Mapping Seismic Hazards in Virginia
Earthquakes in the Commonwealth
Earthquakes are natural geologic events that remind us that we are living on a dynamic planet. For thousands of years, humans have observed the occurrence of seismic events across the world. In modern times, earthquakes are more destructive due to increasing development and population density. Today, millions of dollars of damages can result from a single earthquake.
Chimney damage in Louisa County
caused by the 2011 Mineral earthquake.
Earthquakes occur underground along geologic faults. Although Virginia has many faults, nearly all of them are inactive. Most earthquakes in Virginia are not associated with a known fault, but occur within three distinct seismic zones: the Eastern Tennessee Seismic Zone (ETSZ) includes Lee County in far southwestern Virginia; the Giles County Seismic Zone (GCSZ) extends through the New River Valley; and the Central Virginia Seismic Zone (CVSZ) includes the cities of Richmond and Charlottesville. Although these seismic zones have been defined, there remains much to learn about seismicity in the Commonwealth.
Seismometers have actively been monitoring earthquakes in Virginia since the 1960s. These instruments record ground motion data that help scientists better understand modern eastern earthquakes and the faults that trigger them. Information about older earthquakes that occurred prior to seismometer emplacement, however, can only be found in public records, such as newspapers or personal accounts. In Virginia, a written record of earthquakes exists back to the 18th century. Evidence of pre-historic earthquakes may also exist, preserved within the geologic record. Examples of such paleoseismic evidence include offsets in soil or soft sedimentary deposits, damage to cave formations, and liquefaction features such as "sand dikes" or "sand boils."
Seismic Hazard Mapping
On August 23rd 2011, Virginia’s largest recorded seismic event shook central Virginia, causing almost $90 million in local damages. Residences, schools, and other buildings as far away as Baltimore, Maryland suffered structural damage from the 5.8Mw earthquake. In total, damages amounted to at least $300 million (2011 GEER report). In response to this event, the Federal Emergency Management Agency (FEMA) issued a major disaster declaration (DR-4042) to offer assistance to the residents and businesses that suffered damages in central Virginia.
Earthquakes have been recorded in Virginia for hundreds of years. Most events relate to three distinct seismic zones.
In addition, the Virginia Department of Emergency Management provided funding through the FEMA Hazard Mitigation Grant program to reduce the impact of future earthquakes. DGMR applied for and received a grant entitled “GIS Fault Mapping of Virginia Seismic Zones” (HGMP-4042-000-014) to assess seismic hazards in the Commonwealth.
As part of this project, DGMR geoscientists worked in collaboration with the U.S. Geological Survey, Virginia Tech, and the College of William and Mary to study and compile evidence of modern and prehistoric earthquakes. Results, when paired with cultural and infrastructure data, aid emergency management and planning agencies to identify and mitigate hazards from future earthquakes. This project was completed and delivered to VDEM in May 2017.
Liquefaction sand boils in alluvium along the South Anna River in Louisa County
generated by shaking from the August 23rd 2011 earthquake.
Photo courtesy of Mark Carter, USGS.
Primary goals of the FEMA earthquake hazard mapping project included:
- The development of a comprehensive ArcGIS (geographic information system) fault geodatabase for Virginia;
- Confirmation of existing fault mapping in Virginia using geological field studies;
- Use newly released (2012, 2104) high-resolution LiDAR data for the 2011 epicentral area to help identify possible new faults;
- Development of a comprehensive Virginia earthquake epicenter database and report containing location and damage information;
- General earthquake hazard assessment to identify communities and infrastructure at greatest risk of future earthquake damage;
- Presentation of data products and outreach materials to planners and emergency management agencies in seismically active areas to help reduce earthquake hazards in Virginia.
Additional Seismic Resources:
2011 Mineral earthquake FEMA disaster declaration
In the Event of an Earthquake
USGS: EQ Hazards Program
Virginia Tech Seismological Observatory
US Geological Survey Earthquake Hazards Program
Center for Earthquake Research and Information (CERI)
Incorporated Research Institutions for Seismology (IRIS)
EarthScope US Seismic Array
Seismometers in Virginia