USA Plate Boundaries Affecting US Seismicity Quiz
Transform (San Andreas), subduction (Cascadia/AK), intraplate (New Madrid) (10 questions).
USA Plate Boundaries Affecting US Seismicity Quiz: Quick Study Notes
The United States is a geologically diverse country, experiencing seismic activity driven by various tectonic processes. Understanding the different types of plate boundaries and their effects is crucial for comprehending the nation’s earthquake risks, from the famous San Andreas Fault to the deep subduction zones and enigmatic intraplate regions.
Key Concepts
Plates slide horizontally past each other, like the San Andreas Fault, causing frequent, shallow earthquakes in California.
One plate dives beneath another, such as Cascadia (Pacific NW) and Alaska, generating powerful mega-thrust earthquakes and volcanic activity.
Earthquakes occurring within a tectonic plate, far from boundaries, often linked to ancient rifts, like the New Madrid Seismic Zone.
Different boundary types lead to distinct seismic patterns and hazards, influencing building codes and disaster preparedness across the US.
Key Takeaways
- The San Andreas Fault is a major transform boundary, causing significant strike-slip earthquakes in California.
- Subduction zones like Cascadia and those in Alaska can produce megathrust earthquakes and tsunamis.
- Volcanic arcs are a common feature above active subduction zones.
- Intraplate seismic zones, such as New Madrid, are regions of earthquake activity within a tectonic plate, often related to reactivated ancient faults.
- Seismic waves from intraplate earthquakes can travel farther due to the stable, cold continental crust.
- Understanding plate tectonics is essential for assessing seismic hazards and preparedness across the diverse US landscape.
Frequently Asked Questions
What is the San Andreas Fault and where is it located?
The San Andreas Fault is a major right-lateral strike-slip transform fault extending approximately 1,300 kilometers (800 miles) through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate.
What makes the Cascadia Subduction Zone unique in the contiguous U.S.?
The Cascadia Subduction Zone is a convergent plate boundary where the Juan de Fuca Plate is subducting beneath the North American Plate. It’s unique for its potential to generate powerful megathrust earthquakes (magnitude 8 or 9) and associated tsunamis, similar to those in Japan or Chile, but in the Pacific Northwest.
How do intraplate earthquakes, like those in New Madrid, differ from plate boundary earthquakes?
Intraplate earthquakes occur within a tectonic plate, far from plate boundaries, while plate boundary earthquakes occur at the edges of plates. Intraplate quakes are generally less frequent but can be felt over much wider areas due to more efficient transmission of seismic energy through older, colder, and less fractured continental crust.
Are there volcanoes associated with the subduction zones in the U.S.?
Yes, the subduction zones in the U.S. are associated with significant volcanic activity. The Cascadia Subduction Zone feeds the Cascade Range volcanoes (e.g., Mt. St. Helens, Mt. Hood), and the Alaskan subduction zones are responsible for the extensive Aleutian Arc volcanoes.
Why is the New Madrid Seismic Zone important, despite being far from a plate boundary?
The New Madrid Seismic Zone is important because it experienced a series of powerful earthquakes (estimated M 7.0-8.0) in 1811-1812, which were among the largest historical earthquakes in the contiguous U.S. It remains an active seismic zone with the potential for significant future events, posing a risk to a densely populated region largely unprepared for such seismic activity.
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