长白山—镜泊湖火山区地壳结构接收函数研究

利用71个远震的波形资料,用接收函数方法提取了布设在长白山—镜泊湖火山区的34个宽频带流动数字地震台站的接收函数,通过对接收函数反演,获得了台站下方的S波速度结构.研究结果表明,沈阳—敦化一线莫霍面深度32～33km,向西地壳厚度加厚,到长春附近地壳厚度约为36km.在天池火山口莫霍面深度为达38km,而镜泊湖火山口森林的莫霍面深度约为39km.总体看研究区的地壳厚度是南浅北深.长白山天池火山口附近地下10km左右有一明显的低速层存在;镜泊湖火山口森林附近30km也可能有低速体存在;研究发现莫霍面上S波速度梯度在火山口附近和远离火山口有明显区别.在火山口附近其莫霍面的S波速度梯度比非火山口地区的S波速度梯度明显小,说明火山口下与一般的地壳莫霍面结构有差别.研究发现沈阳—敦化一线两侧的莫霍面深度有较大变化,其位置与地表的敦化—密山断裂基本一致,说明敦化—密山断裂是研究区的一条非常重要的地质构造带.     

Overview of deep structures under the Changbaishan volcanic area in Northeast China

The Changbaishan volcano is an active and considerably hazardous volcano located on the border of China and North Korea. This paper summarizes a series of geophysical surveys as well as seismological and volcano-observational networks around the Changbaishan volcanic area. We characterize deep structures related to the Changbaishan volcanic area. The prominent low-velocity anomalies and low-resistance bodies associated with the magma system under the Changbaishan volcano were detected in the crust and upper mantle, and high-velocity anomalies were imaged within the mantle transition zone,suggesting that the origin of the Changbaishan volcano is related to the subducted Pacific slab. However, there exist a few major obstacles for comprehensively elucidating the deep structure of the Changbaishan volcano as well as for the preparedness for and response toward future volcanic unrest and activity. It is essential to collect data from both China and Korean Peninsula to image the deep structure beneath the Changbaishan volcanic area. A multi-disciplinary approach comprising seismological investigations, deformation information from GNSS and InSar, and gravity and magnetotelluric surveying is a reliable manner for imaging high-resolution structures and fluid movement for the spatial distribution and variation of the volcanic magma chamber.An effective volcano-monitoring network system is considerably important to improve hazard assessments and characterize the potential future eruption of the Changbaishan volcano.     

A palaeomagnetic study of the Nigerian volcanic provinces

Summary Six Younger Granite localities showing normal and reverse magnetizations in equal proportion have given a Jurassic palaeomagnetic pole position =62.5°N, =241.6°E; (Fisher's precision parameter (k)=27.8 and ₉₅=13°). Individual palaeopole-positions have also been obtained for a Cretaceous pyroclastic rock and for two Pleistocene basalt flows.     

A distinction technique between volcanic and tectonic depression structures based on the restoration modeling of gravity anomaly: a case study of the Hohi volcanic zone, central Kyushu, Japan

In this study, we propose a numerical modeling technique which restores the gravity anomaly of tectonic origin and identifies the gravity low of caldera origin. The identification is performed just by comparing the restored gravity anomalies with the observed gravity anomalies, thus we do not need detailed geophysical and geological information around the buried caldera. The technique has been successfully applied to distinguish the gravity low originated in the buried Shishimuta caldera from other gravity lows in the Hohi volcanic zone, central Kyushu in Japan.     

Identification of eruption clouds with the landsat satellites

Landsat satellite images were selected for the analysis of a tephraladen eruption cloud and a volcanic fume cloud. A 35 km long eruption plume from Sakurazima Volcano, Kyushu, Japan was viewed by the satellite on December 2, 1972. Multispectral Scanner (MSS) band 4 was density sliced into eight levels. Grey levels over the tephra-laden cumulus, which had formed at the terminus of the eruption plume, were distinct from most of the nearby cumulus clouds. MSS band 4 is the key band for identifying eruption clouds in overcast volcanic regions. A lume cloud from Stromboli, Italy was studied in the same manner. It is easily identified over land areas and for 8 km over water in areas of clear sky, but cannot be distinguished from banks of cumulus clouds.     

Sakurajima volcano: a physico-chemical study of the health consequences of long-term exposure to volcanic ash

Regular eruptions from Sakurajima volcano, Japan, repeatedly cover local urban areas with volcanic ash. The frequency of exposure of local populations to the ash led to substantial concerns about possible respiratory health hazards, resulting in many epidemiological and toxicological studies being carried out in the 1980s. However, very few mineralogical data were available for determination of whether the ash was sufficiently fine to present a respiratory hazard. In this study, we review the existing studies and carry out mineralogical, geochemical and toxicological analyses to address whether the ash from Sakurajima has the potential to cause respiratory health problems. The results show that the amount of respirable (<4 μm) material produced by the volcano is highly variable in different eruptions (1.1–18.8 vol.%). The finest samples derive from historical, plinian eruptions but considerable amounts of respirable material were also produced from the most recent vulcanian eruptive phase (since 1955). The amount of cristobalite, a crystalline silica polymorph which has the potential to cause chronic respiratory diseases, is ~3–5 wt.% in the bulk ash. Scanning electron microscope and transmission electron microscope imaging showed no fibrous particles similar to asbestos particles. Surface reactivity tests showed that the ash did not produce significant amounts of highly reactive hydroxyl radicals (0.09–1.35 μmol m⁻² at 30 min.) in comparison to other volcanic ash types. A basic toxicology assay to assess the ability of ash to rupture the membrane of red blood cells showed low propensity for haemolysis. The findings suggest that the potential health hazard of the ash is low, but exposure and respiratory conditions should still be monitored given the high frequency and durations of exposure.     

IDOAS: A new monitoring technique to study the 2D distribution of volcanic gas emissions

Imaging Differential Optical Absorption Spectroscopy (IDOAS) is an optical remote-sensing method using scattered sunlight as light source. It combines a “pushbroom” imaging spectrometer with the DOAS technique and thus allows imaging two-dimensional trace gas distributions, e.g., in volcanic plumes. The highly sensitive and specific detection of many trace gases simultaneously (specific molecules, not just elements, e.g. SO₂, BrO, NO₂, O₃, HCHO, etc.) is possible, and the temporal and spatial variation of these gases can be measured. The IDOAS system presented here enables the taking of two-dimensional images of trace gas distributions in a volcanic plume with a spatial resolution of 100 pixels horizontally × 64 pixels vertically, each with a field of view of 0.087° in horizontal and 0.208° in vertical directions. Therefore, IDOAS provides useful information about the chemical composition and chemical variability in a volcanic plume and allows studying plume dispersal and chemical transformations. The technique was applied to map the SO₂ distribution in the plume of Mt. Etna volcano for the first time in October 2003.     

我国火山灾害评估中的问题初探

文中讨论了我国火山灾害准确预报的可能性，对与火山灾害有关的一些重要问题，如高风险火山区的评估预测，火山灾害的预测评估的分期界定等进行了讨论。     

Liparitic volcanism of some regional volcanic structures in Kazakhstan,Middle Asia and Caucasus

Liparitic volcanism is a typical feature of the orogenic phase giving rise to the Kazakhstan, Middle Asia and Caucasus folded systems. The main characteristics of the liparitic volcanism common to these three regions are the following:

1. Geo-structural zonation of the volcanic structures.
2. Dismembered Moho surface within the volcanic structures.
3. Synchronous, yet independent evolution of liparitic and andesitic volcanisms.
4. Ignimbritic character of the liparitic volcanism.
5. Lateral petrochemical zonation with some features common to the liparitic and andesitic rock series.

Geo-structural and petrochemical zonations are likely governed in the regions studied by a deep-seated plutonic body.     

基于微动方法研究五大连池火山区尾山火山锥浅层剪切波速度结构

为了研究五大连池火山区尾山火山锥浅层三维波速结构特征,在尾山火山锥附近区域布设了无线地震检波器密集台阵,记录连续地震背景噪声波形数据.基于微动方法（拓展空间自相关方法）提取了台站间2~5 Hz频率范围的Rayleigh面波相速度频散曲线.利用面波层析成像方法反演获得2~5 Hz Rayleigh面波二维相速度图像,基于每一个网格节点的频散曲线,进一步反演获得了尾山火山锥附近区域地表至700 m深度的三维剪切波速度结构.成像结果显示：在0~150 m较浅深度,靠近尾山火山锥区域显示为相对高速异常,远离火山锥区域则显示为相对低速异常.而至150~700 m较深深度,波速异常特征与浅部相反,靠近尾山火山锥的区域显示为相对低速异常,远离火山锥的区域显示为相对高速异常.在远离尾山火山锥区域,浅层的相对低速异常可能与松散沉积层有关,深部的高速异常则反映了结晶变质岩的影响.在靠近尾山火山锥区域,浅部的相对高速异常应该反映了出露地表的玄武岩,而深部的相对低速异常则可能反映了火山通道周围广泛发育的破碎裂隙结构及其火山喷发后孔隙流体填充的影响.     

浅谈2014年全球火山动态及我国火山灾害预防对策

由于我国现代火山活动案例较少,主要通过搜集全球活动火山区的监测数据,了解全球火山活动状况及应对策略。通过对2014年全球火山活动动态的总结,逐渐对全球现今活动火山分布位置、活动规律和灾害预防有了新的认识;通过对冰岛巴达本加(Bardarbunga)火山的监测和追踪,总结了冰岛政府对火山灾害的监测手段和应对策略,希望弥补我国火山监测及应急等方面的经验空白;通过对最近发表的火山监测技术及火山信息提取方法的总结,了解了各种先进技术在预防和减轻火山灾害方面的应用。最后,结合国内火山监测现状及相关技术的发展趋势,提出作者对火山监测的思考,并提出几点建议:一方面,我们要充分利用先进的计算机技术,将实时的监测数据进行智能化处理,提取出必要的信息;另一方面,我们要利用网络优势共享最新监测成果和先进监测技术,为公众提供一个交流平台,使得灾害信息的发布更智能、更及时、更直观和更人性化。     

Contribution to the knowledge of the magmatic evolution by the study of the variation of the coefficient of viscosity

The determination of the coefficient of viscosity of eruptive products gives useful elements to the knowledge of possible variations of composition and physical conditions of the magmas.     

Correspondence analysis applied to volcanic aerosols

A statistical analysis of volcanic aerosol based on 1,083 variables including concentration, grain-size and site variabilities establishes correlations between sites and among chemical elements.Variation curves of element concentration show parallel behaviour. High coefficients of correlation between anions and cations confirm associations between elements.     

大兴安岭火山群区的深部速度结构及火山成因

中国东北地区新生代板内火山群广泛发育, 其中大兴安岭火山群区的上地幔结构研究匮乏, 火山群的演化机理尚不明确.本文收集近年来大兴安岭地区流动台站和固定台站的观测波形数据, 通过波形互相关从远震事件记录中挑选出64575个P波震相走时残差, 13566个S波震相走时残差, 开展远震体波走时层析成像研究, 获得该区上地幔的V_P、V_S以及V_P/V_S异常结构.研究结果显示, 火山群区的低速异常分布在上地幔的不同深度范围内, 火山群下方的低速异常向下延深并交汇于软流圈内.结合本文和已有的研究结果推断, 岩石圈拆沉导致的软流圈物质上涌是大兴安岭火山群的深部成因.火山群区的速度异常比值优势值为1.5左右, 表明速度异常既有温度变化成因也有物质成份成因.总体而言, 处在地幔不同深度范围内的低速异常极值区基本和高波速比值区域相对应, 暗示火山群下方的岩浆流体处在不同的深度位置, 这可能是阿尔山和诺敏河火山群火山岩性存在差异的原因.

     

Sources of two large ignimbrites in the central andes: Some landsat evidence

Sources of large-volume ignimbrites in the Central Andes are difficult to identify by conventional means. MSS band 7 LANDSAT imagery of the region was obtained with the specific objective of using the synoptic view to identify large ignimbrites and their sources. Two are described. The Guataquina ignimbrite covers some 2300 km² and probably has a volume of some 70 km³. It appears to have a source in Cerro Guacha, a complex caldera-graben structure 25 km across. The Cerro Galan ignimbrite covers an area of some 2000 km' on the flanks of a major resurgent caldera some 30 km by 20 km across. Younger volcanic rocks have been erupted from two points on the caldera wall, and the structure appears to have had a geological history broadly similar to that of the Valles caldera.     

Structural study of the Ballandaz landslide (French Alps) using geophysical imagery

This study of the Ballandaz landslide (Savoie, French Alps) was carried out as part of the ANR/PGCU-SIGMA research project. Its aim was to characterize the slope by different methods of geophysical imagery, and then use this characterization to provide a combined interpretation of the morpho-structures in order to simulate the geomechanical behavior of the sliding mass. First, electromagnetic mapping was used to identify the variations of the surface lithology and moisture from which one can more precisely locate the active zone of the slope. Then, electrical and seismic 2D imagery methods were used along several transverse and longitudinal profiles in order to produce electrical resistivity and seismic-velocity depth sections showing up the slope's structures. The H/V method was also tested locally to determine the depth to basement so as to complement the profiles: it reveals potential seismic site effects from the deeper structures. Helped by drilling and inclinometer surveys, the geophysical interpretations have revealed the various units structuring the landslide: (i) the active, very heterogeneous shallow level overlying (ii) a more rigid, less porous, and probably stable shallow bedrock, (iii) boulders, and (iv) the sound geological basement of quartzite and gypsiferous facies. The study has shown the usefulness of combining such different sounding techniques for studying complex environments like landslides; it has also revealed the limitations of each method when used for studying very heterogeneous environments.