The Cave: Magnitude 2.8 Earthquake - TENNESSEE - 3 mi ESE from Ridgely, TN - Tuesday, August 25, 2009 at 01:32:04 AM at epicenter

Tuesday, August 25, 2009

Magnitude 2.8 Earthquake - TENNESSEE - 3 mi ESE from Ridgely, TN - Tuesday, August 25, 2009 at 01:32:04 AM at epicenter

http://folkworm.ceri.memphis.edu/recenteqs/Quakes/quakes0.html

    MAG    DATE    LOCAL-TIME  LAT     LON    DEPTH    LOCATION
         y/m/d     h:m:s     deg     deg     km

map 2.8  2009/08/25 01:32:04 36.251N 89.434W  7.8    4 km ( 3 mi) E   of Ridgely, TN
map 0.9  2009/08/24 05:05:40 36.238N 89.503W  6.1    3 km ( 2 mi) SSW of Ridgely, TN
map 1.3  2009/08/23 12:29:00 36.286N 89.463W  1.3    3 km ( 2 mi) NE  of Ridgely, TN

Magnitude 2.8 - TENNESSEE

2009 August 25 06:32:04 UTC

Earthquake Details

Magnitude	2.8
Date-Time	Tuesday, August 25, 2009 at 06:32:04 UTC Tuesday, August 25, 2009 at 01:32:04 AM at epicenter Time of Earthquake in other Time Zones
Location	36.251°N, 89.434°W
Depth	7.8 km (4.8 miles)
Region	TENNESSEE
Distances	5 km (3 miles) ESE (109°) from Ridgely, TN 15 km (9 miles) SSE (165°) from Tiptonville, TN 15 km (9 miles) SW (233°) from Hornbeak, TN 135 km (84 miles) NNE (21°) from Memphis, TN 274 km (170 miles) SSE (165°) from St. Louis, MO
Location Uncertainty	horizontal +/- 0.3 km (0.2 miles); depth +/- 0.7 km (0.4 miles)
Parameters	NST= 26, Nph= 32, Dmin=3 km, Rmss=0.04 sec, Gp= 50°, M-type=duration magnitude (Md), Version=B
Source	Cooperative New Madrid Seismic Network
Event ID	nm975

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Earthquake Summary

Tectonic Summary

EARTHQUAKES IN THE NEW MADRID SEISMIC ZONE
The New Madrid seismic zone of southeast Missouri and adjacent States is the most seismically active in North America east of the Rockies. During the winter of 1811-1812 three very large earthquakes devastated the area and were felt throughout most of the Nation. They occurred a few weeks apart on December 16, January 23, and February 7. Hundreds of aftershocks, some severely damaging by themselves, continued for years. Prehistoric earthquakes similar in size to those of 1811-1812 occurred in the middle 1400's and around 900 A.D. Strong, damaging earthquakes struck the southwestern end of the seismic zone near Marked Tree, Arkansas in 1843 (magnitude 6.3), and the northeastern end near Charleston, Missouri in 1895 (magnitude 6.6). Since 1900, moderately damaging earthquakes have struck the seismic zone every few decades. About twice a year people feel still smaller earthquakes that do not cause damage.

Earthquakes in the central and eastern U.S. are typically felt over a much broader region than in the western U.S. 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. The earthquakes of the New Madrid seismic zone occur within a large network of faults called the Reelfoot rift. The rift formed about 500 million years ago, when this region was stretched in the northwest-southeast direction. Along a northeast-southwest zone at least 70 km (40 mi) wide and 500 km (300 mi) long, the rocks in the rift were slowly dropped down about 1-2 km (1 mi) along some of the faults. Now the region is undergoing east- west shortening, and the ancient faults of the Reelfoot rift are being reactivated to generate earthquakes. Today the Reelfoot rift and the New Madrid seismic zone are 2,000 km (1,200 mi) from the nearest plate boundary, which is in the Caribbean Sea.

The network of faults in the seismic zone is buried beneath hundreds to thousands of feet of sand and mud. Four of the largest faults are recognized as alignments of abundant small earthquakes, and movements along two of these faults dammed rivers and created lakes during the earthquakes of 1811-1812. A few more deeply buried faults were detected during oil and gas exploration, and a few small faults are known from geologic mapping. However, many earthquakes occur away from the few known faults, so there must be additional, unknown faults that can generate earthquakes in the seismic zone. Accordingly, the best overall guide to seismic hazard in the New Madrid seismic zone is the earthquakes themselves.