Strain accumulation along an oblique plate boundary: the Reykjanes Peninsula, southwest Iceland

We use annual GPS observations on the Reykjanes Peninsula (RP) from 2000 to 2006 to generate maps of surface velocities and strain rates across the active plate boundary. We find that the surface deformation on the RP is consistent with oblique plate boundary motion on a regional scale, although considerable temporal and spatial strain rate variations are observed within the plate boundary zone. A small, but consistent increase in eastward velocity is observed at several stations on the southern part of the peninsula, compared to the 1993–1998 time period. The 2000–2006 velocities can be modelled by approximating the plate boundary as a series of vertical dislocations with left-lateral motion and opening. For the RP plate boundary we estimate left-lateral motion  18⁺⁴₋₃ mm yr⁻¹  and opening of  7⁺³₋₂ mm yr⁻¹  below a locking depth of  7⁺¹₋₂ km  . The resulting deep motion of  20⁺⁴₋₃ mm yr⁻¹  in the direction of  N(100⁺⁸₋₆)°E  agrees well with the predicted relative North America–Eurasia rate. We calculate the areal and shear strain rates using velocities from two periods: 1993–1998 and 2000–2006. The deep motion along the plate boundary results in left-lateral shear strain rates, which are perturbed by shallow deformation due to the 1994–1998 inflation and elevated seismicity in the Hengill–Hrómundartindur volcanic system, geothermal fluid extraction at the Svartsengi power plant, and possibly earthquake activity on the central part of the peninsula.     

Tertiary compressional structures on the Faroe–Rockall Plateau in relation to northeast Atlantic ridge-push and Alpine foreland stresses

A number of compressional anticlinal structures are identified in the western and northern part of the Faroe–Rockall Plateau. These structures occur on that part of the Faroe–Rockall Plateau which was above sea level during the latest phase of Paleocene plateau basalt extrusion. Three post-basalt compressional phases have affected the plateau. Most of the compressional structures in the northern part of the plateau are related to NE–SW- to ENE–WSW-oriented stress which we date to Late Paleocene–Early Eocene. The Oligocene phase is interpreted as resulting from N–S-directed compressional stress which also mainly affected the compressional structures on the northern part of the plateau. Compressional stress from the northwest seemed to affect the whole of the Faroe–Rockall Plateau and we suggest it to be of Miocene age. It is proposed that during the Late Paleocene–Early Eocene phase of compression local structure, and anomalously oriented gravitational ridge-push from the now extinct Aegir Axis contributed to a local NE–SW compressional stress system. The two later deformation phases were apparently connected to the regional northwest European stress system with small local modifications.     

Klastische und pyroklastische Sedimente des Südharzer Rotliegenden

Ohne Zusammenfassung     

An analytical solution for rainfall infiltration into an unsaturated infinite slope and its application to slope stability analysis

Surficial slope failures in residual soils are common in tropical and subtropical regions as a result of rainfall infiltration. This study develops an analytical solution for simulating rainfall infiltration into an infinite unsaturated soil slope. The analytical solution is based on the general partial differential equation for water flow through unsaturated soils. It can accept soil–water characteristic curve and unsaturated permeability function of the exponential form into account. Numerical simulations are conducted to verify the assumptions of the analytical solution and demonstrate that the proposed analytical solution is acceptable for the coarse soils with low air entry values. The pore‐water pressure (pwp) distributions obtained from the analytical solution can be incorporated into a limit equilibrium method to do infinite slope stability analysis for a rain‐induced shallow slip. The analysis method takes into account the influence of the water content change on unit weight and hence on factor of safety. A series of analytical parametric analyses have been performed using the developed model. The analyses indicate that when the residual soil slope, consisting of a completely decomposed granite layer underlain by a less permeable layer, is subjected to a continuous heavy rainfall, the loss of negative pwp and the reduction in factor of safety were found to be most significant for the shallow soil layer and during the first 12 h. The antecedent and subsequent rainfall intensity, depth of a less permeable layer and slope angle all have a significant influence on the pwp response and hence the slope stability. Copyright © 2012 John Wiley & Sons, Ltd.     

Zircon geochronology reveals polyphase magmatism and crustal anatexis in the Buchan Block,NE Scotland: Implications for the Grampian Orogeny

The type locality for high-temperature,low-pressure regional metamorphism,the Buchan Block in NE Scotland,exhibits profound differences to the rest of the Grampian Terrane.These differences have led some to regard the Buchan Block as an exotic crustal fragment comprising Precambrian basement gneisses and cover rocks thrust into their current position during Grampian orogenesis.Although rocks of the Buchan Block are now generally correlated with Dalradian strata elsewhere,the origin of the gneisses and the cause of the high heat flow and associated magmatism is debated.We report SIMS U-Pb and LA-ICPMS Hf isotopic data in zircon from high-grade rocks from the northeast(Inzie Head Gneiss)and northwest(Portsoy)corners of the Buchan Block.Around Inzie Head,upper amphibolite to granulite facies metasedimentary gneisses coexist with diorite sheets that were emplaced contemporaneously with partial melting of their host rocks,at least locally.U-Pb geochronology indicates a crystallisation age for the diorite of 486±9 Ma.Highly-deformed diorites within the Portsoy Gabbro have a crystallisation age of 493±8 Ma.Ages of ca.490 Ma for magmatism and high-grade metamorphism,which are broadly contemporaneous with ophiolite obduction and the onset of orogenesis,are significantly older than the established peak of Grampian metamorphism(ca.470 Ma).We propose a new model for the Grampian Orogeny involving punctuated tectonothermal activity due to tectonic switching during accretionary orogenesis.Rollback of a NW-dipping subduction zone at ca.490 Ma produced a back-arc environment(the Buchan Block)with associated arc magmatism and high dT/dP metamorphism.Arrival of an outboard arc resulted in shortening(the initial phase of the Grampian Orogeny)at ca.488 Ma.Rollback of a NW-dipping subduction zone to the SE of the ca.488 Ma suture began at 473 Ma and led to lithospheric-scale extension,decompression melting and advective heating of the middle crust,producing the widespread ca.470 Ma Grampian(classic Barrovian and Buchan)regional metamorphism.Resumed hinge advance and the final phase of shortening cut off the heat supply at ca.465 Ma,marking the end of the Grampian Orogeny.     

World Cities in the Pacific Rim: A New Global Test of Regional Coherence

A new evaluation of the Pacific Rim concept is presented. The originality of this test for regional coherence is to be found in the basic units being analysed: cities instead of states. Based on a theoretical framework that identifies world city and world city network formation in terms of the office networks of advanced producer service firms, we use a principal components analysis to analyse a data set of 28 Pacific Rim cities and 46 global service firms. This identifies five main groupings of cities in terms of similar mixes of corporate service firms: a western Rim group; a group of ‘old Commonwealth’ cities; a market communist group of cities; Tokyo as a global city; and US cities as a specific separate group. These results confirm numerous earlier studies that were sceptical of the existence of a coherent Pacific Rim region. However, the particular approach adopted here allows us to identify the Pacific Rim generically as a particularly pernicious construct. We conclude that the Pacific Rim is a geographical chaotic conception.     

Effect of clayey media parameters on the negative response of a coincident loop1

The aim of this work is to consider the phenomenon of negative response and its detectability in a polarizable half-space formed of Clay-water mixture which commonly exists in water aquifers and which can be used as a simple indicator of the presence of Underground water. We make use of an analytical treatment for the transient voltage induced in a coincident loop lying on a half-space as a basis for our computations. A Cole-Cole model is used to represent the Clay with appropriate parameters. As saturated Clay is characterized by high conductivity and moderate chargeability, it is hardly detectable relative to the practical noise level. However, there are optimum Clay parameters that offer a maximum negative response. It is also observed that for a very short time constant τ in the Cole-Cole model, the amplitude of the negative response decreases with the decrease of the time constant due to the fast decay of the polarization current. Finally, it is found that there is an optimum value for the loop radius which gives the largest value of the negative response and this loop radius depends on the model parameters.