Abstract
This study re-examines the effects of the December 22, 1875, Io VII MM, central Virginia earthquake. The previously identified higher intensity area (≥ V MM), which included the central Virginia counties that lie between Richmond and Charlottesville, was focused upon in this investigation. Primary documentary sources were used exclusively for this study. Those sources included previously unused historical documents such as weather observers’ reports, military records, and plantation records. The new documentary evidence included data from sites other than the 1875 population centers.
The new felt reports also helped determine more about the earthquake effects in different parts of the city of Richmond. For example, it was found that residents of the James River waterfront experienced moderately severe shaking (VII MM) while those in upland sections of the city took far less notice of the event (IV MM).
Based on the damage reports and the number and severity of aftershocks, a new meizoseismal area is defined as one centering around Louisa, Goochland, and Powhatan counties. An epicentral location (37.8N - 78.0W) was assigned within that area. The inferred epicenter is located near the small communities of Othma, Sandy Hook, and Gum Spring. Othma lies nearest to the midst of the area with the highest reported intensities and the largest number of aftershocks while Sandy Hook and Gum Spring lie nearest the 1875 transportation routes through that region. The epicentral interpretation (which is rounded to the nearest tenth of a degree) is made in order to place the epicenter near the center of the meizoseismal contour identified by the new documentary evidence. The new epicenter might be at least 20 km in error because of James River alluvial deposits which may have amplified the shock. Another factor contributing to the possibility of a 20 km error is the scarcity of documentary information from this agrarian region of post-Civil War Virginia.
