The Savage Earth: Earthquakes and Volcanos

[lighthouse]

http://rockhoundingar.com/geology/fault.html

How often do these moderate to strong earthquake events occur in our area? The average repeat time for a magnitude 6.3 New Madrid earthquake is 70 years, plus or minus 15 years. In 1843, such a quake occurred near Marked Tree, AR causing damage in the then sparsely settled Memphis area. Not since the 1895 Charleston, MO, earthquake has the central Mississippi Valley been shaken by an earthquake in the magnitude 6 to 7 range. And with the increase in population in the region since then the number of buildings, lifelines and inhabitants that can be affected by an earthquake has increased dramatically. The probability that a significant damaging earthquake will occur within 15 years is 40% - 63%.


http://www.encyclopediaofarkansas.net/encyclopedia/entry-detail.aspx?entryID=2219


The New Madrid Fault, also called the New Madrid seismic zone, is actually a series of faults, or fractures, at a weak spot in the earth’s crust called the Reelfoot Rift. It lies deep in the earth and cannot be seen from the surface. The fault line runs roughly 150 miles from Arkansas into Missouri and Illinois. In 1811–1812, it was responsible for the most violent series of earthquakes in the history of the continental United States, and scientists predict that another large earthquake is due which could inflict great damage to Arkansas as well as up to half the nation.

The New Madrid seismic zone runs roughly northeast from Marked Tree (Poinsett County). It generally follows Interstate 55 in a zigzag pattern through Blytheville (Mississippi County), crossing five state lines and cutting across the Mississippi River in three places.




Indications of prehistoric “sand blows” lead scientists to suspect major earthquakes in the New Madrid zone around the years 900 and 1450 AD

[lighthouse]

5. How Many Earthquakes Happen Every Month? Day? Minute?

Using the previous table:


Per month..........................................App roximately 80,000


Per day.........................................Approx imately 2,600


Per minute..................................Approximat ely 2


And, per second, one earthquake is felt approximately every 30 seconds.

Of these only a relative few are capable of causing damage. Earthquakes are common natural events.


http://www.ceri.memphis.edu/aware/follies.html








The New Madrid fault system, or the New Madrid seismic zone, is a series of faults beneath the continental crust in a weak spot known as the Reelfoot Rift. It cannot be seen on the surface. The fault system extends 150 miles southward from Cairo, Illinois through New Madrid and Caruthersville, Missouri, down through Blytheville, Arkansas to Marked Tree, Arkansas. It dips into Kentucky near Fulton and into Tennessee near Reelfoot Lake, and extends southeast to Dyersburg, Tennessee. It crosses five state lines, and crosses the Mississippi River in at least three places

[jeshurun]

When I lived in the chicagoland area for over a decade, I never felt an earthquake. There was just the one quake that I was aware of but I didn't even feel that one.

[lighthouse]

Update time = Sat Apr 19 0:47:07 UTC 2008


MAG UTC DATE-TIME
y/m/d h:m:s LAT
deg LON
deg DEPTH
km Region
MAP 3.5 2008/04/19 00:13:53 51.519 -176.817 28.4 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA



--------------------------------------------------------------------------------
MAG UTC DATE-TIME
y/m/d h:m:s LAT
deg LON
deg DEPTH
km Region
MAP 5.4 2008/04/18 21:11:01 -27.535 -176.586 35.0 KERMADEC ISLANDS REGION
MAP 4.9 2008/04/18 20:51:49 51.706 -179.838 10.0 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 6.4 2008/04/18 20:39:09 -17.190 -179.172 574.9 FIJI REGION
MAP 3.0 2008/04/18 20:38:51 18.523 -64.570 51.3 VIRGIN ISLANDS REGION
MAP 2.6 2008/04/18 20:33:03 51.783 -178.839 8.4 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 2.7 2008/04/18 20:19:08 51.845 -178.849 8.0 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 4.2 2008/04/18 19:31:50 51.745 -178.744 3.7 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 3.6 2008/04/18 16:55:06 19.193 -65.501 138.8 PUERTO RICO REGION
MAP 5.1 2008/04/18 15:31:56 -52.849 21.396 10.0 SOUTH OF AFRICA
MAP 2.6 2008/04/18 15:18:45 38.038 -114.316 0.0 NEVADA
MAP 4.6 2008/04/18 15:14:17 38.478 -87.869 10.0 ILLINOIS
MAP 2.7 2008/04/18 13:20:30 19.416 -155.631 2.6 ISLAND OF HAWAII, HAWAII
MAP 2.6 2008/04/18 11:55:58 38.465 -87.854 10.0 ILLINOIS
MAP 2.5 2008/04/18 11:54:51 19.260 -64.650 10.2 VIRGIN ISLANDS REGION
MAP 2.9 2008/04/18 11:30:59 51.646 -178.861 12.4 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 3.0 2008/04/18 11:17:14 60.247 -150.844 54.2 KENAI PENINSULA, ALASKA
MAP 2.9 2008/04/18 10:57:46 41.245 -114.858 0.0 NEVADA
MAP 3.4 2008/04/18 10:36:33 38.460 -87.860 17.8 ILLINOIS
MAP 2.5 2008/04/18 10:15:31 38.464 -87.846 10.0 ILLINOIS
MAP 2.7 2008/04/18 10:07:19 51.747 -178.836 15.3 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 2.5 2008/04/18 10:03:59 38.453 -87.805 10.0 ILLINOIS
MAP 2.6 2008/04/18 09:59:31 38.469 -87.795 10.0 ILLINOIS
MAP 5.2 2008/04/18 09:37:00 38.450 -87.890 11.6 ILLINOIS
MAP 2.7 2008/04/18 09:01:56 54.057 -165.941 30.0 FOX ISLANDS, ALEUTIAN ISLANDS, ALASKA
MAP 2.6 2008/04/18 08:02:40 56.268 -158.065 54.7 ALASKA PENINSULA
MAP 2.5 2008/04/18 07:53:42 39.028 -123.359 4.1 NORTHERN CALIFORNIA
MAP 3.1 2008/04/18 07:49:47 19.059 -64.602 52.9 VIRGIN ISLANDS REGION
MAP 4.9 2008/04/18 07:43:50 25.901 128.363 35.0 RYUKYU ISLANDS, JAPAN
MAP 5.3 2008/04/18 07:35:47 49.423 155.630 58.9 KURIL ISLANDS
MAP 2.8 2008/04/18 06:46:49 60.165 -150.659 27.4 KENAI PENINSULA, ALASKA
MAP 2.7 2008/04/18 06:38:38 51.800 -178.838 10.0 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 3.8 2008/04/18 06:19:28 51.593 -178.770 5.3 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 3.1 2008/04/18 06:18:14 51.670 -178.851 8.4 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 3.6 2008/04/18 06:14:17 51.504 -178.952 0.0 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 2.6 2008/04/18 06:03:11 60.730 -150.872 53.9 KENAI PENINSULA, ALASKA
MAP 5.2 2008/04/18 05:58:38 25.999 128.288 35.0 RYUKYU ISLANDS, JAPAN
MAP 4.5 2008/04/18 05:14:03 14.691 -92.553 76.7 OFFSHORE CHIAPAS, MEXICO
MAP 4.1 2008/04/18 04:52:23 14.642 -91.780 74.8 GUATEMALA
MAP 2.5 2008/04/18 04:44:45 62.877 -143.599 0.3 CENTRAL ALASKA
MAP 4.0 2008/04/18 04:44:16 51.451 -179.003 0.0 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 3.2 2008/04/18 04:14:58 62.060 -150.473 18.9 CENTRAL ALASKA
MAP 3.2 2008/04/18 03:25:24 33.789 -116.104 0.4 SOUTHERN CALIFORNIA
MAP 4.6 2008/04/18 03:01:52 34.985 81.145 10.0 WESTERN XIZANG
MAP 2.5 2008/04/18 02:24:40 51.810 -178.035 17.9 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
MAP 2.7 2008/04/18 01:25:13 62.123 -153.489 18.3 CENTRAL ALASKA


http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/quakes_all.php

[Cowgirl4Christ]

Hello Lighthouse...

I asked JDS this question on the Illinois earthquake thread and thought I'd pose it to you as well.... Is it unusual for aftershocks to start increasing in magnitude? Thanks in advance for your reply! ~Linda

[lighthouse]

http://www.britannica.com/eb/article-59567/earthquake

In general, the number of aftershocks per day decreases with time


Most major earthquakes occur without detectable warning, but some principal earthquakes are preceded by foreshocks. In another common pattern, large numbers of small earthquakes may occur in a region for months without a major earthquake. In the Matsushiro region of Japan, for instance, there occurred between August 1965 and August 1967 a series of hundreds of thousands of earthquakes, some sufficiently strong (up to Richter magnitude 5) to cause property damage but no casualties. The maximum frequency was 6,780 small earthquakes on April 17, 1966. Such series of earthquakes are called earthquake swarms. Earthquakes associated with volcanic activity often occur in swarms, though swarms also have been observed in many nonvolcanic regions.



as you can see it can vary

[lighthouse]

it can also be a foreshock of another pending quake
and not an aftershock

[lighthouse]

Magnitude: Bigger earthquakes have more and larger aftershocks. The bigger the main shock the bigger the largest aftershock will be, on average. The difference in magnitude between the main shock and largest aftershock ranges from 0.1 to 3 or more, but averages 1.2 (a M5.5 aftershock to a M6.7 main shock for example). There are more small aftershocks than large ones. Aftershocks of all magnitudes decrease at the same rate, but because the large aftershocks are already less frequent, the decay can be noticed more quickly. Large aftershocks can occur months or even years after the main shock.

http://pasadena.wr.usgs.gov/step/aftershocks.html

[lighthouse]

Earthquakes occur in clusters. One of the first things
recognized about earthquakes is that large events hardly ever occur
alone. When one earthquake happens, we usually see another at a
nearby or identical location. To be able to talk about this
phenomena, seismologists coined three terms -- "foreshock,"
"mainshock," and "aftershock." In any cluster of earthquakes, the
one with the largest magnitude is called the mainshock; anything
before it is called a foreshock and anything after it is called an
aftershock. A mainshock can turn into a foreshock if a subsequent
event comes along with a larger magnitude.

http://www.stat.ucla.edu/cases/northridge/lucy_jones.txt

[lighthouse]

The relative number of small to large aftershocks does not
appear to change with time. However, since the overall rate dies
off, all magnitudes become less common with time. Since small
magnitudes happen much more often, we have more of them later.
But all magnitudes dies off at the same rate -- magnitude 5Us are
1/10 as common on day 10 as day 1, and magnitudes are 1/10 as
common on day 10 as day 1.

It is also possible that the first earthquake will turn out to be
a foreshock to an even larger event (6% of the time in California)