Time dependent piezomagnetic fields in viscoelastic medium

We investigated time dependent piezomagnetic fields due to volcanic sources embedded in a viscoelastic, homogeneous half-space. Especially in volcanic areas, the presence of inhomogeneous materials and high temperatures produce a lower effective viscosity of the Earth's crust that calls for considering anelastic properties of the medium. Piezomagnetic properties are carried by grains of titano-magnetite, which occupy only a small fraction of ordinary rock volume and are supposed to be elastic, while the non-magnetic surrounding matrix is assumed to be viscoelastic. From all the possible rheological models, we investigated two cases in which the bulk modulus is purely elastic and the shear modulus relaxes as: (i) a Maxwell solid and (ii) a standard linear solid (SLS). We applied the Correspondence Principle to the analytical elastic solutions for pressurized spherical sources and dislocation sources in order to determine the time dependent piezomagnetic fields in a viscoelastic medium. The piezomagnetic field completely vanishes after the relaxation process for a Maxwell rheology, whereas it is found to decrease over time and reach some finite offset value for a SLS rheology. These different behaviours provide helpful hints in understanding the temporal evolution of piezomagnetic anomalies in volcanic regions.     

新疆阿什库勒火山群野外地质科学考察

2011年5月4日至5月30日,由中国地震局地质研究所和新疆维吾尔自治区地震局组成的科考队,完成了2010年度地震行业专项“新疆于田7.3级地震与阿什库勒火山综合科学考察”的野外综合科学考察。火山地质组通过对阿什库勒火山群的野外地质、地貌实地考察,初步查明了阿什库勒盆地新生代火山类型、数量、结构参数和火山活动历史,并且对该地区存在的一些有争议的问题, 如阿什火山1951年5月27日喷发事件的报道、大黑山火山的喷发方式、高台山火山的存在与否等问题提供了野外证据。     

Volcanic Debris-avalanche Deposits of the Laoheishan Volcano and Huoshaoshan Volcano in Wudalianchi

Large amounts of volcanic debris-avalanche deposits, which take the shape of hummocks, are distributed around the peripheries of the Laoheishan volcano and Huoshaoshan volcano in Wudalianchi World Geopark. In earlier times, they were called "satellite volcanoes", namely, freestanding volcanoes. This paper points out that these deposits actually came from the collapse of the cones of these two volcanoes. When the lava flow spilled out at the base of the slope of the cones, the slope broke up and collapsed under the action of gravity. Later, ravines were formed on the slope. Caved slope clastics, accompanying lava flow, accumulated at the rims of the volcano cones. Although some accumulations may form very large cones, they are not volcanoes, but deposits of volcanic debris avalanches.     

Influence of volcanic activity on spring water chemistry at Popocatepetl Volcano, Mexico

The results of the 7 years (1994–2000) of monthly monitoring of spring water before and during eruptions show response to volcanic activity. Low salinity and temperature characterize most of the springs, which are located on the flanks of Popocatepetl Volcano. The pH ranges from 5.8 to 7.8 and temperature from 3 to 36 °C. Oxygen and hydrogen isotopic data show that the water is of meteoric origin, but SO₄²⁻, Cl⁻, F⁻, HCO₃⁻, B, and SO₄²⁻/Cl⁻ variations precede main eruptive activity, which is considered linked to influx of magmatic gases and acid fluids that react with sublimates and host rock and mix with the large water system. Na⁺, Ca²⁺, SiO₂ and Mg²⁺ concentrations in the water also increased before eruptive activity. The computed partial pressure of CO₂ in equilibrium with spring waters shows values higher than air-saturated water (ASW), with the highest values up to 0.73 bar of pCO₂. Boron is detected in the water only preceding the larger eruptions. When present, boron concentration is normally under health standard limits, but in two cases the concentration was slightly above. Other components are within health standard limits, except for F⁻ in one spring.     

五大连池、天池和腾冲火山岩Sr、Nd同位素地球化学特征与岩浆演化

在的年来对长白山天池火山、五大连池火山和腾冲火山三个火山区火山岩岩石学的主、微量元素研究的基础上，新做出18个火山岩Sr-Nd同位素数据，进一步讨论地幔源区特征与岩浆成因演化。五大连池富钾火山岩浆源区由原始地幔与EMI两个地幔端员混合而成，岩浆直接来自地幔，未受地壳物质明显混染和分离结晶作用影响；天池火山各阶段火山岩一致的似原始地幔特征，可能指示存在巨大的壳内岩浆房和持续的幔源岩浆的补给；腾冲火山岩的高钾钙碱性岩浆源区为由陆内壳－幔相互作用导致的原始地幔与EMⅡ两个地幔端员不同程度混合而成。     

河北沧州小山火山的ESR年代学研究

河北沧州小山火山是河北平原,包括华北平原少有的出露地表的第四纪火山,也可能是华北平原区最后一个活动的火山。因此,此火山极其重要,可是至今没有确切的年代学数据。本次研究分别从小山火山地表和钻孔中采集了7个样品,进行了电子自旋共振测年。每个样品都分选出了石英颗粒,这表明火山堆积物不是纯的凝灰岩,而是火山活动时,同时带有地表物质的混入。样品ESR测年结果在误差范围内一致,平均值为41.4±8.6ka。小山火山活动可能发生于41ka BP.,测年结果表明小山火山最后一次活动在晚更新世晚期。     

金星薄饼状火山类比研究

金星薄饼状火山(陡边火山)是一类形貌非常独特的火山,有别于太阳系中其他的火山:近圆的底面轮廓、平坦的顶部和较大的顶底直径比。薄饼状火山被认为是高黏度岩浆喷发形成的,但是这一成因并不被广泛接受。火山的形貌特征主要取决于岩浆成分、喷发机制、重力和喷发环境(如大气压)等。因此,通过对比地球火山的形貌特征及形成机制可以为金星薄饼状火山的成因提供指示。我们利用底面不规则度(ii)、高径比(H/W_B)、顶底直径比(W_S/W_B)、侧边最大坡度处的标准化高度(HS_max)、顶部高径比(H_S/W_S)和喷发量(V)这些形貌参数定量地将地球表面的复式火山、盾形火山、火山锥、熔岩穹丘(Peleean型和Coulees型)、海底平顶火山以及泥火山的形貌特征与金星薄饼状火山对比。Coulees型熔岩穹丘、海底平顶火山和泥火山的形貌特征与金星薄饼状火山有一定的相似性。Coulees型熔岩穹丘剖面形态与薄饼状火山最为相似,可能指示了薄饼状火山具有类似的成因机制,而海底平顶火山侧边的上凹特...     

Ground temperature change observed at Unzen Volcano associated with the 1990–1995 eruption

Ground temperature associated with eruptive activity of Unzen Volcano, southwestern Japan, was observed in a cave about 680 m west of the central vent. Based on the data during 1991–1996, eliminating the effects of seasonal change, the temperature rose to the highest level probably around the first half of 1992. Hereafter the temperature decreased gradually year by year at least up to the autumn of 1996, beyond the level recovered at the beginning of the lava extrusion in May 1991. Although it is not necessarily conclusive, the present observation suggests a possible rise in ground temperature prior to the commencement of the first phreatic eruption in November 1990. If so, a careful observation may help to predict future eruptions by detecting a precursory rise of the ground temperature in this volcano.     

日本1995年阪神大地震及火山考察与启示

简述了１９９５年１月１７日日本７．２级阪神大地震的震害,地震断层以及１８９１年浓尾级地震根尾谷地震断裂、北伊豆地震旦那断层和大室火山、伊豆大岛火山的一些特征,最后论述了这次考察的启示。     

东太平洋不同海域多金属结核差异的主控因素

本文以ＤＹ８５－４ 航次在东太平洋的调查为基础,概述了多金属结核在东西两海区的差异;分析了影响这种差异的因素;着重探讨了多金属结核的丰度、品位、覆盖率、Ｍｎ／Ｆｅ、与伴生沉积物、断裂带、火山、侵入岩的关系。发现造成两区结核差异的因素很多,但起主控作用的是断块、火山、岩浆、热液等活动所带来的物质及对海底物理化学环境的影响。