Locating Plate Boundaries of the Pacific Rim Around the Ring of Fire Locating Plate Boundaries of the Pacific Rim

Pacific Northwest Seismic Data This is a map of seismic activity of the Pacific Northwest Each yellow (35-70 km deep) and orange (less than 35 km deep) dot represents an earthquake What pattern do you see? What does this pattern mean? Map generated using the U.S. Geological Survey. “Earthquake Hazards Program :Earthquake Center” The “plate” is actually 3 micro plates that generally get lumped into the overall term “Juan de Fuca”. Starting in the North off the coast of Canada is the Explorer microplate, then the Juan de Fuca, and then the chunk in the South off the coast of northern California is the Gorda microplate. Together they form the Cascadia subduction zone. For information on Cascadia see the “Orphan Tsunami” lesson.

Southeast Asia Seismic Data This is a map of seismic activity of Southeast Asia Each yellow (35-70 km deep) and orange (less than 35 km deep) dot represents an earthquake What pattern do you see? What does this pattern mean? Map generated using the U.S. Geological Survey. “Earthquake Hazards Program :Earthquake Center” Looking at Japan, there is a much different picture than Washington. Japan is located at the junction between 4 different plates. The North American plate extends from the Aleutian Islands around to the Kamchatka Peninsula on the northern boundary of Japan. To the east is the Eurasian Plate, to the west the Pacific Plate and then to the south the Philippine Plate. Each of these plates is moving in a different direction and Japan is caught in the middle. As a result, your students should notice that there are far more earthquakes (dots) in this area than in the Pacific Northwest.

Pacific Rim Seismic Data This is a map of seismic activity of the Pacific Rim Each yellow (35-70 km deep) and orange (less than 35 km deep) dot represents an earthquake Do you see any patterns? What do these patterns tell you? Map generated using the U.S. Geological Survey. “Earthquake Hazards Program :Earthquake Center” Students should notice that in some areas the earthquakes (especially the deeper yellow earthquakes) form “lines”. These lines are inferred as plate boundaries. Shallow earthquakes can be the result of other processes such as hydrothermal explosions, glacial movement, post ice sheet rebound, mining, water extraction , landslides, and nuclear testing just to name a few. That is why there is not as clear of a pattern in the orange dots as the yellow.

Plates of the Pacific Rim This is a good opportunity to discuss inference. Plate boundaries are not visible at the surface so they must be inferred by using earthquakes. As you can see on the earthquake maps, some boundaries are not as “clear” as others. Plate boundaries are regions where two plates interact NOT a single surface so some scientists interpret the data differently than others.

Analyze your map How many plates underlie of the Pacific Ocean also known as the Ring of Fire? Are all plates the same size? How many plates interact near Washington? How many plates interact near Japan? Explain how earthquakes can be used to infer plate boundaries. 8 not including the Pacific Plate No, some are really big –Pacific Plate, North American Plate and some are quite small—Juan de Fuca Plate 2 the North American Plate and the Juan de Fuca Plate 4 the North American, Pacific, Philippine and Eurasian Plates Because earthquakes occur wherever two plates are moving against each other

Ring of Fire Where are the majority of volcanoes found in the Pacific Rim? (Are they found in the middle of the plates or on the edges?) Are volcanoes found everywhere earthquakes are found? Map from U. S. Geological Survey. http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_plate_tectonics_world.html At plate boundaries Mostly on the edges—except for hot spots such as Hawaii Not always, however most of the time volcanoes and earthquakes are found at plate boundaries together. The exception is when two continents collide such as is happening in India and form folded mountains instead of volcanoes.