Ambient noise and ERT data provide insights into the structure of co-seismic rock avalanche deposits in Sichuan (China)

AbstractThe post-seismic history of the 2008 Mw7.9 Wenchuan earthquake shows that marginally stable deposits of large co-seismic landslide dams can pose persistent debris flow hazards for the downstream areas. Here, we combine analyses of single-station recordings of ambient noise with electrical resistivity tomography (ERT) surveys to explore the potential of drawing information on structure and geometry of the deposit of a large rock avalanche triggered by the Mw 7.9 2008 Wenchuan earthquake, which dammed the Yangjia stream in the Sichuan Province (China). The substantial thickness and heterogeneity of this kind of deposits limit the application of standard geophysical techniques, like active seismic surveys, which require highly energetic sources and long linear geophone arrays to reach adequate investigation depths. Passive single-station methods, relying on ambient noise recordings to determine site resonance properties, controlled by the contrast between soft surface layers and a stiffer substratum, offer the opportunity of investigating subsoil properties down to larger depths. In particular, we use a recently developed technique, which isolates the contribution of Rayleigh waves to ambient noise and draws information on sub-soil properties from the inversion of Rayleigh wave ellipticity curves plotted as function of frequency. In this framework, the ERT data can support the ellipticity curve inversion, typically affected by highly non-univocal solutions, by providing constraints for defining of the thickness of the uppermost surficial layers. The results allowed inferring the overlap of different layers within the 2008 rock avalanche deposit, as well as estimating lateral variations in their thickness and S-wave (Vs) velocities

Viscosity and glass transition temperature of hydrous float glass

Viscosity of water-bearing float glass (0.03–4.87 wt% H2O) was measured in the temperature range of 573–1523 K and pressure range of 50–500 MPa using a parallel plate viscometer in the high viscosity range and the falling sphere method in the low viscosity range. Melt viscosity depends strongly on temperature and water content, but pressure up to 500 MPa has only minor influence. Consistent with previous studies on aluminosilicate compositions we found that the effect of dissolved water is most pronounced at low water content, but it is still noticeable at high water content. A new model for the calculation of the viscosities as a function of temperature and water content is proposed which describes the experimental data with a standard deviation of 0.22 log units. The depression of the glass tran- sition temperature Tg by dissolved water agrees reasonably well with the prediction by the model of Deubener [J. Deubener, R. Mu¨ ller, H. Behrens, G. Heide, J. Non-Cryst. Solids 330 (2003) 268]. Using water speciation measured by near-infrared spectroscopy we infer that although the effect of OH groups in reducing Tg is larger than that of H2O molecules, the difference in the contribution of both species is smaller than predicted by Deubener et al. (2003). Compared to alkalis and alkaline earth elements the effect of protons on glass fragility is small, mainly because of the relatively low concentration of OH groups (max. 1.5 wt% water dissolved as OH) in the glasses

Italian Experience and Problems in Deep Geothermal Drilling

Geothermal exploration at depth is being conducted in the Larderello area of Italy, in order to ascertain whether it is possible to extract geothermal fluids from the layers which underlie the reservoir now being exploited. The main operating problems are caused by the high thermality and the chemical corrosiveness of the fluids encountered; and by the practical problems involved in drilling without circulation to the surface in mainly hard but anhomogeneous fractured formations. The technology employed for deep geothermal well drilling plays an important role in this research. In deep geothermal well drilling it is essential that the equipment and the materials employed are suitable for use in areas which are characterized by high thermality and chemical corrosiveness. The results of the experiences gained in Italy concerning the materials and tools employed in deep geothermal exploration are presented. The various problems involved are described in detail and particular mention is made of drift control, fishing operations, cementation of the deep casing, control of the circulation fluid, and choice of the tubular materials

E-Defense 2015 ten-story building: beam–column joint assessment according to different code-based design

Recent devastating earthquakes worldwide pointed out the importance of seismic detailing and their influence on the observed damage and subsequent repairability of reinforced concrete buildings. Several studies and post-earthquake observations remarked the role of beam–column joints (BCJs) on the global building response and the effectiveness of transverse reinforcement in increasing the joint shear strength and the ultimate deformation. Although number of experimental and theoretical studies focused on the seismic response of BCJs, their mechanical behaviour is still a discussed topic. This resulted in number of design approaches available in worldwide code or standards that lead to different quantity of joint stirrups. This study focuses on the response of BCJs of a 10-story prototype building designed according to Japanese standards and tested in 2015 on the E-Defense shaking table. First the damage assessment at global (building) and local (joint) level is performed at increasing intensities and considering the building in the base slip and base fixed configurations. A refined numerical model is then developed and validated against global and local experimental results. Then, the joint stirrups are re-designed according to different international standards (ACI, EC8, NZS) and different numerical models are developed. The numerical results are then compared in terms of interstorey drift demand and joint shear strain. Finally, a comparison in terms of expected damage varying the design approach of joint stirrups is proposed

Effect of glass on the frictional behavior of basalts at seismic slip rates

We performed 31 friction experiments on glassy basalts (GB) and glass-free basalts (GFB) at slip rates up to 6.5 m s−1 and normal stress up to 40 MPa (seismic conditions). Frictional weakening was associated to bulk frictional melting and lubrication. The weakening distance (Dw) was about 3 times shorter in GB than in GFB, but the steady state friction was systematically higher in GB than in GFB. The shorter Dw in GB may be explained by the thermal softening occurring at the glass transition temperature (Tg ~500°C), which is lower than the bulk melting temperature (Tm ~1250°C) of GFB. Postexperiment microanalyses suggest that the larger crystal fraction measured in GB melts results in the higher steady state friction value compared to the GFB melts. The effect of interstitial glass is to facilitate frictional instability and rupture propagation in GB with respect to GFB

Frictional melting of peridotite and seismic slip

The evolution of the frictional strength along a fault at seismic slip rates (about 1 m/s) is a key factor controlling earthquake mechanics. At mantle depths, friction-induced melting and melt lubrication may influence earthquake slip and seismological data. We report on laboratory experiments designed to investigate dynamic fault strength and frictional melting processes in mantle rocks. We performed 20 experiments with Balmuccia peridotite in a high-velocity rotary shear apparatus and cylindrical samples (21.8 mm in diameter) over a wide range of normal stresses (5.4–16.1 MPa), slip rates (0.23–1.14 m/s), and displacements (1.5–71 m). During the experiments, shear stress evolved with cumulative displacement in five main stages (stages 1–5). In stage 1 (first strengthening), the coefficient of friction m increased up to 0.4–0.7 (first peak in friction). In stage 2 (abrupt firstweakening), m decreased to about 0.25–0.40. In stage 3 (gradual second strengthening), shear stress increased toward a second peak in friction (m = 0.30–0.40). In stage 4 (gradual second weakening), the shear stress decreased toward a steady state value (stage 5) with m = 0.15. Stages 1 and 2 are of too short duration to be investigated in detail with the current experimental configuration. By interrupting the experiments during stages 3, 4, and 5, microstructural (Field Emission Scanning Electron Microscope) and geochemical (Electron Probe Micro-Analyzer and Energy Dispersive X-Ray Spectroscopy) analysis of the slipping zone suggest that second strengthening (stage 3) is associated with the production of a grain-supported melt-poor layer, while second weakening (stage 4) and steady state (stage 5) are associated with the formation of a continuous melt-rich layer with an estimated temperature up to 1780 C. Microstructures formed during the experiments were very similar to those found in natural ultramafic pseudotachylytes. By performing experiments at different normal stresses and slip rates, (1) the ‘‘thermal’’ (as it includes the thermally activated first and second weakening) slip distance to achieve steady state from the first peak in strength decreased with increasing normal stress and slip rate and (2) the steady state shear stress slightly increased with increasing normal stress and, for a given normal stress, decreased with increasing slip rate. The ratio of shear stress versus normal stress was about 0.15, well below the typical friction coefficient of rocks (0.6–0.8). The dependence of steady state shear stress with normal stress was described by means of a constitutive equation for melt lubrication. The presence of microstructures similar to those found in natural pseudotachylytes and the determination of a constitutive equation that describes the experimental data allows extrapolation of the experimental observations to natural conditions and to the study of rupture dynamics in mantle rocks

Effect of glass on the frictional behavior of basalts at seismic slip rates

We performed 31 friction experiments on glassy basalts (GB) and glass-free basalts (GFB) at slip rates up to 6.5 m s−1 and normal stress up to 40 MPa (seismic conditions). Frictional weakening was associated to bulk frictional melting and lubrication. The weakening distance (Dw) was about 3 times shorter in GB than in GFB, but the steady state friction was systematically higher in GB than in GFB. The shorter Dw in GB may be explained by the thermal softening occurring at the glass transition temperature (Tg ~500°C), which is lower than the bulk melting temperature (Tm ~1250°C) of GFB. Postexperiment microanalyses suggest that the larger crystal fraction measured in GB melts results in the higher steady state friction value compared to the GFB melts. The effect of interstitial glass is to facilitate frictional instability and rupture propagation in GB with respect to GFB

Recent deformation at Campi Flegrei caldera (Italy) detected by DinSar and leveling techniques

The Campi Flegrei caldera, a volcanic and densely populated area located to the west of Napoli (Italy), was characterized by rapid ground deformation during 1970-72 and 1982-84, for a total amount of 3.5 m in the city of Pozzuoli. Since 1985 a slow deflation was active, with episodic microcrises of uplifts. A new and consistent uplift event is now going on, beginning in November 2004, as revealed by spatial and terrestrial geodetic techniques. In particular, we adopt almost all the available ENVISAT ASAR data acquired from both ascending and descending orbits during 2002-2006, to generate mean deformation velocity maps and time series with spatial resolution of about 100 m. The maps are computed following the Small BAseline Subset (SBAS) approach (Berardino et al., 2002), that implements an appropriate combination of differential interferograms generated from SAR data pairs (60 SAR images for this work). In addition to satellite observations, we show data from the high precision levelling network of the INGV-Osservatorio Vesuviano, consisting in about 320 benchmarks. Levelling measurements are regularly carried out on both the whole network and along the coast line; in case of a bradyseismic crisis, the temporal sampling is strongly increased. Both DInSAR and levelling data evidence the maximum value of the vertical displacement near the city of Pozzuoli. We model the observed deformation by means of 3D pressurized point-source and extended source, performing inversions to constrain their shape and location. The resulting sources are also compared with that inverted for the 1982-84 unrest.UnpublishedWienope

Recent deformation at Campi Flegrei caldera (Italy) detected by DinSar and leveling techniques

The Campi Flegrei caldera, a volcanic and densely populated area located to the west of Napoli (Italy), was characterized by rapid ground deformation during 1970-72 and 1982-84, for a total amount of 3.5 m in the city of Pozzuoli. Since 1985 a slow deflation was active, with episodic microcrises of uplifts. A new and consistent uplift event is now going on, beginning in November 2004, as revealed by spatial and terrestrial geodetic techniques. In particular, we adopt almost all the available ENVISAT ASAR data acquired from both ascending and descending orbits during 2002-2006, to generate mean deformation velocity maps and time series with spatial resolution of about 100 m. The maps are computed following the Small BAseline Subset (SBAS) approach (Berardino et al., 2002), that implements an appropriate combination of differential interferograms generated from SAR data pairs (60 SAR images for this work). In addition to satellite observations, we show data from the high precision levelling network of the INGV-Osservatorio Vesuviano, consisting in about 320 benchmarks. Levelling measurements are regularly carried out on both the whole network and along the coast line; in case of a bradyseismic crisis, the temporal sampling is strongly increased. Both DInSAR and levelling data evidence the maximum value of the vertical displacement near the city of Pozzuoli. We model the observed deformation by means of 3D pressurized point-source and extended source, performing inversions to constrain their shape and location. The resulting sources are also compared with that inverted for the 1982-84 unrest