Earthquake magnitude scales

The earthquake magnitude was introduced into seismology nearly 40 yr ago, as a purely empirical concept. After an unparalleled success in scientific and practical applications the magnitude is developing into a concept with a clearer physical meaning and a more solid theoretical foundation. The magnitude determined from the maximum particle amplitude or velocity reflects the maximum radiation power of the seismic source in the frequency band recorded on a particular seismograph. Recently developed models for seismic sources assist in classifying earthquakes according to size and spectral character. From corresponding scaling laws the relations between various magnitude scales can be established. The magnitude aims at enabling one to compare the sizes of seismic sources ranging in character from nearly aseismic events to explosions. While the former are characterized by a relatively long-peroidic radiation maximum, the latter radiate primarily short-periodic seismic energy. Tectonic earthquakes are likely to range in character between the two extreme spectral cases. A comparison of earthquake magnitude with stellar magnitude leads to analogies in spectral character between earthquakes and stars, whereby seismic sources seem to follow a distribution similar to the Hertzsprung-Russell diagram for stars. Before seismological practice can catch up with the new cognitions, improvements in the definition of the earthquake magnitude are in need.     

新国家标准震级标度与传统震级标度对比研究

使用四川省地震台网2013年4月以来的宽频带数字地震资料,对新国家标准震级标度与传统震级标度中的4类震级进行了对比分析。结果表明:新M_L与传统M_L、M_S（BB）与M_S7之间的差别最小,相关性最高;所有事件的新m_b均大于或等于传统m_b;大部分事件的新M_L大于传统M_L;m_B（BB）大于m_B的事件多于m_B（BB）小于m_B的事件;M_S（BB）小于M_S7的事件数量与M_S（BB）大于M_S7的事件接近;新M_L较传统M_L更符合区域地质实际状况,新m_b较传统m_b更便于测量,M_S（BB）较M_S7、m_B（BB）较m_B更适应当前的宽频带数字地震资料,其测定结果更稳定。新国家标准震级标度充分考虑了我国震级测定的历史连续性,很好地继承和衔接了传统震级标度,在可操作性和资料适用性方面有极大提高。      

Multiple scales in auroral plasmas

A review of the observed space scales of the auroral features ranging from the whole auroral oval of bright discrete forms down to the nonlinear moving solitary structures with the scales of the order of Debye length is given. The characteristic physical scale which determines the generation process is indicated whenever possible. Some problems of the auroral theory and modeling are briefly discussed, and a cross-scale coupling between the auroral and magnetospheric altitudes is stressed. It becomes apparent that the first in situ studied real astrophysical plasma object—the Earth's magnetosphere/ionosphere/aurora—is a unified multi-scale system which seems to be ordered at large scales, but sometimes looks as nearly nondeterministic, or chaotic, at small scales. The most powerful processes in this system operate in a very wide range of scales, with multifarious cross-scale couplings. The statistical behavior of magnetospheric/auroral plasmas in the regions of active auroras often can be reasonably described as the near-critical state.     

传统与现代震级标度

首先阐述并比较传统震级(M_L、m_b、m_B、M_S及M_JMA)所用数据、计算方法及适用范围,系统梳理两种现代震级标度M_e和M_W的理论基础及计算方法。然后根据使用数据及适用场景不同,介绍M_WW、M_WC、M_Wb、M_wp及M_dt等矩震级测定方法;同时,随着越来越丰富的GPS观测数据,基于高频GPS观测也越来越多地被用于地震震级快速测定工作。最后对这些震级测定方法的时效性进行对比分析,讨论不同震级标度的适用场景及其稳定性。     

Tsunami simulations on several scales

The tsunami event generated by the great Sumatra–Andaman earthquake on 26 December 2004 was simulated with the recently developed model TsunAWI. The model is based on the finite element method, which allows for a very flexible discretization of the model domain. This is demonstrated by a triangulation of the whole Indian Ocean with a resolution of about 14 km in the deep ocean but a considerably higher resolution of about 500 m in the coastal area. A special focus is put on the Banda Aceh region in the Northern tip of Sumatra. This area was heavily hit by the tsunami and the highest resolution in this area is about 40 m in order to include inundation processes in the model simulation. We compare model results to tide gauge data from all around the Indian Ocean, to satellite altimetry, and field measurements of flow depth in selected locations of the Aceh region. Furthermore, we compare the model results of TsunAWI to the results of a nested grid model (TUNAMI-N3) with the same initial conditions and identical bathymetry and topography in the Aceh region. It turns out that TsunAWI gives accurate estimates of arrival times in distant locations and in the same mesh gives good inundation results when compared to field measurements and nested grid results.     

Space-Time scales of internal waves

Abstract

We have contrived a model E(αω) α μ^?1ω^?p+1(ω ²?ω _i ²)^?+ for the distribution of internal wave energy in horizontal wavenumber, frequency-space, with wavenumber α extending to some upper limit μ(ω) α ω ^r-1 (ω ²?ω _i ²)^½, and frequency ω extending from the inertial frequency ω _i to the local Väisälä frequency n(y). The spectrum is portrayed as an equivalent continuum to which the modal structure (if it exists) is not vital. We assume horizontal isotropy, E(α, ω) = 2παE(α₁, α₂, ω), with α₁, α₂ designating components of α. Certain moments of E(α₁, α₂, ω) can be derived from observations. (i) Moored (or freely floating) devices measuring horizontal current u(t), vertical displacement η(t),…, yield the frequency spectra F _(u,η,…)(ω) = ∫∫ (U ², Z ²,…)E(α₁, ∞₂, ω) dα₁ dα₂, where U, Z,… are the appropriate wave functions. (ii) Similarly towed measurements give the wavenumber spectrum F _(…)(α1) = ∫∫… dα₂ dω. (iii) Moored measurements horizontally separated by X yield the coherence spectrum R(X, ω) which is related to the horizontal cosine transform ∫∫ E(α1, α2 ω) cos α₁ Xdα₁ dα₁. (iv) Moored measurements vertically separated by Y yield R(Y, ω) and (v) towed measurements vertically separated yield R(Y, α₁), and these are related to similar vertical Fourier transforms. Away from inertial frequencies, our model E(α, ω) α ω ^?p-r for α ≦ μ ω ω ^r, yields F(ω) ∞ ω ^?p, F(α₁) ∞ α₁ ^?q, with q = (p + r ? 1)/r. The observed moored and towed spectra suggest p and q between 5/3 and 2, yielding r between 2/3 and 3/2, inconsistent with a value of r = 2 derived from Webster's measurements of moored vertical coherence. We ascribe Webster's result to the oceanic fine-structure. Our choice (p, q, r) = (2, 2, 1) is then not inconsistent with existing evidence. The spectrum is E(∞, ω) ∞ ω ^?1(ω ²?ω _i ^{2 ?1}, and the α-bandwith μ ∞ (ω ²?ω _i ²)⁺ is equivalent to about 20 modes. Finally, we consider the frequency-of-encounter spectra F([sgrave]) at any towing speed S, approaching F(ω) as S ≦ S _o, and F(α₁) for α₁ = [sgrave]/S as S ≧ S _o, where S _o = 0(1 km/h) is the relevant Doppler velocity scale.     

IASPEI新震级标度与传统震级标度的对比

通过对世界上主要地震台网中心几十年来震级测定结果的对比分析,针对数字地震记录频带宽、动态范围大的特点,国际地震学与地球内部物理学协会（IASPEI）震级工作组于2003年提出了新的震级标度和测定方法,新的震级标度包括地方性震级ML、面波震级Msc（20）和Ms（BB）、体波震级mb和mB、区域Lg震级mb（Lg）和矩震级MW,本文介绍了这些新震级及其测定方法,并将这些震级与我国传统震级mb、mB、MS7、Ms在计算公式、振幅量取、周期范围和震中距范围几个方面进行了详细的比较。     

The comparison of macroseismic intensity scales

The number of different macroseismic scales that have been used to express earthquake shaking in the course of the last 200 years is not known; it may reach three figures. The number of important scales that have been widely adopted is much smaller, perhaps about eight, not counting minor variants. Where data sets exist that are expressed in different scales, it is often necessary to establish some sort of equivalence between them, although best practice would be to reassign intensity values rather than convert them. This is particularly true because difference between workers in assigning intensity is often greater than differences between the scales themselves, particularly in cases where one scale may not be very well defined. The extent to which a scale guides the user to arrive at a correct assessment of the intensity is a measure of the quality of the scale. There are a number of reasons why one should prefer one scale to another for routine use, and some of these tend in different directions. If a scale has many tests (diagnostics) for each degree, it is more likely that the scale can be applied in any case that comes to hand, but if the diagnostics are so numerous that they include ones that do not accurately indicate any one intensity level, then the use of the scale will tend to produce false values. The purpose of this paper is chiefly to discuss in a general way the principles involved in the analysis of intensity scales. Conversions from different scales to the European Macroseismic Scale are discussed.     

A comparison of two radiometric scales

Summary A comparison has been made of the radiometric scale maintained by the National Standards Laboratory of Australia and the International Pyrheliometric Scale 1956 as currently maintained in Australia. The scales appear to differ by 1.4 per cent, the value assigned to a given irradiance by the National Standards Laboratory being the higher.     

Understanding fen hydrology across multiple scales

Fens, which are among the most biodiverse of wetland types in the USA, typically occur in glacial landscapes characterized by geo‐morphologic variability at multiple spatial scales. As a result, the hydrologic systems that sustain fens are complex and not well understood. Traditional approaches for characterizing such systems use simplifying assumptions that cannot adequately capture the impact of variability in geology and topography. In this study, a hierarchical, multi‐scale groundwater modelling approach coupled with a geologic model is used to understand the hydrology of a fen in Michigan. This approach uses high‐resolution data to simulate the multi‐scale topographic and hydrologic framework and lithologic data from more than 8500 boreholes in a statewide water well database to capture the complex geology. A hierarchy of dynamically linked models is developed that simulates groundwater flow at all scales of interest and to delineate the areas that contribute groundwater to the fen. The results show the fen receiving groundwater from multiple sources: an adjacent wetland, local recharge, a nearby lake and a regional groundwater mound. Water from the regional mound flows to an intermediate source before reaching the fen, forming a ‘cascading’ connection, while other sources provide water through ‘direct’ connections. The regional mound is also the source of water to other fens, streams and lakes in this area, thus creating a large, interconnected hydrologic system that sustains the entire ecosystem. In order to sustainably manage such systems, conservation efforts must include both site‐based protection and management, as well as regional protection and management of groundwater source areas. Copyright © 2016 John Wiley & Sons, Ltd.     

Sub-kilometer length scales in coastal waters

Patchiness or spatial variability is ubiquitous in marine systems. With increasing anthropogenic impacts to coastal resources and coastal systems being disproportionately large contributors to ocean productivity, identifying the spatial scales of this patchiness, particularly in coastal waters, is of critical importance to understand coastal ecosystem dynamics. The current work focuses on fine scale structure in three coastal regions. More specifically, we utilize variogram analyses to identify sub-kilometer scales of variability in biological and physical parameters measured by an autonomous underwater vehicle (AUV) in the Mid-Atlantic Bight, Monterey Bay, and in San Luis Obispo Bay between 2001 and 2004. Critical scales of variability in density, turbidity, fluorescence, and bioluminescence are examined as a function of depth and distance offshore. Furthermore, the effects of undersampling are assessed using predictive error analysis. Results indicate the presence of scales of variability ranging from 10s to 100s of meters and provide valuable insight for sampling design and resource allocation for future studies.     

完整岩石在不同尺度上的屈服

对完整岩石力学机制的研究有助于更好地理解与屈服有关的应力-应变关系。屈服准则研究方法包括基于实验数据分析和基于微观力学的研究。屈服数学理论的研究目标是对应力和应变关系的理论描述和对弹塑性界限的识别。本文主要研究完整岩石在不同尺度上的屈服。从Weibull理论可知,岩石强度随尺度增大而减少,这已经通过单轴压缩强度（UCS）的Hoek-Brown方程得到证实。然而,围压能改变岩石强度及屈服。因此,本文利用直径为50mm和96mm的圆柱形砂岩样品在不同围压作用下的压缩实验来研究不同尺度下的岩石屈服,从实验中提取不同尺度下的屈服初始点并描述屈服面,最终给出简单数学形式的屈服准则。     

关于震级标度的讨论

就震级标度的一些议题提出看法,包括震级的国家标准、多种震级标度的存在、“全覆盖”震级、不同震级标度的换算、震级的校准等.文中还对改善震级测定工作提出了建议.     

The Mercalli family of seismic intensity scales

Measurement theory is applied to the seismic intensity scales for the purpose of classifying them. Some basic tenets of scale classification are discussed, along with properties of scales of different ranks. The seismic scale is tested for uniformity. It is shown that the Mercalli-type seismic intensity scales at present in use have the rank of an interval scale, thus proving that arithmetic operations can be applied to macroseismic estimates expressed in the standard intensity grades.     

Estimating restorable wetland water storage at landscape scales

Globally, hydrologic modifications such as ditching and subsurface drainage have significantly reduced wetland water storage capacity (i.e., volume of surface water a wetland can retain) and consequent wetland functions. While wetland area has been well documented across many landscapes and used to guide restoration efforts, few studies have directly quantified the associated wetland storage capacity. Here, we present a novel raster‐based approach to quantify both contemporary and potential (i.e., restorable) storage capacities of individual depressional basins across landscapes. We demonstrate the utility of this method by applying it to the Delmarva Peninsula, a region punctuated by both depressional wetlands and drainage ditches. Across the entire peninsula, we estimated that restoration (i.e., plugging ditches) could increase storage capacity by 80%. Focusing on an individual watershed, we found that over 59% of restorable storage capacity occurs within 20 m of the drainage network, and that 93% occurs within 1 m elevation of the drainage network. Our demonstration highlights widespread ditching in this landscape, spatial patterns of both contemporary and potential storage capacities, and clear opportunities for hydrologic restoration. In Delmarva and more broadly, our novel approach can inform targeted landscape‐scale conservation and restoration efforts to optimize hydrologically mediated wetland functions.     

Estimating ventilation time scales using overturning stream functions

A simple method for estimating ventilation time scales from overturning stream functions is proposed. The stream function may be computed using either geometric coordinates or a generalized vertical coordinate, such as potential density (salinity in our study). The method is tested with a three-dimensional circulation model describing an idealized semi-enclosed ocean basin ventilated through a narrow strait over a sill, and the result is compared to age estimates obtained from a passive numerical age tracer. The best result is obtained when using the stream function in salinity coordinates. In this case, the reservoir-averaged advection time obtained from the overturning stream function in salinity coordinates agrees rather well with the mean age of the age tracer, and the corresponding maximum ages agree very well.     

Solute transport scales in an unsaturated stony soil

Solute transport parameters are known to be scale-dependent due mainly to the increasing scale of heterogeneities with transport distance and with the lateral extent of the transport field examined. Based on a transect solute transport experiment, in this paper we studied this scale dependence by distinguishing three different scales with different homogeneity degrees of the porous medium: the observation scale, transport scale and transect scale. The main objective was to extend the approach proposed by van Wesenbeeck and Kachanoski to evaluating the role of textural heterogeneities on the transition from the observation scale to the transport scale. The approach is based on the scale dependence of transport moments estimated from solute concentrations distributions. In our study, these moments were calculated starting from time normalized resident concentrations measured by time domain reflectometry (TDR) probes at three depths in 37 soil sites 1 m apart along a transect during a steady state transport experiment. The Generalized Transfer Function (GTF) was used to describe the evolution of apparent solute spreading along the soil profile at each observation site by analyzing the propagation of the moments of the concentration distributions. Spectral analysis was used to quantify the relationship between the solid phase heterogeneities (namely, texture and stones) and the scale dependence of the solute transport parameters. Coupling the two approaches allowed us to identify two different transport scales (around 4-5 m and 20 m, respectively) mainly induced by the spatial pattern of soil textural properties. The analysis showed that the larger transport scale is mainly determined by the skeleton pattern of variability. Our analysis showed that the organization in hierarchical levels of soil variability may have major effects on the differences between solute transport behavior at transport scale and transect scale, as the transect scale parameters will include information from different scales of heterogeneities.     

大尺度地幔动力学研究的现状和展望

这篇综述讨论大空间、大时间尺度的地幔动力学近几十年的发展和现状,着重讨论了相关的观测及其动力学意义.这些观测包括现在地球的板块运动的基本特性,中、长波重力异常及大地水准面异常,地震层析成像得到的地幔结构,以及过去10亿年超级大陆Pangea和Rodinia的形成、裂解和演化,及火山岩浆活动.关于地球动力学模型的讨论是围绕着这些相关的观测而进行的.涉及到的一些主要问题包括以下.第一,地幔动力学研究显示,地震层析成像得到的下地幔的二阶结构（比如核幔边界附近的LLSVP结构）,和俯冲带的快速异常体,可以解释为过去1亿年左右的板块运动和地幔对流的结果;第二,地幔三维结构作为地幔对流的驱动力,是导致中、长波重力及大地水准面异常的直接原因;结合地幔动力学模拟,观测的大地水准面异常对地幔黏性结构提供了强有力的约束,很可靠的结果之一是下地幔的黏性比上地幔要高至少一个量级,并且最近的研究确定软流圈的存在;第三,过去10亿年大陆块体经历过的Rodinia和Pangea两期超级大陆的形成和破裂是地幔动力学在地表的反映.地幔结构在Pangea形成过程中是一阶结构（即一个半球是冷的下降流,而另一个半球是热的上涌流）主导的,而现在的二阶为主导的地幔结构是Pangea形成后,破裂前或破裂过程中才形成的;地幔动力学和其他研究支持地幔结构在一阶和二阶间转换的1-2-1模型;第四,板块构造在地球上的起源和动力机制依然是充满争议和不确定的课题,但是这些问题同时也是重要的地球动力学基本问题.