Utah Earthquakes

[1dave]

California usually gets all the "glory," but Utah isn't far behind - ranked 9th in severity among the states.

www.livescience.com/1140-study-lists-top-10-earthquake-states.html

Alaska is first, California, Nevada, Hawaii, Washington, Wyoming, Idaho, Montana, Utah, and Oregon as #10.





many, but not random! Western Utah is moving west.



More than 700 quakes occur here every year in over 215 potentially active faults, the biggest being the northern Wasatch Fault and the southern Hurricane fault.

So the US is becoming wider - separating where the Rio Grand runs north and south, and along the Wasatch Front, And where California is cutting free. 

[1dave]

There is no place on earth that does not suffer from earthquakes, but those on the plate borders suffer more than most.

Interesting to me is that the US is pulling apart west from east in central Colorado and western Utah.

Here in Utah we have around 700 per year.



Look at the line Washington (5), Idaho (6), Utah - Wasatch Fault & Hurricane Fault dividing eastern and western Utah (9), and Arizona - continuation of the Hurricane Fault (13).

The other line is the Texas - The Rio Grande River Bed RGRB (17), New Mexico - RGRB (11), Colorado - RGRB (14), Wyoming (7), and Montana (8).

in both lines, the quakes are generally more common and severe the further northwest they go.

Dec 7, 2017 14:28:25 GMT -7 @lookatthat said:

New Madrid

en.wikipedia.org/wiki/1811%E2%80%9312_New_Madrid_earthquakes
The 1811–12 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude 7.5–7.9 on December 16, 1811, followed by a moment magnitude 7.4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history.[1][2][3] They, 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 the US state of Missouri.

There are estimates that these stable continental region earthquakes were felt strongly over roughly 130,000 square kilometers (50,000 sq mi), and moderately across nearly 3 million square kilometers (1 million square miles). The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 km2 (6,200 sq mi).

The three earthquakes and their major aftershocks

December 16, 1811, 0815 UTC (2:15 a.m.); (M 7.5–7.9)[2][3] epicenter in northeast Arkansas. It caused only slight damage to manmade 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 (a village that was on the site of the former Fort San Fernando, near the site of present-day Caruthersville, Missouri) was heavily damaged by soil liquefaction.[3]
December 16, 1811 (aftershock), 1415 UTC (8:15 a.m.); (M 7.4)[3] epicenter in northeast Arkansas. This shock followed the first earthquake by six hours and was similar in intensity.[2]
January 23, 1812, 1500 UTC (9:00 a.m.); (M 7.3–7.6)[2][3] 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.[3]
February 7, 1812, 0945 UTC (3:45 a.m.); (M 7.5–8.0)[2][3] epicenter near New Madrid, Missouri. New Madrid was destroyed. In 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 what is now Lake County, Tennessee.[3]

Susan Hough, a seismologist of the United States Geological Survey (USGS), has estimated the earthquakes' magnitudes as around magnitude 7.[4]

There were many more aftershocks, including one magnitude 7 aftershock to the December 16, 1811 earthquake which occurred at 0600 UTC (12:00 a.m.) on December 17, 1811, and one magnitude 7 aftershock to the February 7, 1812 earthquake which occurred on the same day at 0440 UTC (10:40 p.m.).[3]