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Tuesday, May 05, 03:38:54pm [ Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: 1, 2, 3, 4, 5, [6], 7, 8, 9, 10 ]

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Date Posted: Friday, May 11, 03:34:39am
Author: Lij
Author Host/IP: adsl-99-31-14-157.dsl.bltnin.sbcglobal.net / 99.31.14.157
Subject: Yes, we had two small earthquakes.....

FIRST QUAKE:
http://earthquake.usgs.gov/earthquakes/eventpage/nm051012b#technical

SECOND QUAKE:
http://earthquake.usgs.gov/earthquakes/eventpage/nm051012c#technical


The first was 2.8 miles northwest. The second was 2.4 miles northwest. Both of them sounded like something exploding on the northeast end of the house and I was in the Kitchen on that end of the house. The first one was more like a very intense sonic boom and I wondered if it might have had anything to do with the coal mine 5 miles north. But the way it mapped out and the depth (6 - 7 miles) the quakes were both focused down in the Precambrian

The second was worse. I was in the kitchen in that NW end of the house. It hit so hard with the sound of an explosion that I half thought that end of the house had blew up. It felt like that hard compression at the bottom off a roller coaster run. I'll have to check for cracks in the foundation and brick-work tomorrow. Just had the chimney made taller too. So far one old piece of my mother's china is all that fell and broke.

I hope this is the end. The quakes that occurred in 2008 started April 18th and the last one of seven ended on July 18th that year. You can see that spread on GoogleEarth by turning you Earthquakes on (under Gallery) and going to Mt Carmel, IL, the quakes were about 12 km WNW of town.

Quakes aren't unknown here. We're in the Wabash Valley Fault Zone (WVFZ) which is generally a number of normal faults that trend just a slight bit east of north in line with the Wabash River. The trend fits up with the Reelfoot Rift which is the main structual feature that set off several possible Mag.8 earthquakes along the Mississippi in the winter of 1811-1812. The Reelfoot Rift was first a Precambrian feature as are the faults of the WVFZ. But the Reelfoot is thought to have doglegged and followed the trend of the Rough Creek Graben in Kentucky.

But there are other features in the Precambrian of the area that have come to light in the last few decades. Like the Vincennes Basin north of Vincennes which holds some 1000 meters of late Precambrian sediments (and could hold some interesting early fossils if you could get down there). And the English Basin of south central Indiana which may hold some 3000 meters of earlier Precambrian sediments and is thought to have undergone some thrust faulting within those sediments.

But it is still the deeper faults cutting the crystalline basement which have been active first due to rifting and second due to external pressures exerted intra-cratonically like the Appalachian mountain building processes in the east after the Pennsylvanian Period. More recent possibly large earthquakes have occurred in the last seven thousand years in the Wabash Valley. Crevasse sand blows along the Wabash and in gravel pits have been discovered and their top zones carbon dated. Geologists have found evidence of eight or more prehistoric earthquakes over the last 25,000 years that were much larger than any observed historically in the entire region of the rifts/fault zones.

...

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[> That's intense. Scary too. -- AurraSing, Friday, May 11, 10:17:19am (d99-199-122-58.bchsia.telus.net/99.199.122.58)

Hope your damage is minimal....


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[> [> Maybe some separation of mortar from brick..... -- Lij, Friday, May 11, 07:53:30pm (adsl-99-14-209-135.dsl.bltnin.sbcglobal.net/99.14.209.135)

..... On the NE side of the house, but it's hard to tell.

Piddly little quakes but the second hit hard and fast.


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