Fault type analysis along the San Andreas Fault zone: A numerical approach

Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was thought justifiable as the variation in depth from 0.5 km to 20 km was considered. Series of calculations were performed with the variation in domain properties. Three types of models were created based on simple geological map of California, namely, 1) single domain model considering whole California as one homogeneous domain, 2) three domains model including the North American plate, Pacific plate, and SAF zone as separate domains, and 3) Four domains model including the three above plus the Garlock Fault zone. Mohr-Coulomb failure criterion and Byerlee's law were used for the calculation of failure state. All the models were driven by displacement boundary condition imposing the fixed North American plate and Pacific plate motion along N34°W vector up to the northern terminus of SAF and N50°E vector motion for the subducting the Gorda and Juan de Fuca plates. Our simulated results revealed that as the depth increased, the fault types were generally normal, and at shallow depth greater strike slip and some thrust faults were formed. It is concluded that SAF may be terminated as normal fault at depth although the surface expression is clearly strike slip.     

Stability Dependence and Diurnal Change of Large-Scale Turbulence Structures in the Near-Neutral Atmospheric Boundary Layer Observed from a Meteorological Tower

Based on the analysis of observations from a 213-m tall meteorological tower at Tsukuba, Japan, we have investigated the favourable conditions for the predominant existence of large-scale turbulence structures in the near-neutral atmospheric boundary layer (ABL). From the wavelet variance spectrum for the streamwise velocity component ( $u$ ) measured by a sonic anemometer-thermometer at the highest level (200 m), large-scale structures (time-scale range of 100–300 s) predominantly exist under slightly unstable and close to neutral conditions. The emergence of large-scale structures also can be related to the diurnal evolution of the ABL. The large-scale structures play an important role in the overall flow structure of the lower boundary layer. For example, $u$ velocity components at the 200-m and 50-m levels show relatively high correlation with the existence of large-scale structures. Under slightly unstable (near-neutral) conditions, a low-speed region in advance of the high-speed structure shows a positive deviation of temperature and appears as the plume structure that is forced by buoyancy in the heated lower layer. In spite of the difference in buoyancy effects between the near-neutral and unstable cases, large-scale structures are frequently observed in both cases and the same vertical correlation of $u$ components is indicated. However, the vertical wind shear is smaller in the unstable cases. On the other hand, in near-neutral cases, the transport efficiency of momentum at the higher level and the flux contribution of sweep motions are larger than those in the unstable cases.     

Standardization of baseline and additionality determination under the CDM

Clean Development Mechanism (CDM) project developers have long complained about the complexities of project-specific baseline setting and the vagaries of additionality determination. In response to this, the CDM Executive Board took bold steps towards the standardization of CDM methodologies, culminating in the approval of guidelines for the establishment of performance standards in November 2011. The guidelines specify a performance standard stringency level for both baseline and additionality of 80% for several priority sectors and 90% for all other sectors. However, an analysis of 14 large-scale CDM methodologies that use performance standard approaches challenges this top-down approach to the performance standard design. An appropriate performance standard stringency level strongly depends on sector and technology characteristics. A single stringency level for baseline and additionality determination is appropriate only for greenfield projects, but not for retrofit ones. Overly simple, highly aggregated performance standards are unlikely to ensure high environmental integrity, and difficult questions regarding stringency and updating frequency will eventually have to be addressed on a rather disaggregated level. A careful balance between data requirements and the practicability of performance standards is essential because the heavy data requirements of the existing performance standard methodologies have been the key barrier to their actual implementation.

Policy relevance

CDM regulators have been pushed by many stakeholders to standardize baseline setting and eliminate project-specific additionality determination. At first glance, performance standards seem to provide the perfect solution for both tasks. However, a one-size-fits-all political decision – e.g. the average of the top 20% performers as enshrined in the Marrakech Accords – is inappropriate. Substantial disaggregation of performance standards is required both technologically and geographically in order to limit over- and under-crediting and close loopholes for non-additional projects. As a lack of reliable and complete data has been and will be a key bottleneck for the development of performance standards, international support for data collection will be indispensable, but costly, and time-consuming. Empirically driven, techno-economic assessments of performance standard stringency levels must be the central task of the future work on standardized methodologies, and should not be sidelined by perceived needs of policy makers to take bold decisions under time pressures.     

Alpine Hydrogeology: The Critical Role of Groundwater in Sourcing the Headwaters of the World

Groundwater discharge in alpine headwaters sustains baseflow in rivers originating in mountain ranges of the world, which is critically important for aquatic habitats, run-of-river hydropower generation, and downstream water supply. Groundwater storage in alpine watersheds was long considered negligible, but recent field-based studies have shown that aquifers are ubiquitous in the alpine zone with no soil and vegetation. Talus, moraine, and rock glacier aquifers are common in many alpine regions of the world, although bedrock aquifers occur in some geological settings. Alpine aquifers consisting of coarse sediments have a fast recession of discharge after the recharge season (e.g., snowmelt) or rainfall events, followed by a slow recession that sustains discharge over a long period. The two-phase recession is likely controlled by the internal structure of the aquifers. Spatial extent and distribution of individual aquifers determine the groundwater storage-discharge characteristics in first- and second-order watersheds in the alpine zone, which in turn govern baseflow characteristics in major rivers. Similar alpine landforms appear to have similar hydrogeological characteristics in many mountain ranges across the world, suggesting that a common conceptual framework can be used to understand alpine aquifers based on geological and geomorphological settings. Such a framework will be useful for parameterizing storage-discharge characteristics in large river hydrological models.     

Quantifying terrain controls on runoff retention and routing in the Northern Prairies

The role of hummocky terrain in governing runoff routing and focussing groundwater recharge in the Northern Prairies of North America is widely recognised. However, most hydrological studies in the region have not effectively utilised information on the surficial geology and associated landforms in large-scale hydrological characterization. The present study uses an automated digital elevation model (DEM) analysis of a 6500-km² area in the Northern Prairies to quantify hydrologically relevant terrain parameters for the common types of terrains in the prairies with different surficial deposits widespread in the prairies, namely, moraines and glaciolacustrine deposits. Runoff retention (and storage) capacity within depressions varies greatly between different surficial deposits and is comparable in magnitude with a typical amount of seasonal snowmelt runoff generation. The terrain constraint on potential runoff retention varies from a few millimetres in areas classified as moraine to tens of millimetres in areas classified as stagnant ice moraine deposits. Fluted moraine and glaciolacustrine deposits have intermediate storage capacity values. The study also identified the probability density function describing a number of immediate upstream neighbours for each depression in a fill-and-spill network. A relationship between depression parameters and surficial deposits, as well as identified depression network structure, allows parametrisation of hydrologic models outside of the high-resolution DEM coverage, which can still account for terrain variation in the Prairies.     

Mineralogy,Fluid Inclusions,and Sulfur Isotopes of the Huanzala Deposits,Peru: Early Skarn and Late Polymetallic Replacement Style Mineralizations

Carbonate‐replacement polymetallic mineralization at the Huanzala deposits (9°51′S, 77°00′W) was conducted in two contrasting stages that occurred in almost the same location. Early‐stage mineralization has a relation with a granodiorite porphyry stock, whereas the late‐stage mineralization is genetically associated with quartz porphyry sills. The early stage involved low to intermediate sulfidation Cu–Zn–(Pb) mineralization associated with metasomatic skarn, and the late stage involved high to intermediate sulfidation Cu–Zn–Pb–(Mn) mineralization associated with hydrothermal alteration characterized by paragonitic sericitization. The orebodies are hosted by steeply dipping (approximately 60°NE) Lower Cretaceous carbonate rocks in a relatively narrow range of approximately 4 km in horizontal extent and less than 1 km in depth. The pathway of the early‐stage brine‐derived fluids (300–>400°C, >33 wt% NaCl equivalent) along a plot of log against 1000/T is best explained by the progressive dual decline of the value and the temperature under rock‐buffering conditions; this decline saw the pathway progress through the stability field of pyrrhotite to reach that of pyrite and promoted a decrease in FeS from 14.5 to 1.6 mol% in the sphalerite. In contrast, an explanation for the pathway of the late‐stage fluids (140–290°C, 3–13 wt% NaCl equivalent) is given by an almost isothermal decline at approximately 270°C, with passing through the stability field of pyrite–bornite to reach that of chalcopyrite, promoting an increase in FeS from 0.1 to 1.6 mol% in the sphalerite, suggesting gas‐buffering conditions. The ore formation pressure records in the fluid inclusions illustrate an approximately 2‐km erosion during the roughly 2‐Myr total lifetime of the hydrothermal system.     

Evaluation of change in subsurface thermal environment due to groundwater flow in the Tokyo Lowland,Japan

Information on the distribution of subsurface temperature and hydraulic heads at 24 observation wells in and around the Tokyo Lowland, the eastern part of the Tokyo Metropolitan area, were examined to make clear the relationship between groundwater and the subsurface thermal environment in the urban area. Minimums in temperature–depth logs due to subsurface temperature increasing at shallow parts were recognized in 21 wells. This fact shows subsurface temperature is affected by ground surface warming in almost all of this area. Deeper than minimums, where the effects of surface warming became relatively small, regional variation is observed as follows: high temperatures are shown in the central part to the southern part, and low temperatures shown in the inland to eastern part. The high temperature area corresponds to an area where the lower boundary of groundwater flow is relatively shallow. This area corresponds also to an area with severe land subsidence resulting from excessive groundwater pumping. It is considered that this high temperature area is formed by the effects of upward groundwater flow affected by hydrogeological conditions and pumping. On the other hand, a comparison between past data (1956–1967) and present data (2001–2003) revealed widespread decreasing temperature in the inland area. This is explained by downward groundwater flow based on an analysis of temperature–depth logs. This fact suggests that subsurface temperature is not only increasing from the effects of surface warming but also decreasing from the effects of groundwater environment change due to pumping.     

Swelling–shrinkage properties and soil improvement of compacted expansive soil, Ning-Liang Highway, China

In this paper, the swelling–shrinkage properties of the compacted expansive soil in the Huaiyin Section of the Ning-Lian Highway are introduced, and swelling–shrinkage mechanisms are discussed based on changes in soil water content, dry density, material composition and fabric. The improvement of the compacted expansive soil by lime is also discussed briefly. It is concluded that careful attention should be paid to this type of compacted expansive soil.