The American oyster as a coastal zone pollution monitor: A pilot study

The Condition Index [(dry meat weight)(100)/(internal cavity volume)] has been analyzed and compared in the American oyster,Crassostrea virginica, from two South Carolina estuaries, one of which was considered polluted by coliform bacteria standards. During the warmer months, oysters from the unpolluted habitat showed a consistently and significantly higher Condition Index. Best fit and power function regressions of Condition Index on total coliform bacteria levels conform with previously cited effects of pollutants on oysters. Condition Index droped markedly as the incidence of total coliforms increased toward levels of 100 per 100 ml of water. Our results and the known sensitivity of oysters to a spectrum of pollutants suggest that their condition could be used to monitor waterborne pollution in coastal zone areas.     

The solubility of quartz in aqueous sodium chloride solution at 350°C and 180 to 500 bars

The solubility of quartz in 2, 3, and 4 molal NaCl was measured at 350°C and pressures ranging from 180 to 500 bars. The molal solubility in each of the salt solutions is greater than that in pure water throughout the measured pressure range, with the ratio of solubility in NaCl solution to solubility in pure water decreasing as pressure is increased. The measured solubilities are significantly higher than solubilities calculated using a simple model in which the water activity in NaCl solutions decreases either in proportion to decreasing vapor pressure of the solution as salinity is increased or in proportion to decreasing mole fraction of water in the solvent.     

Effects of finite rifting times on the development of sedimentary basins

Most thermo-mechanical models for the development of sedimentary basins have assumed that the rifting responsible for the formation of the basin occurred instantaneously and have examined the post-rift development of the basin. This assumption greatly simplifies the mathematical treatment, but is not in accord with what is found in nature, where 10-to 50-m.y. rifting events commonly accompany the formation of sedimentary basins and continental margins. The effects of a finite rifting time on the development of sedimentary basins are examined using an analytic technique which allows an arbitrary rifting history in both time and space and which considers the effects of both vertical and horizontal heat transfer. This technique allows the thermal structure of the lithosphere to be calculated throughout the rifting event and thus permits the subsidence history and surface heat flow of the developing basin to be traced.The effect of a finite-duration extension event is that heat is lost during rifting increasing the syn-rift subsidence at the expense of the post-rift. Lateral heat flow, which was not included in previous studies of the effect of finite rifting times, has a significant effect on the subsidence history, distribution of sediments and thermal history. In particular, the post-rift subsidence is decreased by more than 25% for a 20-m.y. rifting event and by more than 10–15% for a rifting event as short as 10 m.y. This will significantly decrease the subsidence rates in the post-rift stage and implies that inferences concerning the structure, development and thermal history of the basin derived from using “β-curves” to interpret backstripped subsidence can be greatly in error.Variations in syn-rift sediment accumulation and lithospheric thermal structure at the end of rifting resulting from different rifting histories can interact with other factors, such as the flexural response of the lithosphere to sediment loading, to affect the final width of the basin, the total amount of sediments that accumulate and the basin stratigraphy.     

A friction damped base isolation system with fail-safe characteristics

An experimental study of a Coulomb friction damped aseismic base isolation system with fail-safe characteristics is described in this paper. The base isolation system utilized commercially made natural rubber bearings and a skid system which comes into operation at preset-levels of relative horizontal displacement between the structure and the foundation. The fail-safe skid provides hysteretic damping and prevents failure of the isolation system in the event of displacements larger than those assumed in the original design. The isolation system can be designed for an earthquake which can be reasonably expected within the lifetime of the structure; in the event of an earthquake of unanticipated intensity the failsafe system will prevent collapse of the structure. The testing of the system involved an 80,000lb model, approximately 1/3 scale to a real structure mounted on the 20′ × 20′ shaking table at EERC and subject to a variety of earthquake inputs. The results show that the hysteretic effect of the fail-safe system does not greatly increase the accelerations experienced by the structure but considerably reduces the relative displacements at the isolation bearings. The action of the fail-safe system was tested by using an earthquake input that produced a resonant response in the isolated mode of the model. The stability limit of the isolation system was exceeded and the bearings failed but complete failure of the isolation system and thus collapse of the model was prevented by the fail-safe system. The implementation of the system in full scale structures poses no technical or construction problems. An equivalent linearization technique was developed for this system for design purposes using response spectra. The accuracy of this approach was verified by comparison with the experimental results.     

Constitutive relations for fault slip and earthquake instabilities

Constitutive relations for fault slip are described and adopted as a basis for analyzing slip motion and its instability in the form of earthquakes on crustal faults. The constitutive relations discussed include simple rate-independent slip-weakening models, in which shear strength degrades with ongoing slip to a residual frictional strength, and also more realistic but as yet less extensively applied slip-rate and surface-state-dependent relations. For the latter the state of the surface is characterized by one or more variables that evolve with ongoing slip, seeking values consistent with the current slip rate. Models of crustal faults range from simple, single-degree-of-freedom spring-slider systems to more complex continuous systems that incorporate nonuniform slip and locked patches on faults of depth-dependent constitutive properties within elastic lithospheric plates that may be coupled to a viscoelastic asthenosphere. Most progress for the rate and state-dependent constitutive relations is at present limited to single-degree-of-freedom systems. Results for stable and unstable slip with the various constitutive models are summarized. Instability conditions are compared for spatially uniform versus nonuniform slip, including the elastic — brittle crack limit of the nonuniform mode. Inferences of constitutive and fracture parameters are discussed, based on earthquake data for large ruptures that begin with slip at depth, concentrating stress on locked regions within a brittle upper crust. Results of nonlinear stability theory, including regimes of complex sustained stress and slip rate oscillations, are outlined for rate and state-dependent constitutive relations, and the manner in which these allow phenomena like time-dependent failure, restrengthening in nearly stationary contact, and weakening in rapidly accelerated slip, is discussed.     

The seismicity of Kohistan, Pakistan: Source studies of the Hamran (1972.9.3), Darel (1981.9.12) and Patan (1974.12.28) earthquakes

Long period body waves are examined to show that the Hamran (1972.9.3), Darel (1981.9.12) and Patan (1974.12.28) earthquakes in Kohistan had focal depths of about 8–10 km. All involved high angle reverse faulting (thrusting) and had seismic moments of about 2.2 to 2.7·10²⁵ dyne cm. These shallow depths contrast with the deeper hypocentres found in the Hindu Kush and northeast Karakoram to the north and in Hazara to the south. The Hamran and Patan shocks were assigned depths of 45 km by the ISC, indicating that even well-recorded events in this region may have focal depths in error by 30 km     

A comparison of methods used in measuring finite strains from ellipsoidal objects

The available methods for measuring strains in two and three dimensions from passive ellipsoidal objects are compared in an attempt to determine the most useful and precise procedure for the structural geologist. A comparison of data collection techniques showed that the use of thin orthogonally cut slabs or mylar overlays used with a monocomparater provides the most reproducible data. Lisle's theta-curve and Shimamoto and Ikeda's algebraic methods provided the most precise, and probably most accurate, two-dimensional data while Miller and Oertel's procedure and possibly Dunnet's PHASE 5 program gave the best three-dimensional results.An examination of errors encountered in strain analyses suggests that all of the available methods give accurate orientations of the finite strain ellipsoid. However, the magnitudes of strain ratios show large variations that are dependent on the sample size and procedure used. Shimamoto and Ikeda's method again proved to be the most precise, giving reproducible results with as few as ten elliptical objects.The samples used in the above comparison are part of a larger analysis of strains occurring in southeastern Maine. Structural elements observed in four selected areas of Avalonian belt rocks and the strain data collected suggest that the region has undergone at least three non-coaxial deformations with D₁ >D₂ >D₃.     

Proterozoic seawater — felsic volcanics interaction W. Bergslagen,Sweden. Evidence for high REE mobility and implications for 1.8 Ga seawater compositions

Mg enrichment in diffusely bounded, schistose alteration zones occurring in Proterozoic submarine felsic volcanics NE of Hjulsjö, W. Bergslagen is shown to result from felsic rock-seawater interaction in a sub-seafloor hydrothermal system. The alteration is apparently in two stages, feldspar being altered first to a kaolinite-type clay which is then replaced by Mg-chlorite. Major and trace element data are presented for the schist and sheridanite (chlorite). Relative to the least altered felsic volcanics, and for negligible volume change, the schist shows strong addition of Mg and to a lesser extent Si; K, Al and Rb are apparently conserved, while most other elements are strongly depleted, including the REEs which are removed for ～75%, indicating a high degree of mobility. The chlorite, with its HREE enriched pattern, is considered to have equilibrated with the hydrothermal fluid, which consisted predominantly of seawater. Comparison with modern seawater leads to the tentative conclusion that the Proterozoic seawater HREE composition was not drastically different from that of modern seawater.