Horizontal rotation signals detected by “G-Pisa” ring laser for the M w = 9.0, March 2011, Japan earthquake

We report the observation of the ground rotation induced by the M _w = 9.0, 11th of March 2011, Japan earthquake. The rotation measurements have been conducted with a ring laser gyroscope operating in a vertical plane, thus detecting rotations around the horizontal axis. Comparison of ground rotations with vertical accelerations from a co-located force balance accelerometer shows excellent ring laser coupling at periods longer than 100?s. Under the plane wave assumption, we derive a theoretical relationship between horizontal rotation and vertical acceleration for Rayleigh waves. Due to the oblique mounting of the gyroscope with respect to the wave direction of arrival, apparent velocities derived from the acceleration/rotation rate ratio are expected to be always larger than or equal to the true wave propagation velocity. This hypothesis is confirmed through comparison with fundamental mode, Rayleigh-wave phase velocities predicted for a standard Earth model.     

The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone), II. Geochronology and isotope geochemistry

Whole-rock Nd and Sr isotopic compositions of the mafic-ultramafic complex near Finero demonstrate that the magma was derived from a depleted, perhaps MORB-type mantle reservoir. The Sm-Nd data for the Amphibole Peridotite unit can be interpreted as an isochron with an apparent age of 533 ± 20 Ma, which is consistent with a ²⁰⁷Pb/²⁰⁶Pb evaporation age of 549 ± 12 Ma of a single zircon grain from the Internal Gabbro unit. However, the interpretation of these apparent ages remains open to question. We therefore retain the alternative hypotheses that the intrusion occurred either about 533 or 270 Ma ago, the latter being the most likely age of emplacement of the much larger magma body near Balmuccia (Val Sesia). The implication of the older emplacement age (if correct) would be that the igneous complex may be related to the numerous amphibolite units, which are intercalated with the metapelites of the overlying Kinzigite Formation, and together with them may constitute an accretionary complex. In this case, the mafic-ultramafic complex itself might also be part of such an accretionary complex (as has been proposed for the Balmuccia peridotite).

Internal Sm-Nd isochrons involving grt, cpx, plag and amph from the Internal Gabbro unit yield concordant ages of 231 ± 23, 226 ± 7, 223 ± 10, 214 ± 17, and 203 ± 13 Ma. These results confirm published evidence for a separate, regional heating event about 215 ± 15 Ma ago.

Initial _Nd(533) values average +6.3 ± 0.4 for six samples of the Amphibole Peridotite unit and +6.0 ± 1.2 for ten samples of the External Gabbro unit. ⁸⁷Sr/⁸⁶Sr ratios require little or no age correction and range from 0.7026 to 0.7047 (with two outliers at 0.7053 and 0.7071). Strong correlations between ⁸⁷Sr/⁸⁶Sr and K₂O and weaker correlations between initial _Nd and K₂O imply a comparatively minor (≤ 10%) contamination of the External Gabbro magma by crustal material and a later alteration by a crustal or seawater-derived fluid. These results contrast sharply with the isotopic composition (negative _Nd and high ⁸⁷Sr/⁸⁶Sr values) of the associated mantle rocks, the Phlogopite Peridotite unit, which has been pervasively metasomatized by crustal fluids. This type of metasomatism and its isotopic signature are never seen in the magmatic complex. This evidence rules out any direct genetic relationship between the igneous complex and the mantle peridotite. The crust-mantle interaction is the opposite of that seen at Balmuccia, where the mantle peridotite is essentially ‘pristine’ and the magmatic body has been extensively contaminated by assimilation of crustal rocks.     

Potential evidence for slab detachment from the flexural backstripping of a foredeep: Insight on the evolution of the Pescara basin (Italy)

The discrepancy between the size of the Apenninic chain and the depth of the Adriatic foredeep is investigated using 2D flexural backstripping on well‐constrained depth‐converted cross‐sections in the Pescara basin (Central Italy). The procedure consisted of removal, uplift, unfolding and unfaulting of the Pliocene–Pleistocene foreland deposits to produce a palaeogeographic map of the basin at the end of the Messinian and to constrain sedimentary rates since the Miocene. Results are found to support the contribution of an external load to the foreland evolution together with the Apenninic chain load. The interplay of the two types of loads resulted in spatial and temporal variations of the foredeep evolution that are quantified by palaeogeographic maps and sedimentation rates obtained through backstripping. Results are interpreted as representing the effects of a southward‐migrating wave linked to slab detachment beneath the Adriatic foredeep. This procedure can be useful to investigate similar problems on other chains worldwide.     

Crystal chemical variations in Ba-rich biotites from gabbroic rocks of lower crust (Ivrea Zone,NW Italy)

Biotites from mafic rocks occurring at different stratigraphic levels of the Ivrea-Verbano Mafic Complex are studied. The rocks are gabbros and diorites. All the biotites are intermediate between phlogopite and annite [0.282 (up to 7.14 and 9.32 wt%, respectively) with respect to those of the diorites (up to 1.26 and 6.26 wt%, respectively). Systematic compositional variations support the substitution model 2 ^IV Si+( ^IV R²⁺)2 ^IV Al+ ^VI Ti (R²⁺=Fe+Mg+Mn) in gabbros and ^IV Si+ ^VI Al ^IV Al+ ^VI Ti in diorites. A predominance of disordered stacking sequences, coexisting with 1M, 2M ₁ and 3T polytypes was observed in all biotites. It was possible to carry out structural refinements only on three biotites-2M ₁ from diorites (R-values between 2.68 and 3.77) and one biotite-1M from gabbros (R-value=3.09). It was shown that: (1) the reduced thickness of the tetrahedral sheet in Ba-rich biotites supports the coupled substitution ^IV Si+ ^XII K ^IV Al+ ^XII Ba; (2) the interlayer site geometry is affected by the whole layer chemistry and does not reflect only local chemical variations; (3) in two samples of the 2M ₁ polytype, the M(1) octahedral site is larger and more distorted than the M(2) sites because of the preferential ordering of Fe²⁺ in the M(1) site, whereas one sample shows complete cation disorder in the octahedral sites. Biotite-1M shows that Fe²⁺ can also be located in the M(2) site. Some of the differences between the biotites of gabbros and diorites (e.g. Ba concentration and exchange vectors) may be linked to the host rock composition and to its crystallization process. Biotite occurs in trace amounts in gabbros and its crystallization is related to the interstitial melt which contributed to the adcumulus growth of the main rock forming phases and became highly enriched in K, Ba and Ti. Diorites are the result of equilibrium crystallization of a residual melt rich in incompatible elements, where biotite is a major constituent.     

The iron Kα Compton shoulder in transmitted and reflected spectra

We calculate the equivalent width of the core, and the centroid energy and relative flux of the first-order Compton shoulder of the iron Kα emission line from neutral matter. The calculations are performed with Monte Carlo simulations. We explore a large range of column densities for both transmitted and reflected spectra, and study the dependence on the iron abundance. The Compton shoulder is now becoming observable in many objects thanks to the improved sensitivity and/or energy resolution of the XMM – Newton and Chandra satellites, and the present work aims to provide a tool to derive information on the geometry and element abundances of the line-emitting matter from Compton shoulder measurements.     

On the use of infinite elements in the analysis of two-dimensional layered elastic systems via discretized integral equations

A boundary integral equation approach is presented for the two-dimensional plane strain analysis of horizontally layered elastic systems resting on a rough and rigid base. The validity of Somigliana identity for unbounded layers is discussed and an Infinite Boundary Element is proposed in order to take into account the lateral unboundedness of the physical problem in the discretized equations. This element is implemented in a computer code based on a successive stiffness solution procedure. A series of numerical tests concerning single- and multi-layered problems is illustrated, and the performance of the proposed solution method is compared with that of more traditional boundary element and finite element techniques.     

High Energy Astrophysics with INTEGRAL

INTEGRAL is an ESA mission scheduled to be launched in 2001. Its fourcoaligned instruments will allow observations of cosmic sources from afraction of a keV to several MeV plus source monitoring in the opticalband. INTEGRAL will be operated as a space observatory and an Announcementof Opportunity to the astronomical community at large will be issued byESA in the spring of the year 2000. Purpose of this paper is to illustrateINTEGRAL capabilities of the three X and Gamma Ray detectors plus opticalmonitor in order to help potential users to write observing proposals.     

Direct,partitioned and projected solution to finite element consolidation models

Direct, partitioned, and projected (conjugate gradient‐like) solution approaches are compared on unsymmetric indefinite systems arising from the finite element integration of coupled consolidation equations. The direct method is used in its most recent and computationally efficient implementations of the Harwell Software Library. The partitioned approach designed for coupled problems is especially attractive as it addresses two separate positive definite problems of a smaller size that can be solved by symmetric conjugate gradients. However, it may stagnate and when converging it does not prove competitive with a global projection method such as Bi‐CGSTAB, which may take full advantage of its flexibility in working on scaled and reordered equations, and thus may greatly improve its computational performance in terms of both robustness and convergence rate. The Bi‐CGSTAB superiority to the other approaches is discussed and demonstrated with a few representative examples in two‐dimensional (2‐D) and three‐dimensional (3‐D) coupled consolidation problems. Copyright © 2002 John Wiley & Sons, Ltd.     

Reconstruction of hydrocarbons accumulation in sediments affected by the oil refinery industry: the case of Tehuantepec Gulf (Mexico)

The Isthmus of Tehuantepec corresponds to the shortest distance (~200?km) between the Gulf of Mexico and the Pacific Ocean in Southern Mexico, and the main economical activity of this region is oil extraction and refining. Polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs) were determined in a ²¹⁰Pb dated sediment core collected from the continental shelf of Tehuantepec Gulf, in the vicinity of the oil refinery of Salina Cruz, Oaxaca, the main oil refining facility of the country. The sediments were mostly of coarse nature and hence PAHs and TPHs concentrations throughout the core (61?C404???g?g^?1 and 29?C154?mg?kg^?1, respectively) were below international quality benchmarks. Depth profiles of both PAHs and TPHs concentrations showed increasing trends since the early 1900s but the higher values were found from the 1950s to present. PAH congener ratios showed that these contaminants had both petrogenic and pyrolitic sources, although the former has been predominant since the 1970s. The Salina Cruz refinery started operations in 1978 but the oil industry activities in the Tehuantepec Isthmus go back to the beginning of the twentieth century with the operation of Minatitlan refinery in the Gulf of Mexico, and the Gulf of Tehuantepec being the main conduit for oil distribution in the Pacific coast. The observed changes in contaminant distributions described well the oil industry development in the area.