Evolution of In Situ Rock Mass Damage Induced by Mechanical–Thermal Loading

To understand and predict the in situ brittle rock mass damage process induced by a coupled thermo-mechanical loading, the knowledge of rock mass yielding strength, scaling relationship between laboratory and in situ and microstructure characterization is required. Difficulties have been recognized due to the seldom availability of in situ experiment and appropriate numerical methodologies. The Äspö Pillar Stability Experiment was used to monitor the evolution of rock mass damage in a pillar of rock separating two 1.75-m diameter vertical boreholes. The loading of the pillar was controlled using the in situ stresses, excavation geometry, and locally increasing the rock temperature. The induced loading resulted in a complex discontinuum process that involved fracture initiation, propagation, interaction and buckling, all dominated by a tensile mechanism. Tracking this damage process was carried out in two steps. Initially, a three-dimensional numerical model was used to generate the stresses from the excavation geometry and thermal loading. The plane strain stresses, at selected locations where detailed displacement monitoring was available, were then used to track the evolution of damage caused by these induced stresses. The grain-based discrete element modeling approach described in Lan et al. (2010), which captures the grain scale heterogeneity of the rock, was used to establish the extent of damage. Good agreement was found between the predicted and measured temperatures and displacements. The grain-based model provided new insights into the progressive failure process.     

Quantitative high-resolution warm season rainfall recorded in varved sediments of Lake Oeschinen,northern Swiss Alps: calibration and validation AD 1901–2008

High-resolution, well-calibrated records of lake sediments are critically important for quantitative climate reconstructions, but they remain a methodological and analytical challenge. While several comprehensive paleotemperature reconstructions have been developed across Europe, only a few quantitative high-resolution studies exist for precipitation. Here we present a calibration and verification study of lithoclastic sediment proxies from proglacial Lake Oeschinen (46°30′N, 7°44′E, 1,580 m a.s.l., north–west Swiss Alps) that are sensitive to rainfall for the period AD 1901–2008. We collected two sediment cores, one in 2007 and another in 2011. The sediments are characterized by two facies: (A) mm-laminated clastic varves and (B) turbidites. The annual character of the laminae couplets was confirmed by radiometric dating (²¹⁰Pb, ¹³⁷Cs) and independent flood-layer chronomarkers. Individual varves consist of a dark sand-size spring-summer layer enriched in siliciclastic minerals and a lighter clay-size calcite-rich winter layer. Three subtypes of varves are distinguished: Type I with a 1–1.5 mm fining upward sequence; Type II with a distinct fine-sand base up to 3 mm thick; and Type III containing multiple internal microlaminae caused by individual summer rainstorm deposits. Delta-fan surface samples and sediment trap data fingerprint different sediment source areas and transport processes from the watershed and confirm the instant response of sediment flux to rainfall and erosion. Based on a highly accurate, precise and reproducible chronology, we demonstrate that sediment accumulation (varve thickness) is a quantitative predictor for cumulative boreal alpine spring (May–June) and spring/summer (May–August) rainfall (r_MJ = 0.71, r_MJJA = 0.60, p < 0.01). Bootstrap-based verification of the calibration model reveals a root mean squared error of prediction (RMSEP_MJ = 32.7 mm, RMSEP_MJJA = 57.8 mm) which is on the order of 10–13 % of mean MJ and MJJA cumulative precipitation, respectively. These results highlight the potential of the Lake Oeschinen sediments for high-resolution reconstructions of past rainfall conditions in the northern Swiss Alps, central and eastern France and south-west Germany.     

BUSINESS CLUSTERS IN THE SOUTH: A CRITICAL APPRAISAL FROM INDONESIAN EVIDENCE

Advocacy of the advantages accruing to business clusters in developing economies has followed that in developed economies. With doubts emerging about the evidence for these in developed economies, it is therefore appropriate to review the experience in the developing world. A model of cluster emergence and growth has guided accounts of developing country clusters. Drawing on experience from Indonesia, doubts are raised about that model's prediction of the emergence of successful joint action in maintaining cluster advantages. Any advantages from clustering are insufficient to face development challenges arising from the globalisation of economic activity. The significance of business clusters in low income economies needs to be reviewed in the light of actual experience and the reappraisal emerging in developed or high income countries.     

A three-dimensional image of shallow subduction: crustal structure of the Raukumara Peninsula, New Zealand

Earthquake arrival time data from a 36-station deployment of portable seismographs on the Raukumara Peninsula have been used to determine the 3-D Vp and Vp/Vs structure of this region of shallow subduction. A series of inversions have been performed, starting with an inversion for 1-D structure, then 2-D, and finally 3-D. This procedure ensures a smooth regional model in places of low resolution. The subducted plate is imaged as a northwest-dipping feature, with Vp consistently greater than 8.5  km  s⁻¹ in the uppermost mantle of the plate. Structure in the overlying plate changes significantly along strike. In the northeast, there is an extensive low-velocity zone in the lower crust underlying the most rapidly rising part of the Raukumara Range. It is bounded on its arcward side by an upwarp of high velocity. A viable explanation for the low-velocity zone is that it represents an accumulation of underplated subducted sediment, while serpentinization of the uppermost mantle may be responsible for the adjacent high-velocity region. The low-velocity zone decreases and the adjacent high-velocity region is less extensive in the southwest. This change is interpreted to be related to a change in the thickness of the crust of the overlying plate. In the northeast the crust is thinner, and subducted sediment ponds against relatively strong uppermost mantle, while in the southwest the crust is thicker, and the relatively weak lower crust allows sediment subduction to greater depths. A narrow zone of high Vp/Vs parallels the shallow part of the plate interface. This suggests elevated fluid pressures, with the distribution of earthquakes about this zone further suggesting that these pressures may be close to lithostatic. The plate interface at 20  km depth beneath the Raukumara Peninsula may thus be a closed system for fluid flow, similar to that seen at much shallower depths in other subduction décollements.