Accelerograph calibration and accelerogram correction

When measured earthquake accelerations are used as a basis for structural design, then acceleration errors of a few per cent are usually acceptable. However a number of tasks in structural design, and in earthquake engineering research, require measured accelerations with errors limited to a few parts per thousand. Such tasks include those which call for the calculation of angular accelerations, the comparison of acceleration spectra or the calculation of relative displacement Accurate accelerations may be obtained from existing accelerographs by applying the results of an accurate static calibration to an accelerogram, and then applying corrections for the effects of accelerometer resonance. This paper concentrates attention on the correction of static errors, including sensing direction errors and cross-axis interaction errors. For completeness there is a brief discussion of dynamic errors, which depend on accelerometer periods and dampings. It is concluded that earthquake accelerations may be obtained with errors of not much more than 0·001 g, the resolution of a typical accelerograph, at least for periods greater than 0·2 sec. When the accelerations have shorter periods, larger errors may arise due to the limited accuracy of the corrections for dynamic errors The static calibration of accelerographs, and the corresponding record correction procedures, are illustrated by application to the M.O.2 accelerograph.     

Reliability of dipole-dipole electrical resistivity tomography for defining depth to bedrock in covered karst terranes

 Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Because of the irregular distribution of pinnacles and cutters on the bedrock surface, uncertainties arise when "hit-or-miss" borehole drilling is used to locate potential collapse sites. A high-resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding the drilling program. Dipole-dipole electrical resistivity tomography (ERT) was used to map the bedrock surface at a site in southern Indiana where limestone is covered by about 9 m of clayey soils. Forty-nine transects were conducted over an area of approximately 42,037 m². The electrode spacing was 3 m. The length of the transects varied from 81 to 249 m. The tomographs were interpreted with the aid of soil borings. The repeatability of ERT was evaluated by comparing the rock surface elevations interpreted from pairs of transects where they crossed each other. The average difference was 2.4 m, with a maximum of 10 m. The discrepancy between interpreted bedrock-surface elevations for a transect intersection may be caused by variations in the subsurface geology normal to the transect. Averaging the elevation data interpreted from different transects improved the ERT results. A bedrock surface map was generated using only the averaged elevation data at the transect junctions. The accuracy of the map was further evaluated using data from four exploratory boreholes. The average difference between interpreted and actual bedrock surface-elevations was less than 0.4 m. The map shows two large troughs in the limestone surface: one coinciding with an existing sinkhole basin, while the other is in alignment with a small topographic valley. Because sinkholes were observed at the same elevation interval in similar valleys in the vicinity, the delineated trough may have implications for future land use at the site. Received: 4 January 1999 · Accepted: 8 March 1999     

The behaviour of ulvöspinel samples containing magnetized inclusions

Composite samples containing either magnetized iron or a ferrite magnet embedded in ulvöspinel have been cooled through the ulvöspinel Curie point. The observed changes in magnetic moment which occur are shown to be a result of TRM acquisition in the ulvöspinel rather than an effect of high permeability. Nevertheless by defining an effective permeability of about (1 + TRM/H), magnetostatic theory relevant to magnetized inclusions in a permeable medium can be applied to explain the main features observed in this system.     

A major lava tube system from Undara Volcano,North Queensland

The Undara Volcano erupted 0.19 m.y. ago and formed lava fields covering 1,500 km² with a volume of approximately 23 km³. One of the flows extended 160 km on a gradient that averaged only 0.3°. This great length was a result of very high effusion rates, favourable topography and lava tube efficiency. The Undara lavas are rather uniform hawaiites. Lava temperatures are estimated to have been somewhat less than 1175–1220°C and viscosities greater than 10 to 30 Pa s. Long, apparently single lava tubes are well preserved in many places. They are marked by depressions, caves and long level ridges. A system of lava tubes extends for perhaps more than 100 km. The features of the lava tubes are comparable with those described elsewhere. Aligned depressions associated with caves appear to have formed contemporaneously. Most are much wider than the caves and probably represent collapsed lava ponds. The lava tubes appear to have formed by roofing over of lava channels. Close to lava tubes, the rocks developed strongly oxidised characteristics, such as oxidised olivine phenocrysts, ferric clinopyroxene and extensively developed hematite. Differentiated lava forms drips in some caves and is also oxidised.     

Toward spatial understanding of environmentally-based voluntary groups

An attempt is made in this paper to complement existing analyses of voluntary groups by outlining some additional explicitly spatial dimensions which, it is argued, can be useful in examining those organizations with a land use or environmental focus. The distinction is drawn between groups which have direct spatial links and those with indirect spatial links; the hierarchical subdivision of space is considered; the role of scale and its relation to perception and desired use of areas is addressed; and the importance of considering the resolution scale of land use and environmental conflicts noted.     

Coexisting garnets and biotites from Precambrian gneisses of the south coast of Western Australia

Garnet-biotite (-cordierite) phase relations in high-grade gneisses of the south coast of Western Australia reflect at least two metamorphic episodes. Chemical uniformity of the interiors of garnet and cordierite grains suggest thorough equilibration during a major phase of metamorphism. Narrow Mg-depleted rims on garnet grain boundaries in contact with biotite or cordierite, and complementary Mg-enriched rims on contiguous cordierites are the result of subsequent retrograde re-equilibration. The absence of reaction zoning in biotites suggests more complete retrograde modification of this mineral.Comparison between granulite and amphibolite facies garnet-biotite pairs shows that Mn contents of both minerals are higher, and Ti contents of the biotites are lower, in the lower-grade rocks. These differences, although not entirely unrelated to grade, are more directly controlled by variations in host rock chemistry and modal amounts of garnet and biotite.Partitioning of Mg, Fe²⁺ and Mn between garnet and biotite is fairly uniform, with no clear differences between granulite and amphibolite facies pairs. Application of the Mg-Fe²⁺ distributions to the geothermometers devised by Perchuk, Thompson, and Goldman & Albee yields variable T estimates of 600–680°C, 580–780°C, and 475–715°C respectively, for the main metamorphism. These estimates are low compared with the T indicated for the granulite facies rocks by other evidence (i.e. > 750°C at 5 kb P_T). The Mg-Fe²⁺ distributions between contiguous garnet-biotite rims suggest that retrograde re-equilibration occurred at least 20–140°C below the T of the main metamorphism.     

Assessing the effect of domain size over the Caribbean region using the PRECIS regional climate model

This study investigates the sensitivity of the one-way nested PRECIS regional climate model (RCM) to domain size for the Caribbean region. Simulated regional rainfall patterns from experiments using three domains with horizontal resolution of 50 km are compared with ERA reanalysis and observed datasets to determine if there is an optimal RCM configuration with respect to domain size and the ability to reproduce important observed climate features in the Caribbean. Results are presented for the early wet season (May–July) and late wet season (August–October). There is a relative insensitivity to domain size for simulating some important features of the regional circulation and key rainfall characteristics e.g. the Caribbean low level jet and the mid summer drought (MSD). The downscaled precipitation has a systematically negative precipitation bias, even when the domain was extended to the African coast to better represent circulation associated with easterly waves and tropical cyclones. The implications for optimizing modelling efforts within resource-limited regions like the Caribbean are discussed especially in the context of the region’s participation in global initiatives such as CORDEX.     

Adaptation to climate change in glaciated mountain regions

Understanding of the human dimensions of climate change (HDCC) in glaciated mountain regions is limited by a deficit in systematically collated information on where, to what stressors, by whom, at what scale, and with what effect adaptation is occurring. This paper presents a systematic literature review of the recent English language peer-reviewed scholarship on adaptation in glaciated mountain regions. 4050 potentially relevant articles were examined, with 36 included for full review. Results indicate that scholarly investigation into adaptation in glaciated mountains is presently limited to only 40 % of countries with alpine glaciation. Seventy-four discrete adaptation initiatives were identified, with most occurring in Peru (28 %), Nepal (22 %) and India (17 %). Many documented adaptations were initiated in response to intersecting stressors related to cryospheric change and socio-economic development; were autonomous and initiated in reaction to experienced climatic stimuli; and were carried out at the individual, family, or community scale. The study contributes to an emerging literature tracking on-the-ground adaptation processes and outcomes, and identifies a need to raise the profile of human adaptation in glaciated mountain regions within the HDCC scholarship. A research agenda for addressing key knowledge gaps and questions is developed, providing a framework for future investigation.