{"id":514530,"date":"2024-07-10T16:46:10","date_gmt":"2024-07-10T19:46:10","guid":{"rendered":"https:\/\/revistapesquisa.fapesp.br\/?p=514530"},"modified":"2024-07-10T16:46:10","modified_gmt":"2024-07-10T19:46:10","slug":"ground-in-maceio-has-been-sinking-for-20-years","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/ground-in-maceio-has-been-sinking-for-20-years\/","title":{"rendered":"Ground in Macei\u00f3 has been sinking for 20 years"},"content":{"rendered":"

The ground above subterranean rock salt mines can begin sinking silently and gently\u2014by just a few millimeters per year\u2014as has been reported in Macei\u00f3, the state capital of Alagoas, since November. In a study published in the journal Scientific Reports <\/em>in April 2021, researchers from the German Research Center for Geosciences (GFZ) and the University of Hannover, Germany, claimed that areas of three neighborhoods near Munda\u00fa Lagoon\u2014Pinheiro, Mutange, and Bebedouro\u2014have been subsiding since 2004, without drawing much attention. Satellite image analysis indicated that the ground in the mining region sank by around 2 meters (m) between 2004 and 2020.<\/p>\n

Marcos Hartwig, a geologist from the Federal University of Esp\u00edrito Santo (UFES), reached a similar conclusion to the Germans. In an article published in the journal Acta Geotechnica<\/em> in April 2023, he and colleagues from the Brazilian National Institute for Space Research (INPE) and the University of S\u00e3o Paulo (USP) revealed that the ground in some parts of the region sank by one meter between 2016 and 2020. \u201cThe subsidence is greater in areas nearer the mines, suggesting a causal relationship,\u201d he states.<\/p>\n

As a result of earthquakes and cracks appearing in houses and roads, the public authorities have been forced to relocate around 60,000 people. The first residents of the five neighborhoods considered most at risk began to leave in 2019. In December 2023, Macei\u00f3\u2019s local government stated that an area of 3 km2<\/sup>, almost 3% of the city\u2019s urban area, was at risk of sinking.<\/p>\n

The problem worsened that month when the ground above one of the 35 mines, known as mine 18 and covered by the water of the Munda\u00fa Lagoon, sank by around 2 m in just 10 days and then collapsed.<\/p>\n

There have been at least 50 reports of subsidence in urban areas due to salt mining in the USA, Canada, Europe, and Asia. One of the most significant occurred in Tuzla, Bosnia and Herzegovina, where the ground above a mine sank 12 meters, destroying houses, buildings, sewage networks, and electrical lines. The mine was filled with water and closed in 2006, but as recently as 2021, the ground was still sinking by 1\u20134 centimeters (cm) per year.<\/p>\n

\"\"

Deriky Pereira\u2009\/\u2009UFAL<\/span><\/a> Area of Macei\u00f3 previously inhabited and now damaged by the sinking groundDeriky Pereira\u2009\/\u2009UFAL<\/span><\/p><\/div>\n

In Macei\u00f3, the subsidence became more visible in 2018. On March 3, upon returning to her apartment in the capital of Alagoas, economist Natallya Levino of the Federal University of Alagoas (UFAL) was informed by her husband that the lights in the living room had been shaking. Cracks also appeared in the streets and in other homes in the Pinheiro neighborhood.<\/p>\n

On the same day, the Brazilian Seismographic Network, run by the Federal University of Rio Grande do Norte (UFRN), recorded a rare magnitude 2.4 earthquake in the region. Anderson Farias do Nascimento, a geophysicist from UFRN, was intrigued by the situation: \u201cMacei\u00f3 didn\u2019t used to experience such intense seismic activity and the effects reported by residents were never so strong.\u201d<\/p>\n

In May 2019, the Geological Survey of Brazil (SGB), a public company linked to the Ministry of Mines and Energy, attributed the intense tremor\u2014and the smaller ones that followed\u2014to the collapse or merging of underground salt mines, which provide the raw material for caustic soda and plastics and were opened and operated by petrochemical company Braskem in the 1970s.<\/p>\n

Based on analyses carried out a few months after the earthquake between June 2018 and April 2019, the SGB concluded that the mines, at depths of between 800 m and 1,200 m, caused the ground above to subside. As a result, Braskem had to stop work at the mines and fill any collapsing mines with sand or cement. But the earth continued to sink.<\/p>\n

\u201cWhat is happening in Macei\u00f3 is called induced seismicity, caused by human activity such as mining,\u201d says Nascimento, who participated in the analysis of the tremors as part of a research project carried out with the SGB team. \u201cThe signal recorded by the equipment is different from natural tremors, indicating energy released by the earth shifting and collapsing.\u201d<\/p>\n

Hartwig adds that the cavities cause something known as a stress imbalance, which creates deformations in the layers above them. The phenomenon can eventually reach the surface, causing cracks in streets and buildings (see infographic below<\/em>). \u201cGround movements begin subtly and more or less linearly, then evolve into accelerated and irregular movements,\u201d he explains.<\/p>\n<\/div>

\n \n \n \n <\/picture>Alexandre Affonso\/Pesquisa FAPESP<\/span><\/div>
\n

The role of two extensive geological faults (fractures in a block of rock) that run parallel to Munda\u00fa Lagoon is still uncertain. Technical reports issued by the SGB state that they may have been reactivated, which would contribute to ground movements, but Hartwig and his group ruled out the influence of these faults. Nascimento, however, does not rule out the possibility: \u201cDespite being small, the faults could be providing a way for water to infiltrate the mines, causing them to expand and collapse.\u201d<\/p>\n

No dialogue<\/strong>
\nThe scientists are helping shed light on and address these problems. \u201cResidents from the neighborhoods around the lagoon started calling me in 2010, asking me to look at cracks in their houses,\u201d says civil engineer Abel Galindo Marques, a retired professor at UFAL. Marques specializes in building foundations and coauthored the book Rasgando a Cortina de Sil\u00eancios: O Lado B da Explora\u00e7\u00e3o do Sal-Gema de Macei\u00f3 <\/em>(Tearing down the curtain of silence: The B side of rock salt exploration in Macei\u00f3; Instituto Alagoas, 2022).<\/p>\n

Shortly after the 2018 earthquake, he participated in a meeting at the Alagoas Regional Council for Engineering and Agronomy (CREA). \u201cFour people claimed the tremors and cracks had nothing to do with the mines, which I had seen as the cause since 2017.\u201d Hartwig says that in 2022, he asked Macei\u00f3 civil defense agencies for access to field data, which would allow for more consistent analyses. In return, he was offered a report and training for his team on how to interpret satellite data for ground surface movement monitoring. \u201cI received nothing more than a generic response\u2014the conversation didn\u2019t go any further,\u201d he laments.<\/p>\n

In the book A Cidade Engolida <\/em>(The swallowed city; Pedro & Jo\u00e3o Editores, 2023), Levino and Marcele Elisa Fontana, an engineer from the Federal University of Pernambuco (UFPE), reiterate: \u201cThe absence of official data capable of guiding research and discussions has limited further studies.\u201d After the most intense tremors, Levino and colleagues from UFAL and other universities created a WhatsApp group and a website to share studies, videos, and other materials about subsidence in the area, in addition to the YouTube channel \u201cRelatos de uma Trag\u00e9dia\u201d (Reports of a tragedy). She also feels frustrated: \u201cI never got to interview anyone at Braskem.\u201d When asked to comment by Pesquisa FAPESP<\/em>, the SGB stated that no researchers were available to give an interview on the subject and Braskem did not reply.<\/p>\n

The order to evacuate houses in sinking neighborhoods has affected thousands of people. Despite having received or still negotiating compensation from Braskem, some have had to move long distances away or even relocate to nearby cities in search of affordable housing. The situation also resulted in store closures, even in neighboring areas, the deactivation of 10 bus lines, and suspension of the construction of a light rail transit (LRT) line, according to an article published in the journal Logistics <\/em>in September 2023 by the UFAL group in collaboration with researchers from Pernambuco (UFPE) and Bras\u00edlia (UnB).<\/p>\n

\u201cOther tremors could occur until the area stabilizes,\u201d says Hartwig. His prediction is based on studies from the 1940s by American geologist Ruth Doggett Terzaghi (1903\u20131992), who described five stages of subsidence caused by salt mines like those in Macei\u00f3.<\/p>\n

The first two consist of slow, imperceptible movements that can last decades or centuries. The third lasts a few years and leads to the formation of surface depressions. The fourth is collapsing of the ground and subsequent formation of craters, which may be partially filled with water.<\/p>\n

\u201cBefore November, we were in stage 3, with subtle and progressive sinking. We have now entered the fourth stage, in which the movement has accelerated greatly, resulting in holes on the surface filled with water,\u201d explains Hartwig. The final stage is marked by mild and irregular subsoil movements.<\/p>\n

Scientific articles<\/strong>
\n<\/strong>VASSILEVA, M. et al<\/em>. A decade-long silent ground subsidence hazard culminating in a metropolitan disaster in Macei\u00f3, Brazil<\/a>. Scientific Reports<\/strong>. Vol. 11, 7704. Apr. 8, 2021.
\nHARTWIG, M. E. et al.<\/em> The significance of geological structures on the subsidence phenomenon at the Macei\u00f3 salt dissolution field (Brazil)<\/a>. Acta Geotechnica<\/strong>. Vol. 18, pp. 5551\u201373. 2023.
\nFONTANA, M. E. et al<\/em>. Risk analysis of transport requalification projects in the urban mobility problem caused by a mining disaster<\/a>. Logistics<\/strong>. 2023, vol. 7, no. 3. Sept. 4, 2023.<\/p>\n","protected":false},"excerpt":{"rendered":"Salt mines caused tremors and cracks in five neighborhoods in the capital of Alagoas","protected":false},"author":684,"featured_media":514535,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[200,240],"coauthors":[2721],"class_list":["post-514530","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-science","tag-environment","tag-geology"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/514530","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/684"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=514530"}],"version-history":[{"count":3,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/514530\/revisions"}],"predecessor-version":[{"id":524081,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/514530\/revisions\/524081"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media\/514535"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=514530"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=514530"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=514530"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=514530"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}