# Geologic Framework for Seismic Hazards in Central Virginia

## Science Center Objects

The Central Virginia seismic zone (CVSZ) comprises an area of ~13,000 km2 in the central Virginia Piedmont; seismicity in this zone is relatively frequent, but generally mild in magnitude. The August 2011 event was the largest temblor recorded in the CVSZ since the development of modern seismic monitoring and highlighted how little we actually know about the CVSZ, including: 1) the regional geologic framework, 2) paleoseismogenic history, and 3) the extent of regional seismic risk. In coordination with USGS and external partners – The USGS Earthquake Hazards Program, the Virginia Division of Geology and Mineral Resources, Lehigh University, University of Puerto Rico at Mayaguez, and Utah State University – objectives of this USGS NCGMP project are: 1) develop the regional geologic framework through detailed bedrock and surficial mapping; 2) quantify the regional Cenozoic history of erosion and deposition, and identify paleoseismogenic features and possible evidence for neotectonic deformation; and 3) develop methods and models to better understand the driving mechanisms of CVSZ neotectonics and seismicity, for broader application to other CEUS seismic zones.

The M5.8 Virginia earthquake on 23 August 2011 highlighted how little is known of the CVSZ, and how vulnerable the eastern US is to damaging earthquakes – this temblor caused upwards of $300 million in damage (Morello and Wiggins, 2011) from the epicentral area near Mineral, Louisa County, Virginia (Heller and Carter, 2015), as far northeast as Brooklyn, New York (Doll, 2011), including more than$35 million in damage to historic landmarks in Washington, DC (Grass, 2012; Ruane, 2014; Wells et al., 2015; Shahidi et al., 2015).  Prior to this event, the largest quakes recorded in the CVSZ were an M4.8 in 1875 and an M4.5 on 9 December 2003 (Tarr and Wheeler, 2006), although field evidence suggests larger events in the past (Obermeier and McNulty, 1998; Tuttle et al., 2015; Carter et al., 2016; Carter et al., 2017).

The CVSZ includes significant parts of the Richmond Metropolitan Statistical Area to the SE, Albemarle County and the city of Charlottesville to the NW, and Stafford County and the city of Fredericksburg to the NE– the CVSZ is home to more than 1 million people.  Two 1970’s-era nuclear reactors are also located within the CVSZ, and Washington DC is just ~150 km to the northeast.  Because of its location along the densely populated eastern seaboard, and the fact that seismic waves propagate much farther in stable eastern crust (Frankel et al., 1990; Pollitz and Mooney, 2015) than in crust west of the Rocky Mountain front (Nishenko and Bollinger, 1990), the 2011 central Virginia quake generated reports from Maine to Florida, and westward to northern Illinois, an area occupied by a third of the US population (Horton and Williams, 2012).  A thorough understanding of the CVSZ – the Paleozoic-Mesozoic geologic framework, active and potentially active structures, paleoseismic and neotectonic history, integrated to derive recurrence intervals for significant and damaging future events – is paramount for seismic hazard and risk assessment here and in other CEUS seismic zones.

Characterization of the Mw5.8 Mineral earthquake, and potential for future damaging earthquakes in the CVSZ and in other central and eastern US seismic zones, is of particular interest and importance to the USGS and society at large; these intraplate seismic zones remain poorly understood – crustal mechanisms responsible for their occurrence, recurrence processes, intervals and rates, and most importantly, seismic risk.  These research objectives can only be achieved through targeted detailed bedrock and surficial geologic mapping, coupled with regional geologic and tectonic synthesis, earthquake seismology, geophysics and remote sensing.   The goal of this project is a thorough understanding of the CVSZ; knowledge gleaned here can be applied to other CEUS seismic zones, and foster better understanding of aseismic regions in the central and eastern US.

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References:

Carter, M. et al., 2016, Characteristics of paleoliquefaction features in the Central Virginia Seismic Zone (CVSZ):  Geological Society of America Abstracts with Programs, v. 48, n. 3, doi: 10.1130/abs/2016SE-273045

Carter, M. et al., 2017, Paleoliquefaction reconnaissance in eastern North Carolina:  Is there evidence for large magnitude earthquakes between the Central Virginia Seismic Zone and Charleston Seismic Zone?: Geological Society of America Abstracts with Programs, v. 49, n. 3, doi: 10.1130/abs/2017SE-289779.

Doll, J., 2011, Earthquake damage in NYC is minimal; Mike Bloomberg is more concerned about hurricane Irene:  The Village Voice, 23 August 2011 [accessed 3 July 2014 at http://blogs.villagevoice.com/runninscared/2011/08/earthquake_damage_hurricane_irene.php].

Frankel, A. et al., 1990, Attenuation of high-frequency shear waves in the crust: measurements from New York state, South Africa and, southern California:  Journal of Geophysical Research, v, 95, n. B11, p. 17,441–17,457.

Grass, M., 2012, Virginia 2011 earthquake:  DC damage, recovery following 5.8 magnitude temblor:  The Huffington Post, 22 August 2012 [accessed 6 July 2014 at http://www.huffingtonpost.com/2012/08/22/virginia-2011-earthquake-_n_1822965.html].

Horton, J.W. and Williams, R., 2012, The 2011 Virginia earthquake: What are scientists learning?: EOS Transactions, American Geophysical Union, v. 93, n. 33, p. 317-318.

Morello, C. and Wiggins, O., 2011, Region tallies earthquake damage, mostly uninsured:  Washington Post, 24 August 2011 [accessed 31 July 2014 at http://www.washingtonpost.com/local/region-tallies-earthquake-damage-mostly-uninsured/2011/08/24/gIQAFdxScJ_story.html].

Nishenko, S. and Bollinger, G., 1990, Forecasting Damaging Earthquakes in the Central and Eastern United States:  Science, v. 249, n. 4975, p. 1412-1416.

Obermeier, S. and McNulty, W., 1998, Paleoliquifaction evidence for seismic quiescence in central Virginia during the Late and Middle Holocene time:  EOS transactions of the American Geophysical Union, v. 79, n. 17, p. S342.

Pollitz, F.F. and Mooney, W.D, 2015, Regional seismic wave propagation from the M5.8 23 August 2011, Mineral, Virginia earthquake, inHorton, J.W. et al., eds., The 2011 Mineral, Virginia, Earthquake and its Significance for Seismic Hazards in Eastern North America: Geological Society of America Special Paper 509, p. 295-304, doi: 10.1130/2015.2509(6).

Ruane, M., 2014, Recovered from an earthquake, the Washington Monument is set to reopen:  The Washington Post, 10 May 2014 [accessed 3 July 2014 at http://www.washingtonpost.com/local/recovered-from-an-earthquake-the-washington-monument-is-set-to-reopen/2014/05/10/be2c4130-d462-11e3-8a78-8fe50322a72c_story.html].

Shahidi, S. et al., 2015, Behavior and damage to the Washington monument during the 2011 Mineral, Virginia earthquake, in Horton, J.W. et al., eds., The 2011 Mineral, Virginia, Earthquake and its Significance for Seismic Hazards in Eastern North America: Geological Society of America Special Paper 509, p. 235-252, doi: 10.1130/2015.2509(13).

Tarr, A. and Wheeler, R., 2006, Earthquakes in Virginia and vicinity 1774-2004:  USGS Open-File Report 2006-1017, 1 sheet.

Tuttle, M. et al., 2015, Paleoliquefaction study of the earthquake potential of the Central Virginia Seismic Zone (CVSZ):  Geological Society of America Abstracts with Programs, v. 47, n. 7, p. 466.

Wells, D. et al., 2015, Ground shaking and the response of the Washington Monument during the 2011 Mineral Virginia earthquake, inHorton, J.W. et al., eds., The 2011 Mineral, Virginia, Earthquake and its Significance for Seismic Hazards in Eastern North America: Geological Society of America Special Paper 509, p. 199-233, doi: 10.1130/2015.2509(12).