Caveats in Multi-modal Inversion of Seismic Surface Wavefields

We consider several examples demonstrating that the formal modal representation of surface wavefields often does not describe adequately observable wave parameters, such as the phase and group velocity dispersion of higher modes. The main reason for this is the existence in the medium of several waveguides or weakly coupled wavefields in the same waveguide. In such cases the separation of neighboring higher modes may be impossible, and observed dispersion curves may significantly differ from the ones predicted by the theory. From the example related to the studies of the crustal and upper mantle structure we found that the difficulty in the separation of first and second crustal higher modes can be overcome by applying a special inversion procedure. This procedure ignores the existence of a low velocity layer in the upper mantle when fitting the observable higher-mode dispersion curve to the one predicted by the model.     

The Main Features of the Local Geological Conditions Can Explain the Macroseismic Intensity Caused in Xiji-Langfu (Beijing) by the Ms = 7.7 Tangshan 1976 Earthquake

—The special geological conditions in the Xiji-Langfu area are the main reason for the anomalous high macroseismic intensity caused by the Tangshan, 1976 earthquake. The area is formed by deep deposits - mainly alluvium sands and clays poorly consolidated and with high water content - that have been trapped by the Xiadian fault. From simulated ground motion we have computed quantities commonly used for engineering purposes like the acceleration maximum amplitude (AMAX) and the total energy of ground motion (W), which is related to the Arias Intensity. The thick low velocity deposits are responsible for the large increment of the values of AMAX and W inside the basin. On the two sides of the Xiadian fault AMAX and W can vary by 200% and 700% respectively, and these variations are quite stable with varying thickness of the sedimentary deposit used in the models. With the existing relationships between acceleration (AMAX) and macroseismic intensity (I) our results can explain the large values of I observed in the Xiji-Langfu area, in connection with the Tangshan earthquake.     

Properties of the lithosphere-asthenosphere system in Europe with a view toward earth conductivity

Over the past 20 years the study ofP- andS-wave velocities in the upper mantle of the Mediterranean area and continental Europe has been the subject of intensive research work. We present a summary of results based on the inversion of available surface-wave dispersion data andP-wave trave time observations. For areas characterized by different tectonic settings and very large lateral variations, a discussion is made about structural models based on seismological, geothermal and electrical conductivity data.     

Deep structure of southeastern europe from Rayleigh waves

The analysis of Rayleigh-wave phase velocities up to about 250 s has allowed of deepening structural knowledge, down to several hundred kilometers underneath the triangular array formed by the WWSSN stations Athens-Istanbul-L'Aquila. For the path L'Aquila-Istanbul a lid-to-low velocity channel contrast of variable size is always present, while for the other two paths. Athens-Istanbul and Athens-L'Aquila. two alternative patterns are possible, one indicating the presence of a contrast between lid and low-velocity channel, the other suggesting the absence of significant layering down to depths of about 350 km.     

Realistic Modeling of Seismic Wave Ground Motion in Beijing City

— Algorithms for the calculation of synthetic seismograms in laterally heterogeneous anelastic media have been applied to model the ground motion in Beijing City. The synthetic signals are compared with the few available seismic recordings (1998, Zhangbei earthquake) and with the distribution of observed macroseismic intensity (1976, Tangshan earthquake). The synthetic three-component seismograms have been computed for the Xiji area and Beijing City. The numerical results show that the thick Tertiary and Quaternary sediments are responsible for the severe amplification of the seismic ground motion. Such a result is well correlated with the abnormally high macroseismic intensity zone in the Xiji area associated with the 1976 Tangshan earthquake as well as with the ground motion recorded in Beijing city in the wake of the 1998 Zhangbei earthquake.     

Site-specific Microzonation Study in Delhi Metropolitan City by 2-D Modelling of SH and P-SV Waves

— Delhi – the capital of India lies on a severe earthquake hazard threat not only from local earthquakes but also from Himalayan events just 200–250 km apart. The seismic ground motion in a part of Delhi City is computed with a hybrid technique based on the modal summation and the finite-difference scheme for site-specific strong ground motion modelling. Complete realistic SH and #E5/E5#-SV wave seismograms are computed along two geological cross sections, (1) north-south, from Inter State Bus Terminal (ISBT) to Sewanagar and (2) east-west, from Tilak Bridge to Punjabi Bagh. Two real earthquake sources of July 15, 1720 (MMI=IX, M=7.4) and August 27, 1960 (M=6.0) have been used in modelling. The response spectra ratio (RSR), i.e. the response spectra computed from the signals synthesized along the laterally varying section and normalized by the response spectra computed from the corresponding signals, synthesized for the bedrock reference regional model, have been determined. As expected, the sedimentary cover causes an increase of the signal amplitude, particularly in the radial and transverse components. To further check the site-effects, we reversed the source location to the other side of the cross section and recomputed the site amplifications. There are only a few sites where a large amplification is invariant with respect to the two source locations considered. The RSR ranges between 5 to 10 in the frequency range from 2.8 to 3.7 Hz for the radial and transverse components of motion along the NS cross section. Along the EW cross section RSR varies between 3.5 to 7.5 in the frequency range from 3.5 to 4.1 Hz. The amplification of the vertical component is considerable at high frequency (>4 Hz.) whereas it is negligible in lower frequency range.     

Tracing contamination sources through phenotypic characterization of Escherichia coli isolates from surface water and groundwater in an agro-ecosystem

The objective of this research was to evaluate the groundwater chemical and bacteriological quality in the Barranquita-Knutzen basin (Córdoba, Argentina). The main purpose was to trace contamination through the examination of bacteriological parameters and antibiotic resistance of Escherichia coli, relating them to surface water, hydrogeological features and land use. Thus, 40 water samples were collected. The major chemical components and bacterial indicators were determined and antibiotic resistance was analysed using standard methods. Multivariate factorial analysis showed that the first principal component (PC) reveals the process of water mineralization, while the second and the third PCs explain a low percentage of variance, but collect chemical constituents and total and faecal coliform bacteria, respectively, revealing specific contamination situations. The observed antibiotic resistance profiles of E. coli and their relation with the land uses revealed that the source of faecal contamination in water is mainly from animal residues.     

Neo-deterministic seismic hazard scenarios for India—a preventive tool for disaster mitigation

Current computational resources and physical knowledge of the seismic wave generation and propagation processes allow for reliable numerical and analytical models of waveform generation and propagation. From the simulation of ground motion, it is easy to extract the desired earthquake hazard parameters. Accordingly, a scenario-based approach to seismic hazard assessment has been developed, namely the neo-deterministic seismic hazard assessment (NDSHA), which allows for a wide range of possible seismic sources to be used in the definition of reliable scenarios by means of realistic waveforms modelling. Such reliable and comprehensive characterization of expected earthquake ground motion is essential to improve building codes, particularly for the protection of critical infrastructures and for land use planning. Parvez et al. (Geophys J Int 155:489–508, 2003) published the first ever neo-deterministic seismic hazard map of India by computing synthetic seismograms with input data set consisting of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. As described in Panza et al. (Adv Geophys 53:93–165, 2012), the NDSHA methodology evolved with respect to the original formulation used by Parvez et al. (Geophys J Int 155:489–508, 2003): the computer codes were improved to better fit the need of producing realistic ground shaking maps and ground shaking scenarios, at different scale levels, exploiting the most significant pertinent progresses in data acquisition and modelling. Accordingly, the present study supplies a revised NDSHA map for India. The seismic hazard, expressed in terms of maximum displacement (Dmax), maximum velocity (Vmax) and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory.