Friday, 22 August 2014

Magnitude 3.8 Earthquake in Gauteng Province, South Africa.

The South African Council for Geosciences recorded a Magnitude 3.8 Earthquake in Gauteng Province, slightly before 1.15 am local time on Friday 22 August 2014 (slightly before 11.15 pm on Thursday 21 August GMT). There are no reports of any damage or casualties associated with this event, though many people reported feeling it in the Johannesburg area. The initial quake was followed by two aftershocks, with Magnitudes of 3.2 and 2.0, which occurred roughly one and two minutes after the initial event. 

The approximate location of the 22 August 2014 Gauteng Earthquake. Google Maps.

Earthquakes are rare in South Africa, with only 11 Earthquakes exceeding Magnitude 4.5 recorded since 1966 (when instrumental records begin in the country) making this one of the largest Earthquakes ever recorded in South Africa. The most recent of these occurred on 5 August 2014, and resulted in one death and 34 injuries, mostly in the regions mining industry, and damage to around 600 properties. The area has suffered a number of aftershocks since this event, and todays quakes are also likely to be connected to this event.

Because of this rarity it is hard to make precise judgements about the cause of quakes in South Africa, due to a paucity of data. Northwestern South Africa is close the southern end of the Great Rift Valley exits the continent and passes out under the Indian Ocean. The Great Rift Valley is slowly splitting the African Plate in two allow a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.

Witness statements can help geologists to understand Earthquakes and the geological processes that cause them; if you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the South African Council for Geoscience here.

See also...


The South African Council for Geoscience...


The United States Geological Survey recorded a Magnitude 4.9 Earthquake at a depth of 5 km close to Klerksdorp in northern Free...



A Magnitude 4.7 Earthquake was recorded at a depth of 5.0 km, roughly 50 km to the west of Barberton in Mpumalanga Province...

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Assessing the risks of cement casing failure at oil and gas wells in Pennsylvania.

Like other areas of the US, Pennsylvania has seen an increase in oil and gas production in recent years, driven by the expanded targeting of shale gas deposits using hydraulic fracturing (blasting water and chemicals into shale beds at high pressure to break up the shale and release any trapped gas) and directional drilling (drilling in any other direction than straight down; drill bores into shale gas beds often penetrate horizontally along the deposits for some distance). As in other areas this expansion has met with some concern, with residents of Pennsylvania particularly worried about the leakage of methane gas from wells into water supplies and the atmosphere. Methane is often cited as a more environmentally friendly fuel than coal, since burning it produces less of the greenhouse gas carbon dioxide, however methane is itself a powerful greenhouse gas, and if it leaks from wells into the atmosphere at even low levels then any environmental benefits of burning gas over coal are rapidly lost.

A drill rig at Roullette in Potter County, Pennsylvania, targeting the Marcellus Shale. Laurie Barr/Wikimedia Commons.

Raised methane levels have been found both in aquifers from which drinking water is drawn and in the atmosphere close to gas wells in Pennsylvania, strongly suggesting that there is a link between the methane levels and the drilling. One of the most likely ways in which this can happen is loss of integrity along the well bore due to failure of the cement casing, allowing methane to migrate along the borehole, into other strata or the atmosphere. Current regulations in Pennsylvania allow for low pressure leaks to be monitored and periodically bled off, but require that higher pressure leaks must be repaired, or if this is not possible the well must be permanently plugged; however such plugging, while likely to prevent further loss of gas from the wellhead into the atmosphere, may still allow subsurface migration of methane into other strata (including aquifers).

Clearly this makes the rate of failure in drill well cement casings in Pennsylvania a matter of great interest, however most previous studies of such well casings have concentrated on the structural integrity of offshore wells, with little direct relevance to the wells of Pennsylvania, other than the general observation that wells drilled during periods of rapid expansion in the industry are more likely to have problems, as are wells which are drilled in directions other than vertical. 

Data on the monitoring of structural integrity at wells in Pennsylvania is not publically available, however records Notices of Violations issued by the Pennsylvania Department of Environmental Protection are, and several studies on well integrity in the state have used these notices to try to estimate the rate of drill casing integrity failure there.

In a paper published in the Proceedings of the National Academy of Sciences of the USA on 30 June 2014, Anthony Ingraffea of the School of Civil and Environmental Engineering at Cornell University and Physicians, Scientists, and Engineers for Healthy Energy, Martin Wells of the Department of Statistical Sciences at Cornell University, Renee Santoro, also of Physicians, Scientists, and Engineers for Healthy Energy and Seth Shonkoff, again of Physicians, Scientists, and Engineers for Healthy Energy as well as the Department of Environmental Science, Policy, and Management at the University of California, Berkeley, describe the results of a study of the complete inspection records issued by the Pennsylvania Department of Environmental Protection for wells spudded (the spud date of a well is the day on which drilling begins) between 2000 and 2012.

Ingraffea et al. observe that Notices of Violation do not give a complete record of all leaks at well heads, as the inspection agency may not issue such a notice at a well where cement casing failure has been detected but remedial action is being taken by the drill operator, and that accessing the full inspection records for the wells should help to detect problems not identified by studies of Notices of Violation alone. They also not that problems with older wells are more likely to have been detected than problems with newer wells, as the older wells will have been inspected more times since their spud date, giving a better understanding of the full lifetime history of the well, and that many unconventional wells in Pennsylvania have been dug during a fairly recent boom, leading to a combination of two known high risk factors (wells dug during periods of rapid expansion within the industry and wells which deviate from the vertical) with shorter inspection records where problems are unlikely to have been detected.

Ingraffea et al. found that a total of 1.9% of all wells spudded in Pennsylvania between 2000 and 2012 suffered a loss of integrity. They further found that unconventional wells (i.e. wells targeting shale gas) were roughly six times as likely to suffer problems as conventional wells. The highest incidence of failure occurred in the northeast region of the state (Bradford, Cameron, Clinton, Lycoming, Potter, Sullivan, Susquehanna, Tioga, Wayne, and Wyoming counties) in wells targeting the Marcellus Shale spudded before 2009, with a failure rate of 9.84%. They further noted that wells drilled in the same area since 2009 had a failure rate of 9.18%, despite having a shorter inspection record (although wells spudded in 2012, which had an inspection record of less than 12 months when the study was carried out did have a significantly lower failure rate).

Map showing the extent and thickness of the Marcellus Shale beneath New York, Pennsylvania, Ohio and Virginia. Note the shale is thickest in the northeast. Marcellus Connection

The oldest unconventional well in the study was spudded in 2002, and unconventional wells remained a relatively small part of the industry in Pennsylvania until 2009. The rate of inspection also increased in 2009, with 76% of wells inspected in their first year prior to 2009, and 88.7% of wells inspected in their first year subsequently, which may partly account for the high rate of detected failure in post-2009 wells.

Wells in the northeastern counties were more prone to problems than wells in other areas, with 266 well failures recorded in the region, 52% of the total for the state. Within the northeastern region unconventional wells were 8.5 times more likely to have structural integrity problems than conventional wells. Unconventional wells in the northeastern counties had a 20% chance of problems within the first 3-4 years of operation, rising to 40% by year 7.

See also…


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Magnitude 1.1 Earthquake in southwest Herefordshire, England.

The British Geological Survey recorded a Magnitude 1.1 Earthquake at a depth of 7 km in southwestern Herefordshire, England, slightly before 10.00 pm British Summertime (slightly before 9.00 pm GMT) on Sunday 17 August 2014. This was a small event, and there was no danger of any damage or casualties, though it may have been felt locally.

The approximate location of the 17 August 2014 Herefordshire Earthquake. Google Maps.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process. 

(Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.


Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.

See also...


The British Geological Survey recorded a Magnitude 0.9 Earthquake at a depth of 5 km in northeast Neath Port Talbot slightly before...



The British Geological Survey recorded a Magnitude 1.8 Earthquake at a depth of 16 km about 20 km west of Hereford, England...



The British Geological Survey recorded a Magnitude 2.3 Earthquake at a depth of 16 km, about 2 km south of the market town of Stroud...


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Asteroid 2014 MP5 passes the Earth.

Asteroid 2014 MP5 passed by the Earth at a distance of about 6 745 000 km (17.54 times the average distance between the Earth and the Moon, or 4.5% of the average distance between the Earth an the Sun), slightly after 4.35 am GMT on Saturday 16 August 2014. There was no danger of the asteroid hitting us, though were it to do so it would have presented a serious threat. 2014 MP5 has an estimated equivalent diameter of 82-260 m (i.e. it is estimated that a spherical object with the same volume would be 82-260 m in diameter), and an object towards the upper end of this range would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground with an energy equivalent to about 750 megatons of TNT (roughly 44 000 times the energy of the Hiroshima bomb). Such an event would result in a crater about 4 km across, cause devastation on a wide scale and would have the potential to affect the climate globally for years after the impact event.

The calculated orbit of 2014 MP5. JPL Small Body Database Browser.

2014 MP5 was discovered on 19 June 2014 (58 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2014 MP5 implies that it was the 140th asteroid (asteroid P5) discovered in the second half of June 2014 (period 2014 M).

2014 MP5 has a 1163 day year orbital period and an eccentric orbit tilted at an angle of 10° to the plane of the Solar System that takes it from 1.03 AU from the Sun (i.e. 103 % of the average distance at which the Earth orbits the Sun) to 3.30 AU from the Sun (i.e. 330% of the average distance at which the Earth orbits the Sun, considerably more than twice the distance at which the planet Mars orbits the Sun). It is therefore classed as an Amor Group Asteroid (an asteroid which comes close to the Earth, but which is always outside the Earth's orbit). This means that close encounters between the asteroid and Earth are fairly common, with the next predicted in June 2135. As an asteroid on a trajectory which brings it extremely close to Earth which is large enough to cause serious harm should it collide with Earth it is also classified as a Potentially Hazardous Asteroid.

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Asteroid 2014 OF300 passed by the Earth at a distance of 1 468 000 km (3.82 times the average distance between the Earth and the Moon, or 0.98% of the average distance between the Earth and the...



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The Perseid Meteor shower lasts from late July to early September each year, and are expected to be at a peak on 12-13 August 2014, slightly after the Full Moon on 10 August, which may make the meteors harder to spot than when they occur at darker times of the...


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Thursday, 21 August 2014

Iceland evacuates area around Bárðarbunga Volcano.

Iceland has evacuated around 300 people from the area around the Bárðarbunga Volcano following a rise in seismic activity this week, with around 300 Earthquakes recorded close to the volcano since Tuesday 19 August 2014. The area where the volcano is located is remote and inhospitable, and has no permanent residents, but is popular with tourists in the summer. Reaching 2009 meters above sea level, Bárðarbunga is the second highest mountain in Iceland, although it is buried beneath the Vatnajökull Glacier, and not actually visible at all from the surface.

The approximate location of the Bárðarbunga Volcano. Google Maps.

Seismic activity beneath volcanoes can be significant, as they are often caused by the arrival of fresh magma, which may indicate that a volcano is about to undergo an eruptive episode. Bárðarbunga last erupted in about 1862, and has undergone several periods of raised seismic activity since then, most recently in 1996 and 2010, so there is no reason to believe that this weeks events will automatically lead to an eruption, and the evacuations are purely precautionary in nature.

Earthquakes around the Bárðarbunga Volcano in the 48 hours prior to 5.30 pm GMT on Thursday 21 August 2014. Icelandic Met Office.

Iceland lies directly upon the Mid-Atlantic Ridge, a chain of (mostly) submerged volcanoes running the length of the Atlantic Ocean along which the ocean is splitting apart, with new material forming at the fringes of the North American and European Plates beneath the sea (or, in Iceland, above it). The Atlantic is spreading at an average rate of 25 mm per year, with new seafloor being produced along the rift volcanically, i.e. by basaltic magma erupting from below. The ridge itself takes the form of a chain of volcanic mountains running the length of the ocean, fed by the upwelling of magma beneath the diverging plates. In places this produces volcanic activity above the waves, in the Azores, on Iceland and on Jan Mayen Island.

The passage of the Mid-Atlantic Ridge beneath Iceland. NOAA National Geophysical Data Center.

See also...


The United States Geological Survey recorded a Magnitude 4.8 Earthquake at a depth of 10.3 km roughly 8 km south of the...



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On Sunday 21 October 2012, at 1.25 am local time (which is GMT), the United States Geological Survey recorded a Magnitude 5.7 Earthquake at a depth of 9.9 km, roughly 21 km north of Siglufjordur...


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Monday, 11 August 2014

Asteroid 2014 OF300 passes the Earth.

Asteroid 2014 OF300 passed by the Earth at a distance of 1 468 000 km (3.82 times the average distance between the Earth and the Moon, or 0.98% of the average distance between the Earth and the Sun), slightly before 9.45 am GMT on Thursday 7 August 2014. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2014 OF300 has an estimated equivalent diameter of 10-33 m (i.e. it is estimated that a spherical object with the same volume would be 10-33 m in diameter), and an object of this size would be expected to break up in the atmosphere between 32 and 15 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2014 OF300. JPL Small Body Database Browser.

2014 OF300 was discovered on 29 July 2014 (nine days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2014 OF300 implies that it was the 7506th asteroid (asteroid F300) discovered in the second half of July 2014 (period 2014 O).

2014 OF300 has a 1061 day year orbital period and an eccentric orbit tilted at an angle of 5° to the plane of the Solar System, which takes it from 0.78 AU from the Sun (i.e. 78% of the average distance at which the Earth orbits the Sun) to 3.29 AU from the Sun (i.e. 329% of the average distance at which the Earth orbits the Sun, considerably more than twice the distance at which the planet Mars orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). 

See also...


Asteroid (175706) 1996 FG3 is an Apollo Family Near Earth Asteroid (i.e. an asteroid with an orbit that crosses that of the Earth, but which is further from the Sun than...


The Perseid Meteor shower lasts from late July to early September each year, and are expected to be at a peak on 12-13 August 2014, slightly after the Full Moon on 10 August, which may make the meteors harder to spot...



The Rosetta Spacecraft moved into position alongside Comet 67P/Churyumov–Gerasimenko on Wednesday 6 August 2014, the first spacecraft to reach a cometary target, and ten years after the mission was launched. It...


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Major cleanup under way after contaminated water spilled at Mexican mine.

A major cleanup is underway after about 40 million liters of wastewater were discharged into the River Bacanuchi, a tributary of the Sonora, on Thursday 7 August 2014. The precise nature of the event at the Buenavista Copper Mine at Cananea in Sononra State, Mexico, is unclear but it has been linked to heavy rainfall in the area, and is therefore likely to relate to the failure of a tailings pond. A 420 km long stretch of the two rivers has reportedly turned orange following the spill, and the water supply to the towns of Arizpe, Banamichi, San Felipe de Jesus, Aconchi, Baviacora and Ures, and the state capitol Hermosillo, with a combined population of about 800 000 people. Fish and livestock deaths have been reported along the affected stretches of river.

The approximate location of the Buenavista Copper Mine. Google Maps.

Tailings ponds are used to store sediment-laden waters from mines; such waters typically contain a high proportion of fine silt and clay particles, which take time to settle out of the water. The resulting water may be fairly clean, or may contain other pollutants (typically acids, either generated by the local geology or used in the mining process), and need further treatment. The water from the Buenavista Copper Mine spill has been described as containing sulphuric acid, though it is not clear if this originates from the mine tailings (many metal ores are sulphur rich, making sulphuric acid a common problem at metal mines), or whether acid had been added to the water to dissolve metals from the tailings for later recovery (acid leaching). Either way it presents a major environmental problem, and lime has been added to the affected waterways to attempt to neutralize the acid.

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A mine tailings pond at the Imperial Metals operated Mount Polley Mine, an open-pit copper mine in the Cariboo Region of British Columbia was breached on...



Operations were halted at the Padcal Mine, roughly 200 km north of Manila in the Philippines, this week, following intense flooding caused by a series of typhoons hitting the island, including Typhoon Saola...



Heavy rainfall associated with Cyclone Grant (now downgraded to Tropical Storm Grant) has caused...

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