再议走滑断裂与地震孕育和发生条件

走滑断裂是与大地震关系最紧密的活动断裂带。研究走滑断裂带上大地震是如何孕育和发生的是地震学家们极为关心的问题。构造地质学研究表明,走滑断裂是一个复杂的构造系统,反映了在剪切作用下产生的各类变形组合。文中立足于国内外不同走滑断裂带实例,对连续或不连续走滑断裂的几何学、运动学和演化过程进行了研究和总结;分析了走滑断裂的枢纽作用,发现枢纽轴部强烈挤压,形成闭锁,应力在此集中,应变在此局部化,地震在此成核和孕育。当闭锁的枢纽轴被突破时,沿走滑断裂发生失稳错动,产生突发性大位移,伴随大地震发生。而在不连续走滑断裂不同性质的阶区,则遵循其相应的应力场和破裂机制孕育和发生相应规模和类型的地震。     

汶川、鲁甸、康定地震前应变数据由自洽到失洽的转变与地震成核

根据四分量钻孔应变观测的弹性理论模型,四个分量的观测值 S1、S2、S3、S4之间存在“自洽方程”：S1＋S3＝S2＋S4。“十五”期间新建的“数字地震观测网络工程”四分量钻孔应变观测系统中已有一批台站,无论是几天的短期数据,还是6年以上的长期数据,两组面应变相关系数 k 值都超过了0．99。k 值不受降雨、河湖水位、机井抽水等外界干扰影响,具有稳定性。但姑咱台和昭通台,分别在汶川8．0级、鲁甸6．5级和康定6．3级地震前,观测到了 k 值发生明显变化即数据自洽性遭到破坏的现象。导出自洽方程的条件是安装应变仪钻孔附近岩石完整及应力源与观测点间介质的连续性要求,由此,作者认为,姑咱台和昭通台面应变相关系数发生变化可能由于台站附近发生的大地震的地震成核过程中震源区地层介质连续性逐渐受到破坏所致。     

Laboratory acoustic emission study for earthquake generation process

Since the similarity in size distribution of earthquakes and acoustic emissions (AE) was found in the 1960s, many laboratory studies have been motivated by the need to provide tools for the prediction of mining failures and natural earthquakes. This paper aims, on the one hand, to draw an outline of laboratory AE studies in the last 50 years, which have addressed seismological problems. Topics include the power laws in which the similarity between AEs and earthquakes is involved and progress that has been made in AE technology and laboratory AE study. On the other hand, this study will highlight some key issues intensively discussed, especially in the last three decades, such as aspects related to the pre-failure damage evolution, fault nucleation and growth in brittle rocks and discuss factors governing these processes.     

Syntectonic porphyroblast growth in phyllites: textures and processes

Abstract Porphyroblast textures in a Karakorum phyllite reveal that porphyroblast growth was syn-tectonic with respect to a cleavage forming deformation. During and after porphyroblast growth it partitions the deformation such that zones of intensified cleavage are developed which wrap around the porphyroblast whilst the porphyroblast and its strain shadow undergo little deformation. Porphyroblast strain shadows comprise quartz, calcite and felspar with little mica, and are probably formed by solution transfer during deformation. Unless the deformation is so strongly partitioned that no deformation of the porphyroblasts and their immediate surrounds occurs, inequidimensional porphyroblasts will rotate. Porphyroblasts undergo some dissolution after they have finished growing.     

Reaction overstepping and re-evaluation of peak P‒T conditions of the blueschist unit Sifnos,Greece: implications for the Cyclades subduction zone

ABSTRACT

Equilibrium thermodynamic modelling, quartz in garnet (QuiG) Raman geobarometry, and modelling of garnet nucleation at overstepped conditions were applied to three garnet-bearing blueschists from a 1.5 km-long transect across the eclogite-blueschist unit in Sifnos, Greece, in order to evaluate the accuracy of P?T conditions calculated via equilibrium thermodynamics. QuiG barometry uses the Raman shift of quartz inclusions in garnet to estimate the pressure of garnet nucleation and is independent of chemical equilibrium. Garnet nucleation temperatures were estimated by determining the stability field of the palaeo-assemblage inferred from garnet inclusion suites on mineral assemblage diagrams calculated in the MnNCKFMASH system and on temperatures obtained from Zr in rutile thermometry. These conditions were then compared to P?T conditions calculated at the equilibrium garnet isograd, and the method of intersecting isopleths. The P?T conditions calculated with intersecting garnet isopleths over- and underestimated the temperature of nucleation in samples SPH99-1a and SPH99-7, respectively, whereas they significantly underestimated nucleation pressure in SPH99-5. Nucleation of garnet in SPH99-1a at 12 kbar and ~484°C requires overstepping of ~6 kbar and a reaction affinity of 2.2 kJ mol^?1 O. SPH99-5 requires overstepping of ~8 kbar with garnet reaction affinities of at least 2.0 kJ mol^?1 O at 15 kbar and ~520°C. SPH99-7 requires overstepping of approximately 15 kbar and affinities of about 2.0–2.4 kJ mol^?1 O at ~23 kbar and ~530°C. The geotherms calculated from SPH99-7 (~6.7°C km^?1) and SPH99-5 (9.8°C km^?1) are in accordance with previous studies. The geotherm calculated from SPH99-1a, however, is warmer (11.3°C km^?1), and could reflect changes in the rate of subduction or differences in structural position within the down-going slab. The 10 kbar pressure difference between SPH99-7 and SPH99-1a can be explained by thrusting and accretion of thin slices of underplated wedge material facilitated by slab rollback and gravitational collapse.     

Aerosol Indirect Effects on Warm Clouds in the Grid-Point Atmospheric Model of IAP LASG (GAMIL)

Aerosol indirect effects on warm clouds are estimated in the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics(IAP LASG)(GAMIL) with a new two-moment cloud microphysics scheme using two different physically-based aerosol activation parameterizations:Abdul-Razzak and Ghan,and Nenes and Seinfeld.The annual global mean changes in shortwave cloud forcing from preindustrial times to present day(a measure of the aerosol indirect effects) estimated from these two parameterizations are remarkably similar:0.76 W m?2 with the Abdul-Razzak and Ghan parameterization,and 0.78 W m?2 with the Nenes and Seinfeld parameterization.Physically-based parameterizations can provide robust representations of aerosol effects on droplet nucleation,meaning that aerosol activation is no longer the most uncertain factor in modeling aerosol indirect effects.     

冰晶异质核化对雷暴云电过程影响的数值模拟

引入一种新型冰晶异质核化方案,基于二维雷暴云模式,探讨雷暴云电过程对三种异质核化的响应.结果 表明:浸润核化是冰晶生成的最重要异质核化过程,较高数浓度的冰晶消耗雷暴云内液态水含量,抑制淞附过程,导致霰粒子比含水量低,表现为较强的负极性非感应起电率;接触核化生成的冰晶量最少,仅对雷暴云中下层3～5 km处的冰晶有贡献,同...     

Simulation of the influence of aerosol particle characteristics on clouds and precipitation with LM-SPECS: Model description and first results

The novel model system LM-SPECS is presented combining a spectral bin microphysics scheme and the three-dimensional Lokalmodell (LM, today called COSMO) of the German Weather Service (“Deutscher Wetterdienst”). The model is designed to investigate in detail the interaction of atmospheric aerosol particles, clouds and precipitation. The microphysics scheme includes a combined spectrum of wetted aerosols, cloud droplets and rain drops. As a first application of the model, sensitivity studies on an artificial deep convective cloud were done. The results produced by LM-SPECS are satisfying. The studies show, e.g., that a diminished initial particle number leads to larger cloud droplets and thus to a higher efficiency of coalescence. This results in a larger amount of precipitation. Furthermore, studies on mixed phase clouds show the influence of varying ice nuclei, such as bacteria, kaolinite and soot, on cloud properties. Here, a more effective freezing leads to an increased number of ice particles with smaller radii. The results point to the importance of a detailed knowledge of the underlying microphysical processes in order to understand the formation of clouds and precipitation more accurately. Though to date the model was applied to artificial cases only, the use of the mesoscale weather model allows for more complex realistic cases which are subject to further studies.     

Dolomite–silica stromatolites in Miocene lacustrine deposits from the Duero Basin, Spain: the role of organotemplates in the precipitation of dolomite

This research provides an ancient analogue for biologically mediated dolomite precipitation in microbial mats and biofilms, and describes the involvement of highly structured extracellular polymeric secretion (EPS) templates in dolomite nucleation. The structure of EPS is shown to match the hexagonal–trigonal lattice geometry of dolomite, which favoured the epitaxial crystallization of dolomite on the organic substrate. This structure of EPS also matches the arrangement of silica nanospheres in opal, which further accounts for the organically‐templated formation of opal enabling the non‐replacive co‐existence of dolomite and silica. The study is focused on a 50 m thick dolomite succession that is exposed in central areas of the Tertiary Duero Basin and was deposited in a mudflat‐saline lake sedimentary complex during the Middle to Late Miocene (9 to 15 Ma). In the intermediate intervals of the succession, poorly indurated dolomite beds pass gradually into silica beds. On the basis of sedimentological, compositional, geochemical and petrographic data, silica and dolomite beds have been interpreted as mineralized microbial mats. The silica beds formed in marginal areas of the lake in response to intense evaporative concentrations; this resulted in the rapid and early precipitation of opal. Silicification accounted for the exceptional preservation of the microbial mat structure, including biofilms, filamentous and coccoid microbes, and EPS. Extracellular polymeric secretions have a layered structure, each layer being composed of fibres which are arranged in accordance with a reticular pattern, with frequent intersection angles at 120° and 60°. Therefore, the structure of EPS matches the lattice geometry of dolomite and the arrangement of silica nanospheres in opal. Additionally, EPS binds different elements, with preference to Si and Mg. The concurrence of suitable composition and surface lattice morphologies in the EPS favoured the crystallization of dolomite on the substrate. In some cases, dolomite nucleation took place epicellularly on coccoid micro‐organisms, which gave way to spheroid crystals. Organic surfaces enable the inorganic mineral precipitation by lowering the free energy barrier to nucleation. Most of the microbial mats probably developed on the lake floor, under sub‐aqueous conditions, where the decomposition of organic matter took place. The subsequent formation of openly packed dolomite crystals, with inter‐related Si‐enriched fibrils throughout, is evidence for the pre‐existence of fibrillar structures in the mats. Miocene dolomite crystals are poorly ordered and non‐stoichiometric, with a slight Ca‐excess (up to 5%), which is indicative of the low diagenetic potential the microbial dolomite has towards a more ordered and stoichiometric structure; this confirms that microbial imprints can be preserved in the geological record, and validates their use as biosignatures.