Particle size distribution of cataclastic fault materials from Southern California: A 3-D study

The particle size distributions of fault gouge from the San Andreas, the San Gabriel, and the Lopez Canyon faults in Southern California were measured using sieving and Coulter-Counter techniques over a range of particle sizes from 2 m to 16 mm. The distributions were found to be power law (fractal) for the smaller fragments and log-normal by mass for sizes near and above the peak size. The apparent fractal dimensionD of the smaller particles in gouge samples from the San Andreas fault, the San Gabriel fault and the Lopez Canyon gouge were 2.4–3.6, 2.6–2.9 and 2.4–3.0, respectively. The averageD for the Lopez Canyon gouge was 2.7±0.2, which is in agreement with earlier studies of this gouge using planar 2-D sections. The fractal dimension of the finer fragments from all three faults is observed to be correlated with the peak fragment size, with finer gouges tending to have a largerD. A computer automaton is used to show that this observation may be explained as resulting from a fragmentation process which has a grinding limit at which particle reduction stops.     

美国北加州吉塞尔斯诱发地震与热汽田特征的关系

吉塞尔斯地震活动可能是因蒸汽开发引起的.水在一个承受很高构造剪应力和应变的大范围破裂体中汽化为蒸汽。 汽田地震震源机制解与区域构造应变场几乎一致,并且在该区域范围内汽田地震与别的构造地震不易区分。观测中注意到地震活动与注液历史无关,这表明孔隙水压力增高与注液不可能是吉塞尔斯诱发地震的成因。 相反,所有证据都表明诱发地震与孔隙水压力及温度降低有关。形成机制有两种最大可能:其一,是裂隙排水(汽)导致局部剪应力增加所致,其二,是由稳定滑动转化为不稳定滑动(粘滑)。没有其它记载的诱发地震机制与吉塞尔斯汽田条件相符。     

Vertical membrane floating breakwater

The basic purpose of any breakwater is to protect a harbor, moored vessels or an offshore structure from excessive incident wave attack. Breakwater can be classified as either fixed structures or floating ones. The vertical membrane floating breakwater which will be introduced in this paper belongs to the latter.     

Physiological changes in the coastal marine cyanobacterium Synechococcus sp. PCC 7002 exposed to low ferric ion levels

Cyanobacteria are ubiquitous in marine waters. These prokaryotic cells are of particular interest in areas of the ocean where the availability of iron may be limiting for cell growth since these organisms commonly excrete iron-specific organic ligands (siderophores) in response to low levels of iron. It is generally considered that the production of siderophores provides a competitive advantage over the competing microorganisms that do not produce these ligands.In order to ascertain the influence of iron availability on the physiology of picoplanktonic cyanobacteria we performed a series of experiments on the coastal coccoid cyanobacterium, Synechococcus sp. PCC 7002. Physiological responses were examined in cells grown in a continuous cuture system with influx media containing a range of iron concentrations (from 4.2 × 10⁻⁵ to 5.1 × 10⁻⁹ M FeCl₃). Steady-state growth rates, combined with growth data from batch cultures demonstrated a non-linear response between iron availability and cell proliferation: cell yields were considerably higher in the lowest-iron chemostats than predicted based on the yields in the higher-iron chemostats. The higher yields during low-iron growth corresponded with the production of the extracellular siderophores and the induction of the specific iron-siderophore membrane transport proteins. A comparison of iron transport and carbon acquisition rates between the low-iron grown cells and the high-iron grown cells indicates that under low-iron growth conditions, iron and carbon acquisition meets the growth demands of the cells, whereas growth at higher iron levels enabled excessive (luxury) carbon acquisition and storage. We conclude that cyanobacteria are efficiently adapted to grow in low-iron environments (providing sufficient light for photosynthesis is available) and the luxury-uptake of carbon may serve as the source material for the extracellular ligands released by these cells. Since the release of siderophores was at iron levels in excess of the levels that induce the siderophore-mediated transport of iron, cyanobacteria growing in an environment with varying levels of iron may contribute substantial amounts of their stored carbon reserves into the DOC as iron-specific ligands.     

Large-scale oblique features in an active transform fault,the Wilkes fracture zone near 9°S on the East Pacific Rise

The Wilkes fracture zone offsets the East Pacific Rise about 200 km right-laterally near 9°S. The bathymetric expression of the fracture zone ranges from a simple slope or step along its inactive extension to a 100 km wide zone of oblique structural features in the active portion. A low ridge 200 to 300 m high, 5 to 15 km wide and 185 km long is the dominant oblique structure; it trends 23° north of the main transform trend. A high-amplitude magnetic anomaly trends 097° along the southern part of the active portion and apparently marks the main transform direction. The structurally simple, inactive portions of the Wilkes fracture zone trend 105°. Plots of epicenter locations reveal two groupings of earthquakes, one along an 082° trend in the central part of the fracture zone, and a cluster near the southwestern fracture zone — spreading center intersection.Taken together the data suggest that some event, other than a shift in the Nazca-Pacific pole of rotation, occurred 0.9 m.y. ago to change the Wilkes fracture zone from a simple fault to a complex zone of shearing. Since that time the long oblique ridge, probably the surface expression of a Riedel shear, was formed. At present the entire 200 km long, 100 km wide region between the offset axes is seismically active, but transform motion may be largely confined to the southern margin of the active zone, coincident with the high-amplitude magnetic anomaly there.     

PCB resistance within phytoplankton populations in polluted and unpolluted marine environments

A comparison between clones of two species of diatoms, Asterionella japonica and Ditylum brightwellii, isolated from Sandy Hook, New Jersey (polluted site) and Montauk, New York (unpolluted site) indicated that some of the clones from Sandy Hook were more resistant to polychlorinated biphenyls (PCB). A japonica was less sensitive to PCB than D. brightwellii since seven clones of A. japonica from both sites were tolerant of 25 μg litre^?1 PCB whereas no clones from either site of D. brightwellii showed such resistance. Growth under high light intensity increased the sensitivity to PCB in all clones except one super-resistant clone from Sandy Hook which was not affected even by additions of 50 μg litre^?1 to the growth medium. This interactive effect of light on PCB sensitivity may relate to the photo-adaptive characteristics of each clone.     

Seabed measurements of modern corrosion rates on the Florida escarpment

A mooring containing diverse carbonate and anhydrite substrates was exposed to bottom waters for 9 months at the base of the Florida Escarpment to determine the influence of dissolution on the development of this continental margin. Weight loss was measured on all samples. Etching, pitting, and loss of the original framework components were observed on substrates with known characteristics. Extrapolations of modern dissolution rates predict only about 1.6 meters of corrosion per million years. However, more rapid anhydrite dissolution, up to 1 km per million years, would cause exposed anhydrite beds to undercut and destabilize intercalated limestones.     

Le zooplancton du lac de Bret en 1902/03, 1943 et 1951

Summary The Lac de Bret, formerly an “oligotrophic” lake, has by several artificial risings of its level become “eutrophic” with the drawbacks of that state during the summer stagnation. A plant of partial underwater aeration has improved the situation and has been described in this Review (11, 423 [1949]). The above study compares the zooplancton of this lake in the years 1902/03 when it was yet oligotrophic with its plancton in the year 1943 during the investigations in the lake become eutrophic and finally in the year 1951 when it had again grown sound after five seasons of estival acration.