Quake activity along the San Andreas fault is picking up

Mineral was originally known as Tolersville,[3] but adopted its current name when it incorporated in 1902 due to the mining industry that supported the community. It was the center of gold mining activity in Louisa County and during its heyday there were no fewer than fifteen gold mines located within two miles (3 km) of the town. A zinc and lead mine also operated in the area into the 1970s.

Earthquake Summary
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Tectonic Summary

EARTHQUAKES IN THE CENTRAL VIRGINIA SEISMIC ZONE
Central Virginia Seismic Zone Since at least 1774, people in central Virginia have felt small earthquakes and suffered damage from infrequent larger ones. The largest damaging earthquake (magnitude 4.8) in the seismic zone occurred in 1875. Smaller earthquakes that cause little or no damage are felt each year or two.

Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).

FAULTS
Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most bedrock beneath central Virginia was assembled as continents collided to form a supercontinent about 500-300 million years ago, raising the Appalachian Mountains. Most of the rest of the bedrock formed when the supercontinent rifted apart about 200 million years ago to form what are now the northeastern U.S., the Atlantic Ocean, and Europe.

At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Central Virginia seismic zone is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean and in the Caribbean Sea. The seismic zone is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few, if any, earthquakes in the seismic zone can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the seismic zone is the earthquakes themselves.

Virginia

Earthquake History

On February 21, 1774, a strong earthquake was felt over much of Virginia and southward into North Carolina. Many houses were moved considerably off their foundations at Petersburg and Blandford (intensity MM VII). The shock was described as "severe" at Richmond and "small" at Fredericksburg. However, it "terrified the inhabitants greatly." The total felt area covered about 150,000 square kilometers.

The three great earthquakes near New Madrid, Missouri, in 1811 - 1812 (December 11, January 23, and February 7) were felt strongly in Virginia. Reports from Norfolk and Richmond newspapers describe the effects in detail.

An earthquake, apparently centered in southwestern Virginia, on March 9, 1828, was reported felt over an area of about 565,000 square kilometers, from Pennsylvania to South Carolina and the Atlantic Coastal Plain to Ohio. Very few accounts of the shock were available from places in Virginia; it was reported that doors and windows rattled (MM V). President John Quincy Adams felt this tremor in Washington D.C., and provided a graphic account in his diary. He compared the sensation to the heaving of a ship at sea.

The August 27, 1833, earthquake covered a broad felt area from Norfolk to Lexington and from Baltimore, Maryland, to Raleigh, North Carolina - about 135,000 square kilometers. Two miners were killed in the panic the shock caused at Brown's Coal Pits, near Dover Mills, about 30 kilometers from Richmond. At Charlottesville, Fredericksburg, Lynchburg, and Norfold, windows rattled violently, loose objects shook, and walls of buildings were visibly agitated (MM V).

Another moderately strong, widely felt shock occurred on April 29, 1852. At Buckingham and Wytheville, chimneys were damaged (MM VI). The felt area extended to Washington D.C., Baltimore, Maryland, and Philadelphia, Pennsylvania, and also included many points in North Carolina - approximately 420,000 square kilometers. This pattern was repeated on August 31, 1861. The epicenter was probably in extreme southwestern Virginia or western North Carolina. At Wilkesboro, North Carolina, bricks were shaken from chimneys (MM VI). The lack of Virginia reports may perhaps be ascribed to the fact that the Civil War was under way and there was rather heavy fighting in Virginia at the time. This shock affected about 775,000 square kilometers and was felt along the Atlantic coast from Washington, D.C., to Charleston, South Carolina, and westward to Cincinnati, Louisville, and Gallatin, Tennessee, and southwestward to Columbus, Georgia.

A series of shocks in quick succession disturbed the eastern two-thirds of Virginia and a portion of North Carolina on December 22, 1875. At Manakin, many chimneys were broken and shingles on one store were shaken off (MM VII). Damage to chimneys was reported from other places in Goochland and Powhatan Counties. At Richmond, the shock, which was accompanied by a rumbling noise, was severe and lasted from 20 to 30 seconds; plaster fell and several panes of window glass broke. There was general alarm in all parts of the city; many people ran out of their houses in fright. The total felt area was about 130,000 square kilometers.

The largest earthquake to originate in Virginia is historic times occurred on May 31, 1897. The epicenter was in Giles County, where on May 3, an earlier tremor at Pulaski, Radford, and Roanoke had caused damage (MM VI). Loud rumblings were heard in the epicentral region at various times between May 3 and 31. The shock on the latter date was felt from Georgia to Pennsylvania and from the Atlantic Coast westward to Indiana and Kentucky, an area covering about 725,000 square kilometers. It was especially strong at Pearisburg, where the walls of old brick houses were cracked and bricks were thrown from chimney tops. Springs were muddied and a few earth fissures appeared (MM VIII). Chimneys were shaken down at Bedford City, Houston, Pulaski, Radford, and Roanoke. Chimneys were also broken at Raleigh, North Carolina, Bristol and Knoxville, Tennessee, and Bluefied, West Virginia. Minor tremors continued in the epicentral region from time to time until June 6; other disturbances felt on June 28, September 3, and October 21 were probably aftershocks. On February 5, 1898, the residents of Pulaski reported additional chimney damage (MM VI). People rushed into the streets at Pulsaki and East Radford.

An earthquake on February 11, 1907, caused minor damage at Arvonia, Ashby, and Buckingham. At Arvonia, many people became terrified and ran from their houses (MM VI); although no damage was reported from Columbia, many ran from their homes. The felt area was small, approximately 14,500 square kilometers. Other shocks of lesser intensity occurred in the same area on August 23, 1908, and May 8, 1910.

The Shenadoah Valley region was strongly shaken by an earthquake on April 9, 1918. It was called the "most severe earthquake ever experienced" at Luray. Although little damage resulted, people in many places over the northern valley region were greatly alarmed and rushed from their houses (MM VI). Broken windows were reported at Washington, D.C. The tremor was noticed by President Wilson and his family at the White House; the President's secretary called a newspaper office to learn the cause of the terrifying noise. The felt area extended over 155,000 square kilometers, including parts of Maryland, Pennsylvania, and West Virginia. Another shock on September 5, 1919, was felt in the same general region, although the total affected area was much smaller. It was strongest in the Blue Ridge Mountains south of Front Royal. At Arco, plaster fell and some chimneys were damaged (MM VI). Springs and streams were muddied in the epicentral area.

On December 26, 1929, a moderate shock at Charlottesville shook bricks from a few chineys (MM VI). It was reported felt in various parts of Albemarle County. A number of newspaper accounts gave the date of this earthquake as December 25. Giles County was strongly shaken again on April 23, 1959. At Eggleston and Pembroke, several chimneys were damaged, plaster cracked, and pictures fell from walls (MM VI). A wide area (about 7,500 square kilometers) of southwestern Virginia felt the tremor; a few places in West Virginia also reported the shock.

Earthquake Summary
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Tectonic Summary

The Vanuatu earthquakes of August 20, 2011 (M 7.1 and M 7.0) resulted from thrust faulting on or near the subduction zone plate boundary between the Australia and Pacific plates in the Coral Sea region of the southwest Pacific. Near the epicenter of the earthquakes, the Australia plate moves to the east-northeast with respect to the Pacific plate at a velocity of approximately 83 mm/year, and begins its eastward decent beneath the arc at the Vanuatu North New Hebrides trench.

The M 7.1 earthquake (August 20, 2011, 16:55 GMT) preceded the M 7.0 event (August 20, 2011, 18:19 GMT) by 84 minutes, and was located approximately 6 km away horizontally, and 12 km in depth - each within location uncertainties of typical global earthquakes. The two events also had approximately the same focal-mechanism. The latter earthquake was almost certainly triggered by the earlier event. Seismologists sometimes refer to a pair of similarly sized shocks that occur at nearly the same time and location as an earthquake "doublet."

These earthquakes are located approximately 80 km to the south of an M 7.3 earthquake that occurred in August of 2010, and 600 km to the south of a sequence of large subduction thrust earthquakes that occurred in October of 2009. The Vanuatu region experiences a very high level of earthquake activity, with almost 50 events of magnitude 7 and larger having been recorded since 1973. The subducting Australia plate is seismically active to depths of about 350 km beneath the islands.