Studia Geophysica et Geodaetica最新文献

The dating of skeletal remains in archaeology is difficult, especially at findings without burial equipment. In this case, apart from literary and iconographic sources, anthropological and palaeopathological analyses, the radiocarbon dating method can also be used. We present an example where we used this procedure in the dating of the skeletal remains of an anonymous recent mass grave, found in the cellars of one of the houses in Brno (Czech Republic). On the basis of an assessment of the archaeological and anthropological context, in combination with radiocarbon dating, it could be concluded that the found skeletal remains were most likely of soldiers who died in the provisional military hospital as a result of injury or infection after the Battle of Austerlitz in 1805. An alternative hypothesis, that they are the remains of soldiers who died in the Battle of Hradec Králové in 1866, was excluded by radiocarbon dating.

Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Earth’s lithosphere and viscous asthenosphere. A more satisfactory test of isostasy is to determine the depth to and density contrast between crust and mantle at the Moho discontinuity (Moho). Generally, the Moho can be mapped by seismic information, but the limited coverage of such data over large portions of the world (in particular at seas) and economic considerations make a combined gravimetric-seismic method a more realistic approach. The determination of a high-resolution of the Moho constituents for marine areas requires the combination of gravimetric and seismic data to diminish substantially the seismic data gaps. In this study, we estimate the Moho constituents globally for ocean regions to a resolution of 1° × 1° by applying the Vening Meinesz-Moritz method from gravimetric data and combine it with estimates derived from seismic data in a new model named COMHV19. The data files of GMG14 satellite altimetry-derived marine gravity field, the Earth2014 Earth topographic/bathymetric model, CRUST1.0 and CRUST19 crustal seismic models are used in a least-squares procedure. The numerical computations show that the Moho depths range from 7.3 km (in Kolbeinsey Ridge) to 52.6 km (in the Gulf of Bothnia) with a global average of 16.4 km and standard deviation of the order of 7.5 km. Estimated Moho density contrasts vary between 20 kg m^-3 (north of Iceland) to 570 kg m^-3 (in Baltic Sea), with a global average of 313.7 kg m^-3 and standard deviation of the order of 77.4 kg m^-3. When comparing the computed Moho depths with current knowledge of crustal structure, they are generally found to be in good agreement with other crustal models. However, in certain regions, such as oceanic spreading ridges and hot spots, we generally obtain thinner crust than proposed by other models, which is likely the result of improvements in the new model. We also see evidence for thickening of oceanic crust with increasing age. Hence, the new combined Moho model is able to image rather reliable information in most of the oceanic areas, in particular in ocean ridges, which are important features in ocean basins.

In this study, non-stationary iterative time-domain deconvolution (CNS-ITD) is investigated. The propagating wavelets are first estimated in several overlapping Gabor windows of the data. Matrix-vector operations in the time-domain are then performed by estimating a small number of columns of the wavelet matrix by interpolation within a sparse iterative estimation for the largest reflectivities. The iteration process is stopped when a minimum root mean square (RMS) residual or a maximum number of iterations is reached. Although initially formulated on the basis of work in earthquake seismology, CNS-ITD is a matching pursuit type of approach performed continuously in the time-domain for the non-stationary case. The results can then be convolved with a higher frequency wavelet in order to make the results stationary in time and to increase the resolution of the data. We first apply CNS-ITD to synthetic data with a time-varying attenuation, where the method successfully identifies the largest reflectors in the data. We then apply CNS-ITD to two observed shallow seismic datasets where improved resolution is obtained.

In this contribution, an iterative algorithm for variance-covariance component estimation based on the structured errors-in-variables (EIV) model is proposed. We introduce the variable projection principle and derive alternative formulae for the structured EIV model by applying Lagrange multipliers, which take the form of a least-squares solution and are easy to implement. Then, least-squares variance component estimation (LS-VCE) is applied to estimate different (co)variance components in a structured EIV model. The proposed algorithm includes the estimation of covariance components, which is not considered in other recently proposed approaches. Finally, the estimability of the (co)variance components of the EIV stochastic model is discussed in detail. The efficacy of the proposed algorithm is demonstrated through two applications: multiple linear regression and auto-regression, on simulated datasets or on a real dataset with some assumptions.

Seismic interpolation can provide complete data for some multichannel processing techniques such as time lapse imaging and wave equation migration. However, field seismic data often contains random noise and noisy data interpolation is a challenging task. A traditional method applies interpolation and denoising separately, but this needs two workflows. Simultaneous interpolation and denoising combines interpolation and denoising in one workflow and can also get acceptable results. Most existing interpolation methods can only recover missing traces but fail to attenuate noise in sampled traces. In this study, a novel thresholding strategy is proposed to remove the noise in the sampled traces and meanwhile recover missing traces during interpolation. For each iteration, the residual is multiplied by a weighting factor and then added to the iterative solution, after which the sum in the transformed domain is calculated using the thresholding operation to update the iterative solution. To ensure that the interpolation and denoising results are robust, the exponential method was chosen to reduce the threshold values in small quantities. The curvelet transform was used as sparse representation and three interpolation methods were chosen as benchmarks. Three numerical tests results proved the effectiveness of the proposed method on removing noise in the sampled traces when the minimum threshold values are correctly chosen.

Singular value decomposition (SVD) is a useful method for random noise suppression in seismic data processing. A structure-oriented SVD (SOSVD) approach which incorporates structure prediction to the SVD filter is effcient in attenuating noise except distorting seismic events at faults and crossing points. A modified SOSVD approach using a weighted stack, called structure-oriented weighted SVD (SOWSVD), is proposed. In this approach, the SVD filter is used to attenuate noise for prediction traces of a primitive trace which are produced via the plane-wave prediction. A weighting function related to local similarity and distance between each prediction trace and the primitive trace is applied to the denoised prediction traces stacking. Both synthetic and field data examples suggest the SOWSVD performs better than the SOSVD in both suppressing random noise and preserving the information of the discontinuities for seismic data with crossing events and faults.

The Caroline Islands are located in a broad zone near plate boundaries in southwestern Pacific. Accumulating evidence suggests that the hotspot origin alone cannot completely explain the formation of the Caroline Islands. To investigate the tectonic setting of their formation, we calculated the effective elastic thickness (T_e) of the lithosphere beneath the Caroline Islands from an analysis of bathymetry and free-air gravity anomaly data by the admittance method. A synthetic model based on the actual bathymetry data of the Caroline Islands was developed for the finite window size biasing correction. The results show that the T_e values of the Caroline Islands (4.5–11.5 km) are significantly lower than the T_e expected for a normal oceanic lithosphere (23–50 km), and that the T_e values can be approximated by the depth to the 150 ± 100°C isotherm. The low T_e values indicate that the strength of the lithosphere beneath the Caroline Islands has been weakened by geological process. The thermal anomalies related to the Ontong Java Plateau and the South Pacific Isotopic and Thermal Anomaly, and the lithospheric fractures induced by interaction of plates are probable causes of the lithospheric strength reduction of the Caroline Islands.

Imaging of small-scale heterogeneities is important for the geological exploration in complex environments. It requires a processing sequence tuned to high-resolution model building. Conventional methods which use refractions or reflections might face problems in resolving small-scale features since they are visually close to the resolution of the reflection images. Additional information or an unconventional technology, which supports the reflection imaging, is thus of great interest. An unconventional method based on seismic diffractions naturally complements specular reflection imaging. Diffracted waves represent a direct seismic response from small-scale subsurface heterogeneities, such as inclusions with a characteristic size of the prevailing wavelength, or discontinuities in geological interfaces, such as faults and fractures. We investigate the rule of diffracted part of the wavefield on velocity model building using a full-waveform inversion (FWI) example. In order to best acknowledge refracted and reflected parts of the wavefield in FWI, we chose a synthetic data example which mimics the ocean-bottom nodes acquisition survey as it provides almost perfect conditions for FWI of diving waves, a standard tool for high-resolution model building. We show, that FWI using diving waves produces a well-resolved anomaly. Including other part of the wavefield, reflected waves, further improves the resolution of the velocity anomaly but also leads to a gentle overfitting due to missing illumination from the very steep anomaly flanks. Considering diffracted events in FWI improves the model resolution even further resulting in a detailed velocity model and correctly imaged anomaly in both vertical and lateral directions.

The values of regional tidal parameters h₂, l₂ associated with the tidal variations of ground stations were estimated for the Polish Satellite Laser Ranging (SLR) station Borowiec using SLR data. The study is based on satellite observations taken by the global network of ground stations during the period from January 1, 1999 until January 1, 2019 for monthly orbital arcs of the satellites LAGEOS-1 and LAGEOS-2. The adjusted regional values for h₂ equalling 0.7308 ± 0.0008 and l₂ equalling 0.1226 ± 0.0003 are discussed and compared with the nominal values of h₂ and l₂ given in the the International Earth Rotation and Reference Systems Service (IERS) standards and with other estimations of these parameters. Furthermore, the influence of the tidal parameters changes on estimation of the Borowiec station coordinates in the ITRF2014 reference frame was investigated. The analysis was carried out in two variants. The first one consisted in the determination of the Borowiec station coordinates with the use of the nominal values of the tidal parameters: h₂ = 0.6078 and l₂ = 0.0847 (IERS recommended values). In the second one, the Borowiec station coordinates were determined using the local tidal parameters estimated in this paper (h₂ = 0.7308 ± 0.0008 and l₂ = 0.1226 ± 0.0003). The differences between X, Y ,Z for Variant 1 and Variant 2 are ?3.5, 3.3 and 4.2 mm, respectively.