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Two Earthquakes Widely-Felt Across DFW Tuesday
Source: NBC
A magnitude-3.6 earthquake rumbled across North Texas just before 7 p.m. Tuesday, hours after a magnitude-3.5 earthquake was centered in nearly the same location in Irving, the United States Geological Survey confirms.
The epicenters were both located near the former site of Texas Stadium.
...
The earthquakes were centered in an area where at least 18 quakes have been recorded since October 2014.
Prior to Tuesday, the largest magnitude quake to occur in the Irving area since October 2014 had been a 3.3-magnitude quake on Nov. 22. The most recent was a 2.4 MMI III at 8:29 p.m. New Year's Day.
Read more: http://www.nbcdfw.com/news/local/Earthquake-Felt-in-Fort-Worth-Dallas-Irving-287697091.html
Texas seismologists investigate quakes near old Cowboys stadium
DALLAS (Reuters) - Seismologists installed a new earthquake-monitoring device in the Dallas suburb of Irving this week after a series of minor temblors rocked an area near the site of the former Dallas Cowboys football stadium.
Irving was hit by a magnitude 3.5 quake, the U.S. Geological Survey said. It was the strongest in a series of nearly 20 minor quakes to hit around Irving since September.
...
But the seismic series has left residents on edge, wondering if the situation will get worse and what has been behind an uptick in quakes over the last several years.
..
Some residents believe the implosion of Texas Stadium in 2010 may have exacerbated problems. There is also speculation the quakes might be related to hydraulic fracturing, or "fracking," an energy extraction technique that has a long history in north Texas.
http://news.yahoo.com/texas-seismologists-investigate-quakes-near-old-cowboys-stadium-160812555--nfl.html
33 replies
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http://en.wikipedia.org/wiki/River_bank_failure#Tectonic_failure
There mention River bank failure was chartistic of the New Madrid Earthquakes of 1811-1812.
http://onlinelibrary.wiley.com/doi/10.1029/00EO00337/pdf
More on the New Madrid Earthquakes:
http://www.memphis.edu/ceri/compendium/enigma.pdf
Liquefaction during an earthquake is a problem where buildings are built on sediment NOT rock, which was the case with the Mexico City Earthquake of 1985:
More on Soil liquefaction:
Liquefaction can cause other problems for example in Southern California you had this situation, do to ground level slowly falling do to removal of underground water, the fire hydrant stayed at the same height it was installed at, but the surrounding land fell:
http://vizionstudios.blogspot.com/2010/08/i-have-not-blogged-enough-recently.html
If the ground under your home is more solid you do NOT see such a drop in ground level and the effect of any earthquake is less. On the other hand if the ground is loose, it shakes like a piece of jello increasing the level of damages (This is what happened in Mexico City in 1985).
Many river bank communities are built on "fill" either naturel (done by the river itself) or man made (as the result of dredging). For this reason tend to be susceptible to earthquake damage then land that stands on solid rock.
There mention River bank failure was chartistic of the New Madrid Earthquakes of 1811-1812.
http://onlinelibrary.wiley.com/doi/10.1029/00EO00337/pdf
More on the New Madrid Earthquakes:
http://www.memphis.edu/ceri/compendium/enigma.pdf
Liquefaction during an earthquake is a problem where buildings are built on sediment NOT rock, which was the case with the Mexico City Earthquake of 1985:
On the bed of the historic lake, the prevailing silt and volcanic clay sediments amplify seismic shaking. Damage to structures is worsened by soil liquefaction which causes the loss of foundation support and contributes to dramatic settlement of large buildings.Mexico City's downtown area mostly lies on the silt and volcanic clay sediments of the bed of the historic Lake Texcoco, which are between seven and thirty-seven meters deep and have a high water content. Above this is a layer of sand and above this is a layer of sand and rock. The western and northwestern parts of the city are outside the old lakeshores and are located on sands from eroding volcanic cones that surround the Valley of Mexico. The southern part of the city rests on hardened basalt lava flows. The old lakebed, with its high water content, is easily moved or compressed. The old lakeshore area also has a fairly high water content, allowing movement, though not as much as the lakebed. The old lava flows have little water content or movement in comparison and are therefore stable.
http://en.wikipedia.org/wiki/1985_Mexico_City_earthquake
http://en.wikipedia.org/wiki/1985_Mexico_City_earthquake
More on Soil liquefaction:
http://en.wikipedia.org/wiki/Soil_liquefaction
The phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils. This is because a loose sand has a tendency to compress when a load is applied; dense sands by contrast tend to expand in volume or 'dilate'. If the soil is saturated by water, a condition that often exists when the soil is below the ground water table or sea level, then water fills the gaps between soil grains ('pore spaces'). In response to the soil compressing, this water increases in pressure and attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface). However, if the loading is rapidly applied and large enough, or is repeated many times (e.g. earthquake shaking, storm wave loading) such that it does not flow out in time before the next cycle of load is applied, the water pressures may build to an extent where they exceed the contact stresses between the grains of soil that keep them in contact with each other. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose all of its strength (the ability to transfer shear stress) and it may be observed to flow like a liquid (hence 'liquefaction').
The phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils. This is because a loose sand has a tendency to compress when a load is applied; dense sands by contrast tend to expand in volume or 'dilate'. If the soil is saturated by water, a condition that often exists when the soil is below the ground water table or sea level, then water fills the gaps between soil grains ('pore spaces'). In response to the soil compressing, this water increases in pressure and attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface). However, if the loading is rapidly applied and large enough, or is repeated many times (e.g. earthquake shaking, storm wave loading) such that it does not flow out in time before the next cycle of load is applied, the water pressures may build to an extent where they exceed the contact stresses between the grains of soil that keep them in contact with each other. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose all of its strength (the ability to transfer shear stress) and it may be observed to flow like a liquid (hence 'liquefaction').
Liquefaction can cause other problems for example in Southern California you had this situation, do to ground level slowly falling do to removal of underground water, the fire hydrant stayed at the same height it was installed at, but the surrounding land fell:
http://vizionstudios.blogspot.com/2010/08/i-have-not-blogged-enough-recently.html
If the ground under your home is more solid you do NOT see such a drop in ground level and the effect of any earthquake is less. On the other hand if the ground is loose, it shakes like a piece of jello increasing the level of damages (This is what happened in Mexico City in 1985).
Many river bank communities are built on "fill" either naturel (done by the river itself) or man made (as the result of dredging). For this reason tend to be susceptible to earthquake damage then land that stands on solid rock.
I never mentioned it! 
http://earthquake.usgs.gov/earthquakes/eventpage/usc000tca7#summary
Induced Seismicity
As is the case elsewhere in the world, there is evidence that some central and eastern North America earthquakes have been triggered or caused by human activities that have altered the stress conditions in earth's crust sufficiently to induce faulting. Activities that have induced felt earthquakes in some geologic environments have included impoundment of water behind dams, injection of fluid into the earth's crust, extraction of fluid or gas, and removal of rock in mining or quarrying operations. In much of eastern and central North America, the number of earthquakes suspected of having been induced is much smaller than the number of natural earthquakes, but in some regions, such as the south-central states of the U.S., a significant majority of recent earthquakes are thought by many seismologists to have been human-induced. Even within areas with many human-induced earthquakes, however, the activity that seems to induce seismicity at one location may be taking place at many other locations without inducing felt earthquakes. In addition, regions with frequent induced earthquakes may also be subject to damaging earthquakes that would have occurred independently of human activity. Making a strong scientific case for a causative link between a particular human activity and a particular sequence of earthquakes typically involves special studies devoted specifically to the question. Such investigations usually address the process by which the suspected triggering activity might have significantly altered stresses in the bedrock at the earthquake source, and they commonly address the ways in which the characteristics of the suspected human-triggered earthquakes differ from the characteristics of natural earthquakes in the region.
ShakeMap
Contributed by USGS National Earthquake Information Center
http://www.commondreams.org
Induced Seismicity
As is the case elsewhere in the world, there is evidence that some central and eastern North America earthquakes have been triggered or caused by human activities that have altered the stress conditions in earth's crust sufficiently to induce faulting. Activities that have induced felt earthquakes in some geologic environments have included impoundment of water behind dams, injection of fluid into the earth's crust, extraction of fluid or gas, and removal of rock in mining or quarrying operations. In much of eastern and central North America, the number of earthquakes suspected of having been induced is much smaller than the number of natural earthquakes, but in some regions, such as the south-central states of the U.S., a significant majority of recent earthquakes are thought by many seismologists to have been human-induced. Even within areas with many human-induced earthquakes, however, the activity that seems to induce seismicity at one location may be taking place at many other locations without inducing felt earthquakes. In addition, regions with frequent induced earthquakes may also be subject to damaging earthquakes that would have occurred independently of human activity. Making a strong scientific case for a causative link between a particular human activity and a particular sequence of earthquakes typically involves special studies devoted specifically to the question. Such investigations usually address the process by which the suspected triggering activity might have significantly altered stresses in the bedrock at the earthquake source, and they commonly address the ways in which the characteristics of the suspected human-triggered earthquakes differ from the characteristics of natural earthquakes in the region.
ShakeMap
Contributed by USGS National Earthquake Information Center
http://www.commondreams.org
