Earthquake hazard and risk assessment based on Unified Scaling Law for Earthquakes: Greater Caucasus and Crimea

We continue applying the general concept of seismic risk analysis in a number of seismic regions worldwide by constructing regional seismic hazard maps based on morphostructural analysis, pattern recognition, and the Unified Scaling Law for Earthquakes (USLE), which generalizes the Gutenberg-Richter relationship making use of naturally fractal distribution of earthquake sources of different size in a seismic region. The USLE stands for an empirical relationship log₁₀N(M, L)?=?A?+?B·(5 – M)?+?C·log₁₀L, where N(M, L) is the expected annual number of earthquakes of a certain magnitude M within a seismically prone area of linear dimension L. We use parameters A, B, and C of USLE to estimate, first, the expected maximum magnitude in a time interval at seismically prone nodes of the morphostructural scheme of the region under study, then map the corresponding expected ground shaking parameters (e.g., peak ground acceleration, PGA, or macro-seismic intensity). After a rigorous verification against the available seismic evidences in the past (usually, the observed instrumental PGA or the historically reported macro-seismic intensity), such a seismic hazard map is used to generate maps of specific earthquake risks for population, cities, and infrastructures (e.g., those based on census of population, buildings inventory). The methodology of seismic hazard and risk assessment is illustrated by application to the territory of Greater Caucasus and Crimea.     

Accounting for site effect in probabilistic assessment of seismic hazard for Romania and Bucharest: a case of deep seismicity in Vrancea zone

The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania and the capital city of Bucharest caused by the Vrancea focal zone (SE-Carpathians). The zone is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depths 60–170 km. The database that was used for the hazard evaluation includes parameters of seismicity, ground-motion source scaling and attenuation models (Fourier amplitude spectra), and site-dependent spectral amplification functions. Ground-motion characteristics were evaluated on the basis of several hundred records from more than 120 small magnitude (M 3.5–5) earthquakes occurred in 1996–2001 and a few tens of acceleration records obtained during four large (M 7.4, 7.2, 6.9 and 6.3) earthquakes. The data provide a basis for probabilistic seismic hazard assessment in terms of peak ground acceleration, peak spectral acceleration and MSK intensity using Fourier amplitude spectra for various exceedance probabilities or average return periods. It has been shown that the influence of geological factors plays very important role in distribution of earthquake ground-motion parameters along the territory of Romania.     

Statistics and characteristic scales for bed load in a channel flow with sidewall effects

Results are presented for a long-duration sediment transport experiment with a plane bed. High-frequency time series of sediment concentration, sediment velocity and solid discharge per unit width were measured using image analysis of video records. A range of transport intensities from a single experiment has been analysed considering transport at different distances from the sidewalls as an independent variable. First and second order temporal statistics of the spatially-averaged values of the transport parameters are presented, which are in agreement with previous studies. A refined statistical analysis of the sediment concentration dynamics, reflecting bed load process, is also given. The characteristic scales of the sediment concentration dynamics are evaluated and analyzed in conjunction with those of the near-bed and bulk flow fields.     

Generalized Tikhonov's algorithm for accurate calculation of one-dimensional transient responses directly in time domain

In the last two decades, forward modelling for the time domain (transient) electromagnetic method has concentrated almost entirely on multi-dimensional models and algorithms. At the same time, the interpretation of real field data is still mainly one dimensional. This is caused by the lack of an efficient multi-dimensional acquisition procedure supported by sufficiently fast and reliable inversion software, on the one hand, and by the great efficiency of one-dimensional field set up and interpretation of the data on the other hand. The latter is particularly true for the short offset transient electromagnetic method, which is much less sensitive to multi-dimensional effects, compared to long offset methods. The most commonly used one-dimensional forward modelling algorithms are based on the spectral method, which requires calculating rapidly oscillating Fourier–Bessel (Hankel) integrals. Due to the very fast decay of short offset responses, the integrals become computationally unstable at late times of the transient process. Although this problem has been successfully solved for practically feasible measurement times of conventional short offset systems using transverse electric and mixed transverse electric and transverse magnetic fields, it turned out crucial for novel methods based on the use of unimodal transverse magnetic fields. These methods are much more sensitive to geoelectric parameters of the Earth in general and those of resistive targets, in particular, but they generate responses, which drop at late times significantly faster than those of conventional methods. Such behaviour of transverse magnetic fields represents severe computational problem for the spectral method, but is successfully solved by direct time domain algorithms. This article describes a generalization of the well-known Tikhonov's solution to a boundary value problem directly in time domain, which is applied to an arbitrary one-dimensional earth model excited by an arbitrary source. Contrary to existing spectral algorithms, the described method allows accurate calculations of both transverse electric and transverse magnetic transient responses at arbitrarily late times. On the other hand, it is more time efficient than finite-difference/finite element direct time domain algorithms and provides analytical late-stage asymptotic solutions.     

Mossman orogenic gold province in north Queensland,Australia: regional metallogenic controls and undiscovered gold endowment

The Hodgkinson and Broken River provinces of the Mossman Orogen in north Queensland host numerous orogenic gold deposits and still remain under-explored. This paper discusses regional metallogenic controls and results of a probabilistic quantitative assessment of undiscovered gold potential in the region. Significant orogenic gold deposits in the region occur only within relatively small well-endowed metallogenic zones, likely to be controlled by the eastern margin of the Paleoproterozoic continental crust underlying the western Mossman Orogen. Three distinct styles of primary orogenic gold deposits are present in the area: gold–quartz veins, refractory gold associated with quartz–pyrite–arsenopyrite veins and stockworks and stibnite–quartz±gold veins. Refractory gold deposits are estimated to have the highest potential for significant undiscovered resources in the region. The Hodgkinson Province is estimated to host between one and ten significant undiscovered refractory gold ore fields, with a 50 % probability of at least 20 t of total contained gold and a 90 % probability of at least 1 t. The Broken River Province is estimated to host up to five significant undiscovered refractory gold ore fields, with a 50 % probability of at least 12 t of contained gold.     

Evaluation of models for Fourier amplitude spectra for the Taiwan region

In the Taiwan region, the empirical spectral models for estimating ground-motion parameters were obtained recently on the basis of recordings of small to moderate (5.0≤M_L≤6.5) earthquakes. A large collection of acceleration records from the M_L=7.3 Chi-Chi earthquake (21 September, 1999) makes it possible to test the applicability of the established relationships in the case of larger events. The comparison of ground-motion parameters (Fourier amplitude spectra, peak accelerations and response spectra), which were calculated using the models, and the observed data demonstrates that the models could provide an accurate prediction for the case of the Chi-Chi earthquake and the largest aftershocks. However, there are some peculiarities in the ground-motion frequency content and attenuation that, most probably, are caused by the features of the rupture process of the large shallow earthquake source.     

Carbon in Russian Soils

Soil carbon densities and pools have been estimated for Russia. The estimate was derived from the generalized version of the soil map of the country at the scale 1:2.5 million (Fridland, 1988), which has been designated a countrywide standard. At the pre-developed stage, the soils in Russia captured about 373 Pg of organic and 75 Pg of inorganic C in the 0–2.0 m layer. Organic C is intensively accumulated in the topsoil. Inorganic C tends to concentrate in deep soils and is of non-pedogenic origin. The mass of organic matter is captured in the tundra, pre-tundra, and the northern and middle taiga of Russia. Anthropogenic impacts have led to a loss of about 5 Pg of C in the 0–1.0 m layer, which is some 2% of the total C content in Russian soils. From this amount, the topsoil of cropland has lost 2.6 Pg (20% of the initial C content in soils), including 0.4 Pg caused by erosion. The deep soil (0.3–1.0 m) of cropland has lost 1 Pg. Some 0.5 Pg of C are removed from the topsoil (7%) and 0.6 Pg by the deep soil from pastures. Forest soils have roughly lost about 0.3 Pg of C due to the decline of C input into soils caused by various disturbances. The predicted climate warming is expected to enhance the C sequestration by soil in Russia.     

Stability Analysis of the Climate-Vegetation System in the Northern High Latitudes

The stability of the climate-vegetation system in the northern high latitudesis analysed with three climate system models of different complexity: A comprehensive 3-dimensional model of the climate system, GENESIS-IBIS, and two Earth system models of intermediate complexity (EMICs), CLIMBER-2 andMoBidiC. The biogeophysical feedback in the latitudinal belt 60–70° N, although positive, is not strong enough to support multiple steady states: A unique equilibriumin the climate-vegetation system is simulated by all the models on a zonal scale for present-day climate and doubled CO₂ climate.EMIC simulations with decreased insolation also reveal a unique steady state. However, the climate sensitivity to tree cover, T_F, exhibits non-linear behaviour within the models. For GENESIS-IBIS and CLIMBER-2, T_F islower for doubled CO₂ climate than for present-day climate due to a shorter snow season and increased relative significance ofthe hydrological effect of forest cover. For the EMICs, T_F is higher for low tree fraction than for high treefraction, mainly due to a time shift in spring snow melt in response to changes in tree cover. The climate sensitivity to tree coveris reduced when thermohaline circulation feedbacks are accounted for in the EMIC simulations. Simpler parameterizations of oceanic processes have opposite effects on T_F: T_F is lower in simulations with fixed SSTs and higher in simulations with mixed layer oceans. Experiments with transient CO₂ forcing show climate and vegetation not in equilibrium in the northern high latitudes at the end of the 20thcentury. The delayed response of vegetation and accelerated global warming lead to rather abrupt changes in northern vegetation cover in the first halfof the 21st century, when vegetation cover changes at double the present day rate.     

Image-domain wavefield tomography for tilted transversely isotropic media

Transversely isotropic models with a tilted symmetry axis have become standard for imaging beneath dipping shale formations and in active tectonic areas. Here, we develop a methodology of wave-equation-based image-domain tomography for acoustic tilted transversely isotropic media. We obtain the gradients of the objective function using an integral wave-equation operator based on a separable dispersion relation that takes the symmetry-axis tilt into account. In contrast to the more conventional differential solutions, the integral operator produces only the P-wavefield without shear-wave artefacts, which facilitates both imaging and velocity analysis. The model is parameterized by the P-wave zero-dip normal-moveout velocity, the Thomsen parameter δ, anellipticity coefficient η and the symmetry-axis tilt θ. Assuming that the symmetry axis is orthogonal to reflectors, we study the influence of parameter errors on energy focusing in extended (space-lag) common-image gathers. Distortions in the anellipticity coefficient η introduce weak linear defocusing regardless of reflector dip, whereas δ influences both the energy focusing and depth scale of the migrated section. These results, which are consistent with the properties of the P-wave time-domain reflection moveout in tilted transversely isotropic media, provide important insights for implementation of velocity model-building in the image-domain. Then the algorithm is tested on a modified anticline section of the BP 2007 benchmark model.