| 2020 Sparta earthquake | |
| Tags: | y |
| Timestamp: | 2020-08-09 12:07:37 |
| Isc-Event: | 618711487 |
| Anss-Url: | se60324281 |
| Local-Time: | 8:07:47 EDT (UTC-4) |
| Magnitude: | 5.1 |
| Depth: | 4.7miles |
| Location: | 35.766°N -117.605°W |
| Fault: | Little River Fault |
| Type: | Oblique-slip reverse |
| Affected: | North Carolina, Virginia |
| Foreshocks: | Yes |
| Aftershocks: | Yes |
| Casualties: | 1 injured |
The 2020 Sparta earthquake occurred in North Carolina on August 9 at 08:07 EDT. The epicenter of this relatively uncommon intraplate earthquake was near the small town of Sparta, Alleghany County. The thrust-faulting earthquake had a moment magnitude of 5.1, occurring at a shallow depth of 4.7abbr=NaNabbr=. Rupture occurred on the previously unmapped Little River Fault. A surface rupture was documented following the earthquake; the first of its kind in the Eastern United States. Shaking was reported in parts of the Midwestern, and Southeastern United States. It was the strongest earthquake recorded in North Carolina in 104 years,[1] the second-strongest in the state's history, and the largest to strike the East Coast since the 2011 Virginia earthquake.[2] The earthquake significantly damaged homes and businesses in Sparta and injured at least one person. The shaking was also felt in other states along the East Coast. A state of emergency was declared in Sparta, and North Carolina granted $24 million in relief fund for repair works.
Measuring 5.1, it was the state's largest earthquake since a magnitude 5.2 earthquake struck Skyland in 1916. Over 80,000 people reported shaking from the earthquake. The earthquake was also the strongest to strike the East Coast since 2011.
The Piedmont region and Blue Ridge Mountains are part of the eastern Appalachian Mountains which formed due to an ancient continental collision with the African plate, during the Ordovician period, roughly 480 million years ago. This led to the formation of a supercontinent known as Pangaea. Continental collision extended for the next 250 million years, forming the Caledonian, Acadian, Ouachita, Variscan, and Allegheny orogenies. In the process, active thrusting occurred and micro continents were sutured to North America. When the supercontinent broke apart beginning in the Early Mesozoic, uplifting of the Appalachians ceased. This exposed the Appalachians to weathering that eventually eroded them down to an almost flat terrain as the Mesozoic Era concluded. Another period of uplifting the eroded topography occurred during the Cenozoic Era which led to aggressive erosion by rivers and streams.[3] [4] [5]
The mainshock source area was in the Blue Ridge Mountains of the Alleghanian orogeny. Faults in this part of the range typically trend northeast. The earthquake ruptured along a fault trend that is consistent with west–northwest to east–west striking structures that crosses major northeast-trending geological structures of the mountain range. However, the geology of these faults are poorly understood. The earthquake occurred in a region that progresses between thrust and strike-slip tectonics; the dominant crustal strain is configured in a northeast–southwest to east-northeast–west-southwest direction.
According to the United States Geological Survey, the mainshock was the result of oblique-reverse faulting within the shallow crust of the North American plate. The "relatively uncommon" earthquake occurred in the interior of the plate, known as an intraplate earthquake. Four foreshocks of magnitudes between 2.1 and 2.6 were recorded beginning about 25 hours prior to the earthquake. The focal mechanism solutions for the earthquake indicate rupture occurred on a moderately dipping fault either striking to the northwest or south. Further analysis of InSAR, the aftershocks, and field data favored a south-southwest dipping fault trending approximately west-northwest. There were 20 recorded aftershocks by August 28. The strongest in the aftershock sequence was a event that struck two days after the mainshock. In Sparta, the earthquake was assigned a maximum Modified Mercalli intensity of VI–VII and its peak ground acceleration exceeded 0.2 g.[6]
Ground fracturing was discovered south and southeast of Sparta while none were observed in the immediate epicenter area. A surface rupture extending over appeared southeast of the town.[7] The earthquake ruptured along this previously unmapped fault within the upper bedrock, dubbed the Little River Fault. Trenching of the Little River Fault indicate it is a thrust fault. This west-northwest–east-southeast striking fault is located within the local Paleozoic fabric. The surface fault trace is characterised by scarps and folds measuring high, and at its maximum.[8] It was the first ever documented surface rupture from an earthquake in the Eastern United States,[9] and the second observation made in Eastern North America, the other being the 1989 Ungava earthquake (6.3).[10] The rupture buckled a local road and damaged water lines and several properties.
Severe damage occurred in Sparta, further impacting businesses which were already affected by the COVID-19 pandemic. The town's manager, Ryan Wilmoth, said there were "very minor injuries" but did not specify the number of people injured,[11] and there was only one confirmed injury.[12] Many homes and business infrastructure were damaged; most were material damage that left the structure's integrity unaffected. A majority of structural damage was observed in ureinforced brick, masonry and concrete elements.[13] Within a week of the earthquake, there were 60 cases of serious damage and 465 minor damage reports.[14] Seventeen buildings were listed as unsafe for use and five were eventually demolished. At least 19 people lost their homes. Carpark ground fracturing and smashed ceramics were reported at Scott's Landscaping Nursery and Farms while at the Kathy Shore Tree Nursery, its owner estimated the repair cost at several hundred thousand dollars.[15] The Alleghany County administration office and a water supply network were damaged. Headstones were ripped from the ground,[16] and several chimneys were toppled or destroyed.[17] Parts of Tennessee, Ohio, Washington D.C., and Atlanta also felt the earthquake, several hundred miles away from the epicenter.[18] [19]
Sparta mayor Wes Brinegar, issued a state of emergency to apply for FEMA and state financial aid, but did not qualify for the former's disaster assistance criteria. At least $112 thousand in state assistance grants were handed out, and the Small Business Administration issued $1.17 million in loans. The legislature of North Carolina also allocated $24 million for relief. This funding supported a three-year repair project called the Earthquake Recovery Program, operated by the Office of State Budget and Management and North Carolina Emergency Management.[20] By 2021, there were over 230 requests for home repair assistance, averaging $44 thousand per home.[21]
Brinegar also cautioned residents of scams on GoFundMe as officials did not raise any request on the site. Scammers took advantage of the damage, impersonating construction workers and charging people up to $500 for repairs only to never provide the services.[22] Governor of North Carolina, Roy Cooper, toured the damage in Sparta, and reassured its residents; "We’ve dealt with a hurricane, a violent tornado, and now an earthquake all in the middle of a pandemic: North Carolinians are resilient." Nine displaced people from six households received help from the Red Cross.[23]