Tuesday, 21 September 2021

Miner killed in roof-collapse in central Queensland.

A miner has died and another two required hospital treatment following a roof collapse at the Sojitz Gregory Crinum Coal Mine to the north of Emerald in central Queensland. The incident happened at about 11.00 am on Tuesday 14 September 2021, when part of the mine roof collapsed onto a conveyor drift (area through which a conveyer belt runs, carrying coal to the surface). Two men were trapped beneath the fallen debris, one of whom, a 60-year-old miner who has not been named, dying as a consequence, while the other, a 25-year-old, was freed after several hours and airlifted to the Rockhampton Base Hospital with injuries to the legs and pelvis. A third worker was also taken to hospital following a 'medical episode' but discharged later the same day.

The Sojitz Gregory Crinum Coal Mine in Queensland, Australia. Rachel McGhee/ABC News.

The Gregory Crinum Mine site was acquired by Sojitz, a Japanese mining group, in 2018, and recommenced work in May 2021. The mine had previously been mothballed in 2007, in part due to concerns about the stability of the roof, which was considered to be too unstable for the type of room and pillar mining used at the site; this is a system in which a horizontal bed of the target mineral (usually coal) is removed by the excavation of a series of tunnels arranged like streets on a city block, leaving behind blocks of unmined material to support the ceiling of the tunnels.

This is the first mining fatality in Queensland since January 2020, but the ninth since July 2018, with a spate of incidents in 2018-19 having sparked a clampdown on mine safety by authorities in Queensland. Sojitz had reportedly been advertising for inexperienced workers who would be trained at the Gregory Crinum Mine site, due to a shortage of experienced mineworkers in Queensland. The incident is currently under investigation by the Queensland Police Service. 

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Monday, 20 September 2021

Marburg Virus alert in Guinea comes to an end.

The Ministry of Health of Guinea has declared the end of the Marburg Virus Disease outbreak in Guéckédou Prefecture, Nzérékoré Region, according to a press release issued by the World Health Organization on 17 September 2021. In accordance with World Health Organization recommendations, the declaration was made 42 days after the safe and dignified burial of the only confirmed patient reported in this outbreak. This was the first-ever Marburg Virus Disease case reported in Guinea. 

On 16 September 2021, the Ministry of Health of Guinea declared the end of the Marburg virus disease outbreak in Guéckédou prefecture, Nzérékoré Region. In accordance with World Health Organization recommendations, the declaration was made 42 days after the safe and dignified burial of the only confirmed patient reported in this outbreak. This was the first-ever Marburg virus disease case reported in Guinea.

From 3 August 2021 to the end of outbreak declaration, only one confirmed case was reported.  The patient, a man, had onset of symptoms on 25 July. On 1 August he went to a small health facility near his village, with symptoms of fever, headache, fatigue, abdominal pain and gingival hemorrhage. A rapid diagnostic test for Malaria returned a negative result, and the patient received ambulatory supportive care with rehydration and symptomatic treatment. Upon returning home, his condition worsened, and he died on 2 August. An alert was subsequently raised by the sub-prefecture public health care facility to the prefectorial department of health in Guéckédou. The investigation team was immediately deployed to the village to conduct an in-depth investigation and collected a post-mortem oral swab sample, which was shipped on the same day to the Viral Hemorrhagic Fever Laboratory in Guéckédou city. On 3 August, the sample tested positive for Marburg Virus Disease by reverse transcriptase-polymerase chain reaction and negative for Ebola Virus Disease. The deceased patient was buried safely and with dignity on 4 August, with the support of the national Red Cross.

On 5 August, the National Reference Laboratory in Conakry provided confirmation by real-time polymerase chain reaction of the positive Marburg result, and on 9 August, the Institut Pasteur Dakar in Senegal provided an additional confirmation that the result was positive for Marburg Virus Disease and negative for Ebola Virus Disease.

Negative stained transmission electron micrograph of a number of filamentous Marburg Virions, which had been cultured on Vero cell cultures, and purified on sucrose, rate-zonal gradients. Erskine Palmer/Russell Regnery/Centers for Disease Control and Prevention/Wikimedia Commons.

The Ministry of Health activated the national and district emergency management committees to coordinate the response and engage with the community. Additionally, the Ministry of Health together with the World Health Organization, the United States Centers for Disease Control, the Alliance for International Medical Action, the Red Cross, UNICEF, the International Organization for Migration, and other partners, initiated measures to control the outbreak and prevent further spread including the implementation of contact tracing and active case search in health facilities and at the community level.

During the outbreak, a total of one confirmed case who died, and 173 contacts were identified, including 14 high risk contacts based on exposure. Among them, 172 were followed for a period of 21 days, of which none developed symptoms. One high-risk contact was lost to follow up. At the different points of entry in Guéckédou prefecture where passengers were screened, no alerts were generated.

Ongoing activities include:  Capturing and sampling of Bats in the localities of Temessadou M´Boké, Baladou Pébal and Koundou to better understand the involvement of Bats in the ecology of Marburg Viruses; development of a sero-surveillance protocol in the sub-prefecture of Koundou; development and implementation of plans to strengthen Infection Prevention and Control programmes at the national and facility level including establishing and mentoring of Infection Prevention and Control focal persons, Infection Prevention and Control/hygiene committees, ongoing training of health workers and adequate procurement and distribution of supplies such as personal protective equipment; implementation of water, sanitation and hygiene measures with partners including in health facilities and communities; supporting training on community-based surveillance in Guéckédou Prefecture; and risk communication and community mobilization activities in Guéckédou Prefecture as a component of a health emergency preparedness and response action plan. 

A health worker in Gueckedou, Guinea. World Health Organization.

Marburg Virus Disease is an epidemic-prone disease associated with high case fatality ratios (24-90%). In the early course of the disease, clinical diagnosis of Marburg Virus Disease is difficult to distinguish from many other tropical febrile illnesses, because of the similarities in the clinical symptoms. Other viral hemorrhagic fevers need to be excluded, particularly Ebola Virus Disease, as well as Malaria, Typhoid Fever, Leptospirosis, Rickettsial infection and Plague. Marburg Virus Disease is transmitted by direct contact with the blood, bodily fluids and/or tissues of infected persons or wild Animals (e.g. Monkeys and Fruit Bats).

Investigations are ongoing to identify the source of the infection. Guinea has previous experience in managing viral hemorrhagic diseases such as Ebola Virus Disease and Lassa Fever, but this was the first time that Marburg Virus Disease was reported. The country has a fragile health care system due to the overburden of disease outbreaks, COVID-19 pandemic, and the recurrent threat of epidemics such as Malaria, Yellow Fever, Measles, Lassa Fever, Ebola Virus Disease, health care-associated infections, high rates of acute malnutrition, cyclical natural disasters such as floods, and socio-political unrest.

Guinea health authorities responded rapidly to the event, and measures were rapidly implemented to control the outbreak. Cross-border population movement and community mixing between Guinea and neighboring Sierra Leone and Liberia increased the risk of cross-border spread. Sierra Leone and Liberia health authorities activated contingency plans and started public health measures at the points of entry with Guinea.

The affected village is in a remote forest area located at the border with Sierra Leone, about 9 km from a main international border crossing point between the two countries. The proximity of the affected area to an international border, cross-border movement between the affected district and Sierra Leone, and the potential transmission of the Virus between Bat colonies and Humans posed an increased risk for cross-border spread. 

These factors suggested a high risk at the national and regional level, and given that Guéckédou Prefecture is well connected to Foya District in Liberia, and Kailahun District in Sierra Leone, this outbreak required an immediate and coordinated response with support from international partners. The risk associated with the event at the global level was assessed as low. 

Human-to-Human transmission of Marburg virus is primarily associated with direct contact with blood and/or bodily fluids of infected persons, and Marburg Virus transmission associated with the provision of health care has been reported when appropriate infection control measures have not been implemented. 

Health care workers caring for patients with suspected or confirmed Marburg Virus Disease should apply standard and transmission-based infection prevention and control precautions to avoid any exposure to blood and/or bodily fluids, as well as unprotected contact with the possibly contaminated environment. Infection prevention and control precautions include: Early recognition (screening, triage) and isolation of suspected cases; appropriate isolation capacity (including infrastructure and human resources); health care workers’ access to hand hygiene resources (i.e., soap and water or alcohol-based hand rub); appropriate and accessible personal protective equipment for health care workers; safe infection practices (emphasise on single-use only needles); procedures and resources for decontamination and sterilisation of medical devices; and appropriate management of infectious waste.

Infection prevention and control  assessments of health facilities in affected areas using the Infection Prevention and Control Scorecard revealed sub-optimal results highlighting the need for ongoing supportive supervision and mentorship for implementation of infection prevention and control in health care settings in addition to implementing infection prevention and control minimum requirements to support and strengthen future preparedness for emerging and re-emerging infectious diseases. 

Integrated disease surveillance and response activities, including community-based surveillance must continue to be strengthened within all affected health zones.

Raising awareness of the risk factors for Marburg Virus Disease and the protective measures individuals can take to reduce human exposure to the virus are the key measures to reduce Human infections and deaths. Key public health communication messages include: Reducing the risk of Human-to-Human transmission in the community arising from direct contact with infected patients, particularly with their bodily fluids; avoiding close physical contact with patients who have Marburg Virus Disease; a ny suspected case ill at home should not be managed at home, but immediately transferred to a health facility for treatment and isolation. During this transfer, health care workers should wear appropriate personal protective eqipment; regular hand washing should be performed after visiting sick relatives in hospital; and communities affected by Marburg should make efforts to ensure that the population is well informed, both about the nature of the disease itself to avoid further transmission, community stigmatisation, and encourage early presentation to treatment centers and other necessary outbreak containment measures, including safe burial of the dead. People who have died from Marburg should be promptly and safely buried.

To reduce the risk of wildlife-to-Human transmissions, such as through contact with Fruit Bats, Monkeys, and Apes: Handle wildlife with gloves and other appropriate protective clothing; cook Animal products such as blood and meat thoroughly before consumption and avoid consumption of raw meat; and during work, research activities or tourist visits in mines or caves inhabited by Fruit Bat colonies, people should wear gloves and other appropriate protective clothing including masks.

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Sunday, 19 September 2021

Production of dairy products drove the expansion of the Yamnaya peoples of the Eurasian Steppes in the Early Bronze Age.

The nomadic peoples of the Eurasian Steppes have long been a source of fascination to both archaeologists and the general public, with, sometimes less than flattering, fictionalised versions appearing in popular fantasy novels such as JRR Tolkien's Lord of the Rings and GRR Martin's Game of Thrones. The later phases of these groups, such as the Xiongnu and Mongol Empires are relatively familiar, but the origins of these groups in the Eneolithic (the Late Neolithic plus the Chalcolithic, or 'Copper Age') are rather more obscure. The archaeology of these groups has been studied for a long time, but new technologies have recently shed new light on the field. For example, it has been demonstrated that European populations had a significant influx of DNA from steppe-dwelling groups during the late Neolithic. The same Neolithic steppe populations (referred to as Yamnaya by archaeologists) also have also been shown to have genetic links to the Afanasievo people of the Altai Mountains and even the peoples of Mongolia. Both archaeological and genetic data suggest extensive population movements in this area during the Early Bronze Age (roughly 3300 to 2500 BC), with links being established between the Yamnaya peoples of the Pontic–Caspian steppe and the peoples of Siberia and Scandinavia.

Thus, it is understood that the Yamnaya peoples underwent a significant expansion of their geographical range during this period, but the drivers of this expansion are less certain. One popular explanation is that innovations such as the use of Horses and wagons enabled the rapid spread of a pastoralist lifestyle across large swaths of Eurasia, and that this, combined with the consumption of dairy products, made large areas of the Eurasian steppes previously unoccupiable open to Human habitation. However, while this model provides a plausible explanation for the successes of the Yamnaya peoples, it is not, at the current time, very well supported by the available evidence. There is archaeological evidence for the use of carts and bridles in the Eneolithic and Early Bronze Age, but not for the use of Horses or dairy products.

The story of Horse domestication has long been a controversial subject in archaeology. Horse remains are known from the Eneolithic of Botai in northern Kazakhstan, but these have recently been shown to have been Przewalski's (or Mongolian) Wild Horses, Equus przewalskii, not the modern domestic Horse, Equus caballus, a species which has not confidently been found in association with Humans at sites older than the Early Bronze Age, and which cannot be confidently asserted to have been used as a riding Animal or even a beast of burden, rather than something which was being hunted, at Early Bronze Age sites. It is currently thought that Horses were not ridden, or milked, on the Eastern European steppes before about 1200 BC, and they may not have been an Animal used much by the pastorialist peoples of the period at all. 

Data on the early consumption of milk is equally lacking. Isotopic studies of Human remains have been used to suggest that dairy products were being consumed, but cannot confirm this. Palaeoproteomics (the analysis of ancient sets of proteins) could potentially be used to identify dairy consumption, but so far has only been applied to a very limited number of sites on the Eurasian steppes. Studies of the Yamnaya and Afanasievo peoples have only, to date, shown evidence of dairy consumption among a few individuals from the Eastern Steppes, and was only able to give a very ambiguous result on the producer of the peptides (short amino acid chains, or fragments of proteins) found, which was probably a Sheep or Cow.

In a paper published in the journal Nature on 15 September 2021, a group of scientists led by Shevan Wilkin of the Department of Archaeology at the Max Planck Institute for the Science of Human History, and the Institute for Evolutionary Medicine at the University of Zürich, present the results of a study which examined palaeoproteonomic evidence from dental calculus from 56 Humans from across the Eurasian steppes, dated to between 4600 and 1700 BC.

Wilkin et al. collected data from 19 Eneolithic idividuals; six from Murzikha 2, nine from Khvalynsk 1 and Khvalynsk 2, one from Ekaterinovka Mys, one from Lebyazhinka 5, and two from Khlopkov Bugor. Studies of Ancient DNA obtained from Khvalynsk and othe Eneolithic burrials in this area of the the Volga and northern Caucasus, suggest that the local population was related to the Yamnaya Peoples, but lacked the input of genetic materials from Anatolian farmers seen in the later. 

Studies based upon archaeological evidence and stable isotope analysis have suggested this population had a diet based upon the gathering of local plants, fishing, and the consumption of domestic Animals. Wilkin et al. also extracted dental calculus from two individuals from Botai in northern Kazakhstan, a site dating to about 3500 BC, where faunal remains are dominated by domestic Horses, and proteins extracted from ceramics have suggested Horses were being milked.

Map showing sites that yielded individuals with preserved ancient proteins. (a) Eneolithic, (b) Early Bronze Age and (c) Middle–Late Bronze Age sites in the Pontic–Caspian region, showing the number of individuals with a positive dairy identification out of the total number of individuals with preserved ancient proteins for each site. Strong evidence of preservation of Equine or Ruminant milk protein identifiers are depicted with black Animal icons; the single individual with equivocally identified casein peptides is shown with a grey icon. Wilkin et al. (2021).

In addition, Wilkin et al. sampled 35 Bronze Age Humans from 20 sites. These include sixteen Early Bronze Age individuals; two from Krasikovskyi 1, one from Krasnokholm 3, two from Krivyanskiy 9, two from Kutuluk 1, one from Leshchevskoe 1, one from Lopatino 1, two from Mustayevo 5, one from Nizhnaya Pavlovka, one from Panitskoe, one from Podlesnoe, one from Pyatiletka, and one from Trudovoy; as well as fourteen individuals the Middle–Late Bronze Age transition; one from Bolshekaraganskyi, two from Kalinovsky 1, three from Kamennyi Ambar 5, one from Krasikovskyi I, three from Krivyanskiy 9, one each from Lopatino 1 and Lopatino 2, one from Potapovka 1, one from Shumayevo 2, and five from Utevka 6.

Maps of all sites and individuals included in this study from the (A) Eneolithic; (B) Early Bronze Age; and (C) Middle and Late Bronze Age. Wilkin et al. (2021).

Previous archaeological isotopic studies of Early Bronze Age Yamnaya sites have suggested a diet strongly focused on herd Animals, including Cattle, Sheep and Goats. Horse remains have also been found at Early Bronze Age Yamnaya sites, but whether these were domestic Animals or wild Horses hunted for their meat is unclear. The Middle–Late Bronze Age transition was marked by an increased use of Horse-based technologies, such as chariots, which clearly indicates these people were using domestic Horses.

Fifty five of the fifty six dental calculus samples tested yielded identifiable protein data, and forty eight of those produced strong enough signals of proteins commonly found in the oral cavity that they were included in the study. 

The nineteen oldest individuals examined, all dated to between 4600 and 4000 BC, came from five Eneolithic sites close to the Volga River, or tributaries of that river, in southwestern Russia. Of these nineteen, eleven yielded good enough data to be included in the final study, with ten showing no evidence for the consumption of dairy products. The remaining individual yielded to peptides associated with Bovine α-S1-casein milk curd protein, although Wilkin et al. do not take this as absolute proof of milk consumption, as the most common dairy protein, β-lactoglobulin, was not recovered. Neither of the Botai individuals returned any evidence for dairy consumption. 

Fifteen of the sixteen Early Bronze Age individuals included in the study yielded multiple Ruminant dairy peptides including β-lactoglobulin, with some also producing α-S1 casein, α-S2-casein or both. Many of these peptides were identifiable to genus level, with the most common genera being Ovis (Sheep), Capra (Goats), and Bos (Cattle, Buffalo, Bison, and Yaks, although presumably Cattle were the most likely milk-producers). Interestingly, two individuals, both from Krivyanskiy 9, on the southwestern fringe of the study area, yielded Equus (Horse, Donkey and Kiang, although only Horses would have been present in the study area) β-lactoglobulin. These individuals were estimated to have died between 3305 and 2633 BC.

Histogram of taxonomic specificity of dairy peptide spectral matches per individual. Histograms for individuals with evidence for consumption of dairy, from the Eneolithic (a), Early Bronze Age (b) and Middle and Late Bronze Age (c). PSM, peptide spectral match. Wilson et al. (2021).

Fifteen of the nineteen Middle–Late Bronze Age transition yielded positive evidence for the consumption of Bovine milk products, including peptides from β-lactoglobulin, α-S1-casein and α-S2-casein, and the whey protein α-lactalbumin. It was possible to identify some of these peptides as being Ovis or Bos, but both Capra and Equus were absent from the sample.

Wikin et al.'s results point to a clear shift towards milk consumption between the Eneolithic and Early Bronze Age, with 10 of 11 Eneolithic individuals showing no evidence of dairy consumption, whereas 15 of 16 Early Bronze Age individuals showed such evidence. A single Eneolithic individual, from Khvalynsk, showed possible evidence of dairy consumption, but this result cannot be taken with any confidence. This strongly suggests that the widespread adoption of dairy products as part of the Human diet was associated with the Eneolithic-Early Bronze Age transition on the Pontic–Caspian Steppe. This is in contrast to the situation to the west, where settled European farmers were clearly consuming dairy products in the Eneolithic. This in turn suggests a cultural frontier between the European farmers and the Steppe herders. 

The ability of proteonomics to identify the Animals producing the milk used for Human consumption sheds light on the Animals being kept by these peoples. The Pontic–Caspian Steppe provides a rich environment capable of supporting a range of herd Animals, including Cattle, with a relatively high water-demand, and Sheep and Goats, which favour more arid conditions. Interestingly, a recent study of Early Bronze Age individuals from the steppes suggests that the persistence of lactase (the enzyme that allows digestion of whole milk) production into adulthood in these individuals was rare, but this does not rule out the production of milk-derived products such as yogurts, cheeses or fermented milk beverages.

The milking of Horses has previously been suggested for the Botai culture of Kazakhstan, but Wilkin et al. found no evidence of this (although their sample size, two individuals, was quite small). Horse milk was apparently consumed by two individuals from the Early Bronze Age of the Pontic–Caspian Steppe. These findings, combined with the discovery that the Horses of Botai were not the Domestic Horse, Equus caballus, supports the idea that Horse domestication originated on the Pontic-Caspian Steppe rather than with the peoples of Central Asia. The oldest Horse remains shown to contain genetic markers for modern domestic lineages date from between 2074 and 1625, and come from sites in Russia, Romania and Georgia. The discovery of the oldest known evidence in the Pontic-Caspian Steppe region, which also saw the first appearance of Horse-drawn chariots around 2000 BC, contributes further evidence to this hypothesis.

Wilkin et al.'s findings contribute to the growing understanding of a significant cultural and technological revolution associated with the Eneolithic-Early Bronze Age transition on the Pontic-Caspian Steppe. As well as the, obvious, adoption of bronze as a metal for making tools and weapons, this shift included the abandonment of riverine settlement sites, the appearance of kurgan cemeteries on formerly uninhabited arid plateaus, the appearance of wheeled vehicles, and the occasional placement of Horse bones in Yamnaya burials. This was accompanied by a rapid expansion of the range of these peoples, both to the west into Europe and to the east into the Altai Mountains. Wilkin et al.'s findings shed no direct light upon the role of Horses in this expansion, but evidence for the consumption of Horse milk is clearly evidence for Horse domestication, which is likely to also imply Horses were being used for other purposes. The combination of a dietsry shift to include nutritionally rich dairy products, the adoption of Animal-drawn vehicles as a means to transport greated loads, and the domestication of highly versatile Horses is likely to have significantly transformed the cultural and economic environment of the Pontic-Caspian Steppe, enabling Humans to venture into previously uninhabitable areas, and thereby access further new resources, such as seasonally snow-covered upland pastures. It is, of course, possible that all of these elements were present to some extent before the Eneolithic-Early Bronze Age transition, but that transition clearly shows the widespread adoption of all these technologies by populations over a wide geographical area.

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Wednesday, 15 September 2021

Mexico landslide kills at least two people.

Two people, including a three-year-old girld, have now been confirmed dead and another two are still missing following a landslide that hit the city of Tlalnepantla in Mexico State, Mexico, on Friday 10 September 2021. The landslide was caused by the collapse of part of the Cerro del Chiquihuite hillside following heavy rain in the area, which dislodges a series of large boulders, estimated to weigh up to 200 tons, onto a residential district.Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. However, in this case the rains are thought to have been only part of the problem, with the area having been shaken by a Magnitude 7.0 Earthquake which occurred near Acapulco on the coast of Guerrero State, 400 km to the south of Tlalnepantla, on Tuesday 7 September.


Boulders lying on top of residential housing in Tlalnepantla, Mexico, following a landslide on 10 September 2021. Eduardo Verdugo/AP.

The 7 September 2021 Acapulco Earthquake was recorded by the United States Geological Survey as occurring at a depth of 20 km, roughly 17.7 km to the north of the city, slightly after 8.45 pm local time (slightly after 1.45 am on Wednesday 8 September GMT). The event was felt over much of southern area, and caused minor damage to many buildings, but no major casualties or destruction.

The approximate location of the 7 September 2021 Acapulco Earthquake. USGS.

Mexico is located on the southernmost part of the North American Plate. To the south, along the Middle American Trench, which lies off the southern coast off Mexico, the Cocos Plate is being subducted under the North American Plate, passing under southern Mexico as it sinks into the Earth. Guatemala is located on the southern part of the Caribbean Plate, close to its boundary with the Cocos Plate, which underlies part of the east Pacific. The Cocos Plate is being pushed northwards by expansion of the crust along the East Pacific Rise, and is subducted beneath the Caribbean Plate along the Middle American Trench. This is not a smooth process, and the plates frequently stick together then break apart as the pressure builds up, causing Earthquakes on the process.

The position of the Cocos, Nazca and Rivera Plates. MCEER/University at Buffalo.
The Cocos Plate is thought to have formed about 23 million years ago, when the Farallon Plate, an ancient tectonic plate underlying the East Pacific, split in two, forming the Cocos Plate to the north and the Nazca Plate to the south. Then, roughly 10 million years ago, the northwesternmost part of the Cocos Plate split of to form the Rivera Plate, south of Beja California.
In a paper published in the Journal of Geophysical Research, in 2012, a team led by Igor Stubailo of the Department of Earth and Space Sciences at the University of California Los Angeles, published a model of the subduction zone beneath Mexico using data from seismic monitoring stations belonging to the Mesoamerican Seismic Experiment, the Network of Autonomously Recording Seismographs, the USArray, Mapping the Rivera Subduction Zone and the Mexican Servicio Sismologico Nacional.
The seismic monitoring stations were able to monitor not just Earthquakes in Mexico, but also Earthquakes in other parts of the world, monitoring the rate at which compression waves from these quakes moved through the rocks beneath Mexico, and how the structure of the rocks altered the movement of these waves.
Based upon the results from these monitoring stations, Stubailo et al. came to the conclusion that the Cocos Plate was split into two beneath Mexico, and that the two plates are subducting at different angles, one steep and one shallow. Since the rate at which a plate melts reflects its depth within the Earth, the steeper angled plate melts much closer to the subduction zone than the shallower angled plate, splitting the Trans-Mexican Volcanic Belt into sections above the different segments of the Cocos Plate, and causing it to apparently curve away from the subduction zone.
Top the new model of the Cocos Plate beneath Mexico, split into two sections (A & B) subducting at differing angles. (C) Represents the Rivera Plate, subducting at a steeper angle than either section of the Cocos Plate. The Split between the two has been named the Orozco Fracture Zone (OFZ) which is shown extended across the Cocos Plate; in theory this might in future split the Cocos Plate into two segments (though not on any human timescale). Bottom Left, the position of the segments on a map of Mexico. Darker area is the Trans-Mexican Volcanic Belt, orange circles are volcanoes, brown triangles are seismic monitoring stations, yellow stars are major cities. Bottom Right, an alternative model showing the subducting plate twisted but not split. This did not fit the data. Stubailo et al. (2012).

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