A test of the semyenov prediction technique in the central Aleutian Islands

The earthquake-prediction technique based on systematic temporal variations in the ratio of the two body-wave velocities has been tested for selected events in the central Aleutian Islands. The goal was to determine if the phenomenon occurs for earthquakes in an active island arc. Two groups of earthquakes were selected, each in a concentrated source volume and well-placed with respect to the available local seismograph network, one relatively shallow (20 km) and the other along the thrust zone (about 45 km deep).Observational difficulties inherent to an island arc, namely the depth of the hypocenters, the high noise levels, and the complex geology, limit the number of events available for analysis and cause considerable scatter in the data. Nevertheless, a positive result, in which the velocity ratio decreased by about 5%, was obtained for at least one event in the shallow group for which there were sufficient preceding events to establish a definite trend. No premonitory changes were seen for the deeper source volume.A simple extension of the theory of the Wadati diagram permits an estimate of the velocity ratio in the overlying layers as well as in the source medium. The data indicate that under Amchitka Island, the velocity ratio is 1.82 (Poisson's ratio 0.28) in the upper 10 km and 1.71–1.72 (Poisson's ratio 0.24) from 10 km to at least 45 km.     

Carbon content and carbonate 13C abundances in the Early Precambrian Swaziland sediments of South Africa

Carbon content (0.02–0.68% organic), carbonate content (0–69.7%) and carbonate ¹³C abundances (${}^{\mathrm{?}}\text{7.5?+2.3‰}$) were obtained on samples from the Swaziland sediments of South Africa, which are among the oldest known sedimentary rocks on earth (> 3·10⁹ years old). The carbon chemistry of these sediments may serve as evidence for early life and/or for products of chemical evolution. The variation of organic and carbonate carbon concentrations in different sedimentary horizons seems to be controlled by differences in depositional and diagenetic histories. The carbonate δ ¹³C values did not vary significantly from the ordinary range of Phanerozoic limestone values.     

A statistical analysis of tree-ring dating in conjunction with snow avalanches: Comparison of on-path versus off-path responses

Tree-rings were collected from snow-avalanche paths in Colorado, and from positions away from avalanche paths. The rings were examined for morphological responses to avalanche-induced trauma. Use of the Chi-square statistic revealed a significant difference in the number of morphological responses from on-path versus off-path positions. A high number of on-path trees were definitely damaged by avalanche impact in 1973; a lower number of trees from off-path positions illustrated morphologic ring-responses from random, nonavalanche, events in the same year.     

Measurement of cordgrass,Spartina alterniflora,production in a macrotidal estuary,Bay of Fundy

A one-year field study was conducted of the growth, mortality, and loss dynamics of aSpartina alterniflora low marsh in the Minas Basin, a macrotidal estuary at the head of the Bay of Fundy. Data were used to examine the suitability of four methods for estimating annual net aerial primary production (NAPP) of a marsh subject to energetic tidal flooding. Shoots start to grow in April and reach maximum height (about 0.5 m) and weight in October. Maximum shoot density (900–1,600 m^?2) occurs around June and drops thereafter due to the export of entire shoots. The average shoot produces about seven leaves and at least 2–3 are lost during the growing season. All remaining vegetation dies before the end of November. Methods based on harvesting vegetation underestimated NAPP, especially at lower elevations where export is greater due to more frequent and prolonged tidal flooding. The highest NAPP values, on the order of 500–600 g m^?2 y^?1, were obtained using methods based on the population dynamics of individual shoots. These methods are recommended for energetic tidal environments because they include the production of vegetation exported during the growing season.     

Dominance of Tilapia mossambica,an introduced fish species,in three Puerto Rican estuaries

We compared species presence, abundance, and size characteristics of fish in three brackish, coastal marshes at Humacao, Roosevelt Roads, and Boqueron, Puerto Rico, in February and March 1988. The three marsh ecosystems were similar with respect to the presence of large expanses of open water bordered by emergent vegetation, creeks, and mangroves, and all had some recreational use. We sampled fish using gill nets. Tilapia (Oreochromis) mossambica were the most abundant fish, accounting for 55–79% of the samples at all three marshes. Overall, tilapia were both the largest (North Lagoon) and the smallest (Frontera Creek) at Humacao. Tilapia were most common in open lagoons rather than creeks or bays (except for Mandri Creek), and their distribution seemed unrelated to salinity. Tarpon (Megalops atlantica) were more abundant at low salinities, whereas other fish were more abundant at higher salinities.     

The effect of composition on the ferric-ferrous ratio in basaltic liquids at atmospheric pressure

The effects on the ferric-ferrous ratio of varying individual components in a dry basaltic liquid have been determined at atmospheric pressure and constant oxygen fugacity (fO₂). Experiments were conducted by suspending 100 mg samples from pt loops at 1200°C (fO₂ = 10^?8atm) and 1360°C (fO₂ = 10^?6atm) in an atmosphere controlled by mixtures of CO₂ and H₂. A microanalytical wetchemical technique and the electron microprobe were used to determine the composition of the resulting basaltic glasses. In order of decreasing significance, the addition of oxides of K, Na, Si, Al, or Ca produces an increase in the ferric-ferrous ratio of the melt at 1200°C. The change in the ferric-ferrous ratio produced by component addition is less at 1360°C than at 1200°C.     

On the temperature dependence of possible S8 infrared bands in planetary atmospheres

Measurements of the temperature dependence between 77 and 333°K of the infrared spectrum of cyclic octatomic sulfur suggest that the 23 μm Jovian feature very tentatively identified by Houck et al. [Science 189, 720–722 (1975)] is not due to S₈; and that the temperature dependence of the frequency of the 835 cm^? band of S₈ may be a useful temperature marker in planetary studies.     

Physical properties of the particles composing the Martian dust storm of 1971–1972

Infrared spectra obtained from the Mariner 9 spacecraft during the 1971–1972 dust storm are used to derive information on the composition and particle size distribution of the dust and to study the time evolution of the storm. The dust is not composed of pure granite, basalt, basaltic glass, obsidian, quartz, andesite, or montmorillonite. The infrared spectra suggest that the dust is a mixture of materials, dominated by igneous silicates with >62;60% SiO₂, or weathering products such as clay minerals, but the dust could possibly have a significant component of lower SiO₂ materials such as basalt. Substantial quantities of carbonates, nitrates, or carbon suboxide are excluded from the mixture. All infrared, visible, and ultraviolet data on the Martian surface composition seem consistent with a mixture of basalt and clay minerals or high SiO₂ igneous rocks, with a surface patina of oxides of iron. For all candidate compositions, the data are best matched with a size distribution that approximates a differential power law function of slope ?4. This size distribution is quite similar to terrestial size distributions in regions remote from sources of dust. The relative abundance of particles between 1- and 10-μm radius did not change during the Mariner 9 mission; thus suspended particles did not experience Stokes-Cunningham fallout but instead were supported by turbulence with an eddy diffusion coefficient, $\text{K}{}_{\mathrm{<mtext>e</mtext>}}\text{? 7 × 10}{}^6\text{cm}{}^2\text{sec}{}^{\mathrm{?1}}$. The aerosol optical depth, standardized to 0.3-μm wavelength, varied from about 1.5 early in the mission to about 0.2 at Orbit 200.