Attenuation of P,S, and coda waves in Koyna region,India

The attenuation properties of the crust in the Koyna region of the Indian shield have been investigated using 164 seismograms from 37 local earthquakes that occurred in the region. The extended coda normalization method has been used to estimate the quality factors for P waves and S waves , and the single back-scattering model has been used to determine the quality factor for coda waves (Q _c). The earthquakes used in the present study have the focal depth in the range of 1–9 km, and the epicentral distance vary from 11 to 55 km. The values of and Q _c show a dependence on frequency in the Koyna region. The average frequency dependent relationships (Q = Q ₀ f ⁿ) estimated for the region are , and . The ratio is found to be greater than one for the frequency range considered here (1.5–18 Hz). This ratio, along with the frequency dependence of quality factors, indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of Q _c and in the present study shows that for frequencies below 4 Hz and for the frequencies greater than 4 Hz. This may be due to the multiple scattering effect of the medium. The outcome of this study is expected to be useful for the estimation of source parameters and near-source simulation of earthquake ground motion, which in turn are required in the seismic hazard assessment of a region.     

An Empirical Model for Significant Duration of the Ground Motions Containing Velocity Pulses

Izvestiya, Physics of the Solid Earth - ln this study, two relationships have been presented for predicting the significant duration values $$({{D}_{{s5 - 75}}}$$ and $${{D}_{{s5 - 95}}})~$$ of...     

Prediction of $$\hbox {PM}_{2.5}$$PM2.5 concentration based on weighted bagging and image contrast-sensitive features

Stochastic Environmental Research and Risk Assessment - In this paper, we propose an effective method of $$\hbox {PM}_{2.5}$$ prediction based on image contrast-sensitive features and weighted...     

Basaltic thermals and Subplinian plumes: Constraints from acoustic measurements at Shishaldin volcano, Alaska

The 1999 basaltic eruption of Shishaldin volcano (Alaska, USA) included both Strombolian and Subplinian activity, as well as a “pre-Subplinian” phase interpreted as the local coalescence within a long foam in the conduit. Although few visual observations were made of the eruption, a great deal of information regarding gas velocity, gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption. By relating acoustic power to gas velocity, a time series of gas velocity is calculated for the Subplinian and pre-Subplinian phases. These time series show trends in gas velocity that are interpreted as plumes or, for those signals lasting only a short time, thermals. The Subplinian phase is shown to be composed of a thermal followed by five plumes with a total expelled gas volume of .The initiation of the Subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column. A gradual increase in low-frequency (0.01–0.5 Hz) signal prior to this “trigger bubble” may be due to the rise of the bubble in the conduit. This delay corresponds to a reservoir located at ≈3.9 km below the surface, in good agreement with studies on other volcanoes.The presence of two thermal phases is also identified in the middle of the pre-Subplinian phase with a total gas release of and . Gas velocity at the vent is found to be and for the Subplinian plumes and the pre-Subplinian thermals respectively.The agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements, leading to a new method by which eruption physical parameters may be quantified. Furthermore, direct measurements of gas velocity can be used for better estimates of the flux released during the eruption.     

Characteristics of rain electricity in Nigeria II — Experimental and theoretical relations

Analysis of data, covering four rainy seasons, of rain current, point-discharge current and potential gradient reveal novel relations in the form (i) $$Q_{r + } /Q_{r - } = k_1 (T_{r + } /T_{r - } )^{1.1} $$ for rain charge and duration ratios; and (ii) $$Q_{p - } /Q_{p + } = k_2 (T_{p - } /T_{p + } )^{1.1} $$ for point charge and duration ratios, where thek's are constants; and (iii) $$i_r = - \alpha (i_p - c)$$ for rain and point-discharge current densities, where α has the same value for all types of rain andc is a constant controlled by the rainfall intensityR. For rain not associated with point discharge the relation takes the familiar form $$i_r = - AR(E - \bar E)$$ Theoretical values are obtained for \ga andA on the basis of the Wilson ion-capture theory as worked out in detail by Whipple and Chalmers.     

Attenuation relations for strong seismic ground motion in the Himalayan region

Strong motion data from various regions of India have been used to study attenuation characteristics of horizontal peak acceleration and velocity. The strong ground motion data base considered in the present work consists of various earthquakes recorded in the northern part of India since 1986 with magnitudes 5.7 to 7.2. Using these data, relations for horizontal peak acceleration and velocity, which are $$\begin{gathered} log_{10} a = 1.14 + 0.31M + 0.65log_{10} R \hfill \\ log_{10} v = 0.571 + 0.41M + 0.768log_{10} R \hfill \\ \end{gathered} $$ have been proposed wherea is the peak horizontal acceleration in cm/sec²,v is the peak horizontal velocity in mm/sec,M is body wave magnitude, andR is the hypocentral distance in km. The proposed relations are in reasonable agreement with the small amount of strong ground motion data available for the northern part of India. The present results will be useful in estimating strong ground motion parameters and in the earthquake resistant design in the Himalayan region.     

“Pandora box” — Matrix in the calculus of observations

Summary If the condition R(A)=k(n), whereA is the design matrix of the type n × k and k the number of parameters to be determined, is not satisfied, or if the covariance matrixH is singular, it is possible to determine the adjusted value of the unbiased estimable function of the parameters f(), its dispersion D( (x)) and ² as the unbiased estimate of the value of ² by means of an arbitrary g-inversion of the matrix . The matrix , because of its remarkable properties, is called the Pandora Box matrix. The paper gives the proofs of these properties and the manner in which they can be employed in the calculus of observations.     

Calculating the azimuth of mountain waves, using the effect of tilted fine-scale stable layers on VHF radar echoes

A simple method is described, based on standard VHF wind-profiler data, where imbalances of echo power between four off-vertical radar beams, caused by mountain waves, can be used to calculate the orientation of the wave pattern. It is shown that the mountain wave azimuth (direction of the horizontal component of the wavevector), is given by the vector are radar echo powers, measured in dB, in beams pointed away from vertical by the same angle towards north, south, east and west respectively, and W is the vertical wind velocity. The method is applied to Aberystwyth MST radar data, and the calculated wave vector usually, but not always, points into the low-level wind direction. The mean vertical wind at Aberystwyth, which may also be affected by tilted aspect-sensitive layers, is investigated briefly using the entire radar output 1990–1997. The mean vertical-wind profile is inconsistent with existing theories, but a new mountain-wave interpretation is proposed.     

An algorithm for the optimum distribution of a regional seismic network — II. An analysis of the accuracy of location of local earthquakes depending on the number of seismic stations

Summary Seven optimal networks consisting of 4 to 10 stations are compared for a given region, where velocity-depth profiles and the distribution of seismic intensity are known. Assuming that the standard error of arrival time is _t =0.05 s and the standard errors of the parameters of velocity-depth profiles are equal to 5% of their values, the average standard errors of the origin time and focus coordinates are estimated. The application of optimum methods to the planning of seismic networks in the Lublin Coal Basin is presented, and maps of standard errors of origin time , depth and epicenter ( _xy ) for the case of an optimum network of 6 seismic stations are given.     

Comparative soil CO2 flux measurements and geostatistical estimation methods on Masaya volcano, Nicaragua

We present a comparative study of soil CO₂ flux () measured by five groups (Groups 1–5) at the IAVCEI-CCVG Eighth Workshop on Volcanic Gases on Masaya volcano, Nicaragua. Groups 1–5 measured using the accumulation chamber method at 5-m spacing within a 900 m² grid during a morning (AM) period. These measurements were repeated by Groups 1–3 during an afternoon (PM) period. Measured ranged from 218 to 14,719 g m⁻² day⁻¹. The variability of the five measurements made at each grid point ranged from ±5 to 167%. However, the arithmetic means of fluxes measured over the entire grid and associated total CO₂ emission rate estimates varied between groups by only ±22%. All three groups that made PM measurements reported an 8–19% increase in total emissions over the AM results. Based on a comparison of measurements made during AM and PM times, we argue that this change is due in large part to natural temporal variability of gas flow, rather than to measurement error. In order to estimate the mean and associated CO₂ emission rate of one data set and to map the spatial distribution, we compared six geostatistical methods: arithmetic and minimum variance unbiased estimator means of uninterpolated data, and arithmetic means of data interpolated by the multiquadric radial basis function, ordinary kriging, multi-Gaussian kriging, and sequential Gaussian simulation methods. While the total CO₂ emission rates estimated using the different techniques only varied by ±4.4%, the maps showed important differences. We suggest that the sequential Gaussian simulation method yields the most realistic representation of the spatial distribution of , but a variety of geostatistical methods are appropriate to estimate the total CO₂ emission rate from a study area, which is a primary goal in volcano monitoring research.Editorial responsibility: H Shinohara     

The challenge of placing in situ magnetotail observations into global context

The last 4 years have seen an explosion of studies of magnetotail structure and dynamics. Growth in our understanding of the coupling of the magnetotail to the inner magnetosphere and ionosphere and the response of the magnetotail to solar wind dynamics has been made possible because of the International Solar Terrestrial Physics (ISTP) program. In addition, the sophistication of global modeling techniques and algorithms have allowed direct comparison of in situ data with realistic global models to understand better not only the general structure of the magnetosphere but also its dynamics. This brief review will discuss in situ observations made during the ISTP era and attempt to place them into a global context. Magnetotail structure and its dynamics due to external and internal drivers will be the main focus.     

The boundary value problem of Poisson’s equation with Stokes’ boundary condition

The following Poisson’s equation with the Stokes’ boundary condition is dealt with $$\left\{ \begin{gathered} \nabla ^2 T = - 4\pi Gp outside S, \hfill \\ \left. {\frac{{\partial T}}{{\partial h}} = \frac{1}{\gamma }\frac{{\partial y}}{{\partial h}}T} \right|_s = - \Delta g, \hfill \\ T = O\left( {r^{ - 3} } \right) at infinity, \hfill \\ \end{gathered} \right.$$ whereS is reference ellipsord. Under spherical approximation transformation, the ellipsoidal correction terms about the boundary condition, the equation and the density in the above BVP are respectively given. Therefore, the disturbing potentialT can he obtained if the magnitudes aboveO(ε⁴) are neglected.     

Complexity,magnetic field topology,criticality, and metastability in magnetotail dynamics

Recently, it has been shown that certain features of magnetotail dynamics in response to solar wind changes may resemble the behavior of a complex system near a dynamical critical state (Chang, Phys. Plasmas 6 (1999) 4137; Consolini and Chang, Space Sci. Rev. 95 (2001) 309), and of topological phase transitions (Chang, Phys. Scr. (2001), 80). Moreover, the impulsive part of the magnetotail response seems to be well described by cellular automata and other simulation models displaying criticality.Here, the relevance of the magnetic field topological disorder will be discussed in connection with observed complexity and near-criticality, showing how the impulsive character of the magnetotail response could be viewed as fluctuation-induced topological transitions among metastable configurations of magnetic field topology.     

Guided waves in the plasma sheet and triggering of a substorm

A guided propagation of magnetoacoustic wave in the plasma sheet located between two lobes of the magnetotail is investigated. The dispersion equation for the wave and equation connecting a disturbance of plasma pressure inside the plasma sheet and amplitude of the plasma sheet boundary oscillations are obtained. For some value of plasma pressure disturbance, the displacement of the plasma sheet boundaries becomes of order of the half-thickness of the plasma sheet. In the case of symmetrical oscillations of the boundaries (“sausage-like” mode), it creates the favorable conditions for reconnection of the magnetic field lines in the magnetotail and may lead to triggering of a substorm. The magnetoacoustic wave may be generated by sudden impulse of the solar wind plasma pressure.     

中磁尾重联触发亚暴的单事例分析

磁层亚暴的发生与近磁尾（约6～8 R_E）电流片中断和中磁尾（约20～30 R_E）磁场重联密切相关,而极光的极向扩展、电流片中断和磁尾重联的时序过程对于认识亚暴的触发机制至关重要. 本文利用位于中磁尾的CLUSTER卫星,同步轨道附近LANL-01、LANL-97卫星,近磁尾POLAR和 极区IMAGE卫星的观测,分析了单个亚暴事例.结果表明,在此事件中,中磁尾磁场重联起始比近尾电流片中断早3 min发生,电流片中断发生4 min后,IMAGE卫星观测到极光增亮,同时AE指数突然增大,亚暴膨胀相起始. 观测结果与亚暴中性线模型较为吻合.     

Application of the Pi theorem to the wear rate of gouge formation in frictional sliding of rocks

A simple law of wear rate is examined for the process of gouge generation during the frictional sliding of simulated faults in rocks, by use of the Pi theorem method (dimensional analysis) and existing experimental data. The relationship between wear rate (t/d) and the applied stress can be expressed by the power-law relations $$\frac{t}{d} = C_\sigma \sigma ^{m\sigma } ,\frac{t}{d} = C_\tau \tau ^{m\tau }$$ wheret is the thickness of the gouge generated on the frictional surfaces,d is the fault displacement, σ and τ are normal stress and shear stress, respectively, andC _σ,C _τ,m _σ andm _τ are constants. These results indicate that the exponent coefficientsm _σ andm _τ and the coefficientsC _σ andC _τ depend on the material hardness of the frictional surfaces. By using the wear rates of natural faults, these power-law relationships may prove to be an acceptable palaeopiezometer of natural faults and the lithosphere.     

Die Berechnung der totalen Menge gelöster Stoffe in Seen

Total content is used mostly for balances. In order to calculate the areas of different depths, the contours are cut out of a topographical map and weighed. The formula is derived from the substance concentration (taken as a linear function of the depth), times the volume of a truncated cone. Content of one layer: $$\frac{{\Delta z}}{{l2}}\left[ {\left( {f_l + f_u } \right)^2 \cdot \left( {c_l + c_u } \right) + 2c_l f_l^2 + 2c_u f_u^2 } \right]$$ f_u Square root of upper area f₁ Square root of lower area c_u Concentration at upper depth c₁ Concentration at lower depth Δz Difference of depths (i.e. thickness of layer) Sum of contents of all layers gives total content of the lake.     

Estimation du débit de SO2, HCl et HF émis par le volcan Vulcano (Italie)

The flow rate of SO₂, HCl and HF was calculated from a transfer coefficient obtained by measuring the concentration of a tracer gas (SF₆) emitted at the plume and analysed down wind with a field gas chromatograph. The results obtained are: $$\begin{gathered} SO_2 = 2.3 \pm 0.4 t/day \hfill \\ HCl = 6.4 \pm 0.4 t/day \hfill \\ HF = 0.11 \pm 0.3 t/day \hfill \\ \end{gathered} $$      

Cluster探测到磁尾等离子体注入的特征

利用Cluster卫星2001～2004年磁尾运行期间RAPID仪器的数据,确定了115例磁尾等离子体注入事件,借助时序叠加法统计研究磁尾等离子体注入现象的特征.注入事件主要分布于磁地方时夜晚20时至凌晨04时.与同步轨道区观测到的粒子注入事件类似,可以将磁尾粒子注入事件分成五类：（1）只有离子注入;（2）离子先于电子注入;（3）离子和电子同时注入;（4）电子先于离子注入;（5）只有电子注入.磁尾粒子注入时,质子（能量范围0～40 keV）的温度和数密度同时显著增加,沿地球径向的传播速度也明显增大.统计分析磁尾注入期间同时观测到的晨昏对流电场,发现电场可分为两类：（A）注入后电场突然增大,电场强度为正;（B）注入后电场突然增大,电场强度为负.利用磁层磁场（T89c）和电场（Volland-Stern）模型模拟粒子注入后赤道面的电漂移速度矢量,模拟结果与统计结果基本一致,表明晨昏对流电场引起的电漂移是驱动磁尾（-18R_EE）等离子体沿地球径向注入的机制之一.