Flat Stanley Visits the BSL
Ms. Wong's 4th and 5th grade class from Grass Valley School in Oakland sent me to visit the UC Berkeley Seismological Laboratory. Here I am with a seismologist, Dr. Peggy Hellweg. Seismologists study earthquakes, and Dr. Hellweg explained how earthquakes happen.
The outermost layer of the earth, the crust, is broken into huge chunks, called "plates," that move around in different ways. In some places, like right under Chile, one plate is being pushed (subducted) under another. In other places, like Iceland, two plates are spreading apart from one another. And finally, in places like Oakland, two plates (the North American Plate and The Pacific Plate) are sliding past each other. The plates move very slowly, about as fast as your fingernails grow. In some places, some of the movement is very slow and steady. This is called "creep." The Hayward Fault, which runs through Oakland and through UC Berkeley itself, is a fault that creeps. But most of the movement on faults is not slow and steady. Instead, the two sides of the fault are stuck together in place, and pressure builds up where they are stuck. When the stress and pressure get high enough, the stuck area (called an asperity) breaks and there is an earthquake! Lots of energy is released in the form of shaking, and the ground alongside each side of the fault moves suddenly.
On Thursday, October 21, at 10:21 AM, I was in a giant earthquake drill with millions of people! It is called The Great California Shakeout. Here I am with Sanne Cottaar, a UC Berkeley graduate student. She studies the inside of the earth using information from earthquake waves. She helped me to "Drop, Cover, and Hold On!" In an earthquake, you should drop to the floor, take cover under a sturdy piece of furniture like a desk or table, and hold on so that it doesn't move away from you during the shaking.
I wanted to know if there was anything else that I could do to stay safe during an earthquake, so I had a meeting with another very small person, Seismo Susie. She explained that in an earthquake, not only will the ground shake, but everything on the ground, from your house, to your classroom, to the books on your shelves, will also shake. Most injuries that happen during earthquakes happen from things falling on people. So you can prepare for an earthquake by strapping large, tall objects (like bookshelves) to the wall and moving heavy objects to lower shelves. You can also move heavy objects and picture frames with glass in them away from places where people sit or sleep. Seismo Susie showed me this video of how she got smart about earthquake safety. You can also make a disaster kit containing things you would need in an emergency.
Next, Dr. Hellweg took me on a tour of a seismic station! This particular station is on the UC Berkeley Campus in the basement of a building, but the Berkeley Seismo Lab has stations all over Northern California, in old mines, in reservoir and winery tunnels, and in deep holes in the ground. Since seismometers, which record earthquakes, can also record vibrations from things like trucks driving by, scientists try to place them in out of the way places, away from all of this "noise" caused by people. Here I am next to an instrument called a "data logger," which is attached to the seismometer. It records the data and sends a copy back to the lab.
Next, Dr. Hellweg showed me an old way of recording earthquakes. Nowadays, all of our data is recorded digitally and stored on computer disks, but old seismometers recorded earthquakes with heat pens on heat-sensitive paper, with beams of light on photographic film, and even as an etching on paper that was deliberately covered in soot, called smoked paper. Here, I'm standing by a drum recorder with a heat pen and special heat-sensitive paper. Each drum has room for about 26 hours of recording, each line takes about an hour to draw, and each tick mark the pen makes is about a minute apart from the last one. This drum recorder, which gets data from the seismometer in the station we were just at, BKS, still works, but the recordings are only used in college classes, not for scientific research.
Here I am with a recording of the magnitude 7.2 earthquake that happened on April 4th (Easter) of 2010 in Baja California, Mexico.
And here I am with a computer printout of a digital recording of the same earthquake. On this printout, you can see the 3 directions in which the seismometer records ground motion from earthquakes: North/South, East/West, and Up/Down. (The paper recording only shows up and down motion.) In this recording, you can't see the first wiggle (called a P wave), very well, but you can see other waves, called S waves, Rayleigh waves, and Love waves, that arrive later on.
Here is a recording of the magnitude 6.5 earthquake that happened offshore of Northern California on January 10, 2010. The earthquake happened in the Mendocino Triple Junction, a place where three plates meet! Here, the Gorda Plate is sliding under the North American Plate (subduction), while the North American Plate and the Pacific Plate are sliding past each other and the Pacific Plate and the Gorda Plate are also sliding past each other. There are a lot of earthquakes at the Mendocino Triple Junction!
This last picture shows me next to a recording of a magnitude 4.1 earthquake in Milpitas (near San Jose, CA). The earthquake released about 20,000 times less energy than the magnitude 7.2 earthquake in Mexico that we looked at, but since it was so close to station BKS, the height (or amplitude) of the wiggles is still pretty tall.
The seismology lab was very exciting! Remember, when you feel the earth shake, "Drop, Cover, and Hold On!"
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