bluuebunny/crossref_metadata_2025_split huggingface dataset:
Trace elements in migrating high‐temperature fluids: Effects of diffusive exchange with the adjoining solid
Authors: Kenyon Patricia M. 
Published: February 2008

Trace element concentrations and isotopic ratios are frequently used to study the behavior of high‐temperature fluids in both metamorphic and igneous systems. Many theoretical formulations of the effects of fluid migration on trace elements have assumed instantaneous reequilibration between the migrating fluid and the solid material through which it is passing. This paper investigates the additional effects which arise when equilibration is not instantaneous due to a limited rate of diffusion in the solid, using an analytical steady state solution to a set of partial differential equations describing the exchange of trace elements between the fluid and the solid during the migration of the fluid. It is found that the rate of transport of the trace element variations depends on the spatial and temporal scale of the initial variation in the trace element concentration in the fluid, as well as porosity, distribution coefficient, diffusion coefficient in the solid, and channel size. In addition, the amplitude of any initial trace element variations decreases with increasing distance of fluid migration at a rate which depends on the scale of the initial trace element variation, the parameters listed above, and the velocity of fluid migration. The effect of varying the system parameters controlling transport rate and damping is investigated for the case of basaltic magma migrating through a lherzolite matrix. The operation of diffusion‐limited reequilibration during fluid migration can be recognized in nature from studies of the altered regions surrounding veins in peridotite and from time stratigraphic studies of erupted lavas. Consideration of one geochemical study for the East Pacific Rise generates reasonable estimates of migration velocity and suggests that the magma has migrated primarily through macroscopic channels rather than along grain boundaries.Appendices are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N. W.,Washington, DC 20009. Document B93‐006; $2.50. Payment must accompany order.
Microearthquakes and crustal structure off the Makran Coast of Iran
Authors: Niazi M. , Shimamura H. , Matsu’ura M. 
Published: February 2008

On the basis of bathymetric and seismic data collected recently off the coast of Makran in the Gulf of Oman, it has been suggested that the folding of the sediments at the northern edge of the abyssal plain is taking place at the present time. The folding is thought to be the consequence of ongoing subduction of the Arabian plate beneath the Eurasian lithosphere along the Makran coast. The model assigns a far more significant role to the Makran coast in shaping the tectonics of the region than has thus far been assumed.In order to examine whether, despite the lack of teleseismically observable seismicity, the suggested deformation is associated with any microearthquake activity or not, a network of high gain seismographs, including three OBS’s, was installed near the western end of the Makran coast in May 1977 and operated for about two weeks. During the observation period no noticeable microearthquake activity associated with the suggested boundary was observed. Nearly 40 of the earthquakes located by the network data are aftershocks of the destructive earthquake which occurred on March 21, 1977, north of Bandar‐Abbas, more than 400 km from the OBS’s. From the observed travel times of the three 180 kilogram explosions set off for regional calibration, a 20 km thick two layered oceanic crust was obtained.
A search for Co‐variance among seismicity, groundwater chemistry, and groundwater radon in southern California
Authors: Hammond D. E. , Teng T. L. , Miller L. , Haraguchi G. 
Published: February 2008

Several wells and springs near active faults in southern California have been monitored for the concentration of Rn, Na+, K+, Mg+2, and Cl− for periods of up to 24 months in an effort to see if any of these constituents show variations which may be related to seismic activity or environmental phenomena. A few of these sites have shown significant fluctuations.One site in the San Gabriel Mountains has shown relatively high radon in the summer and low radon in the winter, apparently following the annual precipitation cycle. However, this site showed no corresponding change in its chemistry. A second site near Wrightwood, California has shown an annual cycle in its chemical composition, but shows no change in radon. Ten days prior to the Big Bear earthquake (M ∼ 4.9), 70 km to the east, one sample from this site showed a 50% increase in radon, but no change in chemistry. A third site, 20 km north of the Malibu earthquake (M ∼ 5.0) showed radon variation ranging from 0.4 to 4 times the normal concentration for two months preceding and two months following the event. The chemistry at this site did not change.Within this study area, radon appears to exhibit anomalous variations within several tens of kilometers of impending earthquakes. The mechanism creating these signals has not been elucidated, but does not influence the composition of important ionic constituents. Groundwater radon concentrations may also reflect variations in precipitation but do not appear to reflect variations in atmospheric pressure. Data from cold springs are consistent with a model in which ionic constituents are controlled by reactions in the soil zone and radon concentrations are controlled by flow rates in the aquifer.
Experimental studies of the mechanisms of seismo‐geochemical precursors
Authors: Fong‐liang Jiang , Gui‐ru Li 
Published: February 2008

The following aspects of modeling experiments on seismo‐geochemical precursors are described: (1) gas emission during laboratory stress loading and rupture of rocks, (2) field measurements with explosion sources, (3) aquifer mixing tests in the field, (4) experimental studies of physico‐chemical processes caused by stress events. From these studies, three conclusions have been drawn:(1) Long‐term seismo‐geochemical anomalies appear to be related to the stage of elastic deformation of rocks under stress loading prior to a seismic event. Short‐term anomalies appear to be related to the plastic deformation of rock, and spike‐like anomalies appear to be related to shear displacement before an earthquake.(2) Anomalous changes in chemical composition of groundwater and the escape of gases from the ground appear to result from rock fracturing which opens up pathways for the upward migration of water from deep, confined aquifers, and for the upward migration of gases from the deeper crust.(3) Chemical reactions induced by increasing stress in the epicentral region may result in the anomalous changes in chemical composition of groundwater observed before some large earthquakes.
Paleomagnetism of the Late Ordovician Neda iron ore from Wisconsin, Iowa and Illinois
Authors: Kean William F. 
Published: February 2008

The Neda Iron Formation (latest Ordovician) is a hematite and goethite rich oolitic ore which occurs in lens shaped deposits on top of the Maquoketa shale (Late Ordovician), at only a few locations in Wisconsin, Iowa and Illinois. Thermal demagnetization of samples from these three states, indicates the remanence is carried by hematite. Chemical demagnetization suggests the remanence is produced by the interstitial material rather than the oolites.The paleopole averaged for all sites from 25 samples of the Neda ore is at S45.4°, W48° (α95 = 16°). This pole position is similar to late Mississippian to early Permian of North America rather than latest Ordovician. The difference between the known age of the Neda and the time of magnetization suggests that the hematite in the ore was produced from dehydration of goethite probably as a result of tectonic uplift in Wisconsin during late Mississippian time. In addition, these results add evidence to the theory that the Neda ore was formed in two stages. The oolites were produced in a near shore environment during the shoaling of the Ordovician seas. The oolites were then incorporated in iron rich muds. Burial and later uplift dehydrated the iron hydroxide to hematite.
Seismic strain release along the Middle America Trench, Mexico
Authors: Wang Shi‐Chen , McNally Karen C. , Geller Robert J. 
Published: February 2008

We measure the seismic moment of five great (Ms ≥ 7.8) earthquakes from 1928 to 1942 along the Mexican portion of the Middle American Trench directly from recorded seismograms, and obtain considerably lower moment values than had previously been estimated from Ms. Such direct moment determinations are inherently more reliable.As the average seismic slip rate along this portion of the arc appears to be essentially constant, these measurements of the past seismic moment are used to estimate that the current (end of 1980) moment deficiency, is 46 × 1027 dyne‐cm, or an average slip of 97 cm along the arc. Although this is much lower than past estimates, at the current rate of increase, 1.6 × 1027 dyne‐cm/yr (3.4 cm/yr of seismic displacement), the moment deficiency by 1985 will be the equivalent of five magnitude 8 earthquakes; and by 1990, six such events. The slip along this portion of the Middle America Trench arc appears to fit Shimazaki and Nakata's "slip predictable" model, in which the size, but not the time of occurrence, of future large events may be estimated.
Current plate motions based on Doppler satellite observations
Authors: Anderle R. J. , Malyevac C. A. 
Published: February 2008

About 50% of the Doppler observations made on a Navy Navigation Satellite over a 9 year period were analyzed to determine the motion of 8 sites on the North American plate and 12 sites on 7 other plates. The computed plate motions were not statistically significant compared with the standard errors of measurement of 1 to 5 cm/yr except for the Australian plate, European plate and Pacific plate. The measured motions of these plates are about twice those inferred from geologic records, but are in the proper direction.Processing of the balance of the data on one satellite over the 9 year time interval would improve the accuracy of the determination by about 60%, improving the possibility of detecting additional statistically significant motions.Unreasonable altitude changes at most sites are probably due to neglected higher order ionospheric refraction effects on the observations.
Reply to M. Berberian's Comment on the Paper, A. Mohajer‐Ashjai and A. A. Nowroozi “The Tabas Earthquakes of September 16, 1978 in east central Iran,” G.R.L. No. 9L0391
Authors: Mohajer‐Ashjai A. , Nowroozi A. A. 
Published: February 2008

The Tabas earthquake of September 16, 1978, M=7.7, has been associated with extensive thrust faulting; there has been some confusion about the fault‐length associated with this earthquake. At least 70 km of fresh surface faulting is associated with this earthquake together with several branches of secondary faulting.We thank Mr. Berberian for his interest in our paper, however, his aberrant comments have provided this opportunity for us to clarify several points. See Berberian (1982).
Electron Beam Injection Experiments: Replication of flight observations in a laboratory beam plasma discharge
Authors: Bernstein W. , McGarity J. O. , Konradi A. 
Published: February 2008

Recent electron beam injection experiments in the lower ionosphere have produced two perplexing results:1. At altitudes from 140 km to 220 km, the beam associated 391.4 nm intensity is relatively independent of altitude despite the decreasing N2 abundance.2. The radial extent (⊥B) of the perturbed region populated by beam associated energetic electrons significantly exceeds the nominal gyrodiameter for 90° injection.A series of laboratory measurements is described in which both of these flight results appear to have been closely reproduced. The laboratory results are reasonably consistent with the transition from a collision dominated to collisionless beam‐plasma discharge configuration.
Polar stratospheric clouds inferred from satellite data
Authors: Austin J. , Remsberg E. E. , Jones R. L. , Tuck A. F. 
Published: February 2008

Anomalously high radiances from the ozone channel of the Limb Infra‐red Monitor of the Statosphere (LIMS) sounding instrument have been observed in the Northern Hemisphere winter lower stratosphere. Such events, thought to be due to polar stratospheric clouds (PSCs) are examined further by computing relative humidities using Stratospheric Sounding Unit (SSU) temperatures and water vapour measurements from the LIMS Map Archive Tape (MAT) analyses. Regions identified as PSCs are found to correspond closely to regions of high humidity. While instances of saturation were found, the average humidity at the centres of 39 PSCs was calculated to be 58%. Possible reasons for this apparent discrepancy are discussed.Applying a similar approach to the Southern Hemisphere, in 1979, virtually no PSCs are found in the vortex after 10 September at 20 km. This result has important implications for a number of proposed explanations for the Antarctic ozone hole.
Depletion of Antarctic ozone: Height of ozone loss region and its temporal changes
Authors: Iwasaka Y. , Kondoh K. 
Published: February 2008

Ozonesonde measurements at Syowa Station (69°00′S, 39°35′E) from 1971 to 1984 show that ozone depletion is most striking in the region 10km to 25km in the last five years. Active ozone loss region in the spring shows good correspondence to the region where noticeable drop in stratospheric temperature is observed from 1981 to 1985, but only in the spring.Monthly averaged lower‐stratospheric temperature decreased smoothly during the period from about 1975 to the present in the spring. The temperatures in October and November of 1985 are comparable to the frost point temperature of water vapor with 10 ppmv mixing ratio at about 100mb. The temperature drops observed in interannual trends could activate formation of ice particles, and cause noticeable ozone loss in spring through heterogenous ozone reduction reactions.
Grain‐scale deformation and the fold test ‐ evaluation of syn‐folding remagnetization
Authors: van der Pluijm Ben A. 
Published: February 2008

The paleomagnetic fold test examines for pre‐, syn‐ or post‐folding (re)magnetization. Generally, passive limb rotation is used to restore folded units to their original position, and the position of the Fisherian maximum determines the relationship between folding and magnetization. In a more complete analysis, the reorientation of material lines in different fold models is used. However, the magnetic vector should not be considered a material line as it represents the sum of vectors in individual magnetic carriers and does not cross grain boundaries. Therefore, the role of grain‐scale deformation mechanisms was examined, using two end members: rigid‐body rotation (spin) and homogeneous strain.From this study it is concluded that (1) the Fisherian maximum will in general occur before complete unfolding, (2) the sign of the inclination may change during unfolding and, consequently, ’cross‐over’ unfolding is not representative of syn‐folding remagnetization, (3) statistical analysis will not necessarily produce significant results. A number of recommendations are given, which include: stepwise unfolding (and unplunging) should be carried out routinely; local, rather than regional, fold tests should be performed; both limbs and the hinge of a single folded layer should be examined in order to determine the active deformation mechanisms that will enable corrections to be carried out; in addition to Fisherian statistics, the angle between magnetic vector and bedding across a fold should be measured and used for correction.
The 11/25/88, M=6 Saguenay Earthquake near Chicoutimi, Quebec: Evidence for anisotropic wave propagation in northeastern North America
Authors: Hough S. E. , Jacob K. H. , Friberg P. A. 
Published: February 2008

On November 25, 1988, a magnitude 6 earthquake occurred in the province of Quebec, Canada. This earthquake triggered nine digital strong motion instruments in New York and Maine at epicentral distances of 200 to 820 km which were installed as part of an effort by the National Center for Earthquake Engineering Research (NCEER) to study ground motions and wave propagation in eastern North America. We calculate Q(f) at discrete frequencies from 0.6 to 26 Hz, assuming that geometrical spreading causes a l/r0.5 decay in spectral amplitudes.Of the nine stations, four are in the Adirondack Mountains in New York and three are in eastern Maine. If we calculate Q(f) for these two clusters of stations separately, we obtain higher values for the Adirondack stations. The Quebec‐Adirondack path is along the strike of the predominant structural trends in northeastern North America, in the Grenville Province crust, while the Quebec‐Maine path is at high angle to the structural grain and crosses the boundary between the Grenville and the Appalachian provinces. We thus have instrumental data in support of earlier observations based on contours of intensity from historic earthquakes: Seismic wave propagation in northeastern North America is more efficient along the predominantly NE‐SW striking geological trends. We address possible biases due to site effects.
Geodetic point positioning with GPS carrier beat phase data from the CASA UNO Experiment
Authors: Malys Stephen , Jensen Peter A. 
Published: February 2008

The Global Positioning System (GPS) carrier beat phase data collected by the TI4100 GPS receiver has been successfully utilized by the US Defense Mapping Agency in an algorithm which is designed to estimate individual absolute geodetic point positions from data collected over a few hours. The algorithm uses differenced data from one station and two to four GPS satellites at a series of epochs separated by 30 second intervals. The ‘precise’ GPS ephemerides and satellite clock states, held fixed in the estimation process, are those estimated by the Naval Surface Warfare Center (NSWC). Broadcast ephemerides and clock states are also utilized for comparative purposes.An outline of the data corrections applied, the mathematical model and the estimation algorithm are presented. Point positioning results and statistics are presented for a globally‐distributed set of stations which contributed to the CASA UNO experiment. Statistical assessment of 114 GPS point positions at 11 CASA UNO stations indicates that the overall standard deviation of a point position component, estimated from a few hours of data, is 73 centimeters. Solution of the long line geodetic inverse problem using repeated point positions such as these can potentially offer a new tool for those studying geodynamics on a global scale.
Rock magnetism of the Early Pliocene Trubi Formation at Eraclea Minoa (Sicily)
Authors: Van Velzen A. J. , Zijderveld J. D. A. 
Published: February 2008

The most important magnetic mineral in the finegrained marls of the Early Pliocene Trubi formation near Eraclea Minoa is magnetite. Some goethite is also present. The magnetite is of high purity and of primary origin.Hysteresis and low‐temperature measurements show that most magnetite grains are single‐domain. The presence of superpara‐magnetic grains is suspected. Multi‐domain grains are rare. It is stewn that AF demagnetization does not yield correct NRM directions.
Transmission of Alfvén waves through the Earth's bow shock: Theory and observation
Authors: Hassam Adil B. 
Published: February 2008

Alfvén waves, propagating along the magnetic field, are considered to be interacting with strong fast MHD shocks. The wave‐associated magnetic field perturbation is taken to lie in the magnetic field‐shock normal plane. The interaction perturbs the shock surface and gives rise to transmitted waves consisting of a fast magnetoacoustic wave, forward and backward slow magnetoacoustic waves, and an entropy wave. To zeroth order in inverse upstream Mach numbers the wave vectors of the latter three waves are collinear and bend toward the normal, while the fast wave bends away from the normal, propagating parallel to the shock surface for incident angles of 61°. To the same order, for incident angles of less than 61° and for γ = 5/3, the magnetic field amplitude associated with one of the slow waves is roughly the same size as the incident amplitude, while that associated with the other slow wave is amplified 3 times.Magnetic field and plasma data from Explorer 35, taken in the vicinity of 14 bow shock crossings, are analyzed. On spacecraft time scales of 12–20 min the data suggest the presence of hydromagnetic waves on both sides of all the shocks; the presence of predominantly Alfvénic fluctuations is demonstrated in the upstream regions of at least six of the crossings. Magnetic field fluctuations with frequencies of > 1/100 Hz are found to be amplified across the shock by factors ranging from 0.9 through 2.5. It is suggested that the discrepancy in the observed and theoretical field amplifications is due to strong damping of any transmitted magnetoacoustic modes with relatively little damping of any transmitted Alfvén waves (all of which may be excited for a more general incidence).
A comment on the source region of VLF saucers
Authors: Temerin Michael 
Published: February 2008

The source region of VLF saucers is consistent with a source extensive in longitude but narrowly confined in the other two dimensions.James [1976] shows that the source region of VLF saucers is confined in all three dimensions. That is, the horizontal dimensions (the ones perpendicular to the magnetic field) of the source region are typically 0.5 km and the vertical dimension is of the order of 10 km. The source region is thus effectively a point. The purpose of this brief report is to show that there is an alternate geometry to the source region which (1) is consistent with the data presented by James, (2) explains the internal inconsistencies in the data mentioned by James, and (3) is physically more reasonable. The alternate geometry is that the source region is confined in the vertical and in one of the horizontal dimensions as mentioned by James but is extensive in the other, usually the longitudinal, dimension. That is, the source region is effectively a line. I will comment briefly on the three points mentioned above. I refer the reader to James for references, examples of data, and a discussion of the possible importance of VLF saucers to the physical concepts such as double layers. This report is essentially a footnote to that article.