Tuesday, December 24, 2013

Yes, There Really is a "Sandwich Plate"

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

An interesting pair of earthquakes recently occurred in the Scotia Sea region, south of Chile and Argentina: Magnitude 7.7 (November 17, 2013) and Magnitude 7.0 (November 25, 2013).
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Fortunately, because of their remote location, there was little or no damage associated with these earthquakes, and they didn't make a lot of headline news. But they illustrate some interesting earthquake and plate tectonic processes of the Scotia Plate and the Sandwich Plate.
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The Scotia Plate/Sandwich Plate region is a tectonic region between the South American Plate and Antarctic Plate, and stretches from the South Sandwich Islands to the southern tip of South America. The Scotia Plate moves eastward relative to the South American plate, but the motion is complicated by the presence of a divergent boundary in the eastern portion of the Scotia Plate, delineating the western edge of the Sandwich Plate.
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The two recent earthquakes had motion that is consistent with the long-term (millions-of-years time scale) plate motion (shown by the blue and white arrows in the top figure).

The second earthquake might be a remotely-triggered earthquake, an earthquake that is too far away from the first quake to be an aftershock, but (maybe?) too close in time to be just a coincidence...

Sunday, August 18, 2013

New Opportunities for Exploring Global and Regional Earthquakes in the Classroom and Beyond

Alan Kafka, Justin Starr, and Anastasia Moulis
Weston Observatory
Department of Earth and Environmental Sciences
Boston College
Seismological observatories operate a variety of types of seismographs, each “tuned in” to some aspect of watching the Earth quake. At Weston Observatory, we monitor earthquakes recorded by "research seismographs" of the New England Seismic Network (NESN) and by "educational seismographs" of the Boston College Educational Seismology Project (BC-ESP).
The BC-ESP offers opportunities for students of all ages to collaborate with research scientists as part of their experience in school and beyond. Having a seismograph in a classroom, or other publicly accessible location, gives students of all ages direct experience with recording earthquakes. Educational seismographs are inexpensive and can be easily installed and operated in schools, libraries, and any other places that want to have their own seismograph. But these educational seismographs are limited in terms of the quality of seismic recording compared to what can be achieved with much more expensive research seismographs.
The figure below shows two different recordings of a magnitude 6.6 earthquake that occurred in Colombia on August 13, 2013. The seismogram on the left was recorded by an educational seismograph located in Stoughton, MA and the seismogram on the right shows the same earthquake recorded by an NESN research seismograph located at Weston Observatory. The earthquake is much more clearly recorded by the research seismograph, but the educational seismograph is much less expensive and is easily installed and operated at BC-ESP sites.
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A new development is now enabling us to integrate these two aspects of our seismic recording at Weston Observatory. New software (currently in beta testing phase) called "jAmaSeis", being developed by the Incorporated Research Institutions for Seismology (IRIS), in collaboration with Moravian College, makes it possible for us to bring educational and research seismograph data together in the same seismogram viewing and analysis environment. With this new software, students can have their own classroom seismograph, while simultaneously viewing and analyzing seismographs recording data at remote earthquake research observatories.
Our BC-ESP students, and other people who visit Weston Observatory, often ask us why we didn't record some of the California earthquakes that were reported in the news. Being on an active plate boundary, California earthquakes of course occur more frequently than New England earthquakes, but many of those California earthquakes are too small to be seen all the way across the country at BC-ESP sites. But with the new jAmaSeis software, we are able to display the recordings from our own educational seismograph on the same screen as recordings from an educational seismograph located in California. This makes it possible for BC-ESP students to see real-time recordings of these smaller California earthquakes.
Thus, with the new jAmaSeis software, students at a school in New England could monitor earthquakes on both sides of the country, at a plate boundary and in the middle of a plate (and vice versa for students in California). In the figure below, the top seismogram shows what we recorded on August 4, 2013 at Weston Observatory (station WOBC), and the bottom shows what was recorded on the same day at Sitting Bull Academy, located in Apple Valley, CA (SBCA). At SBCA, you can see a magnitude 3.9 California quake and a magnitude 5.3 quake in Western Canada. At WOBC, you only see the bigger, magnitude 5.3 quake.
Click on image to enlarge.
These new developments in software and web-based networking are opening up new opportunities for students of all ages to explore global and regional earthquakes in the classroom and beyond, and to learn about science by participating with research seismologists as together we watch the Earth quake.

Sunday, March 24, 2013

Relative Sizes of Some Recent Seismic Events


A few things about this plot (all numbers are approximate, but they are correct enough for this level of analysis):
kT = kilotons
2013 DA14 refers to how big an event the near-Earth asteroid that missed us on Friday, Feb. 15, 2013 would have been if it crashed.
Japan quake is the 2011 mega-quake, and Haiti quake is the 2010 quake that devastated Haiti.
Haiti quake (magnitude 7) is very small (in terms of magnitude) compared to Japan quake (magnitude 9).
Everything else is very small compared to Japan quake.
In very rough numbers/guesstimate: The meteorite that killed the dinosaurs was equivalent to something like magnitude 10 to 12. If we use the number 11, that's at least 100 times bigger than Japan quake. So, if we plotted the dinosaur meteorite, everything else here would probably be too small to see.