Hydraulic fracturing is a well stimulation technique in which rock is fractured by a pressurized liquid. The process involves the high-pressure injection of'fracking fluid' into a wellbore to create cracks in the deep-rock formations through which natural gas and brine will flow more freely; when the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants hold the fractures open. Hydraulic fracturing began as an experiment in 1947, the first commercially successful application followed in 1950; as of 2012, 2.5 million "frac jobs" had been performed worldwide on gas wells. S; such treatment is necessary to achieve adequate flow rates in shale gas, tight gas, tight oil, coal seam gas wells. Some hydraulic fractures can form in certain veins or dikes. Hydraulic fracturing is controversial in many countries, its proponents advocate the economic benefits of more extensively accessible hydrocarbons, as well as replacing coal with gas, cleaner and emits less carbon dioxide.
Opponents argue that these are outweighed by the potential environmental impacts, which include risks of ground and surface water contamination and noise pollution, the triggering of earthquakes, along with the consequential hazards to public health and the environment. Methane leakage is a problem directly associated with hydraulic fracturing, as a Environmental Defense Fund report in the US highlights, where the leakage rate in Pennsylvania during extensive testing and analysis was found to be 10%, or over five times the reported figures; this leakage rate is considered representative of the hydraulic fracturing industry in the US generally. The EDF have announced a satellite mission to further locate and measure methane emissions. Increases in seismic activity following hydraulic fracturing along dormant or unknown faults are sometimes caused by the deep-injection disposal of hydraulic fracturing flowback, produced formation brine. For these reasons, hydraulic fracturing is under international scrutiny, restricted in some countries, banned altogether in others.
The European Union is drafting regulations that would permit the controlled application of hydraulic fracturing. Fracturing rocks at great depth becomes suppressed by pressure due to the weight of the overlying rock strata and the cementation of the formation; this suppression process is significant in "tensile" fractures which require the walls of the fracture to move against this pressure. Fracturing occurs; the minimum principal stress exceeds the tensile strength of the material. Fractures formed in this way are oriented in a plane perpendicular to the minimum principal stress, for this reason, hydraulic fractures in well bores can be used to determine the orientation of stresses. In natural examples, such as dikes or vein-filled fractures, the orientations can be used to infer past states of stress. Most mineral vein systems are a result of repeated natural fracturing during periods of high pore fluid pressure; the impact of high pore fluid pressure on the formation process of mineral vein systems is evident in "crack-seal" veins, where the vein material is part of a series of discrete fracturing events, extra vein material is deposited on each occasion.
One example of long-term repeated natural fracturing is in the effects of seismic activity. Stress levels rise and fall episodically, earthquakes can cause large volumes of connate water to be expelled from fluid-filled fractures; this process is referred to as "seismic pumping". Minor intrusions in the upper part of the crust, such as dikes, propagate in the form of fluid-filled cracks. In such cases, the fluid is magma. In sedimentary rocks with a significant water content, fluid at fracture tip will be steam. Fracturing as a method to stimulate shallow, hard rock oil wells dates back to the 1860s. Dynamite or nitroglycerin detonations were used to increase oil and natural gas production from petroleum bearing formations. On 25 April 1865, US Civil War veteran Col. Edward A. L. Roberts received a patent for an "exploding torpedo", it was employed in Pennsylvania, New York and West Virginia using liquid and later, solidified nitroglycerin. Still the same method was applied to water and gas wells.
Stimulation of wells with acid, instead of explosive fluids, was introduced in the 1930s. Due to acid etching, fractures would not close resulting in further productivity increase. Harold Hamm, Aubrey McClendon, Tom Ward and George P. Mitchell are each considered to have pioneered hydraulic fracturing innovations toward practical applications; the relationship between well performance and treatment pressures was studied by Floyd Farris of Stanolind Oil and Gas Corporation. This study was the basis of the first hydraulic fracturing experiment, conducted in 1947 at the Hugoton gas field in Grant County of southwestern Kansas by Stanolind. For the well treatment, 1,000 US gallons of gelled gasoline and sand from the Arkansas River was injected into the gas-producing limestone formation at 2,400 feet; the experiment was not successful as deliverability of the well did not change appreciably. The process was further described by J. B. Clark of Stanol
Paleoseismology looks at geologic sediments and rocks, for signs of ancient earthquakes. It is used to supplement seismic monitoring, for the calculation of seismic hazard. Paleoseismology is restricted to geologic regimes that have undergone continuous sediment creation for the last few thousand years, such as swamps, river beds and shorelines. In this typical example, a trench is dug in an active sedimentation regime. Evidence of thrust faulting can be seen in the walls of the trench, it becomes a matter of deducting the relative age of each fault, by cross-cutting patterns. The faults can be dated in absolute terms, if there is human artifacts. Many notable discoveries have been made using the techniques of paleoseismology. For example, there is a common misconception that having many smaller earthquakes can somehow'relieve' a major fault such as the San Andreas Fault, reduce the chance of a major earthquake, it is now known that nearly all the movement of the fault takes place with large earthquakes.
All of these seismic events, leave some sort of trace in the sedimentation record. Another famous example involves the megathrust earthquakes of the Pacific Northwest, it was thought for some time that there was low seismic hazard in the region because few modern earthquakes have been recorded. It was thought that the Cascadia subduction zone was sliding in a benign manner. All of these comforting notions were shattered by paleoseismology studies showing evidence of large earthquakes, along with historical tsunami records. In effect, the subduction zone under British Columbia, Washington and far northern California, is normal, being hazardous in the long term, with the capability of generating coastal tsunamis of several hundred feet in height at the coast; these are caused by the interface between the subducted sea floor stressing the overlaying coastal soils in compression. Periodically a slip will occur which causes the coastal portion to reduce in elevation and thrust toward the west, leading to tsunamis in the central and eastern north Pacific Ocean and a reflux of water toward the coastal shore, with little time for residents to escape.
Paleoseismic investigations are performed through trenching studies in which a trench is dug and a geologist logs the geological attributes of the rock layers. Trenching studies are relevant to seismically active regions, such as many parts of California. Archaeoseismology Paleotempestology Seismite James P. McCalpin Paleoseismology, Academic Press, ISBN 0-12-373576-9, ISBN 978-0-12-373576-8 James P. McCalpin Paleoseismology, Elsevier, ISBN 0-12-481826-9 Paleoseismicity.org - Online platform for paleoseismologists INQUA Paleoseismology/ web site of the International Focus Group on Paleoseismology and Active tectonics. TERPRO Commission, International Union for Quaternary Research
Seismites are sedimentary beds and structures deformed by seismic shaking. The German paleontologist Adolf Seilacher first used the term in 1969 to describe earthquake-deformed layers. Today, the term is applied to both sedimentary layers and soft sediment deformation structures formed by shaking; this subtle change in usage accommodates structures. Caution is urged when applying the term to features observed in the field, as similar-looking features may be products of either seismic or non-seismic perturbation. Several informal classification systems exist to help geologists distinguish seismites from other soft-sediment deformation features, though a formal, standardized system has not been developed. Geologists use seismites, in combination with other evidence, to better understand the earthquake history of an area. If age and distribution of seismically-generated features can be determined recurrence interval and seismic hazard risk can be assessed. Speleoseismite Soft-sediment deformation structures
New Madrid Seismic Zone
The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri. The New Madrid fault system was responsible for the 1811–12 New Madrid earthquakes and has the potential to produce large earthquakes in the future. Since 1812, frequent smaller earthquakes have been recorded in the area. Earthquakes that occur in the New Madrid Seismic Zone threaten parts of eight American states: Illinois, Missouri, Kentucky, Tennessee and Mississippi; the 150-mile -long seismic zone, which extends into five states, stretches southward from Cairo, Illinois. It covers a part of West Tennessee, near Reelfoot Lake, extending southeast into Dyersburg, it is southwest of the Wabash Valley Seismic Zone. Most of the seismicity originates between 15 miles beneath the Earth's surface; the zone had four of the largest North American earthquakes in recorded history, with moment magnitudes estimated to be as large as 7.0 or greater, all occurring within a three-month period between December 1811 and February 1812.
Many of the published accounts describe the cumulative effects of all the earthquakes. Magnitude estimates and epicenters may vary; because uplift rates associated with large New Madrid earthquakes could not have occurred continuously over geological timescales without altering the local topography, studies have concluded that the seismic activity there cannot have gone on for longer than 64,000 years, making the New Madrid Seismic Zone a young feature, or that earthquakes and the associated uplift migrate around the area over time, or that the NMSZ has short periods of activity interspersed with long periods of quiescence. Archaeological studies have found from studies of sand blows and soil horizons that previous series of large earthquakes have occurred in the NMSZ in recent prehistory. Based on artifacts found buried by sand blow deposits and from carbon-14 studies, previous large earthquakes like those of 1811–1812 appear to have happened around AD 1450 and around AD 900, as well as AD 300.
Evidence has been found for an apparent series of large earthquakes around 2350 BC. About 80 km southwest of the presently-defined NMSZ but close enough to be associated with the Reelfoot Rift, near Marianna, two sets of liquefaction features indicative of large earthquakes have been tentatively identified and dated to 3500 BC and 4800 BC; these features were interpreted to have been caused by groups of large earthquakes timed together. Dendrochronology studies conducted on the oldest bald cypress trees growing in Reelfoot Lake found evidence of the 1811–1812 series in the form of fractures followed by rapid growth after their inundation, whereas cores taken from old bald cypress trees in the St. Francis sunklands showed slowed growth in the half century that followed 1812; these were interpreted as clear signals of the 1811–1812 earthquake series in tree rings. Because the tree ring record in Reelfoot Lake and the St. Francis sunk lands extend back to AD 1682 and AD 1321 Van Arsdale et al. interpreted the lack of similar signals elsewhere in the chronology as evidence against large New Madrid earthquakes between those years and 1811.
The first known written record of an earthquake felt in the NMSZ was from a French missionary traveling up the Mississippi with a party of explorers. At 1 pm on Christmas Day 1699, at a site near the present-day location of Memphis, the party was startled by a short period of ground shaking. December 16, 1811, 0815 UTC; the future location of Memphis, Tennessee was shaken at Mercalli level nine intensity. A seismic seiche propagated upriver and Little Prairie was destroyed by liquefaction. Local uplifts of the ground and the sight of water waves moving upstream gave observers the impression that the Mississippi River was flowing backwards. At New Madrid, trees were knocked down and riverbanks collapsed; this event shook windows and furniture in Washington, D. C. rang bells in Richmond, sloshed well water and shook houses in Charleston, South Carolina, knocked plaster off of houses in Columbia, South Carolina. In Jefferson, furniture moved and in Lebanon, residents fled their homes. Observers in Herculaneum, called it "severe" and said it had a duration of 10–12 minutes.
Aftershocks were felt every 6-10 minutes, a total of 27, in New Madrid until what was called the Daylight Shock, of the same intensity as the first. Many of these were felt throughout the eastern US, though with less intensity than the initial earthquake. December 16, 1811, sometimes termed the "Dawn Shock" or "Daylight Shock", 1315 UTC. January 23, 1812, 1515 UTC; this was the smallest of the three main shocks, but resulted in widespread ground deformation, landslides and stream bank caving in the meizoseismal area. Johnston and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. A minority viewpoint holds that this earthquake's epicenter was in so
Soil liquefaction occurs when a saturated or saturated soil loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material, ordinarily a solid behaves like a liquid. In soil mechanics, the term "liquefied" was first used by Allen Hazen in reference to the 1918 failure of the Calaveras Dam in California, he described the mechanism of flow liquefaction of the embankment dam as: If the pressure of the water in the pores is great enough to carry all the load, it will have the effect of holding the particles apart and of producing a condition, equivalent to that of quicksand… the initial movement of some part of the material might result in accumulating pressure, first on one point, on another, successively, as the early points of concentration were liquefied. The phenomenon is most observed in saturated, sandy soils; this is. Dense sands by contrast tend to expand in volume or'dilate'. If the soil is saturated by water, a condition that exists when the soil is below the water table or sea level water fills the gaps between soil grains.
In response to soil compressing, the water pressure increases and the water attempts to flow out from the soil to zones of low pressure. However, if the loading is applied and large enough, or is repeated many times such that the water does not flow out before the next cycle of load is applied, the water pressures may build to the extent that it exceeds the force between the grains of soil that keep them in contact; these contacts between grains are the means by which the weight from buildings and overlying soil layers is transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose its strength, it may be observed to flow like a liquid. Although the effects of liquefaction have been long understood, engineers took more notice after the 1964 Niigata earthquake and 1964 Alaska earthquake, it was a major factor in the destruction in San Francisco's Marina District during the 1989 Loma Prieta earthquake, in Port of Kobe during the 1995 Great Hanshin earthquake.
More liquefaction was responsible for extensive damage to residential properties in the eastern suburbs and satellite townships of Christchurch, New Zealand during the 2010 Canterbury earthquake and more extensively again following the Christchurch earthquakes that followed in early and mid-2011. On 28th September 2018, an earthquake of 7.5 magnitude hit the Central Sulawesi province of Indonesia. Resulting soil liquefaction buried the suburb of Balaroa and Petobo village in 3 meters deep mud; the government of Indonesia is considering designating the two neighborhoods of Balaroa and Petobo, that have been buried under mud- as mass graves. The building codes in many countries require engineers to consider the effects of soil liquefaction in the design of new buildings and infrastructure such as bridges, embankment dams and retaining structures. Soil liquefaction occurs when the effective stress of soil is reduced to zero; this may be initiated by cyclic loading. In both cases a soil in a saturated loose state, one which may generate significant pore water pressure on a change in load are the most to liquefy.
This is because loose soil has the tendency to compress when sheared, generating large excess porewater pressure as load is transferred from the soil skeleton to adjacent pore water during undrained loading. As pore water pressure rises, a progressive loss of strength of the soil occurs as effective stress is reduced. Liquefaction is more to occur in sandy or non-plastic silty soils, but may in rare cases occur in gravels and clays. A'flow failure' may initiate if the strength of the soil is reduced below the stresses required to maintain the equilibrium of a slope or footing of a structure; this can occur due to monotonic loading or cyclic loading, can be sudden and catastrophic. A historical example is the Aberfan disaster. Casagrande referred to this type of phenomena as'flow liquefaction' although a state of zero effective stress is not required for this to occur.'Cyclic liquefaction' is the state of soil when large shear strains have accumulated in response to cyclic loading. A typical reference strain for the approximate occurrence of zero effective stress is 5% double amplitude shear strain.
This is a soil test-based definition performed via cyclic triaxial, cyclic direct simple shear, or cyclic torsional shear type apparatus. These tests are performed to determine a soil's resistance to liquefaction by observing the number of cycles of loading at a particular shear stress amplitude required to induce'fails'. Failure here is defined by the aforementioned shear strain criteria; the term'cyclic mobility' refers to the mechanism of progressive reduction of effective stress due to cyclic loading. This may occur in all soil types including dense soils. However, on reaching a state of zero effective stress such soils dilate and regain strength. Thus, shear strains are less than a true state of soil liquefaction. Liquefaction is more to occur in loose to moderat