Wednesday, 22 November 2017

Magnitude 5.5 Earthquake in Chiayi County, Taiwan.

The Taiwan Central Weather Bureau reported a Magnitude 5.5 Earthquake at a depth of 18.5 km in Chiayi County in central Taiwan at about 10.20 pm local time (about 2.20 pm GMT) on Wednesday 22 November 2017. The event was felt across most Taiwan, as well as in the city of Fuzhou in Fujian Province on the Chinese mainland.

The approximate location of the 22 November 2017 Tainan Earthquake. USGS.

Taiwan has a complex tectonic setting, lying on the boundary between the Eurasian and Philippine Plates, with the Eurasian Plate being subducted beneath the Philippine Plate in the South and the Philippine Plate being subducted beneath the Eurasian in the East. Subduction is not a smooth process even in simple settings, with plates typically sticking together as pressure from tectonic expansion elsewhere builds up, then suddenly breaking apart and shifting abruptly, causing Earthquakes.

The motion of the tectonic plates beneath Taiwan. The University of Memphis.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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Reassessing the Aitape Skull.

Modern Humans are known to have occupied Papua New Guinea for at least 35 000 years, but archaeological remains older than about 2000 years are extremely rare, and therefore of great interest to Archaeologists. One such specimen is the Aitape Skull, a partial Human cranium found at Paniri Creek in the foothills of the Torricelli Mountains in 1929, and originally assessed to date from around the time of the first settlement of the island, due to the presence of Pleistocene Formaninferans in the sediments which produced it. For a long time this specimen was considered to be of great importance in understanding the origins of Human settlement in Australasia, but the introduction of Carbon-dating resulted in the age of the skull being lowered to about 6000 years, so that it was still one of the oldest Human specimens from Papua New Guinea, but was far too young to shed much light on the first Humans in the area, resulting in it being effectively forgotten by the archaeological community for many years.

In a paper published in the journal PLoS One on 25 October 2017, James Goff of the PANGEA Research Centre at the University of New South Wales and the Laboratoire Chrono-Environnement at the Université de Bourgogne-Franche-Comté, Mark Golitko of the Department of Anthropology at the University of Notre Dame, Ethan Cochrane of Anthropology at the University of Auckland, Darren Curnoe of the ARC Centre of Excellence for Australian Biodiversity and Heritage and the PANGEA Research Centre at the University of New South Wales, Shaun Williams of the National Institute of Water & Atmospheric Research in Christchurch, New Zealand, and John Terrell of the Integrative Research Center at the Field Museum of Natural History, report the results of a study which both re-examined the Aitape Skull and revisited the location where it was found.

The Aitape Skull was found at a site 12 km inland from Sissano Lagoon on the modern coast of Papua New Guinea, and about 52 m above modern sea-level. About 6000 years ago the sea-level was begging to stabilise, following a long period of rising waters. This would have created a stable coastal environment in the Paniri Creek region, with a system of lagoons and coastal lakes ideal for Human settlement. This has subsequently been uplifted by tectonic activity, pushing the modern coastline further to the north. 

Site location and skeletal remains. (a) Location of New Guinea in the Pacific Ocean; (b) General study area in northern PNG (red square see (C)) with tectonic setting, CP: Caroline plate, MT: Melanesian trench, MTB: Mamberamo thrust belt, NBP: New Bismarck plate, NGT: New Guinea trench (arrows show approx. direction of plate movement); (c) Site of Aitape Skull where Paniri Creek exits the Barida Range approx. 11 km inland from Sissano Lagoon. Dashed orange line marks approx. edge of approx. 6000±7000 yr. old coastline; (d) Aitape cranium: The early Holocene Aitape frontal bone (scale bar at lower right is 2 cm). Goff et al. (2017).

The locality that produced the skull comprises chiefly laminated intertidal mudflat deposits; however the skull itself was found within a lenticular deposit which also contained coconut shell and fibre, driftwood, other plant remains, marine, intertidal and terrestrial shells and Foraminifera. This has previously been interpreted as a storm deposit, but Goff et al. reason that the presence of reworked Foraminifera indicates a more severe event, with substantial subtidal sediments excavated and dumped onto the beach. For this reason they believe the deposits are likely to have been produced by a tsunami, rather than a storm.

The north coast of Papua New Guinea is a tectonically active region, and tsunamis are not uncommon their. Notably a tsunami event which struck Sissano Lagoon in 1998 is known to have killed more than 2000 people, one of the moset severe tsunami events in recent years. They further note that the fragmentary nature of the Aitape Skull are not at odds with this. Most bodies recovered from tsunami events are relatively intact, but those associated with the 1998 Sissano Lagoon event were often dismembered to some degree, due to the high speeds at which the water hit settled areas.

Most tsunamis accumulate large amounts of sediment early in their progress, which tends to slow them down; for example the 2004 Indian Ocean tsunami hit beaches in India and Thailand at speeds of about 25 km per hour, while the 2011 event in the same region achieves slightly over 30 km per hour. The Sissano Lagoon tsunami appears to have been relatively free of sediments until it reached the lagoon itself, and is estimated to have been travelling at 65 km per hour 200 m from the beach, and was still travelling at over 40 km per hour 600 m inland. This enabled it to very rapidly accumulate large amounts of debris, including sediment, trees and parts of buildings, so that victims were dismembered by debris in a high energy impact.

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Striking miners killed in clash with paramilitary group in Guerro State, Mexico.

Two miners have been killed in a clash with a paramilitary group during a protest near Real de Limón in Guerro State, Mexico. The two men  were taking part in a protest in which miners at the El Limón-Guajes Gold Mine on Saturday 18 November 2017, when they were attacked by members of the Policía Comunitaria de Tonalapa, or Tonalapa Community Police (not an official police organisation). The attackers were reportedly detained briefly by members of the Mexican Army, but were released without charge. Workers at the mine have been on strike since 3 November 2017, demanding improved pay and working conditions, and the right to join a worker-led union, and have been blocking access to the mine site as part of the protest.

The El Limón-Guajes Gold Mine in Guerro State, Mexico. Mining Journal.

The El Limón-Guajes Mine is operated by Canadian mining company Torex Gold. The company had agreed that workers at the site were entitled to join a union following an earlier dispute, but instead enrolled them in the Confederación de Trabajadores de México, an employer-led worker's federation, which provides only limited support for ordinary members, rather than the worker-led National Union of Mine, Metal, Steel and Related Workers of the Mexican Republic, which is allied to the American United Steelworkers, and which the miners wanted to join. The dispute has prompted the Canadian Branch of United Steelworkers to petition Canadian Prime Minister Justin Trudeau to intervene, citing his stated desire to improve worker's rights across the North Amercan Free Trade Agreement nations.

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Tuesday, 21 November 2017

Asteroid 2017 VN13 passes the Earth.

Asteroid 2017 VN13 passed by the Earth at a distance of about 1 141 000 km (2.97 times the average distance between the Earth and the Moon,  or 0.76% of the distance between the Earth and the Sun), slightly before 8.30 pm GMT on Wednesday 15 November 2017. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2017 VN13 has an estimated equivalent diameter of 4-16 m (i.e. it is estimated that a spherical object with the same volume would be 4-16 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 43 and 25 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 VN13. Minor Planet Center.

2017 VN13 was discovered on 14 November 2017 (the day before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2017 VN13 implies that the asteroid was the 288th object (object N13) discovered in the first half of November 2017 (period 2017 V).

2017 VN15 has a 813 day orbital period and an eccentric orbit tilted at an angle of 5.44° to the plane of the Solar System, which takes it from 0.93 AU from the Sun (i.e. 93% of he average distance at which the Earth orbits the Sun) to 2.48 AU from the Sun (i.e. 248% of the average distance at which the Earth orbits the Sun, more than the distance at which the planet Mars orbits). 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). This means that 2017 VN13 has occasional close encounters with the planet Mars, which it is next predicted to pass in May 2029.

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Extensive Coraline Algal Reef discovered on the coast of northern Taiwan.

The tropical seas are noted for their extensive Coral Reef systems, though Corals are far from being the only reef-forming organisms in the seas. Coraline Algae are Rhodophytes (Red Algae) that form extensive reef systems in temperate waters, though they are seldom observed as they favour nutrient rich waters (which tend to be opaque) and depths of greater than 10 m. Algal Reefs also occur in tropical and sub-tropical environments, though they are much less common here, typically only being found in areas of high sedimentation, which excludes most Coral species.

In a paper published in the journal Coral Reefs on 20 September 2017, Ching-Yu Liou of the Endemic Species Research Institute, and Sung-Yin Yang and Chaolun Allen Chen of the Biodiversity Research Center at Academia Sinica, report the discovery of an extensive Coralline Algal Reef system the coastline of Taoyuan City in northwest Taiwan.

The reef covers an area about 27 km long and 450 m wide, in an area with a tidal range of about 4 m, exposing much of the reef at low tides. It has a porous structure, being made up of stacked layers of Algae, predominantly of the genera Mesophyllum, Phymatolithon, and Harveylithon, as well as sediment-tolerant Corals such as Cyphastrea and Dipsastraea. Carbon-dating of drilled cores from the Reef suggests it began to form about 7500 years ago.

Coraline Algal Reef during low tide with windmills in the background. Liou et al. (2017).

Liou et al. suggest that the Taoyuan Reef is likely to perform similar ecosystem services to similar sized Coral Reef systems, and note that it is home to little-known and probably rare species such as the newly discovered Coral Polycanthus chaishanensis, and at least two species of as yet undescribed Corals. They also note that it is threatened by coastal developments in the area, including a planned industrial park and wind farm. 

Detail of a section of the Reef showing undescribed Crustose Coraline Algal species, Phymatolithon sp. nov. (left) and Mesophyllum sp. nov. (right). Liou et al. (2017).

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Spilosmylus spilopteryx & Spilosmylus tephrodestigma: Two new species of Osmylid Lacewing from Luzon Island, the Philippines.

Osmylids (Osmylidae) are a group of Neuropteran Insects with a fossil record dating back to the Early Jurassic, with a stem group lineage (i.e. fossils of species more closely related to them than to anything else, but not descended from the last common ancestor of all living species), that are still in existence today. They appear to have been at their most numerous and diverse in the Middle-Late Jurassic, with a number of lineages apparently disappearing at the Jurassic-Cretaceous boundary.Living Osmylids tend to be large, and often have strongly patterned wings. Their larvae have elongated, lance-like mandibles, giving the group the alternative name 'Lance Lacewings'.

In a paper published in the journal ZooKeys on 26 October 2017, Davide Badano of the Dipartimento di Scienze della Terra at the Università degli Studi di Genova, and Shaun Winterton of the California State Collection of Arthropods, describe two new species of Osmylids from Luzon Island in the Philippines. Both are placed in the genus Spilosmylus, which is found from East Africa across South and Southeast Asia and as far east as Australia. 

The first new species is named Spilosmylus spilopteryx, where 'spilopteryx' means 'marked wing' in reference to the prominent, cloud-like markings in its wings. It is described from a single male specimen collected from the Tigaon area of Camarines Sur Province on southern Luzon. It is 10.48 mm in length, with a forewing length of 17.46 mm, and brown in colour with distinctively marked wings.

Spilosmylus spilopteryx, male specimen in dorsal view. Badano & Winterton (2017).

The second new species is named Spilosmylus tephrodestigma, where 'tephrodestigma' means 'coal spot' in reference to the grey spots found on its forewings. This species is described from a single specimen from the Barlig area of Mountain Province on northern Luzon Island. This specimen has a damaged abdomen, making it impossible to determine its sex or body length, but it has a forewing length of 21.43 mm, and is pale in colour with brown markings on its body and grey markings on its wings.

Spilosmylus tephrodestigma, specimen in dorsal view. Badano & Winterton (2017).

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Magnitude 5.9 Earthquake beneath Posi Posi Rao Island, North Maluku Province, Indonesia.

The United States Geological Survey recorded a Magnitude 5.9 Earthquake at a depth of 20.3km, beneath the northern part of Posi Posi Rao Island in the North Maluku Province of Indonesia, slightly slightly after 1.05 am local time on Sunday 19 November 2017 (slightly after 4.05 pm on Saturday 18 November, GMT). There are no reports of any casualties associated with this event, but it did cause some minor damage to buildings in Posiposi village, on the south part of the island.

Damage to buildings on Posiposi Rao Island following the 19 Novenmber 2017 Earthquake. Earthquake Report.

Posiposi Rao lies at the northern end of the Halmahera Islands chain, a volcanic arc formed where one tectonic plate is being subducted beneath another, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. However the Halmahera Islands are unusual in that they lie on a double subduction zone. The underlying plate, a northeaster extension of the Molucca Sea Plate, is being overridden form the Philippine Plate from the east and the Eurasian Plate from the west. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

 Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

The approximate location of the 19 November 2017 Posiposi Rao Earthquake. USGS.

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