Geology of the Pacific Northwest

Geology-208

Week 6: EARTHQUAKES IN WASHINGTON

Types | Tectonics & Quakes | Resources |

Types of Quakes

Types of earthquakes are:

Deep quakes (subducting slabs) — least destructive

The Seattle-area earthquake this year (2001) was centered 30 miles beneath the earth's surface, underneath Anderson Island, east of Olympia. All our strongly-felt earthquakes have "occurred as one plate of the earth's crust slowly slid farther beneath another." (Christian Science Monitor, March 2, 2001).
Shallow faults — more destructive
Plate boundary quakes — catastrophic

Tectonics and Quakes

Plate Tectonics and Types of Earthquakes
Divergent boundaries: adjacent plates move away from each other	Shallow earthquakes (more destructive) Occurs mid-ocean at depth of less than 5 km below the sea floor Limited volcanic activity near edges of diverging plates (not explosive)
Convergent boundaries: adjacent plates move toward each other	Greater range of depths for earthquakes and volcanoes Marked by trenches, island arcs (i.e., Aleutian Islands), volcanoes Subduction zones Deeper earthquakes (up to 700 km deep; less destructive)
Transform boundaries: adjacent plates slide side by side past each other	Shallow to moderately deep quakes (i.e., San Andreas Fault, California) Little or no volcanic activity
Hot spot: intraplate; volcanism and quakes are caused by the continental plate passing over a “hot spot” in the earth’s mantle	Non-explosive volcanoes Small quakes are common; some are strong enough to ring church bells (Boston) Quakes are caused by motion along old faults in the lithosphere

RESOURCES

• Major Faults in the Puget Sound (fault map) (University of Washington)
• PNSN Webicorder Displays (Real Time seismic data) (University of Washington)
• Recent Washington Earthquakes in the Pacific Northwest (University of Washington)
• Paton, Dean, 2001, Why Seattle's Big Quake Had Little Impact, Christian Science Monitor, v93, n67, p3
• Slattery, William, 1996, Earthquakes, Volcanoes, and The Information Superhighway, Science Activities, v33, n3, p8-13

GLOSSARY

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Send comments to Rob Viens (e-mail: rviens@bcc.ctc.edu) or call him at his Bellevue Community College office at (425) 564-3158. Office hours are by appointment.