New Madrid fault and earthquake-prone region considered at high risk today
The 1811-1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes remain the most powerful earthquakes ever to hit the eastern United States in recorded history. These events, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within Missouri.
There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometres (50,000 sq mi), and moderately across nearly 3 million square kilometers (1 million square miles). The historic 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 square kilometres (6,200 sq mi).
- December 16, 1811, 0815 UTC (2:15 a.m.); (M ~7.2 – 8.1) epicenter in northeast Arkansas. It caused only slight damage to man-made structures, mainly because of the sparse population in the epicentral area. The future location of Memphis, Tennessee experienced level IX shaking on the Mercalli intensity scale. A seismic seiche propagated upriver and Little Prairie was heavily damaged by soil liquefaction.
- December 16, 1811, 1415 UTC (8:15 a.m.); (M ~7.2–8.1) epicenter in northeast Arkansas. This shock followed the first earthquake by six hours and was similar in intensity.
- January 23, 1812, 1500 UTC (9 a.m.); (M ~7.0–7.8) epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.
- February 7, 1812, 0945 UTC (4:45 a.m.); (M ~7.4–8.0) epicenter near New Madrid, Missouri. New Madrid was destroyed. At St. Louis, Missouri, many houses were severely damaged, and their chimneys were toppled. This shock was definitively attributed to the Reelfoot Fault by Johnston and Schweig. Uplift along a segment of this reverse fault created temporary waterfalls on the Mississippi at Kentucky Bend, created waves that propagated upstream, and caused the formation of Reelfoot Lake by obstructing streams in Lake County, Tennessee.
Susan Hough, a seismologist of the United States Geological Survey (USGS), has recently estimated the earthquakes' magnitudes as "right around magnitude 7. Possibly a bit below, possibly a bit above, but not as big as 7.5."
in Wikipédia
Sem comentários:
Enviar um comentário