Showing papers by "Geophysical Survey published in 2016"

Natural and human-induced sinkhole hazards in Saudi Arabia: distribution, investigation, causes and impacts

Abstract: Approximately 60 % of the 2,150,000 km2 area of Saudi Arabia is underlain by soluble sediments (carbonate and evaporite rock formations, salt diapirs, sabkha deposits). Despite its hyper-arid climate, a wide variety of recent sinkholes have been reported in numerous areas, involving significant property losses. Human activities, most notably groundwater extraction, have induced unstable conditions on pre-existing cavities. This work provides an overview of the sinkhole hazard in Saudi Arabia, a scarcely explored topic. It identifies the main karst formations and the distribution of the most problematic sinkhole areas, illustrated through several case studies covering the wide spectrum of subsidence mechanisms. Some of the main investigation methods are presented through selected examples, including remote sensing, trenching and geophysics. Based on the available data, the main causal factors are identified and further actions that should be undertaken to better assess and manage the risk are discussed.

Broadband NDSHA computations and earthquake ground motion observations for the Italian territory

Abstract: The aim of this work is two-fold: 1) to compare the results of national scale NDSHA modelling for the Italian region at 10 Hz cut-off, based on the relevant available knowledge, with observations (eg, peak ground motion values) and existing empirical attenuation relations; 2) to update the scaling law for source spectra (SLSS) to be used for the selected area The new set of source spectra, defined along the lines suggested by the comparison with empirical attenuation relations, produces acceptable results in terms of PGV and spectral acceleration at long periods Synthetic PGA and SA at short periods show a faster attenuation with respect to the observed ones and, therefore, the effect of complex attenuation factors should be explored in future ad hoc studies

Petrology, geochemistry, and geochronology of mafic rocks from the Taoxinghu Devonian ophiolite, LongmuCo–Shuanghu–Lancang suture zone, northern Tibet: evidence for an intra-oceanic arc–basin system

Abstract: A newly discovered Devonian ophiolite located in the Taoxinghu area of central Qiangtang on the Qinhai–Tibet Plateau is described. The ophiolite consists of gabbro and diabasic dikes, and invasive cumulate gabbros-leucogabbros. The ophiolite has undergone greenschist facies metamorphism and minor deformation. Dating of the metagabbro by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U–Pb techniques yielded a weighted mean age of 367.2 ± 3.3 Ma (Late Devonian). Whole-rock geochemical analyses show that the rocks belong to the tholeiite series, with weak depletion in light rare-earth elements (LREEs), almost no Eu anomalies, weak enrichment in large-ion lithophile elements (LILEs), depletion in Nb and Ta, and weak negative Hf and Ti anomalies. These characteristics are similar to those of back-arc basin basalts. Together, these characteristics suggest that the rocks of the Devonian ophiolite formed by ~30% partial melting of spinel lherzolite, which was enriched by in...

Filtering SAR interferometric phase noise using a split-window model

Abstract: For interferometric synthetic aperture radar (InSAR) processing, the features of interferometric phase obtained in different coherence regions usually differ from each other. This is called region effect and exists in InSAR coherence map. When coherence value is used as a parameter to filter the phase noise, the result will be highly affected by this region effect. In this paper, we propose a new method of filtering InSAR phase noise using a split-window model. The idea of this method is to incorporate several filters into the model. Different filters will be used when dealing with phase noise locates in different coherence regions. The over-filtering or under-filtering caused by the coherence region effect can be eliminated in this method. As an example to demonstrate the superiority of this method, we incorporated an improved Goldstein filter and empirical mode decomposition filter into the current model. They were included to control phase noise level in the low- and high-coherence regions, res...

Source Spectra of Near Kamchatka Earthquakes: Recovering them from S-Wave Spectra, and Determination of Scaling for Three Corner Frequencies

Abstract: We describe a procedure for mass determination of the “source-controlled f max”—an important though not conventional parameter of earthquake source spectrum, relabeled here as “the third corner frequency,” f c3, and discuss the results of its application. f max is the upper cutoff frequency of Fourier acceleration spectrum of a record of a local earthquake; both source and path attenuation contribute to f max. Most researchers believe the role of attenuation (“κ” parameter) to be dominating or exclusive. Still, source effect on f max is sometimes revealed. If real, it may be important for source physics. To understand better the f max phenomena, the constituents of f max must be accurately separated. With this goal, we process seismograms of moderate earthquakes from Kamchatka subduction zone. First, we need reliable estimates of attenuation to recover source spectra. To this goal, an iterative processing procedure is constructed, that adjusts the attenuation model until the recovered source acceleration spectra become, on the average, flat up either to f c3, or up to the high-frequency limit of the frequency range analyzed. The latter case occurs when f c3 is non-existent or unobservable. Below f c3, the double-corner source spectral model is thought to be valid, and the lower bound of acceleration spectral plateau is considered as the second corner frequency of earthquake source spectrum, fc2. The common corner frequency, f c1, is also estimated. Following this approach, more than 500 S-wave spectra of M = 4–6.5 Kamchatka earthquakes with hypocentral distances 80–220 km were analyzed. In about 80 % of the cases, f c3 is clearly manifested; the remaining cases show, at high frequency, flat source acceleration spectra. In addition, in about 2/3 of cases, f c2 is clearly above f c1, showing that double-corner spectra may dominate even at moderate magnitudes. Scaling behavior was examined for each of the corners. The f c1 vs. M 0 trend is common and close to similarity (f c1 ∝ M 0 −1/3 ), whereas the trends for two other corners (f c2 ∝ M 0 −0.17 ; f c3 ∝ M 0 −0.11 ) dramatically contradict the concept of similarity. Physical interpretation of such a behavior is discussed. The origin of f c3 is ascribed to existence of the lowermost wavelength/size of fault heterogeneity. Its dependence on M 0 may reflect evolution of maturity of a fault in geological time. The approximate scaling f c2 ∝ $$f_{c1}^{0.5}$$ suggests that during propagation of slip pulse over a fault, its width, assumedly related to 1/f c2, grows in a stochastic manner; this reminds the random evolution of propagating boundary in the framework of the known Eden model of random growth.

Performance of Hybrid and Single-frequency Impulse GPR Antennas on USGA Sporting Greens

Abstract: The utility of employing ground-penetrating radar (GPR) technologies for environmental surveys can vary, depending upon the physical properties of the site. Environmental conditions can fluctuate, altering soil properties. Operator proficiency and survey methodology will also influence GPR findings. Therefore, GPR equipment performance evaluation involves standardized tests that are frequently conducted indoors within laboratory-controlled environments. This study uses outdoor United States Golf Association (USGA) putting greens as a structure for GPR testing for surveying practitioners. These USGA putting greens provide a tightly controlled environment because many golf courses and sports turf fields adhere to strict USGA construction and irrigation guidelines. Past studies on several USGA greens show that GPR provided precise and accurate profiles of root-mixture depth, gravel-blanket thickness, and drain-tile layout. Results are independent of locale, as all USGA putting greens are virtually i...

Chemical composition of natural waters of contaminated area: The case for the Imandra Lake catchment (the Kola Peninsula)

Abstract: The study of the current chemical composition of natural waters in the eastern and western parts of the Imandra Lake catchment was performed using ion chromatography, potentiometry and inductively coupled plasma mass spectrometry. It was found that the content of trace elements in the surface water is considerably higher than that in the groundwater. The nickel and copper concentrations exceed the background levels over 19 and 2 times respectively in groundwater, and 175 and 61 times in the surface waters. These data show that the Severonikel influences negatively air and surface water.

Prestack migration velocity analysis based on simplified two-parameter moveout equation

Abstract: Stacking velocity VC2, vertical velocity ratio γ0, effective velocity ratio γeff, and anisotropic parameter χeff are correlated in the PS-converted-wave (PS-wave) anisotropic prestack Kirchhoff time migration (PKTM) velocity model and are thus difficult to independently determine. We extended the simplified two-parameter (stacking velocity VC2 and anisotropic parameter keff) moveout equation from stacking velocity analysis to PKTM velocity model updating and formed a new four-parameter (stacking velocity VC2, vertical velocity ratio γ0, effective velocity ratio γeff, and anisotropic parameter keff) PS-wave anisotropic PKTM velocity model updating and process flow based on the simplified two-parameter moveout equation. In the proposed method, first, the PS-wave two-parameter stacking velocity is analyzed to obtain the anisotropic PKTM initial velocity and anisotropic parameters; then, the velocity and anisotropic parameters are corrected by analyzing the residual moveout on common imaging point gathers after prestack time migration. The vertical velocity ratio γ0 of the prestack time migration velocity model is obtained with an appropriate method utilizing the P- and PS-wave stacked sections after level calibration. The initial effective velocity ratio γeff is calculated using the Thomsen (1999) equation in combination with the P-wave velocity analysis; ultimately, the final velocity model of the effective velocity ratio γeff is obtained by percentage scanning migration. This method simplifies the PS-wave parameter estimation in high-quality imaging, reduces the uncertainty of multiparameter estimations, and obtains good imaging results in practice.

Spatial-temporal deformation characteristics in the urban area of Beijing using high resolution X-band images

Abstract: In this paper, 42 X-band COSMO-Skymed (CSK) images are processed using Permanent Scatterer InSAR (PSI) technique in order to monitor and analyze deformation phenomena in Beijing urban areas between January 2009 and August 2011. Italian COSMO constellation composed of four satellites is capable of acquiring SAR data with 8 day repeat cycle with up to 1 meter resolution. The results show significant X-shape subsidence tendency in the east of urban areas. Displacement values of up to 90 mm/ year along the line of sight of are detected in the area near Shuangqiao subway station. The results from CSK data are consistent with those from C-band ENVISAT ASAR data. Spatial characteristics and temporal changes of linear projects in inhomogeneous subsidence region are analyzed to evaluate the safety of subways and railways.