2013年甘肃岷县漳县M_s6.6地震前地壳形变特征研究

基于2013年岷县漳县M6.6地震震源区及其邻区1999年以来的GPS观测资料,通过应变率动态特征分析、多期次GPS剖面分析和基线变形速率的分析讨论了地震的震前变形特征.GPS速度场和块体应变率表明,汶川地震的发生导致了柴达木地块运动与变形状态发生明显调整,但由于西秦岭北缘等深大断裂的存在,岷-秦地块对其响应不明显;GPS连续应变率显示,在汶川地震引起的区域地壳变形调整过程中岷县漳县地震震源区附近的应变积累速率有减缓的迹象;GPS剖面显示,平行于岷县漳县主破裂带的运动分量对汶川地震响应显著,汶川震后表现为剪切变形速率的增强,而垂直于主破裂带的运动分量则对汶川地震响应不明显;震中周边GPS基线变形速率表明,基线伸缩变化率总体呈现NW向拉张、NE向压缩状态,且拉张量明显小于压缩量.上述地壳变形动态特征表明西秦岭北缘断裂及其附近地区的应变积累水平和断层闭锁程度可能处于较高水平,在岷县漳县地震前该区表现出局部“硬化”迹象.     

青藏高原东北缘M_s≥6.0强震活动特征及未来形势研究

2013年7月22日甘肃岷县漳县6.6级地震打破了青藏高原东北缘地区自2003年以来近十年的6级平静,该地震的意义及该区未来震情发展受到了地震学家的关注.本文运用Morlet小波变换分析了1875-2013年青藏高原东北缘MS≥6.0强震活动的周期特征,结果表明该区强震存在2～3年、8～10年、25～30年等尺度的显著周期;1977年以来青藏高原东北缘地区强震活动频度虽然正常但活动强度处于一个相对较低的阶段.在讨论了岷县漳县6.6级地震的发震背景基础上,认为该地震在青藏高原东北缘强震活动长时间较弱的背景下发生,可能是该区强震活动强弱的一个拐点,未来该区强震活动的频度与强度有增加的趋势.研究结果对该区震情跟踪工作有一定的参考价值.     

Combined analysis of precipitation and water deficit for drought hazard assessment

Abstract

The combined analysis of precipitation and water scarcity was done with the use of the Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI), developed as a monthly, two-variable SPI-SRI indicator to identify different classes of hydrometeorological conditions. Stochastic analysis of a long-term time series (1966–2005) of monthly SPI-SRI indicator values was performed using a first-order Markov chain model. This provided characteristics of regional features of drought formation, evolution and persistence, as well as tools for statistical long-term drought hazard prediction. The study was carried out on two subbasins of the Odra River (Poland) of different orography and land use: the mountainous Nysa K?odzka basin and the lowland, agricultural Prosna basin. Classification obtained with the SPI-SRI indicator was compared with the output from the NIZOWKA model that provided identification of hydrological drought events including drought duration and deficit volume. Severe and long-duration droughts corresponded to SPI-SRI Class 3 (dry meteorological and dry hydrological), while severe but short-term droughts (lasting less than 30 days) corresponded to SPI-SRI Class 4 (wet meteorological and dry hydrological). The results confirm that, in Poland, meteorologically dry conditions often shift to hydrologically dry conditions within the same month, droughts rarely last longer than 2 months and two separate drought events can be observed within the same year.     

Analysis and usage of linear relationships between the magnetic field components recorded by INTERMAGNET

An analysis of linear relationships between the ground-level components of the Earth’s magnetic field measured at different sites is a relatively new topic compared to the analysis of data at a single location. The data collected by the INTERMAGNET observation network provide perfect set of data to which this analysis can be used. An important tool in this analysis may be developing a method of determination of the impulse response for linear systems in the time domain. An advantage of calculations in the time domain over the generally known and applied methods in the frequency domain is the possibility of determining prediction of output signals. By that, simultaneously with the analysis of linear relationships, a tool for recovering missing records in incomplete observation data is obtained. Filling-in the missing data may increase interest and possibility of using the observational data by researchers experimenting with the analysis in the frequency domain where gaps in data records are a significant limitation.     

An approach to response-based reliability analysis of quasi-linear Errors-in-Variables models

The paper presents an approach to internal reliability analysis of observation systems known as Errors-in-Variables (EIV) models with parameters estimated by the method of least squares. Such problems are routinely treated by total least squares adjustment, or orthogonal regression. To create a suitable environment for derivations in the analysis, a general nonlinear form of such EIV models is assumed, based on a traditional adjustment method of condition equations with unknowns, also known as the Gauss–Helmert model. However, in order to apply the method of reliability analysis based on the approach to response assessment in systems with correlated observations, presented in the earlier work of this author, it was necessary to confine the considerations to a quasi-linear form of the Gauss–Helmert model, representing quasi-linear EIV models. This made it possible to obtain a linear disturbance/response relationship needed in that approach. Several specific cases of quasi-linear EIV models are discussed. The derived formulas are consistent with those already functioning for standard least squares adjustment problems. The analysis shows that, as could be expected, the average level of response-based reliability for such EIV models under investigation is lower than that for the corresponding standard linear models. For EIV models with homoscedastic and uncorrelated observations, the relationship between the average reliability indices for the independent and the dependent variables is formulated for multiple regression and coordinate transformations. Numerical examples for these two applications are provided to illustrate this analysis.     

Graphically supported evaluation of mapping techniques used in presenting spatial accessibility

ABSTRACT

Given the rising availability of alternative ways of spatial data mapping, there is a growing need to study their usability. An important aspect here is the diversity of the cartographic visualizations that are used to draw conclusions about the usability of various mapping techniques. In our study we evaluated the usability of six various mapping techniques used in presenting spatial accessibility, taking into consideration four components: effectiveness and efficiency (objective criteria) and graphical attractiveness and user-perceived effectiveness (subjective criteria). Using Internet questionnaires, we conducted a graphical perception experiment with respondents performing tasks on a hypothetical monocentric road network model displayed using mapping techniques of spatial accessibility, differing in the applied parameters of graphical and non-graphical factors influencing effectiveness and efficiency. The results showed that non-graphical factors had a greater influence than the graphical factors. In total usability comparison the three-dimensional (3D) point technique was ranked the highest, while the worst result was achieved by the 3D area technique. The proposed graphical form of study results made it possible to compare the influence of various effectiveness factors, to analyze mapping techniques in terms of considered criteria and finally to present their total usability using a chart inspired by Uhorczak’s typogram.     

北吕宋岛菲律宾活动带蛇绿岩及其上覆浊积岩的放射虫研究新进展

The basement of the Philippine Mobile Belt (PMB) is mainly composed of ophiolites that are mostly overlain by Paleogene to Miocene turbidites in central Luzon. To clarify the geological development of the PMB with respect to the initial stage of the arc volcanism (eg. Yumul et al., 2003, 2008; Dimalanta and Yumul, 2003; Suzuki et al., 2011), radiolarian dating was examined in siliceous sediments associated with the ophiolites and turbidites. The samples were collected from sites identified with the Zambales and Montalban ophiolites, basic tuff phyllites in NW Din-galan, and their overlying formations.     

The evolution of the hydrothermal IOCG system in the Mantoverde district,northern Chile: new evidence from microthermometry and stable isotope geochemistry

New microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested cooling–mixing model for the iron oxide–copper–gold mineralization in the Mantoverde district. Fluid inclusions show characteristics of a CO₂-bearing aqueous NaCl ± CaCl₂ salt system. The evolution of the Mantoverde hydrothermal system is characterized by (1) an early hypersaline, high to moderate temperature fluid; (2) a moderate saline, moderate temperature fluid; and (3) a low saline, moderate to low temperature fluid. Early magnetite formation took place at median temperatures of 435.0°C, whereas hematite formed at median temperatures of 334.4°C. The main sulfide mineralization texturally post-dates the iron oxides and occurred before late-stage calcite, which developed at a median temperature of 244.8°C. Boiling occurs only locally and is of no relevance for the ore formation. The microthermometric and stable isotope data are supportive for a fluid cooling and mixing model, and suggestive for a predominantly magmatic–hydrothermal fluid component during the iron oxide and main sulfide mineralization. Thereafter, the incursion of a nonmagmatic fluid of ultimately meteoric or seawater gains more importance.     

Talc mineralisation associated with soft hematite ore, Gongo Soco deposit, Minas Gerais, Brazil: petrography, mineral chemistry and boron-isotope composition of tourmaline

Talc mineralisation occurs as hematite–talc schist between soft hematite ore and dolomitic itabirite at Gongo Soco, Quadrilátero Ferrífero of Minas Gerais, Brazil. The hematite–talc schist and soft hematite have a prominent tectonic foliation of tabular hematite. Tabular hematite without preferential orientation is superimposed on the tectonic foliation. The talcose schist is enriched in F and has a constant Fe/S ratio. Electron-microprobe analyses indicate trace amounts of S in different generations of hematite. The whole-rock Fe/S ratio possibly represents sulfate S from hematite-hosted fluid inclusions. Fluid inclusions in foliation-overprinting hematite and chlorite geothermometry from talcose rocks suggest, respectively, temperatures from <200°C to ~300°C. Tourmaline, a rarely observed mineral in the hematite–talc schist, belongs to the alkali group and falls in the dravite compositional field. Boron-isotope determinations of tourmaline crystals, using secondary ion mass spectrometry, vary from −20‰ to −12‰ δ¹¹B. This compositional isotopic range and the tourmaline chemical composition suggest a meta-evaporitic origin. A non-marine evaporitic setting is the most likely source of acidic, highly oxidising fluids, which resulted in the abundant F-bearing talc and the presence of otherwise immobile Ti in hematite. Oxidising brines were channelled along shear zones and converted dolomitic itabirite into the Gongo Soco soft hematite and the talc mineralisation. The latter is envisaged as the hydrothermal wall-rock alteration of dolomitic itabirite, which gave rise to the soft hematite ore.