Inversion of Multiconfiguration Complex EMI Data with Minimum Gradient Support Regularization: A Case Study

Mathematical Geosciences - Frequency-domain electromagnetic instruments allow the collection of data in different configurations, that is, varying the intercoil spacing, the frequency, and the...     

Use of seismic early warning information to calibrate variable dampers for structural control of a highway bridge: evaluation of the system robustness

The seismic events occurred in recent years highlighted the extreme vulnerability of large part of the existing constructed facilities and the need to adopt innovative solutions to improve their seismic performance. With this purpose, the possible exploitation of a seismic early warning system (SEWS) in the framework of semi-active structural control using magnetorheological (MR) dampers is herein investigated. The main idea consists in the use of these time-varying properties devices to control an hosting structure by changing their behaviour according to an anticipate estimate, provided by the SEWS, of the peak ground acceleration (PGA) of the incoming earthquake. In this way, the dampers are able to adapt their mechanical characteristics to the specific earthquake obtaining the optimal seismic response. The present paper describes the application of this protection technique to a case-study problem, a highway bridge located in Southern California. The seismic response of the benchmark bridge is investigated by nonlinear time-history analyses by adopting 16 real earthquake ground excitations. These accelerograms cover a wide variety of magnitudes, distances to fault and soil types. Possible errors on estimation of PGA provided by SEWS and their effects on the proposed control system are also considered. The results obtained confirm that unavoidable errors in the PGA estimates provided by the SEWS do not propagate to the seismic response. Conversely, the proposed strategy turns out to damp these errors, resulting in a robust seismic behaviour of the protected structure.     

Adsorption of dissolved organic matter on clay minerals as assessed by infra-red, CPMAS C NMR spectroscopy and low field T1 NMR relaxometry

Dissolved organic matter (DOM) is a very important environmental constituent due to its role in controlling factors for soil formation, mineral weathering and pollutant transport in the environment. Prediction of DOM physical-chemical properties is achieved by studying its chemical structure and spatial conformation. In the present study, dissolved organic matter extracted from compost obtained from the organic fraction of urban wastes (DOM-P) has been analysed by FT-IR, CPMAS ¹³C NMR spectroscopy and ¹H T₁ NMR relaxometry with fast field cycling (FFC) setup. While the first two spectroscopic techniques revealed the chemical changes of dissolved organic matter after adsorption either on kaolinite (DOM-K) or montmorillonite (DOM-S), the latter permitted the evaluation of the conformational variations as assessed by longitudinal relaxation time (T₁) distribution at the fixed magnetic field of 500 mT. Alterations of T₁ distributions from DOM-P to DOM-K and DOM-S were attributed to a decreasing molecular complexity following DOM-P adsorption on the clay minerals. This study applied for the first time solid state ¹H T₁ NMR relaxometry to dissolved organic matter from compost obtained from the organic fraction of urban wastes and revealed that this technique is very promising for studying environmentally relevant natural organic systems.     

Comparison of PFS and TES observations of temperature and water vapor in the martian atmosphere

The interval from L_s = 330° in Mars Year (MY) 26 until L_s = 84° in MY 27 has been used to compare and validate measurements from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and the Mars Express Planetary Fourier Spectrometer (PFS). We studied differences between atmospheric temperatures observed by the two instruments. The best agreement between atmospheric temperatures was found at 50 Pa between 40°S and 40°N latitude, where differences were within ±5 K. For other atmospheric levels, differences as large as ∼25 K were observed between the two instruments at some locations. The largest temperature differences occurred mainly over the Hellas Planitia, Argyre Planitia, Tharsis and Valles Marineris regions.On this basis we report on the variability of the martian atmosphere during the 5.5 martian years of Mars climatology obtained by combining the two data sets from TES and PFS. Atmospheric temperatures at 50 Pa responded to the global-scale dust storms of MY 25 and in MY 28 raising temperatures from ∼220 K to ∼250 K during the daytime. An atmospheric temperature of ∼140 K at 50 Pa was observed poleward of 70°N during northern winter and poleward of 60°S during southern winter each year in both the PFS and TES results. Water vapor observed by the two spectrometers showed consistent seasonal and latitudinal variations.     

A detrital apatite fission‐track study of the CIROS‐2 sedimentary record: Tracing ice pathways in the Ross Sea area over the last 5 Ma

The Ross Sea is a crucial area to investigate pathways of ice during the Cenozoic as it records the evolution of both the East and West Antarctic Ice Sheets. This work is based on detrital apatite fission track (AFT) data extracted from the sedimentary record of well CIROS‐2, which spans the last 5 Ma. The AFT data show a large range of ages, and most of the grains fit well with two main components that fall between 24 and 42 Ma and between 43 and 70 Ma, whereas the other components are not regularly distributed through the well, thus indicating a mixture of provenance from different areas along the Transantarctic Mountains. As a whole, our work suggests glacial expansion over the McMurdo Sound during the Pliocene, and ice periodically invading and retreating in Pleistocene.     

Seismic expression of active extensional faults in northern Umbria (Central Italy)

This paper deals with the geometry and kinematics of the active normal faults in northern Umbria, and their relationship with the seismicity observed in the area. In particular, we illustrate the contribution of seismic reflection data (a network of seismic profiles, NNW–SSE and WSW–ENE trending) in constraining at depth the geometry of the different active fault systems and their reciprocal spatial relationships. The main normal fault in the area is the Alto Tiberina fault, NNW trending and ENE dipping, producing a displacement of about 5 km, and generating a continental basin (Val Tiberina basin), infilled by up to 1500 m with Upper Pliocene–Quaternary deposits. The fault has a staircase trajectory, and can be traced on the seismic profiles to a depth of about 13 km. A set of WSW-dipping, antithetic faults can be recognised on the profiles, the most important of which is the Gubbio fault, bordering an extensional Quaternary basin and interpreted as an active fault based on geological, geomorphologic and seismological evidence. The epicentral distribution of the main historical earthquakes is strictly parallel to the general trend of the normal faults. The focal mechanisms of the major earthquakes show a strong similarity with the attitude of the extensional faults, mapped at the surface and recognised on the seismic profiles. These observations demonstrate the connection between seismicity in the area and the activity of the normal faults. Moreover, the distribution of the instrumental seismicity suggests the activity of the Alto Tiberina fault as the basal detachment for the extensional tectonics of the area. Finally, the action of the Alto Tiberina fault was simulated using two dimensional finite element modelling: a close correspondence between the concentration of shear stresses in the model and the distribution of the present earthquakes was obtained.     

Modeling landslide recurrence in Seattle, Washington, USA

To manage the hazard associated with shallow landslides, decision makers need an understanding of where and when landslides may occur. A variety of approaches have been used to estimate the hazard from shallow, rainfall-triggered landslides, such as empirical rainfall threshold methods or probabilistic methods based on historical records. The wide availability of Geographic Information Systems (GIS) and digital topographic data has led to the development of analytic methods for landslide hazard estimation that couple steady-state hydrological models with slope stability calculations. Because these methods typically neglect the transient effects of infiltration on slope stability, results cannot be linked with historical or forecasted rainfall sequences. Estimates of the frequency of conditions likely to cause landslides are critical for quantitative risk and hazard assessments. We present results to demonstrate how a transient infiltration model coupled with an infinite slope stability calculation may be used to assess shallow landslide frequency in the City of Seattle, Washington, USA. A module called CRF (Critical RainFall) for estimating deterministic rainfall thresholds has been integrated in the TRIGRS (Transient Rainfall Infiltration and Grid-based Slope-Stability) model that combines a transient, one-dimensional analytic solution for pore-pressure response to rainfall infiltration with an infinite slope stability calculation. Input data for the extended model include topographic slope, colluvial thickness, initial water-table depth, material properties, and rainfall durations. This approach is combined with a statistical treatment of rainfall using a GEV (General Extreme Value) probabilistic distribution to produce maps showing the shallow landslide recurrence induced, on a spatially distributed basis, as a function of rainfall duration and hillslope characteristics.     

Applicability of piezocone and dilatometer to characterize the soils of the Venice Lagoon

The effectiveness of two geotechnical investigation tools—the piezocone and the dilatometer—to characterize the soils forming the shallowest deposits of the upper quaternary basin of the Venice lagoon soil is examined in this study. For this purpose, the results of a comprehensive site and laboratory investigation carried out recently over a small lagoon area—the Malamocco Test Site—are used to evaluate the applicability of the most widely used charts or correlative equations to characterize soil profile and estimate the main geotechnical properties of these soils, when applied to the interpretation of CPTU and DMT results. The particular interest of this site—apart from its unquestionable historical relevance—is the presence, apparently without any regular pattern in depth and site, of a predominantly silty fraction combined with clay and/or sand, thus forming an erratic interbedding of various types of sediments. This case represents therefore the opposite condition of that which has been normally utilized in the past to calibrate the two devices, namely the presence of particularly homogeneous natural deposits or artificially sedimented homogeneous layers of sand or clay. The Malamocco Test Site may therefore be considered as test benchmark for the applicability of the two devices to characterize highly heterogeneous silty deposits.