Predicting the next Northwest mega-quake still a struggle for geologists

Apr 20, 2010 | Posted by: roboblogger | Full story: Oregonlive.com

The earthquake in Haiti earlier this year left buildings crumbled. A mega-quake in Oregon would be a different kind -- one from the Cascadia subduction zone off the coast -- but would carry tremendous punch.

Comments
1 - 5 of 5 Comments Last updated Apr 30, 2010

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

#1 Apr 23, 2010
Very handy article, not least of which is that finally the dates of the large rebound/long Duration mecalli X events (r/lx) have finally been logged and published.

The critical problem with the Cascadia zone is that it fronts a spreading backarc basin driven by hotspots at the backarc backfault. Namely Chilcotin (BC, Canadian rockies SW. vector spread), Yellowstone (NE. of the supervolcano WSW. vector spread & radial), Colorado (NE. of Hot sulphur springs, WNW vector spread), Panguitch (Utah, NW & radial spread, and also Raton-Clayton in the SE. rockies (Capulin) which is now underplating the continental crust and partly drives Mexico SW. spread in megaquakes, having been cut off from the basin & range by the Panguitch hotspot.

The result is that r/lx affects cascadia in several different vectors as a result of backarc basin spread with variable runout and variable recompression interval time.

This variability in vectors and runout crossing the forearc gives you the cluster effect.

Have a nice day: Ag

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

#2 Apr 24, 2010
Also note in passing.

The Gorda backarc basin has a backarc main rift in the Owens valley region of California, with the bulk of the magma incorporated during the regular r/lx of Aceh sized runouts being produced at the arc sector emergent at the Lassen volcanic complex & environs, and the bulk of the magma @ the rift being produced at the Mono-Inyo supervolcano which is still advancing through the crust.

If goldfinger's dates are correct, then the 1500AD event is the r/lx at the Gorda arc and the activity at Mono-Inyo is driven by overcompression of the Mono-Inyo pluton by the recompressing rift due to spreading at the Gulf of california rift heading upward into the Panguitch hotspot.

Mono-Inyo is currently quiet, but the backarc basin is now recompressed to the Owens valley rift, hence the "Zit" effect at Mammoth Mountain and the now erupted and degassed high level chamber of Long Valley caldera.

Also note that a further hotspot driving rifting appears at Edziza in NW.Canada, with megaquakes at Queen Charlotte (SW.vector) producing magma which eventually ends up in the Edziza region. A SW. vector event at the garibaldi arc will eventually produce magma in the volcanic fields at the Queen Charlotte rift.

A further hotspot responsible for the initiation of the gulf of California rift lies just NW. of Durango in Mexico. The NE. arm of that rift & its warm oceanic crust is now being subducted under the Sierra madre range.

Megaquakes here initiate at Jalisco and run out practically all of the Mexican central plateau & also the arc down to Guatemala(!) Magma is produced In the mexico arc and the long fractures emerge at the Mogollon rim volcanic fields (SW. USA).

For Mexico, the Mexico arc and backarc recompress rapidly due to Cocos plate convergence and re break with the last event 1014AD, which caused r/lx of the Guatemala backrange as well and a Caribbean megaquake.

The lock point @ Jalisco is the fastest convergent point of the remaining mexican backarc basin & is within tyhe error bar time of the next r/lx.

Have a nice day: Ag
whatingscominto

London, UK

#3 Apr 25, 2010
we are due fo a large earthquake in the uk now;
earthquakes in the uk are usually caused by ground slip faults or rare drop faults!

the uk has just completed 100 years of mining and the resultant water table shift leads to drop faulting;

when water goes deep into cazams deeper than 1 mile
then the heat expansion causes rock faults that generate significant amounts of heat and will generate gas release which will be ignited by rock friction, this gets so hot it melts the rock into moulten larva!

note; as over a billion tons of gas and oil has been extracted from the north sea this then causes fault movement because sea water dissolves clays and chalk soft rock formations this leads to massive earth quakes; I calibrate there is a very large earthquake due now! so some sort of planning needs to be considered quickly;

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

#5 Apr 30, 2010
whatingscominto wrote:
we are due fo a large earthquake in the uk now;
earthquakes in the uk are usually caused by ground slip faults or rare drop faults!
the uk has just completed 100 years of mining and the resultant water table shift leads to drop faulting;
when water goes deep into cazams deeper than 1 mile
then the heat expansion causes rock faults that generate significant amounts of heat and will generate gas release which will be ignited by rock friction, this gets so hot it melts the rock into moulten larva!
note; as over a billion tons of gas and oil has been extracted from the north sea this then causes fault movement because sea water dissolves clays and chalk soft rock formations this leads to massive earth quakes; I calibrate there is a very large earthquake due now! so some sort of planning needs to be considered quickly;
The only result of the average aquifer change is a rubble pile type quake (correctly labelled as drop faulting).

The maximum richter magnitude of one of these is approximately 5.0 and the maximum depth is 5Km. Rubble pile quakes of natural origin where the ground compacts around exposed joints dilated due to glacial rebound isostasy or basin margin uplift, occur down to 10Km max and again have a maximum magnitude of 10Km.

Below this depth they are exclusively tectonic.

Intraplate rubble pile quakes are typified when moment tensors are applied... by a combined rift/transform solution at headwall and margins of the rubble pile, and most are too weak to be typified by an accurate moment tensor.

That said, an aquifer breach in volcanics bound by Cambrian shale in Camp Hill adjacent to me caused an aquifer depressurisation due to the production of a fishpond (~120m3 water per day), culminating in 2 weak rubble pile events in Late march & Early April 2010 which caused my house to ring like a bell,~1.5Km away along strike.
Those builders did me a favour, as the spring seep next door up the hill has now dried up.

Also note rubble pile quakes in the overriding continent and also plate bend rifting is typical in the overriding plate and the descending plates decompressed by r/lx.

Compression tectonics are also now becoming noticeable in the SE. part of the UK as a result of pressure between Anatolia, the carpatic block, the Alps, and the Calabrian/Appennine interface due to Eurasia/Arabian plate convergence. R/lx is due in the Calabrian backarc basin in a few centuries, SE. vector. The same vector r/lx is due on the Agaean Backarc basin and also in the Toros-Cyprus arc.

The entire r/lx series may however be breceded by range r/lx at the Iran/Pakistan/Afghan borders through the "Pashtun range", where the locals are even more gaga than the Inquisition used to be. This is one of a triplet of range megathrusts, the others at risk are the Caucasus & Elbrus ranges, last r/lx was @ the "Pashtun range" on approx 2650BC (14c date +- 100 years) which destroyed the brick city of Kabalingan in Hanumangarh (India) in the foothills margin of the range, and sent the Indus valley civilisation back into the late stone age.

Note also:
Iranians in Elbrus range also going gaga. Israel incidentally sits on the forethrust of an arc & range,(tentatively called "Armageddon", due to the location exposure of the megathrust front), forming the front of a slice of the Arabian plate now becoming attached to Anatolia. Range r/lx will produce a plate lurch which will r/lx this arc and the associated Lebanon range. This r/lx will do what the labey says on the tin. Israelis also currently going gaga but this is due to Toros/Cyprus arc convergence with Israel & Environs sitting on the margin of the descending plate with the Dead sea rift locked and recompressing with a nice low frequency "graunch".

Have a nice day: Ag
sophia brown derby uk

UK

#6 Apr 30, 2010
Adrian Godsafe MSc wrote:
<quoted text>
The only result of the average aquifer change is a rubble pile type quake (correctly labelled as drop faulting).
The maximum richter magnitude of one of these is approximately 5.0 and the maximum depth is 5Km. Rubble pile quakes of natural origin where the ground compacts around exposed joints dilated due to glacial rebound isostasy or basin margin uplift, occur down to 10Km max and again have a maximum magnitude of 10Km.
Below this depth they are exclusively tectonic.
Intraplate rubble pile quakes are typified when moment tensors are applied... by a combined rift/transform solution at headwall and margins of the rubble pile, and most are too weak to be typified by an accurate moment tensor.
That said, an aquifer breach in volcanics bound by Cambrian shale in Camp Hill adjacent to me caused an aquifer depressurisation due to the production of a fishpond (~120m3 water per day), culminating in 2 weak rubble pile events in Late march & Early April 2010 which caused my house to ring like a bell,~1.5Km away along strike.
Those builders did me a favour, as the spring seep next door up the hill has now dried up.
Also note rubble pile quakes in the overriding continent and also plate bend rifting is typical in the overriding plate and the descending plates decompressed by r/lx.
Compression tectonics are also now becoming noticeable in the SE. part of the UK as a result of pressure between Anatolia, the carpatic block, the Alps, and the Calabrian/Appennine interface due to Eurasia/Arabian plate convergence. R/lx is due in the Calabrian backarc basin in a few centuries, SE. vector. The same vector r/lx is due on the Agaean Backarc basin and also in the Toros-Cyprus arc.
The entire r/lx series may however be breceded by range r/lx at the Iran/Pakistan/Afghan borders through the "Pashtun range", where the locals are even more gaga than the Inquisition used to be. This is one of a triplet of range megathrusts, the others at risk are the Caucasus & Elbrus ranges, last r/lx was @ the "Pashtun range" on approx 2650BC (14c date +- 100 years) which destroyed the brick city of Kabalingan in Hanumangarh (India) in the foothills margin of the range, and sent the Indus valley civilisation back into the late stone age.
Note also:
Iranians in Elbrus range also going gaga. Israel incidentally sits on the forethrust of an arc & range,(tentatively called "Armageddon", due to the location exposure of the megathrust front), forming the front of a slice of the Arabian plate now becoming attached to Anatolia. Range r/lx will produce a plate lurch which will r/lx this arc and the associated Lebanon range. This r/lx will do what the labey says on the tin. Israelis also currently going gaga but this is due to Toros/Cyprus arc convergence with Israel & Environs sitting on the margin of the descending plate with the Dead sea rift locked and recompressing with a nice low frequency "graunch".
Have a nice day: Ag
most excellent information thankyou! kind regards sophia X

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