Uma massiva "bolha" de esticamento de rochas sob a Ásia pode estar desencadeando centenas de terremotos

Por Brandon Specktor, escritor sênior | 15 de maio de 2019 10h01 ET

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Crédito: Shutterstock

A cordilheira Hindu Kush - que se estende por 800 quilômetros ao longo da fronteira do Afeganistão com o Paquistão - estremece com mais de 100 terremotos em uma magnitude de 4,0 ou mais a cada ano. A área é um dos locais mais sismicamente ativos do mundo, especialmente para tremores de profundidade intermediária (tremores que se formam entre 45 e 190 milhas, ou 70 e 300 km, abaixo da superfície do planeta). E, no entanto, os cientistas não têm certeza do porquê.
 
As montanhas não ficam em uma grande falha geológica, onde se espera alta atividade sísmica, e a região fica a muitas milhas de distância da zona de colisão em movimento lento, onde as placas tectônicas euro-asiática e indiana colidem continuamente. Então, qual é o problema com a epidemia do terremoto nas montanhas?
 
Um novo estudo publicado em 17 de abril na revista Tectonics pode ter uma resposta para os tremores misteriosos do Hindu Kush - e, como todos os grandes mistérios geológicos, envolve bolhas .
De acordo com o estudo, as montanhas Hindu Kush devem sua incrível reputação sísmica a uma longa "bolha" de rocha que lentamente escorre da parte subterrânea da cordilheira para o manto quente e viscoso abaixo . Como uma gota de água solitária se afastando da borda de uma torneira, a faixa de 150 quilômetros de montanha pode estar se afastando da crosta continental a uma velocidade de até 10 centímetros por ano. e esse estresse subterrâneo pode estar desencadeando terremotos, escreveram os autores do novo estudo.
 
Os pesquisadores descobriram a problemática bolha após coletar vários anos de observações de terremotos perto das montanhas Hindu Kush. Eles viram que os terremotos se formaram em um padrão, criando o que parecia ser um "caminho redondo" de atividade sísmica na superfície do planeta, disse a co-autora Rebecca Bendick, geofísica da Universidade de Montana em Missoula, no site Eos.org. . Esses terremotos também se formaram ao longo de um eixo vertical claro, começando entre 160 e 230 km abaixo do continente, e eram mais comuns mais abaixo, onde a sólida crosta continental encontra o manto superior, quente e viscoso. Aqui, os pesquisadores escreveram, é onde a bolha de alongamento lento é mais tensa.
 
Todas essas observações foram consistentes com uma bolha de rocha sólida que lentamente escorria no submundo pegajoso abaixo - uma hipótese que foi usada anteriormente para explicar a atividade sísmica similar sob as Montanhas dos Cárpatos na Europa central . De acordo com os pesquisadores, a mancha Hindu Kush provavelmente começou a pingar não antes de 10 milhões de anos atrás, e continua a se estender quase 10 vezes mais rápido que a superfície das montanhas, enquanto as placas da Índia e da Eurásia colidem.
 
Se precisos, esses resultados podem ser mais evidências de que forças geofísicas além da subducção de placas tectônicas podem enviar terremotos pelo planeta. Como foi melhor colocar em 1958: Cuidado com o blob .

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Saving snow leopards in a war zone

Conflict and conservation became unlikely bedfellows in Afghanistan, finds Thomas McCarthy.

Thomas McCarthy

Snow leopards in the high Asian mountains have been aided by the creation of national parks. Credit: Steve Winter/National Geographic Creative

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The Snow Leopard Project: And Other Adventures in Warzone Conservation Alex Dehgan PublicAffairs (2019)

Imagine a scientific field where success is at least partly measured by staying alive. This is conservation biology in the world’s many war zones, where researchers face despair over the accelerating extinction crisis, and the risk of stray bullets. It is, as pioneer Michael Soulé put it more than 30 years ago, a “mission-oriented crisis discipline”.

Alex Dehgan weathered all this, and more, working in far-flung corners of Afghanistan, including the peaks of the Pamir Mountains — one of Earth’s most remote, inhospitable natural environments — on animals including the rare and elusive snow leopard (Panthera uncia). Over two years in the mid-2000s, Dehgan established the Wildlife Conservation Society (WCS) Afghanistan Program. It became one of the most successful conservation efforts to be set up in an active conflict zone. His new book, The Snow Leopard Project chronicles this story.

In 2006, wildlife conservation in Afghanistan seemed almost a counter-intuitive undertaking, Dehgan notes. Three decades of war, along with insurgency by the Taliban and a nascent democratic government that was weak and decentralized, did not provide the most suitable underpinnings for a national conservation awakening. Even assessing the status of wildlife in the country, a prerequisite to any on-the-ground conservation, would have to happen amid more than half a million landmines, which litter even the most remote parts of the country. Yet Dehgan viewed this as a clean slate for reinventing conservation practices at a country-wide level.
Afghanistan has for centuries been a “crossroads of human cultures and empires” and an important stop on the Silk Road. But, as Dehgan notes, it is an equally important crossroads for the fauna and flora of Asia, Europe and Africa. In what many in the West felt to be dusty, war-weary and desolate, he saw beauty, biological diversity and an opportunity to reverse environmental disruption from the country’s long litany of conflicts.

Born in Iran, Dehgan emigrated to the United States with his family at the age of two, in the early 1970s. A career that veered from law to diplomacy to conservation, with stints in Russia, Madagascar and Iraq, gave him a remarkable skill set. Yet his impressive experience barely prepared him for the challenges of setting up shop in Kabul. Here, the most mundane tasks had to be done while keeping one eye out for improvised explosive devices on the roadside and suicide bombers in markets or oncoming vehicles. Finding staff, from biologists to cooks, and a safe office for them, was one of the first hurdles. The programme’s main funder, the US Agency for International Development (USAID), was little help at the time: its interests seemed weighted towards nation-building, not nature. Dehgan laments that the agency’s focus was expenditure — an easy metric. (He notes with pride that he was involved in changing that culture when he later became USAID’s chief scientist.)

As a conservationist leading field programmes in Asia, I gravitate towards books by others doing similar work. I’m often disappointed by dry accounts that omit the human stories. By contrast, Dehgan introduces nearly every actor in his saga with witty observations on demeanour and personality, not just professional credentials. Drawn deep into his story, we feel his burden when sending ‘his people’ into areas where safety concerns — from drowning in freezing rivers to falling from precipitous cliffs frequented by snow leopards — are compounded by the risk of being shot at, blown up or worse.

Thus, this is less a book about research than about the trials, triumphs and occasional absurdity of building a conservation programme in extreme circumstances. More than once, Dehgan and his team find themselves staring down the barrel of an AK-47 rifle, trying in multiple languages to defuse a tense situation. The hazards of their fieldwork go far beyond the norm. Veering accidentally into a minefield means a painstaking reversal along their tyre tracks to safety. As they are returning from Tajikistan after a mission to push for an international peace park, loose tow cables send the team’s already questionable ferry careering downriver. Surveys for rare species along the border with Pakistan mean trekking along steep mountain paths too narrow for pack animals, while keeping one eye out for insurgents who could end the researchers’ lives on the spot. Political pitfalls are as abundant, such as when an Iranian diplomat mistakenly believes Dehgan is the conduit to renewed diplomatic relations with the United States.

Ultimately, The Snow Leopard Project is a story of conservation success from a nation where good news is scant. Afghanistan’s first national park, Band-e-Amir, was created in 2009. At about the same time, the Wakhan Corridor — a sliver of land between Pakistan and Tajikistan known as the Roof of the World — saw a return of tourists drawn by the possibility of seeing the majestic Marco Polo sheep (Ovis ammon polii) that thrive there. In 2014, the wider Wakhan area became Afghanistan’s second national park. Larger than Yellowstone National Park in Wyoming, it encompasses nearly three-quarters of the country’s snow-leopard range. Elsewhere, species long thought locally extinct, such as the Kashmir musk deer (Moschus cupreus), were rediscovered in the Eastern Forests Complex, one of the last temperate coniferous forests in the greater Himalayas.
Dehgan gives credit to his many Afghan colleagues, and the Afghan people, for their openness to the idea of conserving their unique natural heritage, and embracing it with the same determination that has kept them resilient in the face of conflict for centuries.

There is a shadow side to these successes, Dehgan reveals. There was, for instance, the issue of how military forces, and even some humanitarian aid agencies, unwittingly participated in the illegal wildlife trade — for instance, by buying furs made from pelts of restricted animals, including snow leopards. The WCS’s public diplomacy campaign made a difference. The military and even Afghan shop owners embraced efforts to stop the loss of the country’s natural treasures, despite an impact on their livelihoods.

The Snow Leopard Project is also a personal record. We learn of Dehgan’s journey to get closer to his Iranian roots, and his anguish over war’s senseless ravaging of nature and culture. But he is optimistic, too, about the country, its people and its wildlife. After his departure, the WCS Afghanistan Program continued its field-oriented mission, helping to establish a third national park in 2017. In the same year, nearly 200,000 people, mostly Afghan citizens, visited Band-e-Amir National Park.

Nature 565, 292-293 (2019)

doi: 10.1038/d41586-019-00125-w