The March, 2013, meeting of the Potomac Geophysical Society will be held March 21st at the Fort Myer Officers’ Club in Arlington, VA (http://www.jbmhhmwr.com/index/Maps_and_Directions.html) in the Glassed-in room in the Fife and Drum (main dining room).
Airborne magnetic, gravity, and radiometric data delineate shallow and subsurface geological features associated with the Aug. 23, 2011 earthquake in Louisa County, VA
The M5.8 August 23, 2011 Louisa County, VA intraplate earthquake was felt by more people than any other in U.S. history not only because of population density, but also because of the associated geology. However, because the earthquake hypocenter is located at a depth of ~6 km, and limited bedrock exposures in central Virginia pose a challenge to geologic mapping, many questions remain. Potential field and gamma-ray spectrometry data thus provide key tools for imaging and understanding both shallow and deep subsurface geologic features.
In 2012, the USGS commissioned a high-resolution airborne magnetic, gravity, and radiometric (gamma-ray spectrometry for K, Th, and U) survey over the epicenters of the Louisa County earthquake and its aftershocks. This survey, flown ~120 m above ground with 200-m flight line spacing, provides up to a 20-fold improvement over existing geophysical data coverage. The new data show anomalies that correspond strongly to mapped geologic features as well as other anomalies that suggest how contacts might extend into areas lacking detailed mapping, or how they might continue at depth. Features of particular interest include granitoid intrusions, Jurassic dikes, contacts between metavolcanic and metasedimentary rocks, and shallow faults. Matched filtering and forward modeling of the potential field data was conducted to consider deeper features that may be related to the M5.8 causative fault. Additionally, maps derived by merging the 2012 data with regional surveys suggest how geologic structures may have impacted the propagation of seismic energy along the eastern seaboard.
Bio: Anjana (“Anji”) Shah has been a research geophysicist with the USGS’s Crustal Imaging and Characterization Science Center in Denver, CO since 2007. She specializes in the use of gravity and magnetics for geologic characterization and interpretation, and is currently working on several projects focused on mineral resource and earthquake hazard applications in the Eastern U.S. and southern Alaska. She received her Ph.D. from Columbia University’s Lamont-Doherty Earth Observatory, where she developed numerical models of tectonic and magmatic processes at mid-ocean ridges, and conducted studies of high-resolution AUV seafloor bathymetry and magnetic anomalies. Following that she was an NRC postdoc at the Naval Research Laboratory, where she used gravity and magnetic data to constrain structure and melt properties of the buried Chesapeake Bay Impact Structure. Prior to joining the USGS, Dr. Shah was a research scientist at Dynamics Technology (now part of Raytheon), where she developed methods of interferometric synthetic aperture sonar (InSAS) and approaches to fusing acoustic and magnetic sensor data for high-resolution seafloor mapping and mine detection.
Meeting Room and Dining Arrangements: We now meet in the glassed-in room at the back of the main dining room—The Fife and Drum. We order individually from the Club menu, which has a nice variety of dinner offerings. We pay a single bill (I pay it with my Officers Club credit card), so we collect at least $25 from each diner with the agreement, that if one orders more than $20 in food and drink, he adds the amount over $20 to his contribution. The $5 overcharge goes to the Room Fee, Tax, Gratuity, and the Speaker’s Dinner. We collect on the Honor System. We did this throughout the last year, and it worked well. This room change and use of the menu have greatly reduced the loss that we have incurred in the past for having fewer than 20 people dining, and the change has preserved the viability of using the Officers Club for our meetings.
Reception at 6:00. Order Dinner at 7:00. Talk at 8:30 PM. Please note that the meal orders will be taken at 7:00. Allow 15 minutes for security entering Ft. Myer as all civilian vehicles are searched. To ensure access to and from Fort Myer use the Hatfield Gate, open 24 hours a day (http://www.jbmhhmwr.com/index/Maps_and_Directions.html). Reservations are not necessary, however, we need a head count, so, if you wish to attend dinner ($25), please inform Bob Fraser at 540-888-3001 or via E-mail at email@example.com. If you wish, please feel free to attend the talk without dinner. Non-members and guests are welcome. Visit the PGS web site at http://www.potomacgeophysical.com for new meeting announcements, etc. Please send changes of address or email to firstname.lastname@example.org.