Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland

The Bárðarbunga eruption in Iceland in 2014 and 2015 produced about 1.6 km3 of lava. Magma propagated away from Bárðarbunga to a distance of 48 km in the subsurface beneath Vatnajökull glacier, emerging a few kilometres beyond the glacier's northern rim. A puzzling observation is the lack of shallow (<3 km deep), high-frequency earthquakes associated Q.1 with shallow dyke formation near the subaerial and subglacial eruptive sites, suggesting that near-surface dyke formation is seismically quiet. However, seismic array observations and seismic full wavefield simulations reveal the presence and nature of shallow, pre-eruptive, long-duration seismic tremor activity. Here we use analyses of seismic data to constrain therelationships between seismicity, tremor, dyke propagation and magma flow during the Bárðarbunga eruption. We show that although tremor is usually associated with magma flow in volcanic settings, pre-eruptive tremor at Bárðarbunga was probably caused by swarms of microseismic events during dyke formation, and hence is directly associated with fracturing of the upper 2-3 km of the crust. Subsequent magma flow in the newly formed shallow dyke was seismically silent, with almost a complete absence of seismicity or tremor. Hence, we suggest that the transition from temporarily isolated, large, deep earthquakes to many smaller, shallower, temporally overlapping earthquakes (< magnitude 2) that appear as continuous tremor announces the arrival of a dyke opening in the shallow crust, forming a pathway for silent magma flow to the Earth's surface. European Commission - Seventh Framework Programme (FP7)Geological Survey of Irelan

RESÍDUOS DE FENITROTION EM FRUTOS E FOLHAS DE TOMATEIRO (Lycopersicon esculentum Mill) ESTAQUEADO

Estudou-se o comportamento dos resíduos de fenitrotion em frutos e folhas de tomateiro estaqueado, através de cromatografia gasosa. O experimento de campo foi instalado quando as plantas tinham 90 dias após o transplante das mudas, e constou de quatro tratamentos: (1) uma aplicação de fenitrotion em dosagem simples, de 100 g i.a./100 litros de água, (2) uma aplicação em dosagem dobrada, de 200 g i.a./100 litros de água, (3) quatro aplicações espaçadas de sete dias, na dosagem simples e (4) testemunha. As amostras de fruto e folha foram colhidas um dia antes da aplicação (-1) e aos zero , 1, 2, 3, 5, 7 e 14 dias após. Basicamente, a metododogia para análises dos resíduos dos frutos e das folhas constou da extração com acetona e partição em clorofórmio; limpeza dos extratos em coluna de florisil (no caso de folhas) e eluição procedida com benzeno. As determinações quantitativas foram feitas por cromatografia gasosa, usando-se detector fotométrico de chama com filtro específico para fósforo. Os resíduos nas folhas foram sempre maiores do que os dos frutos (cerca de 80 vezes, em média) durante todo o período de colheita das amostras. Os valores de meia-vida de degradação de fenitrotion em frutos e folhas foram: 1,6 a 1,9 e 0,7 a 0,8 dia, respectivamente, mostrando uma diminuição mais rápida dos resíduos em folhas. As meias-vidas de persistência foram semelhantes para os dois substratos: 4,2 a 7,3 e 5,6 a 6,2 dias, respectivamente. Os resíduos encontrados nos frutos logo após a aplicação, foram menores que a tolerância oficial (0,5 ppm) para os tratamentos que utilizaram 100 g i.a./100 litros em uma ou quatro pulverizações espaçadas de sete dias. Uma única aplicação de 200 g i.a./100 litros resultou em resíduos menores que 0,5 ppm, desde um dia após a aplicação.<br>The behavior of fenitrothion in fruits and leaves of staked tomato plants was studied with gas chromatography. The field experiment begun when plants had 90 days post-transplant and consisted of four treatments: (1) a single application of fenitrothion at 100 g a.i./100 liters of water; (2) a double dose application of 200 g a.i./100 liters of water; (3) four applications at 7 day intervals at the lower dosage; and (4) control. Fruit and leaf samples were collected one day before application (-1) and at zero, 1, 2, 3, 5, 7 and 14 days post-application. Residual analysis of fruit and leave consisted of acetone extraction and partition with chloroform; extract cleaning in a florisil column and benzene elution (for leaves). Quantitative estimates were obtained in a gas chromatograph, using flame photometric detector, with a special phosphorus filter. Leaf residues were always higher than those in fruits (approximately 80 times), during all sampling intervals. Half-live degradation values of fenitrothion in fruits and leaves were: 1.6 to 1.9 and 0.7 to 0.8 days, respectively. Half-lives of persistence were similiar for both substrates: 4.2 to 7.3 and 5.6 to 6.2 days, respectively. Fruit residues immediately after application were below the official tolerance level (0.5 ppm) for treatments of 100 g a.i./100 liters in one or four weekly applications. A single application of 200 g a.i./100 liters resulted in residual levels lower than 0.5 ppm after one or more days post-application