Magnetic evidence of a crustal fault affecting a linear laccolith: The Guadiana Fault and the Monchique Alkaline Complex (SW Iberian Peninsula)

Magnetic anomalies can help reveal the structure of the upper crust in regions with intermediate or basic igneous rocks, and their continuity is essential to determine the position of crustal faults. The southwestern Iberian Peninsula constitutes the foreland of the Betic Cordillera and is characterized by an elongated E-W dipole extending 200 km toward its external zones. The anomaly is related to the outcropping Monchique Alkaline Complex, characterized by rocks of moderate magnetic susceptibility (0.029 SI) intruding into the metapelitic host rock of the South Portuguese Zone. Analysis of aeromagnetic and field magnetic anomalies serves to constrain the geometry of this laccolith. Toward the east, the magnetic dipole has a 60 km long N-S sharp boundary that coincides with the southern part of the Guadiana River. Field magnetic and gravity anomalies confirm the presence of this structure. It is produced by a sharp step in the elongated anomalous body, with an E downthrown block, interpreted as the offset produced by a deep N-S crustal fault—the Guadiana Fault. Therefore, the Guadiana River has three long linear segments near its mouth, locally coinciding with a N-S trending joint set, that support the presence of this major fault. To date, no evidence of this tectonic discontinuity, coinciding with the Spanish-Portuguese border, has been reported. Magnetic research is essential for understanding the structure of wide regions intruded by intermediate and/or basic igneous rocks.     

Kinematic model of crustal deformation of Fenwei basin,China based on GPS observations

Using high precision GPS data for the period of 1999–2007 from the China Crustal Movement Observation Network, we have constructed a plate kinematic model of crustal deformation of Fenwei basin, China. We have examined different kinematic models that can fit the horizontal crustal deformation of the Fenwei basin using three steps of testing. The first step is to carry out unbiasedness and efficiency tests of various models. The second step is to conduct significance tests of strain parameters of the models. The third step is to examine whether strain parameters can fully represent the deformation characteristics of the 11 tectonic blocks over the Fenwei basin. Our results show that the degree of rigidity at the Ordos, Hetao, Yinshan and South China blocks is significant at the 95% confidence level, indicating the crustal deformation of these blocks can be represented by a rigid block model without the need to consider differential deformation within blocks. We have demonstrated that homogeneous strain condition is suitable for the Yinchuan basin but not for other 6 blocks. Therefore, inhomogeneous strains within blocks should be considered when establishing the crustal deformation model for these blocks. We have also tested that not all of the quadratic terms of strain parameters are needed for the Yuncheng-Linfen block. Therefore, four kinds of elastic kinematic models that can best represent the detailed deformation characteristics of the 11 blocks of Fenwei basin are finally obtained. Based on the established model, we have shown that the current tectonic strain feature of the Fenwei basin is mainly characterized by tensile strain in the NW–SE direction, and the boundaries betweem the Ganqing and Ordos blocks and the Shanxi graben possess the maximum shear strain. A comparison between our results and past geological and geophysical investigations further confirms that the model established in this paper is reasonable.     

Detailed crustal structure in the area of the southern Apennines–Calabrian Arc border from local earthquake tomography

We present a new seismic velocity model for the southern Apennines–Calabrian Arc border region with the aim to better define the crustal structures at the northern edge of the Ionian subduction zone. This sector also includes the Pollino Mts. area, where a seismic sequence of thousands of small to moderate earthquakes has been recorded between spring 2010 and 2013. In this sector a seismic gap was previously hypothesized by paleoseismological evidences associated with the lack of major earthquakes in historical catalogs.To perform the tomographic inversion we selected ca. 3600 earthquakes that have occurred in the last thirty years and recorded by permanent and temporary networks managed by INGV and Calabria University. Using for the first time the Local Tomography Software for passive tomography inversion (LOTOS hereinafter) to crustal analysis in southern Italy, we have computed the distribution of Vp, Vs, and the Vp/Vs ratio. The obtained velocity model, jointly evaluated with results of synthetic modeling, as well as with the hypocenter distribution and geological information, gives us new constraints on the geodynamical and structural knowledge of the study area.The comparison between the shallow tomography sections and surface geology shows good correlation between velocity patterns and the main geological features of the study area. In the upper crust a low-velocity anomaly of P- and S-waves is detectable beneath the Pollino Mts. area and seems to separate the Calabrian and southern Apennines domains, characterized by higher velocities. The distributions of high Vp/Vs ratio, representing strongly fractured rocks with likely high fluid content, clearly correlate with areas of significant seismicity.In the lower crust we detect a clear transition from high to low seismic velocities in correspondence with the Tyrrhenian coast of the study area, which may represent the transition from the thinner Tyrrhenian crust to the thicker one beneath Calabria. In this area, also characterized by a progressive detachment of a retreating lithospheric slab, the generation of a Subduction-Transform Edge Propagator (STEP) fault zone, that laterally decouples subducting lithosphere from non-subducting lithosphere in a scissor type of fashion, may have taken place. These conditions imply the existence of a kinematic decoupling which allows for differential movement between the Calabrian Arc and the southern Apennine chain. The low velocity anomaly separating the southern Apennines and the Calabrian Arc domain may be related to fluid upwelling occurring in correspondence with the northern edge of the Calabrian subducting slab.     

Oblique wave scattering by undulating porous bottom in a two-layer fluid: Fourier transform approach

The problem involving scattering of oblique waves by small undulation on the porous ocean bed in a two-layer fluid is investigated within the framework of linearised theory of water waves where the upper layer is free to the atmosphere. In such a two-layer fluid, there exist waves with two different wave numbers (modes): wave with lower wave number propagates along the free surface whilst that with higher wave number propagates along the interface. When an oblique incident wave of a particular mode encounters the undulating bottom, it gets reflected and transmitted into waves of both modes so that some of the wave energy transferred from one mode to another mode. Perturbation analysis in conjunction with Fourier transform technique is used to derive the first-order corrections of velocity potentials, reflection and transmission coefficients at both modes due to oblique incident waves of both modes. One special type of undulating bottom topography is considered as an example to evaluate the related coefficients in detail. These coefficients are shown in graphical forms to demonstrate the transformation of water wave energy between the two modes. Comparisons between the present results with those in the literature are made for particular cases and the agreements are found to be satisfactory. In addition, energy identity, an important relation in the study of water wave theory, is derived with the help of the Green’s integral theorem.     

2014年新疆于田MS7.3地震序列的深度测定

An Ms7. 3 earthquake occurred on February 12, 2014 in Yutian County, Xinjiang Uygur Autonomous Region, which was followed by a series of aftershocks. This paper calculates the depth of the Ms7. 3 earthquake sequence by using the deterministic approach with the seismic phase data from the catalog database of the China Earthquake Networks Center, combined with original seismic wave records from the Digital Seismic Network Center of the Earthquake Administration of Xinjiang Uygur Autonomous Region.     

新疆东准噶尔花岗岩类岩石高温高压弹性波速度及其对地壳结构的约束

应用超声波反射-透射法,在最高压力为1.0 GPa（室温）,最高温度为700℃（1.0 GPa）的条件下对新疆东准噶尔地区的卡拉麦里花岗岩带和野马泉岩体的典型花岗岩类岩石（碱长花岗岩、碱性花岗岩、花岗闪长岩、二长花岗岩和石英闪长岩）的纵波速度（V_P）和横波速度（V_S）进行了测量.结果显示,在常温、压力0.4~1.0 GPa条件下,东准噶尔地区花岗岩类岩石的V_P和V_S均随压力呈线性增加,说明在这个压力段岩石中的微裂隙已基本闭合.室温、1.0 GPa时花岗岩类岩石的V_P是5.79~6.84 km·s^-1,V_S是3.26~3.85 km·s^-1.依据压力与V_P及压力与V_S的线性关系,拟合得到常温常压下花岗岩类岩石的纵波和横波压力系数分别是0.1568~0.4078 km/（s·GPa）和0.0722~0.3271 km/（s·GPa）,V_P0和V_S0分别是5.62~6.47 km·s^-1和3.15~3.75 km·s^-1.恒压1.0 GPa、室温到700℃条件下,花岗岩类岩石的V_P和V_S均随温度的升高呈线性降低,温度系数分别为（-3.41~-4.96）×10^-4 km/（s·℃）和（-0.88~-3.22）×10^-4 km/（s·℃）.利用实验获得的花岗岩类岩石的V_P0、V_S0及温度系数和压力系数,结合东准噶尔地区的地热资料,建立了V_P和V_S随深度变化的剖面.将获得的V_P和V_S-深度剖面与该区地球物理探测结果对比,发现东准噶尔地区的碱长花岗岩、碱性花岗岩、二长花岗岩和部分花岗闪长岩的V_P和V_S与该区上地壳速度吻合很好,同时这几种岩石的平均泊松比也与上地壳泊松比一致,因此我们认为这几种类型的岩石是该区上地壳的重要组成部分.另外,石英闪长岩的V_P和V_S均符合中地壳的速度,可能为中地壳中的一种岩石.     

近地表大气环境变化对地壳形变观测的影响研究

近地表大气环境变化主要包括近地表气象因素（大气压强、温度、降雨）变化及台风、日食活动等。利用小波分析方法对2003—2013年湖北省数字化地壳形变潮汐分钟值资料进行处理后发现,近地表大气环境因素对形变观测数据具有不同频段上的特征变化影响。大气压强和温度对形变观测的响应频段主要集中在较低频段（64—128分钟）;降雨的影响主要集中在0-全日波（0—32分钟）范围内且存在高频、非潮汐成份。而台风在较高频段上有明显响应,频段分布在1—4秒和2—4分钟之间。黄梅台应变观测对2009年日食事件在128—256分钟低频段上有响应。     

渤海湾盆地北西盆山边界地区泊松比分布

泊松比做为了解地球内部介质一个非常重要的参数,在地震学上可以通过P波和S波速度的比值来确定.利用远震P波波形记录中包含的壳-幔速度间断面的Ps转换波及其多次反射/转换波信息,采用在地壳厚度－波速比平面上对接收函数转换波能量的叠加搜索方法,可以测定台站下方区域内地壳的平均厚度和泊松比.我们对渤海湾盆地北西盆山边界地区68个宽频带台站近两年的远震记录资料进行了处理研究,得到了该区域的地壳厚度以及泊松比分布.结果表明,渤海湾盆地北西盆山边界的泊松比值分布横向变化复杂, 山区侧与盆地侧存在明显差异;山区侧泊松比值分布相对均匀,盆地侧变化剧烈,但存在小区域范围内(100～200km)的一致性,与地表出露岩石的对比表明:形成渤海湾盆地的新生代伸展作用在下地壳深度有明显的响应,从地震学上获得的泊松比分布对于了解该地区地壳物质组成可起到很好的约束作用.     

东亚地区矿物尘气溶胶直接辐射强迫的初步模拟研究

为研究东亚地区矿物尘气溶胶的直接辐射效应,在区域气候模式RegCM3中加入起尘方案、建立矿物尘气溶胶输送模式,并将其辐射过程加入区域气候模式的辐射方案.通过对2001年3月～2002年3月的模拟发现：中国西北和蒙古国年平均地表起尘率在1μg/(m2·s)以上,最大达到90μg/(m2·s)是东亚地区最主要的矿物尘气溶胶源地;东亚地区矿物尘气溶胶柱含量最大值达5g/m2,出现在塔克拉玛干沙漠和秦岭地区;气溶胶大气顶直接辐射强迫基本呈现大陆上为正、海洋上正负均有的分布特征,区域平均辐射强迫在春夏秋冬分别为108, 088, 037,040W/m2,短波辐射强迫在陆上为正、海上正负均有,长波辐射强迫均为正值;四季的地表辐射强迫分别为-564, -225, -137, -187W/m2;辐射强迫数值对矿物尘气溶胶单次散射反照率的变化较敏感.     

内蒙古一次强沙尘暴过程综合观测分析

利用高空、地面常规观测资料和内蒙古沙尘暴监测站的沙尘暴器测资料,对2010年3月19～20日一次强沙尘暴天气过程进行了综合观测分析.结果表明:本次沙尘暴发生前,大气层结稳定并不利于对流的发展.但在700 hPa至500 hPa的强冷平流与850 hPa以下层次的平流差异有利于温度垂直递减率增大,强冷平流的作用使其中心以下层次形成热力不稳定层结,是沙尘暴发生的有利层结条件.当干对流风暴发生并形成沙尘暴天气时,不稳定能量释放,使该层大气趋于中性层结即混合层,混合层可能是其间的一个平衡态.对流层中低层冷平流的强度、位置和层次,一定程度上影响着混合层的厚度和沙尘暴的强度.过程中混合层以下气层温度下降的比较快,加之沙尘暴顶层短波辐射有增温效果,在混合层顶(约500 hPa处)出现逆温盖.强冷空气活动是引发沙尘暴天气的主要原因,沙尘暴天气的发生伴随着地面剧烈降温,相对湿度骤降,气压涌升,地面风速直接影响沙尘暴强度.可吸入颗粒物(PM10)浓度能更加精细的反映和描述沙尘暴强度的变化.粒子散射系数的变化趋势和PM10浓度的变化趋势非常一致,沙尘暴阶段,散射系数基本在1000Mm-1以上,达到强沙尘暴强度阶段,散射系数基本在2000Mm-1以上.