Formation and Suppression of Strike–Slip Fault Systems

Strike–slip faults are a defining feature of plate tectonics, yet many aspects of their development and evolution remain unresolved. For intact materials and/or regions, a standard sequence of shear development is predicted from physical models and field studies, commencing with the formation of Riedel shears and culminating with the development of a throughgoing fault. However, for materials and/or regions that contain crustal heterogeneities (normal and/or thrust faults, joints, etc.) that predate shear deformation, kinematic evolution of strike–slip faulting is poorly constrained. We present a new plane-stress finite-strain physical analog model developed to investigate primary deformation zone evolution in simple shear, pure strike–slip fault systems in which faults or joints are present before shear initiation. Experimental results suggest that preexisting mechanical discontinuities (faults and/or joints) have a marked effect on the geometry of such systems, causing deflection, lateral distribution, and suppression of shears. A lower limit is placed on shear offset necessary to produce a throughgoing fault in systems containing preexisting structures. Fault zone development observed in these experiments provides new insight for kinematic interpretation of structural data from strike–slip fault zones on Earth, Venus, and other terrestrial bodies.     

Flood–ebb and spring–neap variations of mixing,stratification and circulation in Chesapeake Bay

A three-dimensional hydrodynamic model is used to investigate intra-tidal and spring–neap variations of turbulent mixing, stratification and residual circulation in the Chesapeake Bay estuary. Vertical profiles of salinity, velocity and eddy diffusivity show a marked asymmetry between the flood and ebb tides. Tidal mixing in the bottom boundary layer is stronger and penetrates higher on flood than on ebb. This flood–ebb asymmetry results in a north–south asymmetry in turbulent mixing because tidal currents vary out of phase between the lower and upper regions of Chesapeake Bay. The asymmetric tidal mixing causes significant variation of salinity distribution over the flood–ebb tidal cycle but insignificant changes in the residual circulation. Due to the modulation of tidal currents over the spring–neap cycle, turbulent mixing and vertical stratification show large fortnightly and monthly fluctuations. The stratification is not a linear function of the tidal-current amplitude. Strong stratification is only established during those neap tides when low turbulence intensity persists for several days. Residual circulation also shows large variations over the spring–neap cycle. The tidally averaged residual currents are about 50% stronger during the neap tides than during the spring tides.     

Dynamic response of structures subjected to pounding and structure–soil–structure interaction

During strong earthquakes, adjacent structures with non-sufficient clear distances collide with each other. In addition to such a pounding, cross interaction of adjacent structures through soil can exchange the vibration energy between buildings and make the problem even more complex. In this paper, effects of both of the mentioned phenomena on the inelastic response of selected steel structures are studied. Number of stories varied between 3 and 12 and different clear distances up to the seismic codes prescribed value are considered. The pounding element is modeled within Opensees. A coupled model of springs and dashpots is utilized for through-the-soil interaction of the adjacent structures, for two types of soft soils. The pounding force, relative displacements of stories, story shears, and plastic hinge rotations are compared for different conditions as the maximum responses averaged between seven consistent earthquakes. As a result, simultaneous effects of pounding and structure–soil–structure interaction are discussed.     

Ottoman archives and the assessment of the seismicity of Greece 1456–1833

This article examines the contribution of Ottoman sources of historical information for the study of the seismicity of Greece, in particular of Athens during the period of the Ottoman domination, a period during which relatively few original Greek sources of data are available. An annotated list of a number of case histories of earthquakes in Greece from Ottoman sources is presented translating only a summary of the information for those who want to access the whole document. They contain not only a valuable record of earthquakes, but also, for the earthquake historian, a wealth of information about locations where earthquakes were not felt. The article discusses the effects of earthquakes, of the 1826–7 siege on the Acropolis its purpose being to provide information with such annotation as would facilitate its use by engineering seismologists with additional macroseismic data that could supplement the rather meagre information.     

Using GPS–GLONASS–GALILEO data and IRI modeling for ionospheric calibration of radio telescopes and radio interferometers

VHF and HF radio signals are widely used to observe the Sun and pulsars. Nowadays, large low-frequency radio astronomical arrays (LOFAR, 30–240 MHz; MIRA, 80–300 MHz) are being constructed to record radiation of pulsars at the maximum distance. registration of the solar radio emission intensity at fixed frequencies and in the spectral VHF band is very important along with other methods of monitoring of coronal mass ejections. Interpreting radio astronomical data is known to be necessary to take into account possible distortions of these signals in the Earth ionosphere. However, in contrast to modern navigation systems (Global Position System (GPS), GLObal NAvigation Satellite System (GLONASS), GALILEO), in which a very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ionosphere transfer characteristics has not been appropriately worked out. This collides with increasing requirements to accuracy of the analysis of a radio emission amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation (LOFAR, SKA, etc.). We have developed a method and software to calculate the ionosphere rotation measure (RM) and dispersion measure (DM). We used the ionosphere model IRI-2001, magnetic field model IGRF-10, and the ionosphere total electron content values obtained from GPS measurements. The obtained values of DM and RM were recalculated into characteristics of the phase delay, Faraday amplitude modulation, and polarization changes. We calculated ones for different levels of geomagnetic activity as well as different angular positions of radio sources. Our main idea is to use a signal of navigation satellites (GPS, GLONASS, GALILEO) as a testing signal from a “reference” source located at minimal angle distance from a source studied. Our project allows development of methods and systems of ADAPTIVE RADIO ASTRONOMY, adaptive to the non-uniform and non-stationary ionosphere, by analogy with known systems of adaptive optics intended to adapt optical telescopes to varying conditions of the optically non-uniform and non-stationary troposphere.     

Evaluation of static and dynamic properties of sand–fines mixtures through the state and equivalent state parameters

The results of an experimental investigation on sands with low plastic fines content are presented. Specimens with a low plastic fines content of 0%, 15%, 30%, 40%, 50% and 60% by weight were tested in drained and undrained triaxial compression tests. The soil specimens were tested under three different categories: (1) at a constant void ratio index; (2) at the same peak deviator stress in a triaxial test; and (3) at a constant relative density. By a combination with our published experimental data in recent years, the critical state line and various state parameters have been proposed and discussed for a further understanding the behavior of sand–fines mixtures. Results indicated that a unique critical line was obtained from drained and undrained triaxial compression tests for each fines content. The effects of fines content on critical state line (CSL) were recognized and discussed. In addition, the results revealed that normalized peak undrained shear stress, cyclic resistance ratio, and compression index were found to be a good correlation with state parameter Ψ as well as equivalent state parameter Ψ*. An increasing state parameter decreased the normalized peak undrained shear stress, and cyclic resistance ratio; however, the compression index increased with an increase in state parameter. Finally, there were no correlations such as the coefficient of consolidation–state parameter and maximum shear modulus–state parameter due to the different testing condition.     

Numerical simulation of surf–swash zone motions and turbulent flow

A two-dimensional numerical model was presented for the simulation of wave breaking, runup and turbulence in the surf and swash zones. The main components of the model are the Reynolds-Averaged Navier–Stokes equations describing the average motion of a turbulent flow, a k–ε turbulence closure model describing the transformation and dissipation processes of turbulence and a volume of fluid technique for tracking the free surface motion. Nearshore wave evolution on a sloping bed, the velocity field and other wave characteristics were investigated. First, the results of the model were compared with experimental results for different surf zone hydrodynamic conditions. Spilling and plunging breakers were simulated and the numerical model investigated for different wave parameters. The turbulence field was also considered and the spatial and time-dependent variations of turbulence parameters were discussed. In the next stage of the study, numerical results were compared with two sets of experimental data in the swash zone. Generally, there is good agreement except for turbulence predictions near the breaking point where the model does not represent well the physical processes. On the other hand, turbulence predictions were found to be excellent for the swash zone. The model provides a precise and efficient tool for the simulation of the flow field and wave transformations in the nearshore, especially in the swash zone. The numerical model can simulate the surface elevation of the vertical shoreline excursion on sloping beaches, while swash–swash interactions within the swash zone are accounted for.     

Four decades of geomagnetic and solar activity: 1960–2001

We analyze the relationship between some space weather indices (Dst, Ap, F10.7) and geomagnetic effects on the regional (European) scale, over the period 1960–2001. The remaining external field signal (RES) detected in the Northward magnetic component of the European observatory annual means are used as an indicator of the regional geomagnetic activity. Relationship RES-F10.7 suggests correction factors for getting the geomagnetic annual means of the Northern component less affected by the external sources. We have found some time lags among investigated parameters. These delays may suggest that the Ap responds to the solar activity in a differently than Dst and RES, Ap being more sensitive to the high-speed streams (HSS) and the Alfvenic waves present in HSS, while Dst and RES being more influenced by the coronal mass ejections activity (CME).     

Bayesian estimation of intensity–duration–frequency curves and of the return period associated to a given rainfall event

Intensity–duration–frequency (IDF) curves are used extensively in engineering to assess the return periods of rainfall events and often steer decisions in urban water structures such as sewers, pipes and retention basins. In the province of Québec, precipitation time series are often short, leading to a considerable uncertainty on the parameters of the probabilistic distributions describing rainfall intensity. In this paper, we apply Bayesian analysis to the estimation of IDF curves. The results show the extent of uncertainties in IDF curves and the ensuing risk of their misinterpretation. This uncertainty is even more problematic when IDF curves are used to estimate the return period of a given event. Indeed, standard methods provide overly large return period estimates, leading to a false sense of security. Comparison of the Bayesian and classical approaches is made using different prior assumptions for the return period and different estimation methods. A new prior distribution is also proposed based on subjective appraisal by witnesses of the extreme character of the event.     

Ecological–Geochemical Conditions of Surface Water and Groundwater and Estimation of the Anthropogenic Effect in the Basin of the Ganjiang River

Water Resources - Data of studies of 2013–2019 were used to assess the current environmental-geochemical conditions of surface water and groundwater in the basin of the Ganjiang River, the...     

Asymmetry of Sunspot Distribution in Solar Cycles 12–24 and the Gnevyshev–Ohl Rule

Geomagnetism and Aeronomy - The nonaxisymmetric component of the sunspot distribution (longitudinal asymmetry) is considered based on the Greenwich–USAF/NOAA data for 1874–2016. Vector...     

Simulation and control of the linked systems of water quantity–water quality–socio-economics in the Huaihe River basin

Abstract

This work makes explicit an algebraic expression giving the matrix of transient influence coefficients associated with a one-dimensional semi-confined aquifer model. The domain studied is divided into a series of connected and completely mixed compartments over which the governing equation is discretized. The discrete equations obtained are solved for the compartmental hydraulic head and used to derive the algebraic expression in question. The basic properties of the so-called algebraic influence coefficients are investigated. In particular, their consistency with the exact Green function is highlighted. Finally, the newly derived influence coefficients are applied to a simplified aquifer system in order to formulate and solve the problem of identifying illegal groundwater pumping.     

Trends and discontinuities in regional rainfall of West and Central Africa: 1951–1989

Abstract

Standardized regional mean annual rainfall series are analysed over the period 1951–1989 from a data set of 891 rainfall stations which covers 23 countries of West and Central Africa. Missing values are estimated by using regionalized indexes computed on the basis of a morpho-climatic delimitation of 44 homogeneous climatic units. Searches for statistical discontinuities in rainfall series show no discontinuity for most units of Central Africa. For several units of West Africa the first discontinuity occurs at the end of the 1950s. The main discontinuity period occurs between 1968 and 1970, followed by a second one at the beginning of the 1980s. Rainfall deficit is greater north of 10°N, and is also important in the Guinean Mountains and on the northern coast of the Gulf of Guinea, west of the Atakora Mountains. Regions leeward of mountainous areas experienced moderate rainfall decrease.     

Amplitude–frequency characteristics of ion–cyclotron and whistler-mode waves from Van Allen Probes data

Using two-hour (from 2300 UT January 25, 2013 to 0100 UT January 26, 2013) measurement data from Van Allen Probes on fluxes of energetic particles, cold plasma density, and magnetic field magnitude, we have calculated the local growth rate of electromagnetic ion–cyclotron and whistler-mode waves for field-aligned propagation. The results of these calculations have been compared with wave spectra observed by the same Van Allen Probe spacecraft. The time intervals when the calculated wave increments are sufficiently large, and the frequency ranges corresponding to the enhancement peak agree with the frequency–time characteristics of observed electromagnetic waves. We have analyzed the influence of variations in the density and ionic composition of cold plasma, fluxes of energetic particles, and their pitch-angle distribution on the wave generation. The ducted propagation of waves plays an important role in their generation during the given event. The chorus VLF emissions observed in this event cannot be explained by kinetic cyclotron instability, and their generation requires much sharper changes (“steps”) for velocity distributions than those measured by energetic particle detectors on Van Allen Probes satellites.     

Role of wave–mean flow interaction in sun–climate connections: Historical overview and some new interpretations and results

Quasi-decadal variations in solar irradiance – termed the 11-year solar cycle (SC) – have been linked to variations in a variety of atmospheric circulation features, including the polar vortex, the Brewer–Dobson circulation, and the quasi-biennial oscillation. These features share an underlying commonality: they are all rooted in wave–mean flow interaction. The purpose of this paper is to provide a historical overview of the connection between the SC and wave–mean flow interaction and to propose a more complete theoretical framework for solar modulated wave–mean flow interaction that includes both zonal-mean and zonally asymmetric ozone as intermediaries for communicating variations in solar spectral irradiance to the climate system. We solve a quasi-geostrophic model using the WKB formalism to highlight the physics connecting the SC to planetary wave-drag. Numerical results show the importance of the zonally asymmetric ozone field in mediating the effects of solar variability to the wave-driven circulation in the middle atmosphere.     

Equivalent linear substructure approximation of soil–foundation–structure interaction: model presentation and validation

An equivalent linear substructure approximation of the soil–foundation–structure interaction is proposed in this paper. Based on the inherent linearity of the approach, the solution of the structural and the soil domain is obtained simultaneously, incorporating the effects of the primary and secondary soil nonlinearities. The proposed approximation is established theoretically and then validated against centrifuge benchmark soil–foundation–structure interaction tests. The equivalent linear substructure approximation is proved to simulate efficiently the effects of the nonlinear soil behavior on the soil–foundation–structure system under a strong earthquake ground motion.     

Some characteristics and precipitation effects of the El Niño of 1997–1998

The 1997–1998 El Niño was the strongest in known history. However, its effects on rainfall in different parts of the globe were not all as expected (floods were expected in some regions and droughts in others). The characteristics of this El Niño, and the expected and observed precipitation effects are described; the reasons for the expectations not coming true in some regions are discussed. This paper attempts to review the important scientific issues involved in El Niño phenomena for the general reader.