In addition to the usual flurry of getting ready for the meeting, the evening of November 30 provided us, and everyone in the immediate area, a geophysical reminder in the form of a magnitude 4.1 earthquake. The earthquake, just to the east of Dover, Delaware, is an exceedingly rare event for the area with no other recorded earthquake occurring anywhere nearby. The earthquake allowed Diana Roman, Lara Wagner, and DTM postdoc Helen Janiszewski the opportunity to put the DTM-developed "Quick Deploy Box" or QDB to good use the morning after the quake. The QDB, designed by Roman and Wagner, built by DTM Instrument Maker Tyler Bartholomew, and funded by grants from the Brinson Foundation, reduces the equipment needed for a seismometer deployment to a single checked baggage-size suitcase. Previously, the necessary components to install a single field seismic station filled the bed of a good sized pick-up truck. Their efforts even made it to the evening news in Philadelphia. Along with colleagues from several local universities and federal agencies, the group set up a total of 17 seismometers near the epicenter to capture information on the aftershocks. The location, magnitude, and direction of fault movement of the aftershocks can provide critical information on the causes of the main quake that may well relate to the rifting of Europe and North Africa away from the North American eastern seaboard some 200 million years ago.
The DTM team examined grains of silicon-carbide – a mineral made up of two abundant elements, and one that condenses at very high temperatures. They measured the titanium isotopic composition of these grains and were able to come up with their longer than 2-year estimate for grain formation because one of the titanium isotopes is produced by the radioactive decay of an isotope of vanadium. Both elements are produced by nucleosynthesis in the star. If the grains formed within a couple of half-lives of the vanadium isotope, and given their ratio of vanadium to titanium, they should have contained an excess of the titanium-49 isotope, the decay product of vanadium-49. They did not. They would have, given the 330-day half-life of vanadium-49, if the grains formed within 2 years of the cessation of nucleosynthesis when the star exploded.
Carnegie Institution for Science
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