Sub-seismic scale fracture pattern and in situ permeability data in the chalk atop of the Krempe salt ridge at Lägerdorf, NW Germany: Inferences on synfolding stress field evolution and its impact on fracture connectivity

Chalk is exposed in the Heidestrasse quarry at Lägerdorf, at the top of the NE-SW trending Krempe salt ridge. Structural data indicate the presence of two joint sets, striking almost parallel and perpendicular to the salt ridge, respectively, and of a set of conjugate extensional faults and fault zones striking NW-SE, i.e. almost perpendicular to the salt ridge. Within the overall NW-SE trend of joints and faults, strike variations occur from the massive chalk exposed in the lower half of the quarry, to the overlying layered chalk. A large variability characterizes the normalized spacing of both joint sets, which does not show any clear trend with layer dip. In situ measurements indicate that the cross-sectional permeability of tight joints increases 1-2 orders of magnitude with respect to the undeformed chalk. We propose that joint and fault azimuthal variability resulted from changes through time of the stress ellipsoid at the top of the salt ridge, while joint spacing variability is associated with the weak mechanical influence of bedding in chalk. Azimuthal variability improves fracture connectivity and, hence, permeability and fluid flow.     

The Density and Masses of Obscured Black Holes

Recent Chandra and XMM-Newton surveys have uncovered a large fraction of the obscured AGN responsible of the hard X-ray background. One of the most intriguing results of extensive programs of follow-up observations concerns the optical and near-infrared properties of the hard X-ray sources counterparts. More specifically, for a significant fraction of hard X-ray obscured sources the AGN responsible of the high X-ray luminosity remains elusive over a wide range of wavelengths from soft X-rays to near-infrared. This very observational result opens the possibility to investigate the host of bright obscured quasars in some detail. Here we briefly report on some preliminar results obtained for a small sample of elusive AGN in the HELLAS2XMM survey.     

On the nature of the z=0 X-ray absorbers: I. Clues from an external group

We describe the main features of the evolutionary code ATON 3.1 and its latest version, particularly deviced to be apt for follow up asteroseismology applications. An older version of the code including rotational evolution is also shortly described.     

Carbonatites in a subduction system: The Pleistocene alvikites from Mt. Vulture (southern Italy)

We report here, for the first time, on the new finding of extrusive calciocarbonatite (alvikite) rocks from the Pleistocene Mt. Vulture volcano (southern Italy). These volcanic rocks, which represent an outstanding occurrence in the wider scenario of the Italian potassic magmatism, form lavas, pyroclastic deposits, and feeder dikes exposed on the northern slope of the volcano. The petrography, mineralogy and whole-rock chemistry attest the genuine carbonatitic nature of these rocks, that are characterized by high to very high contents of Sr, Ba, U, LREE, Nb, P, F, Th, high Nb/Ta and LREE/HREE ratios, and low contents of Ti, Zr, K, Rb, Na and Cs. The O–C isotope compositions are close to the “primary igneous carbonatite” field and, thus, are compatible with an ultimate mantle origin for these rocks. The Sr–Nd–Pb–B isotope compositions, measured both in the alvikites and in the silicate volcanic rocks, indicate a close genetic relationship between the alvikites and the associated melilitite/nephelinite rocks. Furthermore, these latter products are geochemically distinct from the main foiditic-phonolitic association of Mt. Vulture. We propose a petrogenetic/geodynamic interpretation which has important implications for understanding the relationships between carbonatites and orogenic activity. In particular, we propose that the studied alvikites are generated through liquid unmixing at crustal levels, starting from nephelinitic or melilititic parent liquids. These latter were produced in a hybrid mantle resulting from the interaction through a vertical slab window, between a metasomatized mantle wedge, moving eastward from the Tyrrhenian/Campanian region, and the local Adriatic mantle. The occurrence of carbonatite rocks at Mt. Vulture, that lies on the leading edge of the Southern Apennines accretionary prism, is taken as an evidence for the carbonatation of the mantle sources of this volcano. We speculate that mantle carbonatation is related to the introduction of sedimentary carbon from the Adriatic lithosphere during Tertiary subduction.     

Earthen barriers to control lava flows in the 2001 eruption of Mt. Etna

Preceded by four days of intense seismicity and marked ground deformation, a new eruption of Mt. Etna started on 17 July and lasted until 9 August 2001. It produced lava emission and strombolian and phreatomagmatic activity from four different main vents located on a complex fracture system extending from the southeast summit cone for about 4.5 km southwards, from 3000 to 2100 m elevation (a.s.l.). The lava emitted from the lowest vent cut up an important road on the volcano and destroyed other rural roads and a few isolated country houses. Its front descended southwards to about 4 km distance from the villages of Nicolosi and Belpasso. A plan of intervention, including diversion and retaining barriers and possibly lava flow interruption, was prepared but not activated because the flow front stopped as a consequence of a decrease in the effusion rate. Extensive interventions were carried out in order to protect some important tourist facilities of the Sapienza and Mts. Silvestri zones (1900 m elevation) from being destroyed by the lava emitted from vents located at 2700 m and 2550 m elevation. Thirteen earthen barriers (with a maximum length of 370 m, height of 10–12 m, base width of 15 m and volume of 25 000 m³) were built to divert the lava flow away from the facilities towards a path implying considerably less damage. Most of the barriers were oriented diagonally (110–135°) to the direction of the flow. They were made of loose material excavated nearby and worked very nicely, resisting the thrust of the lava without any difficulty. After the interventions carried out on Mt. Etna in 1983 and in 1991–1992, those of 2001 confirm that earthen barriers can be very effective in controlling lava flows.     

Love wave tomography in Italy from seismic ambient noise

We estimate Love wave empirical Green's functions from cross-correlations of ambient seismic noise to study the crust and uppermost mantle structure in Italy.Transverse-component ambient noise data from October 2005 through March 2007 recorded at 114 seismic stations from the Istituto Nazionale di Geofisica e Vulcanologia (INGV) national broadband network,the Mediterranean Very Broadband Seismographic Network (MedNet) and the Austrian Central Institute for Meteorology and Geodynamics (ZAMG) yield more than 2 000 Love wave group velocity measurements using the multiple-filter analysis technique.In the short period band (5-20 s),the cross-correlations show clearly one-sided asymmetric feature due to non-uniform noise distribution and high local activities,and in the long period band (20 s) this feature becomes weak owing to more diffusive noise distribution.Based on these measurements,Love wave group velocity dispersion maps in the 8-34 s period band are constructed,then the SH wave velocity structures from the Love wave dispersions are inverted.The final results obtained from Love wave data are overall in good agreement with those from Rayleigh waves.Both Love and Rayleigh wave inversions all reveal that the Po plain basin is resolved with low velocity at shallow depth,and the Tyrrhenian sea is characterized with higher velocity below 8 km due to its thin oceanic crust.     

Mid-Holocene to present-day evolution of the Indian monsoon in transient global simulations

The low-frequency evolution of Indian rainfall mean-state and associated interannual-to-decadal variability is discussed for the last 6000 years from a multi-configuration ensemble of fully coupled global transient simulations. This period is marked by a shift of Indian Summer Monsoon Rainfall (ISMR) distribution towards drier conditions, including extremes, and a contraction of the rainy season. The drying is larger in simulations with higher horizontal resolution of the atmosphere and revised land surface hydrology. Vegetation–climate interactions and the way runoff is routed to ocean modulate the timing of the monsoon onset but have negligible effects on the evolution of seasonal rainfall amounts in our modeling framework in which carbon cycling is always active. This drying trend is accompanied by changes in ISMR interannual-to-decadal variability decreasing over north and south India but increasing over central India (20°–25° N). The ISMR interannual-to-decadal variability is decomposed into six physically consistent regimes using a clustering technique to further characterize its changes and associated teleconnections. From 6 to 3.8 kyr bp, the century-to-century modulations in the frequency of occurrence associated to the regimes are asynchronous between the simulations. Orbitally-driven trends can only be detected for two regimes over the whole 6–0 kyr bp period. These two regimes reflect increased influence of ENSO on both ISMR and Indian Ocean Dipole as the inter-hemispheric energy gradient weakens. Severe long-term droughts are also shown to be a combination of long-term drying and internally generated low-frequency modulations of the interannual-to-decadal variability.

     

Archaeoseismological evidence of past earthquakes in Rome (fifth to ninth century A.D.) used to quantify dating uncertainties and coseismic damage

The transformation of Rome during the Late Antiquity and the Early Middle Ages has been investigated by archaeologists and historians. Social and political changes are the main aspects which led to a progressive modification of the urban framework; abandonment, spoliation and transformation of buildings are quite diffused as documented by the archaeological literature. The consequence of these practices is a higher vulnerability of the buildings which, from the seismological point of view, played a main role in increasing the effects of seismic shaking. A number of earthquakes have struck Rome during the period of investigation (fifth to ninth century A.D.), known from historical sources: 443, 484–508, 618, 801, 847; in some cases (443, 484–508, 801) damage has been documented. In contrast, the archaeological sources characterise collapse layers and evidence of destruction at different sites with changing and not always conclusive chronological constraints. Consequently, collapse and destruction have been alternatively attributed to the above-mentioned earthquakes. Through a geoarchaeological and stratigraphic analysis of potentially coseismic collapse units, we want (1) to describe the archaeoseismic evidence derived from recent excavations and from the available literature (e.g. Piazza Madonna di Loreto, Piazza Venezia, Palazzo Valentini Crypta Balbi, Colosseo, Basilica Hilariana, Basilica di Santa Petronilla, Santa Maria Antiqua,…); (2) to discuss the chronological problems and the uncertainty of attribution of the collapse units to known historical earthquakes; (3) to discuss the earthquake damage exaggeration due to erroneous attribution of seismic origin to the evidence of destruction derived from archaeological data. Finally, we will infer the role that earthquakes may have had on the development of the urban landscape in the fifth to ninth century A.D.     

1D velocity structure of the Po River plain (Northern Italy) assessed by combining strong motion and ambient noise data

Strong ground motions recorded on the sedimentary deposits of the Po River alluvial plain during the Emilia (Northern Italy) Mw 5.7 earthquake of May 29, 2012 are used to assess the vertical profile of shear-wave velocity above the limestone basement. Data were collected by a linear array installed for site effect studies after the Mw 5.9 mainshock of May 20, 2012. The array stations, equipped with both strong and weak motion sensors, are aligned in the South–North direction, at distances ranging from 1 to 26 km from the epicenter. The vertical components of ground motion show very distinctive, large-amplitude, low-frequency dispersive wave trains. Wavelet analysis yields group-velocity dispersion curve in the 0.2–0.7 Hz frequency band. The availability of a long ambient noise record allows estimates of the site resonance frequency along with its stability among stations. The joint inversion of dispersion of surface waves and ellipticity curves derived from ambient noise H/V allows extending investigations down to the sediment-limestone interface, at a depth of about 5,000 m. Our results add new information about the velocity structure at a scale that is intermediate between the local scale already investigated by other authors with small-aperture arrays using ambient noise and the regional scale inferred from modeling of seismogram waveforms recorded at hundreds of kilometers from the source.