Scientists Revising Thoughts on Continental Plate Shifts

In a article on Phys, they report scientists have found clues in Alaska that has them rethinking how to continental crust forms based upon research published in Nature Geoscience.

A new study appearing in this week’s Nature Geoscience raises questions about one popular theory and provides new support for another, in which arc lava from the surface and shallow “plutons” – magma that solidified without erupting – are pulled down into the Earth at subduction zones and then rise up to accumulate at the bottom of the arc crust like steam on a kitchen ceiling. Scientists have found compelling evidence to suggest that this could have produced the vast majority of lower continental crust through Earth history.

The process, called relamination, starts at the edge of a continental plate, where an oceanic plate is diving under the continental plate and magma is rising to form a volcanic arc. As the oceanic plate dives, it drags down sediment, lava and plutonic rock from the edge of the arc. As arc material descends, minerals within it become unstable with the rising pressure and heat, and they undergo chemical changes. New minerals form, and chunks of the rock and sediment can break off. When those chunks are denser than the mantle rock around them, they continue to sink. But when they are less dense, such as those that form silica-rich granulites, they become buoyant and float upward until they reach the bottom of the arc crust and accumulate there.

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Cascadia Subduction Zone: Unprepared and Liquefaction

Call me paranoid, but when I see a 7.8 earthquake in Indonesia, and the news recalls the 8.9 magnitude earthquake that triggered the deadliest tsunami in history in 2004 killing more than 200,000 people, I’m reminded that we live in the shake zone of earthquakes and tsunamis, the Cascadia Subduction Zone. It doesn’t help when The New Yorker Magazine tells us that the “Really Big One” is coming and we’ll be able to surf to Idaho soon.

Last year, OPB-TV won awards for their “Unprepared” television series and documentary on the historical “big one” coming to the Pacific Northwest. It led to discussions around the state of Oregon involving geologists, seismologists, and area experts, all asking if we are prepared and what are we going to do or not do about it. They talked about the state of our bridges, schools, and the impact of liquefaction on our ports, home to fuel tanks, some almost 100 years old, that could rupture, dump into our precious waterways, and burn for ages. It was a wake-up call for all of us.

As a rock lover, I started questioning the ground under my feet. According to FEMA’s Earthquake Risk and Cascadia Region Earthquake Workgroup (CREW) and their educational Cascadia Subduction Zone Earthquakes 9.0 Magnitude Scenario (PDF), while I’m personally outside of the tsunami zone, besides being cut off from the rest of the world, the thing to fear most is: Liquefaction.

Tilted Victorian Home in San Francisco due to liquefaction - Photograph by G.K. Gilbert of the U.S. Geological Survey

Liquefaction is the process in which soil, often thought to be firm and solid, is “reduced” by earthquake shaking. While most commonly associated with saturated soils, liquefaction occurs in dry soils where there is space between the particles. Take a jar and fill it full of flour or grains. Tap it against the counter and you will see the level drop. Depending upon the space and shape of the grains, it might drop a little or a lot. That’s liquefaction in action. Continue reading “Cascadia Subduction Zone: Unprepared and Liquefaction”

Smartphones Help Create Global Sesmic Network

MyShake App - Zoom Into Map for Recent Earthquakes ViewIf you have a smartphone, why not join others worldwide to help track earthquakes.

For the past few years, the US Geological Survey department and others want to know how cell phones can be used to monitor and possibly detect earthquakes. Inside of each phone are sensors that can be used to create a worldwide seismic network to help with the study of earthquakes.

A couple weeks ago, it was announced that The University of California at Berkely has released MyShake and MyQuake. MyShake is for Android users and MyQuake is the Apple version.

The app is free and runs “silently” in the background. The app has the ability to distinguish between natural body and transportation movements and ground disturbances. The goal of the app is to collect enough data to help track earthquakes in a way that may lead to a global early warning system.

The app offers four key features in addition to collecting and transmitting earth movement data to Berkeley.

  • Recent: The Recent tab displays earthquake data globally with a magnitude of 2.5 or more within the past 7 days. Using a Google Map, the user may zoom around the globe to observer recent earthquake activity.
  • Safety: Simple steps to ensure the user is familiar with how to take cover before, during, and after an earthquake.
  • Senor: While mostly for fun, shake the phone around and you will see the phone’s senor record the movement.
  • Past: This is another Google Map highlighting the most powerful and noteworthy earthquakes throughout known history, some dating back hundreds of years.

According to “With “MyShake” App, Your Phone Feels Earthquakes and Automatically Warns Scientists” in Popular Mechanics, says: Continue reading “Smartphones Help Create Global Sesmic Network”