Plate Tectonics | Pacific Northwest Seismic Network
There are a few handfuls of major plates and dozens of smaller, or minor, plates. within them, such as the North American, African, and Antarctic plates. for the volcanoes that dot the Pacific Northwest of the United States. Most geologic activity stems from the interplay where the plates meet or divide. by Timber Press on October 18, The geologic story of North America is a fascinating one. American Plate rides over the top of the Pacific Plate, forcing the oceanic plate downward, Tectonic plates are bounded and fractured by faults, where two adjacent masses of rock meet and move relative to each other. The largest one, the Pacific Plate is moving north west relative to the plate that holds North America, and relative to hot spots coming up plate boundaries: where two plates meet there can be three types of boundaries: transform faults where.
Interactives . Dynamic Earth . Plates & Boundaries
Prior to that, it was a fragment of the supercontinent Pangaea, known as Laurentia. Pangaea amassed around million years ago and began to break up around million years ago, when the Mid-Atlantic Ridge a spreading ridge that runs under Iceland began opening, forcing apart the conjoined landmasses that would become North and South America, Eurasia, and Africa—and creating the Atlantic Ocean.
As the Atlantic Ocean continues to widen at a rate of about an inch per year, the North American Plate is pushed toward the southwest, where it collides with the Pacific Plate—the major plate underlying the Pacific Ocean—and several smaller oceanic plates.
Continental crust is less dense than waterlogged oceanic crust, so the more buoyant North American Plate rides over the top of the Pacific Plate, forcing the oceanic plate downward, forming a subduction zone. The tremendous forces generated at these plate boundaries, or subduction zones, fuel earthquakes and volcanism along the active western margin of the continent, such as the magnitude 9 megaquake unleashed by the Cascadia Subduction Zone on January 26,and the eruption of Mount Saint Helens on May 18, Here, steam and gases escape from a post-eruption lava dome of Mount Saint Helens.
Tectonic plates are bounded and fractured by faults, where two adjacent masses of rock meet and move relative to each other. Major types of faults include transform faults, thrust faults, and normal faults.
Transform faults, also known as strike-slip faults, occur when bordering volumes of rock slide past one another in a lateral motion, with little or no vertical movement. This movement sometimes occurs smoothly—aseismically—and other times makes violent jumps that unleash earthquakes.
Earthquakes can also be generated in the interiors of tectonic plates, where tectonic forces are squeezing the lithosphere together or pulling it apart in compressional and extensional landscapes. Vancouver Island to Cape Mendicino California and a large tract of sea floor real estate in between. It was subducted beneath California leaving the San Andreas fault system behind as the contact between the North America and Pacific plates.
The Juan de Fuca Plate is still actively subducting beneath N. Its motion is not smooth, but rather sticky; strain builds up until the fault breaks and a few meters of Juan De Fuca slips under North America in a big earthquake. This action takes place along the interface between the plates from the Juan de Fuca Trench off shore down-dip until the fault is too weak to store up any elastic stress.
The locked zone varies in width from a few tens of kilometers km along the Oregon coast to perhaps a hundred km or more off of Washington's Olympic Penninsula, and is about 1, km long. These plate motions are the primary source of strain in the lithosphere that lead to earthquakes in our region. In California, much of the strain generated by the grinding of the Pacific Plate against North America is taken up in earthquakes on the San Andreas Fault and related structures.Meet the Press w Chuck Todd 12 9 18 NBC Dec 9, 2018
British Columbia however is part of rigid North America and moves with it. Shoveling off all the sedimentary deposits from the basement rocks underlying the Puget Lowland would certainly be one way to reveal this pattern.
But that would involve way too much digging! Fortunately geophysics allows us an much easier way to uncover the basement--measure the gravity.