A harmonic approach to global ocean tide analysis based on TOPEX/Poseidon satellite

The constant and harmonic parts of the global ocean tide are modeled by up to nine major tidal constituents, namely, S2, M2, N2, K1, P1, O1, Mf, Mm, and Ssa. Our computations start with the Fourier sine and cosine series expansion for the tidal constituents, including the constant Mean Sea Level (MSL). Although the frequencies of the tidal constituents are considered known, the coefficients of the sine and cosine functions are assumed to be unknown. Subsequently, the coefficients of the sine and cosine functions, as well as the constant part of the Fourier expansion, were expanded into spherical harmonics up to degree and order n, where n corresponds to the number of linearly independent spherical harmonic base functions needed to model the tidal constituents, determined via independent columns of the Gram matrix. The unknown coefficients of the spherical harmonic expansions are computed using sea level observations within cycles #1–#350 of the TOPEX/Poseidon satellite altimetry over 11 years of its mission. A set of orthonormal base functions was generated for the marine areas covered by TOPEX/Poseidon observations from the spherical harmonics using a Gram-Schmidt orthogonalization process. These were used for modeling the dominant tidal constituents. The computed models based on orthonormal base functions for the nine tidal constituents and the constant part of the Fourier expansion, were tested numerically for their validity and accuracy, proving centimeter accuracy.     

Copper isotope fractionation in the Meiduk porphyry copper deposit,Northwest of Kerman Cenozoic magmatic arc,Iran

The Meiduk deposit possesses three different Cu reservoirs each with a unique Cu isotope signature. δ⁶⁵Cu for the leached cap minerals ranges from ?2.5 to +0.49‰ to ?0.45 to +0.3‰ for hypogene minerals and from +1.3 to +4.4‰ for supergene enrichment minerals. Oxidation of hypogene sulphides and effective trapping of copper (from solutions derived from the leached cap) in the supergene enrichment zone caused this relationship. A systematic pattern of low Cu isotope values close to the surface and higher isotope values with depth reveals a palaeo‐fluid pathway in the northwest–southeast direction over the deposit. Thus, the copper isotope data from leached cap and enrichment minerals can be used to monitor copper migration during supergene weathering at the Meiduk deposit.     

Monitoring and projection of climate change impact on 24-h probable maximum precipitation in the Southeast of Caspian Sea

Natural Hazards - Due to the impacts of climate change on probable maximum precipitation (PMP) and its importance in designing hydraulic structures, PMP estimation is crucial. In this study, the...     

Compounding effects of human activities and climatic changes on surface water availability in Iran

Climatic Change - By combining long-term ground-based data on water withdrawal with climate model projections, this study quantifies the compounding effects of human activities and climate change...     

Cost–benefit analyses to assess the potential of Operational Earthquake Forecasting prior to a mainshock in Europe

In the past couple of decades, Operational Earthquake Forecasting (OEF) has been proposed as a way of mitigating earthquake risk. In particular, it has the potential to reduce human losses (injuries and deaths) by triggering actions such as reinforcing earthquake drills and preventing access to vulnerable structures during a period of increased seismic hazard. Despite the dramatic increases in seismic hazard in the immediate period before a mainshock (of up to 1000 times has been observed), the probability of a potentially damaging earthquake occurring in the coming days or weeks remains small (generally less than 5%). Therefore, it is necessary to balance the definite cost of taking an action against the uncertain chance that it will mitigate earthquake losses. In this article, parametric cost–benefit analyses using a recent seismic hazard model for Europe and a wide range of inputs are conducted to assess when potential actions for short-term OEF are cost–beneficial prior to a severe mainshock. Ninety-six maps for various combinations of input parameters are presented. These maps show that low-cost actions (costing less than 1% of the mitigated losses) are cost–beneficial within the context of OEF for areas of moderate to high seismicity in the Mediterranean region. The actions triggered by OEF in northern areas of the continent are, however, unlikely to be cost–beneficial unless very large increases in seismicity are observed or very low-cost actions are possible.

     

Surface-wave analysis for static corrections in mineral exploration: A case study from central Sweden

In mineral exploration, increased interest towards deeper mineralizations makes seismic methods attractive. One of the critical steps in seismic processing workflows is the static correction, which is applied to correct the effect of the shallow, highly heterogeneous subsurface layers, and improve the imaging of deeper targets. We showed an effective approach to estimate the statics, based on the analysis of surface waves (groundroll) contained in the seismic reflection data, and we applied it to a legacy seismic line acquired at the iron-oxide mining site of Ludvika in Sweden. We applied surface-wave methods that were originally developed for hydrocarbon exploration, modified as a step-by-step workflow to suit the different geologic context of hard-rock sites. The workflow starts with the detection of sharp lateral variations in the subsurface, the existence of which is common at hard-rock sites. Their location is subsequently used, to ensure that the dispersion curves extracted from the data are not affected by strong lateral variations of the subsurface properties. The dispersion curves are picked automatically, windowing the data and applying a wavefield transform. A pseudo-2D time-average S-wave velocity and time-average P-wave velocity profile are obtained directly from the dispersion curves, after inverting only a reference curve. The time-average P-wave velocity profile is then used for the direct estimation of the one-way traveltime, which provides the static corrections. The resulting P-wave statics from the field data were compared with statics computed through conventional P-wave tomography. Their difference was mostly negligible with more than 91% of the estimations being in agreement with the conventional statics, proving the effectiveness of the proposed workflow. The application of the statics obtained from surface waves provided a stacked section comparable with that obtained by applying tomostatics.     

Deep reflection seismic imaging of iron-oxide deposits in the Ludvika mining area of central Sweden

Reflection seismic data were acquired within two field campaigns in the Blötberget, Ludvika mining area of central Sweden, for deep imaging of iron-oxide mineralization that were known to extend down to 800–850 m depth. The two surveys conducted in years 2015 and 2016, one employing a seismic landstreamer and geophones connected to wireless recorders, and another one using cabled geophones and wireless recorders, aimed to delineate the geometry and depth extent of the iron-oxide mineralization for when mining commences in the area. Even with minimal and conventional processing approaches, the merged datasets provide encouraging information about the depth continuation of the mineralized horizons and the geological setting of the study area. Multiple sets of strong reflections represent a possible continuation of the known deposits that extend approximately 300 m further down-dip than the known 850 m depth obtained from historical drilling. They show excellent correlation in shape and strength with those of the Blötberget deposits. Furthermore, several reflections in the footwall of the known mineralization can potentially be additional resources underlying the known ones. The results from these seismic surveys are encouraging for mineral exploration purposes given the good quality of the final section and fast seismic surveys employing a simple cost-effective and easily available impact-type seismic source.     

Intensity measures for the seismic response evaluation of buried steel pipelines under near-field pulse-like ground motions

Ground-motion Intensity Measures (IMs) are used to quantify the strength of ground motions and evaluate the response of structures. IMs act as a link between seismic demand and seismic hazard analysis and therefore, have a key role in performance-based earthquake engineering. Many studies have been carried out on the determination of suitable IMs in terms of efficiency, sufficiency and scaling robustness. The majority of these investigations focused on ordinary structures such as buildings and bridges, and only a few were about buried pipelines. In the current study, the optimal IMs for predicting the seismic demand of continuous buried steel pipelines under near-field pulse-like ground motion records is investigated. Incremental dynamic analysis is performed using twenty ground motion records. Using the results of the regression analysis, the optimality of 23 potential IMs are studied. It is concluded that specific energy density (SED) followed by \(\sqrt {VSI[{\omega _1}(PGD + RM{S_d})]} \) are the optimal IMs based on efficiency, sufficiency and scaling robustness for seismic response evaluation of buried pipelines under near-field ground motions.

     

b-value and fractal dimension variations in Iran

Iran sits on a region with a high intrinsic level of seismic activity due to its tectonic setting. Through statistical examination of the earthquakes listed in the catalogue from International Institute of Earthquake Engineering and Seismology (IIEES), this research attempted to calculate some seismicity factors and find correlation between them. A preliminary analysis indicated changes in the b-value of the Gutenberg-Richter relationship over the study region. Thus, the study area was divided into five zones (Alborz, Zagros, Azerbaijan, Central and East) and b-value was computed for each zone. Considering faulting mechanism styles and the b-values in the region, it was found that the lowest b-values belong to the thrust events and strike-slip faulting earthquakes have intermediate values. These findings support previous studies. Furthermore, results of b-value calculation were used for the estimation of accumulated differential stresses (σ₁–σ₂) over each zone. Overall, the b-value for Iran is averagely low which signifies the high stress tectonic regime in this region. Also, by having calculated fractal dimension (D) in each zone, a correlation obtained showing that in Iran region, the b-value correlates to fractal dimension by D = 4.2b–2 relation which does not support Aki's (1981) speculation of D = 3b/c.     

Dynamic Positioning System Design for A Marine Vessel with Unknown Dynamics Subject to External Disturbances Including Wave Effect

China Ocean Engineering - In this paper, a new control system is proposed for dynamic positioning (DP) of marine vessels with unknown dynamics and subject to external disturbances. The control...