Novidades sobre a subida de magma em São Jorge, em 2022

 Irrupção silenciosa de magma elevou ilha açoriana 6,35 cm e parou de súbito sob a superfície

 

Morro Grande, na ilha de São Jorge, nos Açores

    

Uma série de sismos na ilha de São Jorge, nos Açores, revelou magma acumulado a apenas 1,6 quilómetros de profundidade. Segundo um novo estudo, falhas subterrâneas impediram a erupção. Tratou-se de uma quase-erupção, que nunca chegou a concretizar-se.

Em março de 2022, a pequena ilha açoriana de São Jorge foi subitamente atingida por uma série de sismos, após quase 60 anos sem atividade sísmica significativa.

Os tremores prolongaram-se durante meses, com micro-sismos a persistirem ao longo de dois anos, mas o que se estava a passar nas profundezas do subsolo da ilha açoriana continuava a ser um mistério.

Num novo estudo, uma equipa internacional de investigadores acredita ter clarificado a cadeia de eventos que na altura teve lugar.

O estudo, publicado na quinta-feira na revista Nature Communications, descreve como o magma irrompeu em direção à superfície em apenas dois dias, num volume equivalente a aproximadamente 32.000 piscinas olímpicas.

Ao analisarem dados sísmicos recolhidos em terra e no fundo do mar, juntamente com imagens de satélite, os investigadores concluíram que o magma subiu a partir de mais de 19 km de profundidade, acabando por estancar a cerca de 1,6 km abaixo da superfície.

Resumindo, tratou-se de uma quase-erupção que nunca chegou a concretizar-se, dizem os autores do estudo.

“Esta foi uma intrusão furtiva”, afirmou Stephen Hicks, investigador da University College London e autor principal do estudo, num comunicado publicado no EurekAlert.

“O magma deslocou-se rapidamente através da crosta, mas grande parte do seu percurso foi silenciosa, o que dificultou a previsão sobre se ocorreria ou não uma erupção”, acrescenta o investigador.

 

Acumulação subterrânea de magma fez a ilha crescer

Quando o magma empurra para cima através das camadas da crosta terrestre, frequentemente provoca erupções vulcânicas. Mas nem sempre. Por vezes, estanca a diversas profundidades, sem conseguir romper a superfície, explica a Discover Magazine.

Foi exatamente o que aconteceu sob São Jorge. Os Açores situam-se ao longo do Rift da Terceira, onde as placas tectónicas euroasiática e africana se afastam lentamente uma da outra, tornando a atividade sísmica relativamente comum.

A própria ilha, com apenas cerca de 56 km de comprimento e e cerca de 6,4 km de largura, tem um historial de sismos poderosos, incluindo um evento de magnitude 7,5 em 1757, um dos maiores sismos registados nos Açores.

Após o início dos sismos de 2022, os investigadores reconstituíram a atividade subterrânea recorrendo a uma combinação de registos sísmicos, medições por GPS e dados de satélite

Estes instrumentos revelaram que o solo se tinha elevado cerca de 6,35 cm - uma evidência forte de que o magma tinha penetrado na crosta superficial. Em escalas temporais longas, este tipo de soerguimento é, na verdade, uma das formas como as ilhas ganham altitude.

Os autores do estudo descobriram ainda que o magma se deslocou ao longo de um importante sistema de falhas que atravessa a ilha, conhecido como a Zona de Falha do Pico do Carvão.

   

As falhas podem guiar o magma e reduzir a pressão

As falhas e fraturas na crosta terrestre podem funcionar como vias de passagem para o magma ascendente, embora os cientistas continuem a trabalhar para compreender plenamente esta relação. No caso de São Jorge, o sistema de falhas parece ter desempenhado um papel surpreendentemente complexo.

Estudos anteriores já tinham demonstrado que esta zona de falha era capaz de produzir grandes sismos no passado. Durante a crise sísmica de 2022, em vez de um grande sismo, os investigadores observaram numerosos sismos de menor magnitude, agrupados ao longo da falha, desencadeados pelo movimento do magma em profundidade.

Segundo os investigadores, a falha funcionou como uma espécie de guia, facilitando a irrupção do magma. Ao mesmo tempo, poderá ter permitido que gases e fluidos escapassem lateralmente, reduzindo a pressão no interior do magma e impedindo, em última instância, a erupção.

“A falha funcionou simultaneamente como uma autoestrada e como uma fuga“, explica Pablo González, investigador do Conselho Superior de Investigações Científicas de Espanha e o coautor  do estudo, no comunicado. “Ajudou o magma a subir, mas pode também ter impedido uma erupção”.

Compreender como o magma se desloca abaixo da superfície é fundamental para interpretar a agitação vulcânica e prever o que poderá acontecer a seguir.

Os Açores são um raro laboratório natural, onde sistemas magmáticos ativos se cruzam com grandes falhas geradoras de sismos, o que facilita o estudo, por parte dos cientistas, da interação em tempo real entre estruturas tectónicas e rocha fundida.

As observações dos eventos de São Jorge sugerem que irrupções maciças de magma podem desenvolver-se rapidamente e sem aviso prévio, mas revelam também de que forma as falhas geológicas influenciam se esse magma atinge a superfície ou fica retido em profundidade.

Ambas as conclusões são cruciais para tornar a atividade vulcânica mais previsível.

“Este estudo apoiou as autoridades locais na avaliação de uma potencial ameaça vulcânica”, explica  Ricardo Ramalho, investigador da Universidade de Cardiff e também coautor do estudo, no comunicado.

“O estudo evidencia o valor de combinar dados geofísicos em terra e no mar para uma deteção e localização precisas de eventos sísmicos e de deformação do solo”, conclui o investigador português.

 

in ZAP 

A crise sísmica de New Madrid, nos Estados Unidos, começou há 214 anos

The Great Earthquake at New Madrid, a 19th-century woodcut from Devens' Our First Century (1877)

      
The 1811–1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude (7,5 -7,9) on December 16, 1811 followed by a moment magnitude 7,4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. They, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within Missouri.

There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers, and moderately across nearly 3 million square kilometers. The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 km².

  

New Madrid fault and earthquake-prone region considered at high risk today

  

 The three earthquakes and their major aftershocks

• December 16, 1811, 08.15 UTC (2:15 a.m.); (M 7,5 -7,9) epicenter in northeast Arkansas. It caused only slight damage to manmade structures, mainly because of the sparse population in the epicentral area. The future location of Memphis, Tennessee, experienced level IX shaking on the Mercalli intensity scale. A seismic seiche propagated upriver, and Little Prairie (a village that was on the site of the former Fort San Fernando, near the site of present-day Caruthersville, Missouri) was heavily damaged by soil liquefaction.
• December 16, 1811 (aftershock), 14.15 UTC (8:15 a.m.); (M 7,4) epicenter in northeast Arkansas. This shock followed the first earthquake by five hours and was similar in intensity.
• January 23, 1812, 15.00 UTC (9:00 a.m.); (M 7,3 -7,6) epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.
• February 7, 1812, 09.45 UTC (3:45 a.m.); (M 7,5 -8,0) epicenter near New Madrid, Missouri. New Madrid was destroyed. In St. Louis, Missouri, many houses were severely damaged, and their chimneys were toppled. This shock was definitively attributed to the Reelfoot Fault by Johnston and Schweig. Uplift along a segment of this reverse fault created temporary waterfalls on the Mississippi at Kentucky Bend, created waves that propagated upstream, and caused the formation of Reelfoot Lake by obstructing streams in what is now Lake County, Tennessee.

Susan Hough, a seismologist of the United States Geological Survey (USGS), has estimated the earthquakes' magnitudes as around magnitude 7.

There were many more aftershocks including one magnitude 7 aftershock to December 16, 1811 earthquake which occurred on December 17, 1811 at 0600 UTC (12:00 a.m.) and one magnitude 7 aftershock to February 7, 1812 earthquake which occurred on the same day at 0440 UTC (10:40 p.m.).

  
Eyewitness accounts

John Bradbury, a Fellow of the Linnean Society, was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811, published in 1817.

After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by the most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings.
By the time we could get to our fire, which was on a large flag in the stern of the boat, the shock had ceased; but immediately the perpendicular banks, both above and below us, began to fall into the river in such vast masses, as nearly to sink our boat by the swell they occasioned ... At day-light we had counted twenty-seven shocks.

Eliza Bryan in New Madrid, Territory of Missouri, wrote the following eyewitness account in March 1812.

On the 16th of December, 1811, about two o'clock, a.m., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of the fowls and beasts of every species—the cracking of trees falling, and the roaring of the Mississippi— the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed— formed a scene truly horrible.

John Reynolds (February 26, 1788 – May 8, 1865) who was the 4th governor of Illinois, among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life (1855):

On the night of 16th November [sic], 1811, an earthquake occurred, that produced great consternation amongst the people. The centre of the violence was in New Madrid, Missouri, but the whole valley of the Mississippi was violently agitated. Our family all were sleeping in a log cabin, and my father leaped out of bed crying aloud "the Indians are on the house" ... We laughed at the mistake of my father, but soon found out it was worse than the Indians. Not one in the family knew at the time that it was an earthquake. The next morning another shock made us acquainted with it, so we decided it was an earthquake. The cattle came running home bellowing with fear, and all animals were terribly alarmed on the occasion. Our house cracked and quivered, so we were fearful it would fall to the ground. In the American Bottom many chimneys were thrown down, and the church bell in Cahokia sounded by the agitation of the building. It is said the shock of an earthquake was felt in Kaskaskia in 1804, but I did not perceive it. The shocks continued for years in Illinois, and some have experienced it this year, 1855.

The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union (Busro), Indiana, where the earthquakes contributed to the temporary abandonment of the westernmost Shaker community.

     

Reelfoot Rift

    

Geologic setting

The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain, known as the Reelfoot Rift. The New Madrid Seismic Zone (NMSZ) is made up of reactivated faults that formed when what is now North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era (about 750 million years ago). Faults were created along the rift and igneous rocks formed from magma that was being pushed towards the surface. The resulting rift system failed but has remained as an aulacogen (a scar or zone of weakness) deep underground.

In recent decades minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. It can be seen that they originate from the seismic activity of the Reelfoot Rift. The zone which is colored in red on the map is called the New Madrid Seismic Zone. New forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811–1812, which likely had magnitudes of between 7,6 and 8,0. There is a 25 to 40 percent chance, in a 50-year time span, of a magnitude 6,0 or greater earthquake.

In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7,7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.

    

4000 earthquake reports since 1974

      

in Wikipédia

A crise sísmica de New Madrid, nos Estados Unidos, começou há 213 anos

The Great Earthquake at New Madrid, a 19th-century woodcut from Devens' Our First Century (1877)

      
The 1811–1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude (7,5 -7,9) on December 16, 1811 followed by a moment magnitude 7,4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. They, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within Missouri.

There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers, and moderately across nearly 3 million square kilometers. The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 km².

  

New Madrid fault and earthquake-prone region considered at high risk today

  

 The three earthquakes and their major aftershocks

• December 16, 1811, 08.15 UTC (2:15 a.m.); (M 7,5 -7,9) epicenter in northeast Arkansas. It caused only slight damage to manmade structures, mainly because of the sparse population in the epicentral area. The future location of Memphis, Tennessee, experienced level IX shaking on the Mercalli intensity scale. A seismic seiche propagated upriver, and Little Prairie (a village that was on the site of the former Fort San Fernando, near the site of present-day Caruthersville, Missouri) was heavily damaged by soil liquefaction.
• December 16, 1811 (aftershock), 14.15 UTC (8:15 a.m.); (M 7,4) epicenter in northeast Arkansas. This shock followed the first earthquake by five hours and was similar in intensity.
• January 23, 1812, 15.00 UTC (9:00 a.m.); (M 7,3 -7,6) epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.
• February 7, 1812, 09.45 UTC (3:45 a.m.); (M 7,5 -8,0) epicenter near New Madrid, Missouri. New Madrid was destroyed. In St. Louis, Missouri, many houses were severely damaged, and their chimneys were toppled. This shock was definitively attributed to the Reelfoot Fault by Johnston and Schweig. Uplift along a segment of this reverse fault created temporary waterfalls on the Mississippi at Kentucky Bend, created waves that propagated upstream, and caused the formation of Reelfoot Lake by obstructing streams in what is now Lake County, Tennessee.

Susan Hough, a seismologist of the United States Geological Survey (USGS), has estimated the earthquakes' magnitudes as around magnitude 7.

There were many more aftershocks including one magnitude 7 aftershock to December 16, 1811 earthquake which occurred on December 17, 1811 at 0600 UTC (12:00 a.m.) and one magnitude 7 aftershock to February 7, 1812 earthquake which occurred on the same day at 0440 UTC (10:40 p.m.).

  
Eyewitness accounts

John Bradbury, a Fellow of the Linnean Society, was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811, published in 1817.

After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by the most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings.
By the time we could get to our fire, which was on a large flag in the stern of the boat, the shock had ceased; but immediately the perpendicular banks, both above and below us, began to fall into the river in such vast masses, as nearly to sink our boat by the swell they occasioned ... At day-light we had counted twenty-seven shocks.

Eliza Bryan in New Madrid, Territory of Missouri, wrote the following eyewitness account in March 1812.

On the 16th of December, 1811, about two o'clock, a.m., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of the fowls and beasts of every species—the cracking of trees falling, and the roaring of the Mississippi— the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed— formed a scene truly horrible.

John Reynolds (February 26, 1788 – May 8, 1865) who was the 4th governor of Illinois, among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life (1855):

On the night of 16th November [sic], 1811, an earthquake occurred, that produced great consternation amongst the people. The centre of the violence was in New Madrid, Missouri, but the whole valley of the Mississippi was violently agitated. Our family all were sleeping in a log cabin, and my father leaped out of bed crying aloud "the Indians are on the house" ... We laughed at the mistake of my father, but soon found out it was worse than the Indians. Not one in the family knew at the time that it was an earthquake. The next morning another shock made us acquainted with it, so we decided it was an earthquake. The cattle came running home bellowing with fear, and all animals were terribly alarmed on the occasion. Our house cracked and quivered, so we were fearful it would fall to the ground. In the American Bottom many chimneys were thrown down, and the church bell in Cahokia sounded by the agitation of the building. It is said the shock of an earthquake was felt in Kaskaskia in 1804, but I did not perceive it. The shocks continued for years in Illinois, and some have experienced it this year, 1855.

The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union (Busro), Indiana, where the earthquakes contributed to the temporary abandonment of the westernmost Shaker community.

     

Reelfoot Rift

    

Geologic setting

The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain, known as the Reelfoot Rift. The New Madrid Seismic Zone (NMSZ) is made up of reactivated faults that formed when what is now North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era (about 750 million years ago). Faults were created along the rift and igneous rocks formed from magma that was being pushed towards the surface. The resulting rift system failed but has remained as an aulacogen (a scar or zone of weakness) deep underground.

In recent decades minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. It can be seen that they originate from the seismic activity of the Reelfoot Rift. The zone which is colored in red on the map is called the New Madrid Seismic Zone. New forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811–1812, which likely had magnitudes of between 7,6 and 8,0. There is a 25 to 40 percent chance, in a 50-year time span, of a magnitude 6,0 or greater earthquake.

In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7,7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.

    

4000 earthquake reports since 1974

      

in Wikipédia

Crise sísmico-vulcânica na Terceira (Vulcão de Santa Bárbara) - ponto da situação...

  
CRISE SISMOVULCÂNICA DA TERCEIRA E ESTRUTURAS ADJACENTES - VULCÃO DE SANTA BÁRBARA – V2

 

O Instituto de Vulcanologia da Universidade dos Açores (IVAR), com base na informação obtida através da rede de monitorização gerida pelo Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA), informa que a crise sismovulcânica que se vem registando na ilha Terceira desde o dia 24 de junho de 2022 se mantém. 

A atividade sísmica registada no âmbito desta crise tem-se centrado com maior incidência dentro do perímetro do Vulcão de Santa Bárbara e sido caracterizada pela ocorrência de microssismos. Até à data, o evento mais energético ocorreu no dia 30 de abril, pelas 07:17 horas, atingiu a magnitude de 3,6 na Escala de Richter e teve epicentro a cerca de 2 km a E da Serreta, tendo sido sentido na ilha Terceira com intensidade máxima de V na Escala de Mercalli Modificada. 

A sismicidade registada tem abrangido igualmente, embora com menor frequência, o Sistema Vulcânico Fissural da Terceira, de direção aproximada NW-SE, num troço que atravessa a Serra de Santa Bárbara em direção às Furnas do Enxofre. Pontualmente, continua a registar-se alguma atividade sísmica noutras estruturas ativas da ilha Terceira e nos sistemas submarinos adjacentes, sendo de realçar que nos últimos dias, em particular desde 10 de junho, têm sido registados vários microssismos com epicentro na zona de Angra do Heroísmo, ao longo de um alinhamento de direção aproximada NE-SW que se estende desde sul de S. Mateus até à parte central da ilha, e que poderá ter continuidade até às Lajes. 

Até ao momento, com a rede de monitorização existente e o programa de recolha de amostras em curso, não foram detetadas variações significativas em termos de deformação crustal, nem obtidos resultados anómalos ao nível das análises a gases e águas, continuando a decorrer as campanhas de amostragem, o processamento e reprocessamento de dados e a avaliação permanente da situação. 

O facto de a sismicidade se encontrar claramente acima dos valores de referência e estar localizada num aparelho vulcânico com atividade eruptiva histórica justificam a situação de Alerta V2 no Vulcão de Santa Bárbara. 

O fenómeno que está a afetar a ilha Terceira não se pode dissociar do incremento da atividade sismovulcânica que se tem verificado na região dos Açores e, em particular, no Grupo Central, desde o início de 2022, e o padrão de atividade observado indicia a possibilidade de continuarem a ocorrer eventos sentidos pela população, que podem, eventualmente, atingir magnitudes e intensidades superiores às registadas até à data. 

Caso a situação descrita se altere ou sejam obtidos dados que permitam novas interpretações, serão produzidas novas informações. 

 

in CIVISA

A estranha crise sísmica de New Madrid começou há 212 anos

The Great Earthquake at New Madrid, a 19th-century woodcut from Devens' Our First Century (1877)

      
The 1811–1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude (7,5 -7,9) on December 16, 1811 followed by a moment magnitude 7,4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. They, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within Missouri.

There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers, and moderately across nearly 3 million square kilometers. The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 km².

  

New Madrid fault and earthquake-prone region considered at high risk today

  

 The three earthquakes and their major aftershocks

• December 16, 1811, 08.15 UTC (2:15 a.m.); (M 7,5 -7,9) epicenter in northeast Arkansas. It caused only slight damage to manmade structures, mainly because of the sparse population in the epicentral area. The future location of Memphis, Tennessee, experienced level IX shaking on the Mercalli intensity scale. A seismic seiche propagated upriver, and Little Prairie (a village that was on the site of the former Fort San Fernando, near the site of present-day Caruthersville, Missouri) was heavily damaged by soil liquefaction.
• December 16, 1811 (aftershock), 14.15 UTC (8:15 a.m.); (M 7,4) epicenter in northeast Arkansas. This shock followed the first earthquake by five hours and was similar in intensity.
• January 23, 1812, 15.00 UTC (9:00 a.m.); (M 7,3 -7,6) epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.
• February 7, 1812, 09.45 UTC (3:45 a.m.); (M 7,5 -8,0) epicenter near New Madrid, Missouri. New Madrid was destroyed. In St. Louis, Missouri, many houses were severely damaged, and their chimneys were toppled. This shock was definitively attributed to the Reelfoot Fault by Johnston and Schweig. Uplift along a segment of this reverse fault created temporary waterfalls on the Mississippi at Kentucky Bend, created waves that propagated upstream, and caused the formation of Reelfoot Lake by obstructing streams in what is now Lake County, Tennessee.

Susan Hough, a seismologist of the United States Geological Survey (USGS), has estimated the earthquakes' magnitudes as around magnitude 7.

There were many more aftershocks including one magnitude 7 aftershock to December 16, 1811 earthquake which occurred on December 17, 1811 at 0600 UTC (12:00 a.m.) and one magnitude 7 aftershock to February 7, 1812 earthquake which occurred on the same day at 0440 UTC (10:40 p.m.).

  
Eyewitness accounts

John Bradbury, a Fellow of the Linnean Society, was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811, published in 1817.

After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by the most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings.
By the time we could get to our fire, which was on a large flag in the stern of the boat, the shock had ceased; but immediately the perpendicular banks, both above and below us, began to fall into the river in such vast masses, as nearly to sink our boat by the swell they occasioned ... At day-light we had counted twenty-seven shocks.

Eliza Bryan in New Madrid, Territory of Missouri, wrote the following eyewitness account in March 1812.

On the 16th of December, 1811, about two o'clock, a.m., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of the fowls and beasts of every species—the cracking of trees falling, and the roaring of the Mississippi— the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed— formed a scene truly horrible.

John Reynolds (February 26, 1788 – May 8, 1865) who was the 4th governor of Illinois, among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life (1855):

On the night of 16th November [sic], 1811, an earthquake occurred, that produced great consternation amongst the people. The centre of the violence was in New Madrid, Missouri, but the whole valley of the Mississippi was violently agitated. Our family all were sleeping in a log cabin, and my father leaped out of bed crying aloud "the Indians are on the house" ... We laughed at the mistake of my father, but soon found out it was worse than the Indians. Not one in the family knew at the time that it was an earthquake. The next morning another shock made us acquainted with it, so we decided it was an earthquake. The cattle came running home bellowing with fear, and all animals were terribly alarmed on the occasion. Our house cracked and quivered, so we were fearful it would fall to the ground. In the American Bottom many chimneys were thrown down, and the church bell in Cahokia sounded by the agitation of the building. It is said the shock of an earthquake was felt in Kaskaskia in 1804, but I did not perceive it. The shocks continued for years in Illinois, and some have experienced it this year, 1855.

The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union (Busro), Indiana, where the earthquakes contributed to the temporary abandonment of the westernmost Shaker community.

     

Reelfoot Rift

    

Geologic setting

The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain, known as the Reelfoot Rift. The New Madrid Seismic Zone (NMSZ) is made up of reactivated faults that formed when what is now North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era (about 750 million years ago). Faults were created along the rift and igneous rocks formed from magma that was being pushed towards the surface. The resulting rift system failed but has remained as an aulacogen (a scar or zone of weakness) deep underground.

In recent decades minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. It can be seen that they originate from the seismic activity of the Reelfoot Rift. The zone which is colored in red on the map is called the New Madrid Seismic Zone. New forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811–1812, which likely had magnitudes of between 7,6 and 8,0. There is a 25 to 40 percent chance, in a 50-year time span, of a magnitude 6,0 or greater earthquake.

In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7,7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.

    

4000 earthquake reports since 1974

      

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A falha de New Madrid está outra vez a mexer...?!?

The epicenter of both earthquake to hit Arkansas today is at the orange dot located within the broader orange circle

 

Pair of Weak Earthquakes Rattle Arkansas, Not Far from New Madrid Fault Zone

 

The New Madrid Seismic zone remains active and another large earthquake strong enough to shake the entire eastern United States continues to loom

 

A crise sísmico-vulcânica em S. Jorge - ponto da situação...

  

O Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA) informa que a atividade sismovulcânica que se tem vindo a registar na ilha de S. Jorge desde as 16.05 (hora local = UTC-1) do dia 19 de março de 2022 continua acima do normal, estendendo-se, grosso modo, ao longo de uma faixa com direção WNW-ESE, desde a Ponta dos Rosais até à zona do Norte Pequeno – Silveira.

Até ao momento, foram registados aproximadamente 56.801 eventos de baixa magnitude e de origem tectónica. Entre as 00.00 e as 10.00 de hoje foram contabilizados aproximadamente 2 sismos. O sismo mais energético desta crise ocorreu no dia 29 de março de 2022, às 21.56 (hora local = UTC), teve epicentro a cerca de 2 km a SSW de Velas e uma magnitude 3,8 (Richter). Até ao momento foram identificados cerca de 347 sismos sentidos pela população.​

Globalmente, a atividade sísmica das últimas semanas apresenta uma ligeira tendência decrescente, por vezes interrompida por pequenos períodos de maior frequência e/ou energia libertada, situando-se presentemente os hipocentros, no geral, a profundidades superiores a 5 km.

No âmbito da monitorização geodésica, os dados existentes desde o início de abril não evidenciam deformação significativa na zona epicentral.

As campanhas de medição de gases e temperatura no solo que se vêm desenvolvendo desde o início desta crise na área epicentral não resultaram, até à data, na identificação de anomalias resultantes da atividade sismovulcânica, mantendo-se os levantamentos de campo.

As campanhas de hidrogeoquímica nas águas subterrâneas dos dois furos de captação monitorizados (Queimada II e Ribeira do Nabo - IROA) não têm revelado variações significativas que possam ser associadas à crise sismovulcânica em curso.

A integração da informação disponível permite concluir que as estruturas tectónicas onde se desenvolveram as erupções históricas de 1580 e 1808, e a crise sismovulcânica de 1964, no Sistema Vulcânico Fissural de Manadas, foram reativadas, sendo de admitir que no início do fenómeno ocorreu uma intrusão magmática em profundidade.

A diminuição da atividade sísmica, ainda que de forma lenta, e a observação de tal padrão ao longo das últimas semanas, assim como a ausência de outros sinais anómalos ao nível da deformação, dos gases e das águas, levaram o CIVISA a determinar, no dia 9 de junho de 2022, às 09:20, a descida do Nível de Alerta Científico de V4 para V3 na ilha de S. Jorge. A atividade sísmica continua, no entanto, muito acima dos valores de referência para a região, pelo que se mantém a possibilidade de se registarem eventos sentidos e não se pode excluir a eventual ocorrência de sismos de magnitude mais elevada.

O CIVISA mantém os níveis de monitorização na ilha de S. Jorge e está a providenciar o reforço da rede de observação sismovulcânica permanente, no sentido de, caso o padrão de atividade se inverta, poder detetar sinais precursores de uma nova situação pré-eruptiva.

Alertas anteriores:
Alerta V2 – Dia 20 de março de 2022 às 00.40;
Alerta V3 – Dia 20 de março de 2022 às 02.40;
Alerta V4 – Dia 23 de março de 2022 às 15.30;

Alerta V3 – Dia 09 de junho de 2022, às 09.20.

O CIVISA retirou igualmente o alerta para o Centro de Controlo Aéreo de Santa Maria (ACC Santa Maria), para o Volcanic Ash Advisory Centre (VAAC) de Toulouse e para o Instituto Português do Mar e da Atmosfera (IPMA).

in CIVISA

A crise sísmica de New Madrid começou há 211 anos

The Great Earthquake at New Madrid, a 19th-century woodcut from Devens' Our First Century (1877)

      
The 1811–1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude (7,5 -7,9) on December 16, 1811 followed by a moment magnitude 7,4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. They, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within Missouri.

There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers, and moderately across nearly 3 million square kilometers. The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 km².

  

New Madrid fault and earthquake-prone region considered at high risk today

  

 The three earthquakes and their major aftershocks

• December 16, 1811, 08.15 UTC (2:15 a.m.); (M 7,5 -7,9) epicenter in northeast Arkansas. It caused only slight damage to manmade structures, mainly because of the sparse population in the epicentral area. The future location of Memphis, Tennessee, experienced level IX shaking on the Mercalli intensity scale. A seismic seiche propagated upriver, and Little Prairie (a village that was on the site of the former Fort San Fernando, near the site of present-day Caruthersville, Missouri) was heavily damaged by soil liquefaction.
• December 16, 1811 (aftershock), 14.15 UTC (8:15 a.m.); (M 7,4) epicenter in northeast Arkansas. This shock followed the first earthquake by five hours and was similar in intensity.
• January 23, 1812, 15.00 UTC (9:00 a.m.); (M 7,3 -7,6) epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.
• February 7, 1812, 09.45 UTC (3:45 a.m.); (M 7,5 -8,0) epicenter near New Madrid, Missouri. New Madrid was destroyed. In St. Louis, Missouri, many houses were severely damaged, and their chimneys were toppled. This shock was definitively attributed to the Reelfoot Fault by Johnston and Schweig. Uplift along a segment of this reverse fault created temporary waterfalls on the Mississippi at Kentucky Bend, created waves that propagated upstream, and caused the formation of Reelfoot Lake by obstructing streams in what is now Lake County, Tennessee.

Susan Hough, a seismologist of the United States Geological Survey (USGS), has estimated the earthquakes' magnitudes as around magnitude 7.

There were many more aftershocks including one magnitude 7 aftershock to December 16, 1811 earthquake which occurred on December 17, 1811 at 0600 UTC (12:00 a.m.) and one magnitude 7 aftershock to February 7, 1812 earthquake which occurred on the same day at 0440 UTC (10:40 p.m.).

  
Eyewitness accounts

John Bradbury, a Fellow of the Linnean Society, was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811, published in 1817.

After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by the most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings.
By the time we could get to our fire, which was on a large flag in the stern of the boat, the shock had ceased; but immediately the perpendicular banks, both above and below us, began to fall into the river in such vast masses, as nearly to sink our boat by the swell they occasioned ... At day-light we had counted twenty-seven shocks.

Eliza Bryan in New Madrid, Territory of Missouri, wrote the following eyewitness account in March 1812.

On the 16th of December, 1811, about two o'clock, a.m., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of the fowls and beasts of every species—the cracking of trees falling, and the roaring of the Mississippi— the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed— formed a scene truly horrible.

John Reynolds (February 26, 1788 – May 8, 1865) who was the 4th governor of Illinois, among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life (1855):

On the night of 16th November [sic], 1811, an earthquake occurred, that produced great consternation amongst the people. The centre of the violence was in New Madrid, Missouri, but the whole valley of the Mississippi was violently agitated. Our family all were sleeping in a log cabin, and my father leaped out of bed crying aloud "the Indians are on the house" ... We laughed at the mistake of my father, but soon found out it was worse than the Indians. Not one in the family knew at the time that it was an earthquake. The next morning another shock made us acquainted with it, so we decided it was an earthquake. The cattle came running home bellowing with fear, and all animals were terribly alarmed on the occasion. Our house cracked and quivered, so we were fearful it would fall to the ground. In the American Bottom many chimneys were thrown down, and the church bell in Cahokia sounded by the agitation of the building. It is said the shock of an earthquake was felt in Kaskaskia in 1804, but I did not perceive it. The shocks continued for years in Illinois, and some have experienced it this year, 1855.

The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union (Busro), Indiana, where the earthquakes contributed to the temporary abandonment of the westernmost Shaker community.

     

Reelfoot Rift

    

Geologic setting

The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain, known as the Reelfoot Rift. The New Madrid Seismic Zone (NMSZ) is made up of reactivated faults that formed when what is now North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era (about 750 million years ago). Faults were created along the rift and igneous rocks formed from magma that was being pushed towards the surface. The resulting rift system failed but has remained as an aulacogen (a scar or zone of weakness) deep underground.

In recent decades minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. It can be seen that they originate from the seismic activity of the Reelfoot Rift. The zone which is colored in red on the map is called the New Madrid Seismic Zone. New forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811–1812, which likely had magnitudes of between 7,6 and 8,0. There is a 25 to 40 percent chance, in a 50-year time span, of a magnitude 6,0 or greater earthquake.

In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7,7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.

    

4000 earthquake reports since 1974

      

in Wikipédia

A crise sísmico-vulcânica em S. Jorge - baixou o risco de erupção

Atividade Sísmica na ilha de S. Jorge - atualização

09.06.2022 - 13.20

O Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA) informa que a crise sismovulcânica que se tem vindo a registar na ilha de S. Jorge desde as 16:05 (hora local = UTC-1) do dia 19 de março continua acima do normal, estendendo-se, grosso modo, ao longo de uma faixa com direção WNW-ESE, desde a Ponta dos Rosais até à zona do Norte Pequeno – Silveira.

Até ao momento (10:00 hora local = UTC), foram registados aproximadamente 37.411 eventos de baixa magnitude e de origem tectónica. O sismo mais energético desta crise ocorreu no dia 29 de março, às 21:56 (hora local = UTC), teve epicentro a cerca de 2 km a SSW de Velas e uma magnitude 3,8 (Richter). Até ao momento foram identificados cerca de 287 sismos sentidos pela população.

 

Globalmente, a atividade sísmica das últimas semanas apresenta uma ligeira tendência decrescente, por vezes interrompida por pequenos períodos de maior frequência e/ou energia libertada, situando-se presentemente os hipocentros, no geral, a profundidades superiores a 5 km.

 

No âmbito da monitorização geodésica, os dados existentes desde o início de abril não evidenciam deformação significativa na zona epicentral.

 

As campanhas de medição de gases e temperatura no solo que se vêm desenvolvendo desde o início desta crise na área epicentral não resultaram, até à data, na identificação de anomalias resultantes da atividade sismovulcânica, mantendo-se os levantamentos de campo.

 

As campanhas de hidrogeoquímica nas águas subterrâneas dos dois furos de captação monitorizados (Queimada II e Ribeira do Nabo - IROA) não têm revelado variações significativas que possam ser associadas à crise sismovulcânica em curso.

 

A integração da informação disponível permite concluir que as estruturas tectónicas onde se desenvolveram as erupções históricas de 1580 e 1808, e a crise sismovulcânica de 1964, no Sistema Vulcânico Fissural de Manadas, foram reativadas, sendo de admitir que no início do fenómeno ocorreu uma intrusão magmática em profundidade. 

 

A diminuição da atividade sísmica, ainda que de forma lenta, e a observação de tal padrão ao longo das últimas semanas, assim como a ausência de outros sinais anómalos ao nível da deformação, dos gases e das águas, levaram o CIVISA a determinar a descida do Nível de Alerta Científico de V4 para V3 na ilha de S. Jorge. A atividade sísmica continua, no entanto, muito acima dos valores de referência para a região, pelo que se mantém a possibilidade de se registarem eventos sentidos e não se pode excluir a eventual ocorrência de sismos de magnitude mais elevada.

 

O CIVISA mantém os níveis de monitorização na ilha de S. Jorge e está a providenciar o reforço da rede de observação sismovulcânica permanente, no sentido de, caso o padrão de atividade se inverta, poder detetar sinais precursores de uma nova situação pré-eruptiva.

Alertas anteriores:

Alerta V4 – Dia 23 de março às 15h30;

Alerta V3 – Dia 20 de março às 02h40;

Alerta V2 – Dia 20 de março às 00h40.

O CIVISA retirou igualmente o alerta para o Centro de Controlo Aéreo de Santa Maria (ACC Santa Maria), para o Volcanic Ash Advisory Centre (VAAC) de Toulouse e para o Instituto Português do Mar e da Atmosfera (IPMA).

 

in CIVISA

E a crise sísmico-vulcânica em S. Jorge continua...

Sismos sentidos na ilha de São Jorge (ponto de situação, 13-05-2022, 22:00) 

 

O Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA) informa que atividade sísmica que se tem vindo a registar desde as 16:05 (hora local = UTC-1) do dia 19 de março na ilha de São Jorge, mais concretamente ao longo de uma faixa com direção WNW-ESE, desde a Ponta dos Rosais até à zona do Norte Pequeno - Silveira, continua acima do normal.

O sismo mais energético ocorreu no dia 29 de março, às 21:56 (hora local = UTC) e teve magnitude 3,8 (Richter).

Até ao momento foram identificados cerca de 273 sismos sentidos pela população. Desde as 10:00 às 22:00 do dia 13 de maio não foi sentido nenhum sismo.

O CIVISA continua a acompanhar o evoluir da situação

 

in CIVISA

A crise sísmico-vulcânica em S. Jorge continua...

São Jorge 

Sismos sentidos na ilha de São Jorge - ponto de situação, 13.04.2022, 10.00 horas 

  

 

O Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA) informa que atividade sísmica que se tem vindo a registar desde as 16:05 (hora local = UTC-1) do dia 19 de março na ilha de São Jorge, mais concretamente ao longo de uma faixa com direção WNW-ESE, desde a Ponta dos Rosais até à zona do Norte Pequeno - Silveira, continua acima do normal.

O sismo mais energético ocorreu no dia 29 de março, às 21.56 (hora local) e teve magnitude 3,8 (Richter).

Até ao momento foram identificados cerca de 244 sismos sentidos pela população. Desde as 20.00 do dia 12 de abril às 10.00 horas do dia 13 de abril, foram sentidos 2 sismos:

 

 

Dia	Hora local	Mag.	Epicentro	Int. (EMM)	Freguesia
12.04	20.41	2,3	8 km WSW Velas	III	Urzelina (Velas, S. Jorge)
13.04	08.15	2,3	7 km WSW Velas	III/IV	Santo Amaro (Velas, S. Jorge)
				III	Rosais (Velas, S. Jorge)

 

O CIVISA continua a acompanhar o evoluir da situação.

 

in CIVISA