascades Mountain Range.

### Ghost Forests of the Pacific Northwest (evidence for Giant earthquake & tsunami) Time: / Level: Novice

Ghost forests are part of the evidence that a Great earthquake and devastating tsunami occurred last on January 26th, 1700 in the Pacific Northwest. How do we know this?

### GPS Records Variable Deformation across a Subduction Zone Time: 1m 17s / Level: Novice

Subduction zones show that there are 3 distinct areas of movement in the overlying plate:

1. constant movement above the locked leading edge,
2. see-saw pattern of back-&-forth movement above a zone that alternately locks then slips, and
3. no movement far inland above the deeper part of the diving oceanic plate.

### Pacific Northwest vs Japan: Similar tectonic settings Time: 4m 12s / Level: Novice

This UNAVCO animation compares Japan's subduction zone at the location of the 2011 earthquake with a mirror-image subduction zone in the Pacific Northwest. There are many similarities.

### The Turtle Story, a Native American Account of Earthquakes Time: 5m 52s / Level: Novice

The “Turtle Story” is a Native American story of how earthquakes occur, told by Jacque Tahuka-Nunez who is a tribal descendant of the Acjachemen Nation also known as the Juaneño Band of Mission Indians. This story is derived from the Gabrielina-Tongva Tribe, also known as the San Gabriel Band of Mission Indians in California. This story is catered to children and youth but can be enjoyed by all ages.

### Remembering Ridgecrest Time: 4m / Level: Novice

On July 4, 2019, a M6.4 earthquake shook Ridgecrest, California. A M7.1 earthquake followed a little over a day later. These earthquakes struck in the California desert near the towns of Trona and Ridgecrest, which is where the earthquake got its name. Had these earthquakes occurred closer to an urban area, the damage could have been much worse.

### CGS Geologists Remember San Fernando Earthquake Time: 1m / Level: Novice

Scientists from the California Geological Survey recall their personal experiences and reactions on the morning of February 9, 1971, when a magnitude 6.5 earthquake struck the San Fernando Valley of Southern California. Their responses illuminate the human dimension of earthquake hazards and emphasize the importance of preparedness for all Californians.

### Basin & Range: Structural Evolution Time: 53s / Level: Novice

Over most of the last 30 million years, movement of hot mantle beneath the region caused the surface to dome up and then partially collapse under its own weight, as it pulled apart. Currently, there is very little actual stretching going on, and the small amount is concentrated on the Western and Eastern edges of the Basin and Range.

### Alaska: Tectonics and Earthquakes Time: 8m 40s / Level: Novice

Alaskan tectonics are dominated by the Pacific-North American plates. The megathrust boundary between the plates results in both the 4,000-km-long Aleutian Trench and in the arc of active volcanoes that lie subparallel to the trench.

### Alaska: The Great Alaska Earthquake of 1964 Time: 6m 42s / Level: Novice

The 1964 Great Alaska Earthquake occurred on Good Friday, March 27th. Liquefaction in and around Anchorage tore the land apart. At magnitude 9.2, it was the second largest quake ever recorded by seismometers.