Goddard Space Flight Center, Greenbelt, Maryland 20771
ENGINEERING COLLOQUIUM
Monday, , 2011 / 3:30 PM, Building 3 Auditorium
Jonathan M.G. Glen
"When Earth's Magnetic Field Flips: Polarity Reversals And Rapid Transitional Field Change"
ABSTRACT -- A 15.6 million year old sequence of lava flows from north central Nevada erupted during a time when Earth's magnetic field was switching polarity. One lava flow from that section yields a surprising result: the ancient field direction that it had recorded while it cooled reveals a distinctive, two-part remanence that reinforces a controversial hypothesis that geomagnetic change during a polarity transition can be much faster than normal. Our data show that, when this flow erupted and began to cool, the Earth's magnetic field was pointed east and down. By the time it finished cooling, however, the field was pointing in a north-down direction. A simple conductive cooling calculation indicates that a 53° change from the east-down to north-down field occurred at an average rate of approximately 1°/week, several orders of magnitude faster than that typical of secular variation.
SPEAKER -- Jonathan M.G. Glen is a researcher at the U.S. Geological Survey working in the Geophysics Unit in Menlo Park, California. He received his B.A. in geophysics in 1986 from the University of California, Berkeley and his Ph.D. in geophysics in 1994 at the University of California, Santa Cruz. Since 1999, he has been a research geophysicist at the U.S. Geological Survey and, since 2008, a consulting professor at Stanford University's Geophysics Department. His recent work has mostly focused on applying potential-field methods to identifying crustal structures (such as faults, fractures, and contacts), and to mapping the depth and extent of geologic units in the subsurface. He uses this technique, together with rock-magnetic and paleomagnetic methods, to address geologic and tectonic problems in the western U.S. that bear on earthquake hazard, mineral resource, and geothermal resource issues.