Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka

A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases. Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo. The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from the main feeding system of the volcano.     

Settlement Due to Uniform Circular Load: On Finite Two-Layer System

Structures are commonly founded on layered soil deposits. In this study, settlement due to a circular load on a two-layer soil system overlying a rock stratum or a stiff soil deposit is estimated and compared with the values obtained using Steinbrenner’s and Finite element approaches. Design tables are proposed for settlements due to uniform circular loading (of radius equal to a) applied on two-layer soil system for top-layer thickness H ₁ = 0.2a–6.0a, bottom-layer thickness H ₂ = 1.0a–6.0a, moduli ratio of top and bottom layers E ₁ /E ₂ = 0.01–100 and Poisson’s ratio v = 0.2–0.5. The settlement factors from the study were also compared with the Ueshita and Meyerhof’s values for a finite top layer overlying a semi-infinite bottom layer. Results were compared with the observed settlement of a structure resting on a layered soil profile overlying a rock stratum. Proposed settlement of the two-layer system shows good agreement with these studies.     

New results of 40Ar/39Ar dating constrain the timing of transition from fissure-type to central volcanism at Mount Etna (Italy)

Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncertainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the ⁴⁰Ar/³⁹Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-controlled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130–126 ka) without significant temporal hiatus.     

Optimal lower bound of passive earth pressure using finite elements and non-linear programming

The present study pertains to the finding of the lower bound solution, formulating it as a non-linear programming problem using the generalized method developed by Lysmer with certain variations to incorporate the non-linear no-yield condition constraints directly in the analysis. The method considers the family of plane stress fields having the property that all stresses vary linearly within each triangular element of some mesh which covers the soil mass under study. For this type of stress field it is possible to express all equilibrium conditions as a set of linear constraints and the no-yield as a set of non-linear constraints. The boundary condition constraints may be of linear equality or inequality type. By expressing some of the design variables in terms of the remaining variables the linear equality constraints are implicity satisfied. Such a technique minimizes the complexity of the problem by eliminating the equality constraints and reduces the dimensionality of the problem, saving much, computational effort. The optimal lower bound is isolated by formulating it as a non-linear programming (NLP) problem subjected to both linear and non-linear inequality constraints. The sequential unconstrained minimization technique using the extended penalty function method as suggested by Kavlie has been used to isolate the optimal lower bound. The method has successfully been applied to the passive earth pressure and bearing capacity problem. Numerical results are obtained and compared with Lysmer's solution to show the effectiveness of the present approach.     

Seismic hazard scenario and attenuation model of the Garhwal Himalaya using near-field synthesis from weak motion seismometry

In this paper, we present a seismic hazard scenario for the Garhwal region of the north-western Himalayan range, in terms of the horizontal Peak Ground Acceleration. The scenario earthquake of moment magnitude M _w 8.5 has a 10% exceedance probability over the next 50 years. These estimates, the first for the region, were calculated through a stepwise process based on:

• An estimation of the Maximum Credible Earthquake from the seismicity of the region and Global Seismic Hazard Assessment Program considerations, and
• four seismotectonic parameters abstracted from near field weak-motion data recorded at five stations installed in Chamoli District of the Garhwal region in the aftermath of the 1999 Chamoli earthquake. The latter include
• The frequency dependent power law for the shear wave quality factor, Q _S
• the site amplification at each station using horizontal-to-vertical-spectral ratio and generalized inversion technique
• source parameters of various events recorded by the array and application of the resulting relations between the scalar seismic moment M ₀ (dyne-cm) and moment magnitude M _w and the corner frequency, ? _c (Hz) and moment magnitude M _w to simulate spectral acceleration due to higher magnitude events corresponding to the estimated Maximum Credible Earthquake, and
• regional and site specific local spectral attenuation relations at different geometrically central frequencies in the low, moderate and high frequency bands.

     

Hydrogeologically controlled freshwater dynamics in the coastal sand dune aquifer of Ongole coast (AP), India

Abstract

A sand dune area, ~50 km² in size, the only source of freshwater in the coastal zone of Prakasham district, Andhra Pradesh, India, is bounded by marine sediments in the northwest, and the Bay of Bengal in the southeast. Measurements of groundwater level, hydrochemistry and stable isotopes for three years facilitated the identification of the aquifer response to drought and intense cyclonic storms. There was no major change in hydrochemistry and isotope values between drought and highly saturated conditions, except in a few wells in the northwest. During drought, the groundwater remained fresh, although the levels dipped to 2–5 m b.m.s.l., signifying no saline water ingression (no measurable bromide). Based on the field observations, resistivity soundings, electrical conductivity and groundwater level change due to pumping, the existence of impermeable boundaries in the northwest and southeast are hypothesized. Thus, the existing hydrogeological settings appear to be inhibiting the movement of the freshwater–saline water interface into the freshwater zone.

Editor D. Koutsoyiannis     

Plant remains from the Tharumsa Formation of Ladakh,India

Plant remains, including both mega and micro collected from the middle part of the Tharumsa Foramtion (early Miocene) are described for the first time from the Tharumsa village of the Kargil district, Jammu and Kashmir to reconstruct the palaeoenvironment. They indicate their affinities with Broussonetia of the Moraceae and Abies, Cedrus and Pinus of the Pinaceae. Their presence indicates warm and moist tropical to sub-tropical climate in the Kargil area during the depositional period against the cold and dry climate prevailing at present.