GeoLog

Laura Roberts-Artal

Laura Roberts Artal is the Communications Officer at the European Geosciences Union. She is responsible for the management of the Union's social media presence and the EGU blogs, where she writes regularly for the EGU's official blog, GeoLog. She is also the point of contact for early career scientists (ECS) at the EGU Office. Laura has a PhD in palaeomagnetism from the University of Liverpool. Laura tweets at @LauRob85.

Mexico earthquakes: What we know so far

Mexico earthquakes: What we know so far

On Friday 8 September 2017 at 04:49 am UTC, a magnitude 8.1 earthquake hit off the coast of Mexico, 87 km SW of Pijijiapan. According to the U.S. Geological Survey, the epicentre was at 15.07 N, 93.72 W at a depth of about 69.7 km. Yesterday, another strong (magnitude 7.1) earthquake hit central Mexico, 55 km SSW of the city of Puebla and 120 km south of Mexico City.

Despite the lower magnitude, yesterday’s earthquake, which struck at a depth of 51 km, has caused widespread destruction. At the time of writing, official estimates put the death toll at 217 (according to Mexico’s National Coordinator for Civil Protection, Luis Felipe Puente), with shaking causing damage to and the collapse of hundreds of buildings in Mexico City and surrounding areas.

“The M 7.1 earthquake was much closer to Mexico City, a city build on a dried lake bed; this caused presumably (needs to be confirmed by data) much higher shaking in the densely populated capital then the larger, but farther M 8.1 event,” explains Martin Mai, President of the EGU’s Seismology Division.

“Both earthquakes were intraplate normal faulting events, not occurring on the interface between the subducting and overriding plates but rather inside the subducting plate,” adds Vala Hjorleifsdottir, a researcher at the National Autonomous University of Mexico.

These intraplate earthquakes generate relatively strong and rapid shaking, compared to their counterparts breaking the plate interface.  Furthermore, as the waves are generated deeper in the Earth, they do not travel through shallower material that damp them as they travel, and they are still strong when they arrive to the City of Mexico and neighbouring areas.  For these reasons, combined with their proximity to populated areas, these events can be more destructive than expected by their magnitude.

The U.S. Geological Survey estimated that significant causalities are likely in the region. Given the mix of vulnerable and earthquake resistant structures, the economic loss is also expected to be high. For more information visit impact pages of the event on the USGS website.

Six days after the latest earthquake, rescue workers are still search for victims among the rubble. This visual of Mexico City gives an impression of the scale of the devastation in the country’s capital city.

“Mexico City [is] built on a dried-out lake bed, or on ‘landfill’ of unconsolidated sediments.  The interaction between the incoming seismic waves and the sediments cause the waves to amplify and the duration of shaking to increase.  Both of these factors are devastating to buildings,” explains Hjorleifsdottir.

As to whether the two earthquakes are linked, scientists are fairly certain that the normal mechanisms which are known to trigger an earthquake after another didn’t come into play for the M 8.1 and the later M 7.1. At more than 600 km between the two quakes, they occurred, too far from one another. In addition, if shaking from an early earthquake is going to trigger a second, it is expected to happen shortly after the initial tremor, not 12 days later.

However, there are other mechanisms, which are less well understood, for example the triggering of earthquakes in hydrothermal areas and volcanoes, over large distances, for a period after large events.

“We believe this has to do with the behaviour of fluids in these areas, that promote the occurrence of earthquakes in these regions.  More research is needed to tell whether any of these other methods caused triggering of the second event,” says Hjorleifsdottir. Mai also adds: “It could be that stress changes caused by the M 8.1 event brought the fault (system) on which the M 7.1 earthquake happened closer to failure; but this requires detailed quantitative analysis”.

Editor’s note: Last updated 02.10.2017. This post will be update as more information about the earthquake becomes available.

With thanks to Martin Mai (EGU Seismology Division President), Vala Hjorleifsdottir, Paco Sánchez and Marco Calo (National Autonomous University of Mexico).

Further reading and resources:

U.S. Geological Survey overview of 19.09.2017 M 7.1 earthquake (includes interactive, shake and regional information maps)

U.S. Geological Survey overview of 08/09.2017 M 8.1 earthquake (includes interactive, shake and regional information maps, as well as finite fault results and moment tensor information)

Temblor blog post on M 7.1 earthquake

Temblor blog post on M 8.1 earthquake

Did Mexico dodge a bullet in last week’s M=8.1 earthquake? (Temblor blog post on dynamics of 8th September quake)

European-Mediterranean Seismological Centre information about yesterday’s earthquake

SSN (Mexico) page about yesterday’s earthquake (in Spanish)

GFZ GEOFON Global Seismic Network event page for yesterday’s earthquake

Mexico City, Before and After the Earthquake (New York Times visualisation)

Are Mexico’s two major earthquakes related, and what could happen next? (Temblor blog)

Shocked and shaken to the ground: An eyewitness report from Mexico City (Temblor blog)

Mexican Earthquakes: Chain Reaction or Coincidence? (Temblor blog)

Imaggeo on Mondays: What happens to mines when they become redundant?

Imaggeo on Mondays: What happens to mines when they become redundant?

When the minerals run out, or it is no longer profitable to extract the resources, mines shut down. Prior to issuing a permit for the exploitation of a resource, most regulators require assurance that once the mine closes it, or the activities carried out at the site, will not present a risk to human health or the environment.

Ongoing monitoring of a mine once it is decommissioned is required to ensure this is the case.

“The goal of my work is to study the environmental impact of mining waste in the north-east part of Algeria,” explains Issaad Mouloud, author of today’s featured image.

Algeria has a long history of mining. Since the antiquity and the time of the Berbers, many minerals and ores deposits were exploited. The northeast was the most productive region in the country. The geology of the study area is composed of magmatic and metamorphic rocks, sandstone and limestone.

Kef Oum Theboul mining district is located on the Eastern cost of Algeria, 4 km west of the Tunisian border. It is located 15 km from the town of El Kala. The Kef Oum Theboul site covers an area of 26.6 km2 and which contains copper lead and zinc ore

Discovered in 1845, the Kef Oum Teboul ore deposits were mined from 1849 to the 1970s. The Messida ore plant, pictured above and located not far from the Kef Oum Teboul deposit, is one of Issaad’s study sites.

The ore plant, situated in the Algerian Mediterranean coast, on Messida beach (located 6km from Kef Oum Teboul) processed copper, lead and zinc mineralizations.  Processing at the plant started in 1899.  It had three water jacket furnaces, with a capacity of 50 tons of ore per 24 hours. The obtained matte contained 20-22% copper, 200 grams of silver and 11-12 grams of gold per ton.

“The plant is now totally destroyed but mining waste, mainly sulphur ore and slag, is still stored in the Messida area,” explains Issaad, who goes on to say “the main pollution factor which I study is the acid mine drainage and heavy metals.”

 

Abandoned sulphurous ore and slag stored in the ruins of the ore processing plant of Messida. Credit: Issaad Mouloud

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Educators: apply now to take part in the 2018 GIFT workshop!

Educators: apply now to take part in the 2018 GIFT workshop!

The General Assembly is not only for researchers but for teachers and educators with an interest in the geosciences also. Every year the Geosciences Information For Teachers (GIFT) is organised by the EGU Committee on Education to bring first class science closer to primary and high school teachers.

The topic of the 2018 edition of GIFT is ‘Major events that shaped the Earth’. This year’s workshop will be taking place on 9–11 April 2018 at the EGU General Assembly in Vienna, Austria.

Teachers from Europe and around the world can apply to participate in the 2018 edition of GIFT, and to receive a travel and accommodation stipend to attend the workshop, by November 15. Application information is available for download in PDF format, a document which also includes the preliminary programme of the workshop.

Not sure what to expect? More information about GIFT workshops can be found in the GIFT section of the EGU website. You can also take a look at a blog post about the 2015 workshop and also learn what the workshop is like from a teacher’s perspective here. You might also find videos of the 2017 workshop useful too.

 

Imaggeo on Mondays: A prehistoric forest

Imaggeo on Mondays: A prehistoric forest

This stunning vista encompasses the south-western wilderness of Tasmania as seen from the Tahune air walk 60 m above the Huon river valley. In front lies the beginning of a huge UNESCO World Heritage Site, covering almost a fourth of the area of Tasmania. The site mostly consists of a pristine, temperate rainforest of Gondwanan origin that is home to the tallest flowering trees in the world; Eucalyptus spp. reach up to 100 m height in this region.

“I have never tasted the sense of a more remote place than this one. Give me more,” says Vytas Huth, who captured this stunning shot.

Gondwana was a supercontinent, consisting of present day Africa, South America, India, Madagascar, Australia and New Zealand. It formed when the even larger supercontinent of Pangaea broke up 250 million years ago.

Slowly, Gondwana started to break apart too. India tore away first, followed by Africa and then New Zealand. By the end of the Cretaceous, 65 million years ago, only South America, Australia and Antarctica remained joined.  It took a further 20 million years before Australia and Antarctica separated.

By the time Australia started being pulled northwards, the first glaciers were forming on Antarctica, as it began freezing over. Atop the old rocks which made up its bulk, animals and plants of ancient origin, travel northwards with the Land Down Under.

Because India and Africa broke away from the supercontinent so early on, few hallmarks of ancient Gondwana wildlife are left in their present biodiversity. In contrast, Australia and Tasmania remained connected to Antarctica and South America much longer and there are clear similarities in species across these continents.

“Fossil evidence suggests that temperate rainforest once extended across Australia, Antarctica, South America and New Zealand around 45 million years ago. Such fossils and the surviving species in Tasmania provide evidence of the ancient link to Gondwana”, reports the Tasmania Parks & Wildlife Service.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.