Effect of sampling and linkage on fault length and length–displacement relationship

The power-law exponent (n) in the equation: D=cL ⁿ , with D = maximum displacement and L = fault length, would be affected by deviations of fault trace length. (1) Assuming n=1, numerical simulations on the effect of sampling and linkage on fault length and length–displacement relationship are done in this paper. The results show that: (a) uniform relative deviations, which means all faults within a dataset have the same relative deviation, do not affect the value of n; (b) deviations of the fault length due to unresolved fault tip decrease the values of n and the deviations of n increase with the increasing length deviations; (c) fault linkage and observed dimensions either increase or decrease the value of n depending on the distribution of deviations within a dataset; (d) mixed deviations of the fault lengths are either negative or positive and cause the values of n to either decrease or increase; (e) a dataset combined from two or more datasets with different values of c and orders of magnitude also cause the values of n to deviate. (2) Data including 19 datasets and spanning more than eight orders of fault length magnitudes (10⁻²–10⁵ m) collected from the published literature indicate that the values of n range from 0.55 to 1.5, the average value being 1.0813, and the peak value of n _d (double regression) is 1.0–1.1. Based on above results from the simulations and published data, we propose that the relationship between the maximum displacement and fault length in a single tectonic environment with uniform mechanical properties is linear, and the value of n deviated from 1 is mainly caused by the sampling and linkage effects.     

Petrology of ultramafic and mafic xenoliths in picrite of Kahoolawe Island,Hawaii

A picrite lava (22 wt% MgO; 35 vol.% ol) along the western shore of the1.3–1.4 Ma Kahoolawe tholeiitic shield, Hawaii, contains small xenoliths of harzburgite, lherzolite, norite, and wehrlite. The various rock types have textures where either orthopyroxene, clinopyroxene, or plagioclase is in a poikilitic relationship with olivine. The Mg#s of the olivine, orthopyroxene, and clinopyroxene in this xenolith suite range between 86 and 82; spinel Mg#s range from 60 to 49, and plagioclase is An_75–80. A ⁸⁷Sr/⁸⁶Sr ratio for one ol-norite xenolith is 0.70444. In comparison, the host picrite has olivine phenocrysts with an average Mg# of 86.2 (range 87.5–84.5), and a whole-rock ⁸⁷Sr/⁸⁶Sr ratio of 0.70426. Textural and isotopic information together with mineral compositions indicate that the xenoliths are related to Kahoolawe tholeiitic magmatism, but are not crystallization products of the magma represented by their host picrite. Rather, the xenoliths are crystalline products of earlier primitive liquids (FeO/MgO ranging 1 to 1.3) at 5–9 kbar in the cumulate environment of a magma reservoir or conduit system. The presence of ultramafic xenoliths in picrite but not in typical Kahoolawe tholeiitic lava (6–9 wt% MgO) is consistent with replenishment of reservoirs by dense Mg-rich magma emplaced beneath resident, less dense tholeiitic magma. Mg-rich magmas have proximity to reservoir cumulate zones and are therefore more likely than fractionated residual liquids to entrain fragments of cumulate rock.     

Marine geology in the environs of Bouvet Island and the South Atlantic triple juction

It is suggested that Bouvet Island is the surface manifestation of a mantle plume which has resulted in the creation of a chain of seamounts in the South Atlantic and a general shoaling of the region.The strike of two newly defined large fracture zones borth and south of the Bouvet Island pedestal have been utilized to determine a pole of rotation at 12.5°S, 12.5°W for the Africa-Antarctica motion. A pole at 75°S, 13°E has been calculated for the South America-Antarctica motion. At the triple junction the South America-Africa relative motion is 3.3 cm yr^-1 (whole rate) at 075°. The Africa-Antarctica motion is 1.7 cm yr^-1 at 065° and the South America-Antarctica motion is 1.6 cm yr^-1 at 085.     

Palaeointensity In the Pelagic Realm: Marine Sediment Data Compared With Archaeomagnetic and Lake Sediment Records

Summary. Four box cores collected from the Ontong—Java plateau during the Eurydice expedition have been used to make relative geomagnetic palaeo-intensity measurements. Rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy, and that they are suitable for relative intensity estimates. These are obtained by normalizing the NRM by an ARM imparted in a low DC bias field. the palaeoceanographic event known as the preservation spike is used to establish a crude time-scale for the record so that it may be compared with other data from the same region, and also with global palaeointensity estimates. the marine sediment data are quite similar to Australian intensity data from lake sediments and archaeomagnetic sources, but as might be expected exhibit some obvious differences from the global record.     

A numerical study of the nocturnal heat island over a medium-sized mid-latitude city (Columbus,Ohio)

A numerical investigation is conducted of the nocturnal heat island over Columbus, Ohio, a relatively flat mid-latitude city. Specifically, a cross-sectional steady-state numerical model to simulate the (thermal) structure of the nocturnal urban boundary layer is developed from a one-dimensional, time-dependent model due to Estoque. The model is applied to Columbus for special periods in September 1968 and March 1969 during which comparable experimental data were collected. The numerical simulations agree well with the observed data with respect to the detailed spatial form of the surface-based thermal boundary layer across the city. The use of the model for other metropolitan areas, for ascertaining the relative effect of city size and building geometry on the development of the thermal boundary layer, and for determining the effect of alternate land-use strategies on the thermal stratification are also discussed.Digest of portion of a dissertation submitted to the Pennsylvania State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.Presented in part at the Air Pollution, Turbulence and Diffusion Symposium, Las Cruces, New Mexico, 7–10 December 1971.On assignment from the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce.     

The effects of source size on concentration fluctuations in plumes

The effects of source size on plume behaviour have been examined in a 1.2 m wind tunnel boundary layer for isokinetic sources with diameters from 3 to 35 mm at source heights of 230 mm and at ground level. Experimental measurements of mean concentration and the variance, intermittency and probability density functions of the concentration fluctuations were obtained. In addition, a fluctuating Gaussian plume model is presented which reproduces many of the observed features of the elevated emission. The mean plume width becomes independent of source size much more rapidly than the instantaneous plume width. Since it is the meandering of the instantaneous plume which generates most of the concentration fluctuations near the source, these are also dependent on source size. The flux of variance in the plume reaches a maximum, whose value is greatest for the smallest source size, close to the source and thereafter is monotonically decreasing. The intermittency factor reaches a minimum, whose value is lowest for the smallest source, and increases back towards one. Concentration fluctuations for the ground-level source are much less dependent on source size due to the effects of the surface.     

Long-term comparison of macrobenthos within the soft bottoms of the Bay of Banyuls-sur-mer (northwestern Mediterranean Sea)

The macrofauna present at seven of the stations within the Bay of Banyuls-sur-mer (northwestern Mediterranean) initially sampled by Guille during the late 1960s was reassessed in 1994, using the same gear and techniques as those used during the reference study. Results showed an increase both in the number of species and of individuals (all species pooled) per unit of surface area at nearly all stations. This trend was not significant for total biomass. The most important changes were linked to the increase of the polychaete Ditrupa arietina (both within the Spisula subtruncata and the Nephtys hombergii community) and the decrease of the polychaetes Scoloplos armiger and Notomastus latericeus within the Scoloplos armiger community. The possible causes underlying these changes are discussed. The most probable cause is considered to be a slight modification of sediment composition (decrease of fine material in the sediment) within the Spisula subtruncata, the Nephtys hombergii and the Scoloplos armiger communities. Temporal changes in (1) Rhone river input, (2) small coastal river inputs, and (3) frequency of easterly storms may all have contributed to such a decrease.