bluuebunny/crossref_metadata_2025 huggingface dataset:
Mode of strain release of three graben‐associated earthquakes
Authors: Chung Wai‐Ying
Published: February 2008

The nature of graben‐associated earthquakes has been investigated through a study of three earthquake sequences using various seismological, geophysical and geological data. The three earthquake sequences are the Hsingtai, China earthquakes (maximum magnitude Ms = 7.2) of March, 1966, the Nevada earthquakes (maximum M = 7.1) of 1954, and the New Madrid earthquakes (maximum Ms = 8.8) of 1811–1812. These earthquake sequences represent a unique mode of strain release away from plate margins and have bearings on earthquake hazard evaluation. A number of similarities have been observed during these earthquake sequences. For instance, all the three sequences are characterized by large multiple shocks or swarms, which last from several weeks to several months. Among the large multiple shocks in each sequence, the largest one usually is not the first one. Migrations of epicenters were observed during the Hsingtai and the New Madrid earthquakes. Significant amount of strike slip motion was associated or inferred with all these three sequences, in particular for the Hsingtai earthquakes. The swarm of multiple shock activities is probably due to induced instability or strong coupling and interactions among a series of adjacent faults in a heterogeneous graben. The strike slip motion can be explained by a change or a rotation of stress orientation after the formation of a graben. The graben events are similar to the earthquake swarms associated with spreading oceanic ridges but with significant differences. Available data indicate that the recurrence intervals for the three graben earthquake sequences studied are of the order of thousands of years.
On the stability of triple junctions and its relation to episodicity in spreading
Authors: Patriat Philippe , Courtillot Vincent
Published: February 2008

A convenient representation of triple junctions that involve only ridges (R) and transform faults (F) is proposed: this representation combines in a simple way information from geographic and velocity spaces. The velocity triangle provides the budget of lithospheric surface change which directly results from interactions of the three plates. A discussion of the relative positions of the triple junction with respect to the velocity triangle demonstrates that, in general, there are several triple junction configurations that are compatible with a given triangle. This discussion stresses the importance of oblique and asymmetric spreading. Pairs of triple junction configurations that are of particular interest are RRR‐RRF and RRR‐FFR. When the triple junction lies outside of the triangle, at least one of the ridges will shorten, leading to yet another type of potentially unstable configuration. The present configurations of the Bouvet, Galapagos, and Indian Ocean triple junctions are reviewed. A method is proposed to reconstruct past configurations of the Indian Ocean junction at the time of anomalies 23 and 28. The main parameters that influence triple junction evolution are the lengths of transform faults, the availability of magma and related connectivity of magma chambers and the (also related) spreading velocities. This study confirms an earlier suggestion that activity at constructive plate boundaries occurs in two preferred modes: the effusive and tectonic modes, corresponding here to RRR and to RRF‐RFF configurations respectively. These modes apparently alternate in episodes of typically 1 Ma duration. The significance of this time constant and consequences for lithospheric mechanics are briefly discussed.
Implications of paleomagnetic data on the collision related bending of island arcs
Authors: McCabe Robert
Published: February 2008

Paleomagnetic studies from the Marianas, central Philippines, Ryukyus, Sulawesi, Fiji‐New Hebrides all show major differences in the declination values observed from individual islands within the same arc. Comparable differences are not observed in the inclination values. A simple plate tectonic model would predict that each island arc should experience the same rotation along its entire length as the plate moves around its rotation axis. Bathymetry from each of these arcs show that the differentially rotated segments of the upper plate occur in areas where the downgoing plate carries a feature such as a seamount chain, rifted continental fragment, or an island arc. The coincidence of the bathymetric feature and the discordant paleomagnetic declination data support an earlier hypothesis of Vogt [1973] that these features are buoyant zones on the downgoing plate which interact with the margin of the upper plate. As a result of this interaction, the upper plate boundary is locally deformed. In addition to the paleomagnetic evidence, other geologic and geophysical data from these areas suggest such interactions. For example there appears to be a good correlation between the deflections in major structures around the collision zone and the paleomagnetic directions that are reported. As this deformation proceeds, eventually the stresses resulting from the collision may result in any of the following tectonic processes: 1) slip‐line style strike‐slip faults allowing for the sideward extrusion of portions of the upper plate [Tapponnier et al. 1983]; 2) changes in the polarity of the subduction zone; 3) development of strike‐slip faults around the margin of the indenter; or 4) reorganization of the entire plate margin. In addition, data from the Marianas, southern end of the RyuKyu arc, and the Lau Basin suggest that back arc basin development may result from the collision related deformation.
Evolution of the Xialiao Basin
Authors: Shedlock Kaye M. , Hellinger S. J. , Ye Hong
Published: February 2008

The Xialiao depression is one of several small depressions that comprise the North China basin. Formed during the Cenozoic era, the Xialiao depression is a wedge shaped rift basin with a central horst situated between two grabens. The basin is approximately 65 km wide and the grabens reach maximum depths of 6–7 km. We present a quantitative analysis of the evolution of the Xialiao depression (hereafter, the Xialiao basin) within the framework of simple models of crustal extension. We find that both uniform and modified (two‐layer) extension modelling techniques provide reasonable regional estimates of the rate of extension and subsidence of the basin. However, estimations of heat flow and subsidence based on the parameters calculated using either modelling technique are not consistent with either the present basin configuration of a central horst flanked by two grabens or the high heat flow in the Xialiao basin. Combining the results of our attempts to model the extension of the basin with results from both body and surface wave studies of the crust and upper mantle beneath northeast China, we infer that the Xialiao basin has been extended at least 30% of its initial width.
Rotation of the Colorado Plateau
Authors: Steiner M. B.
Published: February 2008

Consistent displacement of its paleomagnetic pole positions suggests that the Colorado Plateau has rotated with respect to cratonic North America. Since pole positions derived from the Colorado Plateau form a significant portion (35%) of the pre‐Cretaceous population of North American paleomagnetic data, the rotation has significant impact on the continent's data base. Comparison of paleopoles from nearly coeval strata on and off the plateau shows that the plateau pole positions are always displaced clockwise from non‐plateau counterparts, in amounts varying from 9° to 14°. The time periods for which such comparisons are possible are the Late Triassic, the Early Triassic, the Late Pennsylvanian, and the Middle to Late Devonian. Other time periods contain data which appear to be consistent with a clockwise displacement of plateau pole positions, but poor age control, rapid apparent polar wander, and late Paleozoic remagnetization all hamper comparisons. Only one of the time periods examined, the Permian, does not show net rotation of the plateau. Observation of the rotation of the plateau has been obscured by the fact that a great many of the plateau poles are from times of rapid apparent polar wander (APW), and the displacement effected by rotation parallels the major APW trends. This renders the discrepancy of plateau poles relatively inconspicuous and is only readily observable between poles from the same age strata. The rotation of the plateau has particular impact on the early and middle Mesozoic paleopoles, to which the plateau had contributed heavily. In particular, for the Late Jurassic, plateau poles are the only data available for the analysis of western North America allochthonous terrane movements.
Strain reorientation of hematite and its bearing upon remanent magnetization
Authors: Cogné J. P. , Perroud H. , Texier M. P. , Bonhommet N.
Published: February 2008

Using a computer‐based numerical model, we suggest that passive reorientation of hematite planar particles induced by strain perturb significantly the remanent magnetization carried by the hematite. The evolution of its direction and dispersion in a progressively increasing strain can be correlated with the evolution of passive lines. In real rocks, the amount of reorientation can be approched by measuring one of the three following tensors: strain tensor, orientation tensor of some hematite cristallographic axes, or magnetic susceptibility tensor. From examples taken in the Maritime Alps and in Brittany, we emphasize the possible correlations between these tensors (orientation of principal axes and axial ratios). Finally, we use our best estimate of strain to correct the paleomagnetic results by the strain removal technique we have already used in the Maritime Alps (Cogné and Perroud, 1985). When applied to the preliminary paleomagnetic results obtained from Ordovician deformed redbeds of Brittany, it allows to recover a conclusive primary magnetization direction, although the characteristic magnetizations appear post‐folding with respect to the classical fold test.
Injection of Indian crust into Tibetan lower crust: A temperature‐dependent viscous model
Authors: Zhao Wu‐Ling , Yuen Dave A.
Published: February 2008

The process of continental convergence between India and Eurasia has been postulated to be one in which the Indian crust is injecting into the Tibetan lower crust [W.‐L. Zhao and W.J. Morgan, this issue]. This scenario is studied with two‐dimensional steady state models with a temperature‐dependent viscosity. The effects of viscous heating are included in the governing equations; shear heating could play an important role in the process of Indian crustal injection. The spatially uniform uplift of the Tibetan Plateau is used as a constraint to define a maximum allowable vertical stress difference on the top of the Tibetan lower crust and to denote the related critical viscosity. When both viscous heating and temperature‐dependent viscosity are included, an average viscosity of the Tibetan lower crust as high as 1020 Pa s would still not be able to produce a noticeable stress difference. Numerical calculations reveal a negative feedback mechanism in the thermal structure: Initial high viscosity would cause a large increase in viscous dissipation and raise the temperatures, thus serving to decrease the viscosity of the Tibetan lower crust as the steady state is approached. This mechanism provides a favorable condition for the injection of relatively stiff Indian crust.
New paleomagnetic data from the Aleutian Islands: Implications for terrane migration and deposition of the zodiac fan
Authors: Harbert William
Published: February 2008

Sedimentary rocks of late Eocene to early Oligocene age from the Aleutian Islands, have been paleomagnetically studied to determine the paleolatitude of this island arc. Samples were collected from gently dipping, thin‐bedded, laminated siltstone, mudstone, and very fine grained sandstone of marine origin. After demagnetization, samples from each locality showed both polarities of a remanent magnetization that thermal, isothermal remanent magnetization, and Js‐T experiments suggest is carried by magnetite. After tectonic correction, the α95 decreases in both localities, suggesting magnetization was acquired before folding of the beds. The characteristic magnetization shows that no significant poleward motion of the Aleutian arc has occurred with respect to the North American plate since the early Oligocene (Amlia, F =−4 °, ΔF=5 °; Umnak, F = 0.8 °, ΔF=3.5 °), but the declinations are rotated significantly clockwise (Amlia, R=70 °, ΔR=23 °; Umnak, R=36.7 °, ΔR=11.2 ° ). Using these paleomagnetic data, relevant Euler poles, and hotspot locations, we propose a new model for the formation of the Zodiac fan. In this model, the start of Zodiac fan deposition corresponds to accretionary, igneous, and erosional events in the Pacific Northwest and fragmentation of the Farallon plate along the margin of the North American plate into small plates. Fan deposition on the Pacific plate was controlled by the geometry of the Bowie and Cobb seamount chains, which prevented sediment from being dispersed over the bathymetrically lower oceanic crust to the west, and by the bathymetry of the Pacific plate, which focused sedimentation in the magnetic bight region of the plate. Our model suggests that the present‐day Zodiac fan is only a remnant of a much larger fan system.
An example of intraplate neotectonic activity, Vilariça Basin, northeast Portugal
Authors: Cabral J.
Published: February 2008

The Vilariça tectonic basin (NW Iberian Peninsula) is presented as an example of intraplate neotectonic activity. The regional geological setting is first introduced then followed by a brief view on the neotectonic activity in Portugal. The basin consists of an elongated depression approximately 20 km long and 2 to 3 km wide, trending NNE–SSW. It is located astride a late Variscan strike‐slip fault (the Manteigas‐Bragança fault), suggesting that it might correspond to a structural depression related to reactivation movements on that fault, Mapping of Neogene and Quaternary cover deposits preserved in the basin and its vicinity was accomplished, and numerous evidence of tectonic deformation (tilting and faulting) affecting the sediments were found. Other geomorphological criteria are discussed, showing the structural origin of the Vilariça basin and its neotectonic activity. Attending to its location on the Manteigas‐Bragança fault, the Vilariça depression is interpreted as a "pull‐apart" basin resulting from left‐lateral strike‐slip displacement on that fault in the Quaternary. Average fault slip rates are estimated, with values comprised between 0.2 mm/yr and 0.5 mm/yr. These slip rates are typical of moderate to moderately high degrees of fault activity and are compatible with the regional faulting geomorphic expression and the relatively important historical and instrumental seismicity affecting the Vilariça region. Finally, a geodynamical model is proposed, and the studied area is presented in the geodynamic framework.
Deformation in portions of the distal continental margin to ancestral North America: An example from the westernmost internal zone, central and southern Appalachian Orogen, Virginia
Authors: Patterson Judith G.
Published: February 2008

Late Precambrian(?)–early Paleozoic metasedimentary and metavolcanic rocks of the Evington Group crop out in a belt along the eastern flank of the Blue Ridge, Virginia. Near Lynchburg, where the sequence is well preserved, the Evington Group is interpreted as a transitional rift/drift succession of the distal continental margin to ancestral North America, caught up in the internal zone of the southern Appalachian orogen. The initial deformation of the Evington Group involved recumbent folding and nappe thrusting, which emplaced distal facies over proximal facies rocks. A penetrative schistosity, axial planar to the early folds, developed under greenschist facies conditions. Nearly coaxial refolding about upright, NE trending, SE dipping axial surfaces followed, also under greenschist facies, and was contemporaneous with high‐angle reverse faulting vergent westward toward the craton. The age of metamorphism and tectonostratigraphic correlations along strike indicate that these deformations were coincident with arc convergence and collision during the Taconic Orogeny. Transpressional stresses related to NE striking Alleghanian (late Paleozoic) dextral strike‐slip faults outboard of the Evington Group rocks studied here are interpreted by others to have caused domes and basins to form 35 km along strike southwest of Lynchburg in the Roanoke River region. Integration of data collected along strike of the belt from the Roanoke River to Lynchburg indicates that dome formation produced F2 plunge variations NE in the belt of Evington Group rocks. Many orogens developed through continent‐arc collision which proceeded from internal to external zones. Comparison of the Evington Group with rock sequences from tectonostratigraphic settings similar to those in other orogens (e.g., Wopmay Orogen) indicates that they have roughly similar histories of deformation. Recumbent folding and thrust nappe emplacement in the internal zone is an early phase of orogenic evolution and proceeds toward the craton through time. Second‐stage coaxial refolding about upright axial planes may or may not occur or be recorded. Late stage strike‐slip faulting in the internal zone is a common feature of many orogens that may reflect oblique convergence or tectonic escape.
Paleomagnetic results from Mallorca (Balearic Islands, Spain)
Authors: Freeman R. , Sàbat F. , Lowrie W. , Fontboté J.‐M.
Published: February 2008

We studied the paleomagnetism of Jurassic limestones on the island of Mallorca (Balearic Archipelago, western Mediterranean) to determine if two thrust sheets exhibiting different structural patterns were rotated relative to one another. After correction for tilt the circle of confidence for the mean paleomagnetic direction from sites in areas associated with frontal ramps overlaps with the confidence circle of the mean for those sites associated with oblique‐lateral ramps. This indicates that there has been no differential rotation in spite of the fact that the fold axes in these areas trend almost perpendicular to one another. Although the age of magnetization is prefolding (i.e., before Oligo‐Miocene), it is not certain that the paleomagnetic directions reflect Jurassic magnetization since they may have been acquired during a period of emersion in the Upper Cretaceous or Paleocene. The resulting mean direction for nine sites from both thrust sheets (declination = 41°, inclination = 48°, α95 = 7°) implies significant clockwise rotation of the whole island, or at least of the Mesozoic cover, since acquisition of magnetization. If part of this rotation occurred, as we believe, in the Neogene, then structural data from pre‐Miocene rocks must be corrected before being used for regional tectonic interpretation. The mechanism to produce 40° of clockwise rotation since the Oligo‐Miocene could be combined regional extension, Alpine compression, and block rotation.
Cenozoic Plate tectonic history of the northern Venezuela‐Trinidad Area
Authors: Erlich R. N. , Barrett S. F.
Published: February 2008

Geological and geophysical data, coupled with recent plate tectonic reconstructions, suggest that the Cenozoic geologic history of the northern Venezuela‐Trinidad area has been dominated by strike‐slip displacement of discrete crustal blocks. Allochthonous terranes within the area include metavolcanic rocks of the Cretaceous Villa de Cura Group and metamorphic rocks of the Precambrian to Cretaceous Cordillera de la Costa. A relatively competent crustal block (Margarita Block) is defined by an outline around the metamorphic basement of Margarita Island, the Araya/Paria peninsula, the Northern Range of Trinidad, and Tobago Island. Reconstruction of the Margarita Block to its original position requires at least partial closure of the Falcon Basin, closure of the Bonaire and Cariaco basins, and restoration of about 50 km of motion on both the Oca and Bocono faults. Post middle Eocene eastward translation of the Caribbean plate caused eastward motion of the Margarita Block. A minor change in relative plate motion during the late Oligocene or early Miocene produced a right step in the Moron fault, forming the Cariaco pull‐apart basin and El Pilar fault zone. Maximum offset on El Pilar fault is estimated to be no more than 125 km, though displacement along the entire fault zone may have been greater. Transpressional stresses between the Caribbean plate and northern South America caused folding of the Serrania del Interior of Venezuela and the Central Range of Trinidad. Eastward migration of transpressional stresses at the southeastern corner of the Caribbean‐South American plate boundary is being accommodated by formation of oblique thrusts, transpressive anticlines, and downwarping of the crust. Bouguer gravity data suggest that Jurassic‐aged Atlantic oceanic crust is being depressed as the Caribbean plate expands into the Demerara Plateau area. This study suggests that the faults and transtensional/transpressional/compressional structures identified in this study are the result of stresses produced during the large eastward translation of the Caribbean plate since the Paleocene, and are not the product of a shear couple.
Origin of overlapping spreading centers: A finite element model
Authors: De Bremaecker J. Cl. , Swenson D. V.
Published: February 2008

Overlapping spreading centers (OSCs) appear to result from two ridges propagating head‐on toward each other. The origin of the most elongated and the largest ones is almost perfectly accounted for by the stresses due to the relative elevation of the tips of the propagating ridges rather than to the elevation of the whole ridges (ridge push); on the other hand, stresses due to the ridge push, or to the forcible injection of magma at stationary centers, produce wider OSCs than those on the East Pacific Rise between 3°N and 13°N. We conclude that cross sections of ridges more than a few kilometers away from spreading centers are essentially in a state of plane stress. Our modelling method uses the finite element method and dynamic fracture propagation; the mesh is modified at every time step to minimize computational errors.
Regional gravity anomalies, depth of the Foreland Basin and isostatic compensation of the New Guinea Highlands
Authors: Abers Geoffrey A. , Lyon‐Caen Hélène
Published: February 2008

The New Guinea Highlands form an active thrust belt advancing southward over the Australian continental margin. Surface geology indicates thin‐skinned deformation of sediments and continental basement, building mountains 2–4 km in average elevation. The depth of the adjacent foreland basin is no more than 1500 m in Papua New Guinea and in many places only 100–200 m, indicating little deflection of the Australian lithosphere beneath the load of the mountains. Calculations of elastic loading, in which the topographic load of the entire mountain range is supported by Australian lithosphere of uniform flexural rigidity (D), predict a basin 2–10 times deeper than observed in eastern New Guinea for a wide range of flexural rigidities (1021–1025 Nm). Bouguer gravity anomalies in the eastern highlands between 143°E and 144°E are consistent with local Airy compensation of the mountains, and preclude a continuous plate with D > 1022 Nm underlying any significant portion of the mountains. In contrast, the observed broad foredeep flexure in central New Guinea near 141°–142°E requires a strong lithosphere (D = 1024–1025 Nm), and limited gravity and sediment thickness observations farther west indicate similar flexural rigidities. Bouguer gravity measurements and observed foreland basin depths throughout New Guinea can be explained by a strong and continuous lithosphere beneath the foreland basin extending no more than 20–60 km north of the range front, implying that the plate has weakened beneath the thrust belt. Collateral evidence for plate weakening beneath the highlands may be found in earthquakes at 10–25 km depth with high‐angle thrust mechanisms and in widespread Quaternary volcanism throughout the eastern thrust belt. A 50‐mGal positive residual anomaly over the northern 100 km of the eastern highlands cannot be explained by local compensation or mechanical support from the south, indicating either a large excess mass at depth or some additional form of support for the northeastern highlands. The gravity observations in eastern New Guinea require 10–15 km of crustal thickening, but observed sediment thicknesses can only account for 0–5 km, necessitating 5–15 km of thickening in the basement.
Is there a 428‐day period in terrestrial magnetism?
Authors: Hayford John F.
Published: February 2008

That terrestrial latitudes vary with an average period of 428 days seems now to be an established fact. In other words, the pole of figure of the Earth is known to be moving continuously around its pole of rotation in the direction of decreasing west longitudes at a mean rate of one complete circuit in 428 days (ignoring for our present purpose the corresponding annual motion of the pole of figure). For each position of the pole of figure a set of stresses must be produced in the Earth representing its tendency to assume a new figure,—a new ellipsoid of revolution with its axis of figure coincident with the axis of revolution. These stresses are doubtless partially relieved, and only partially, by actual movements of matter to new positions in the oceans, in the envelope of atmosphere, and perhaps in the so‐called rigid Earth. Even with this partial relief each portion of the Earth is subjected to periodic stresses which repeat their various phases every 428 days. This suggests that there may possibly be corresponding periodic variations in the elements of terrestrial magnetism produced by these stresses.
Über einige Probleme des Erdmagnetismus und die Nothwendigkeit einer internationalen Organisation
Authors: Eschenhagen Von M.
Published: February 2008

Der Vergleich der zu absoluten Messungen des Erdmagnetismus dienenden Instrumente verschiedener Observatorien ist eine vielfach erhobene und durchaus gerechtfertigte Forderung. Die Erfüllung derselben ist nothwendig, wenn man die magnetischen Laudesaufnahmen verschiedener Länder mit einander combiniren, ja wenn man auch nur die Constanz der Werthe ein und desselben Observatoriums mit genügender Sicherheit verbürgen will. Man kann sich nun die allgemeine Aufgabe stellen, die augenblicklichen Werthe der erdmagnetischen Kraft an zwei oder mehreren Orten mit grösster Präcision zu vergleichen, eine Aufgabe, welche besonderes Interesse hat, wenn man die Frage nach der Existenz verticaler, die Erdrinde durchsetzender Ströme aufwirft, oder auch schon wenn man gelegentlich der magnetischen Landesaufnahme die auf den Stationen erhaltenen Werthe auf die des Observatoriums bezw. auf eine einheitliche Epoche reduciren will.
Über die tägliche Periode des Erdmagnetismus und der erdmagnetischen Störungen an polarstationen
Authors: Lüdeling Von Dr. G.
Published: February 2008

In seiner Abhandlung “Zur Theorie des Erdmagnetismus”1 weist Herr von Bezold nochmals auf die seiner Zeit schon von Gauss und in neuerer Zeit auch von Anderen, wie den H. H. A. Schuster und Ad. Schmidt betonte Wichtigkeit hin, an Stelle der Declination und Horizontal‐Intensität die Componenten der erdmagnetischen Kraft in der horizontalen Ebene und ihre Variationen zu betrachten.

Bezeichnet man die Componenten mit X und Y und zwar so, dass X die Nord‐Süd‐Componente, Y die Ost‐West‐Componente darstellt (wobei die Richtungen nach Nord und Ost positiv gerechnet sind), bedeuten ferner ΔX und ΔY die Variationen dieser Componenten, so lassen sich die beiden Variationen der Componenten zu einer Resultante vereinigen. Indem man für die 24 Stunden des Tages derartige, aus den Variationen der Componenten sich ergebende Resultanten nach Grösse und Richtung an einen festen Anfangspunkt legt, erhält man durch die Verbindung der Endpunkte der Resultanten eine geschlossene Curve. Solche Curven, die Herr von Bezold “Vectordiagramme” nennt, sind zwar schon von Gauss empfohlen und später auch von Lloyd, Airy und Anderen construirt und benutzt worden, doch hat man ihnen jedenfalls nicht diejenige Bedeutung zugelegt, die ihnen wohl ohne alle Frage für die Untersuchung der täglichen Periode der erdmagnetischen Erscheinungen zukommt. Das mag zu nicht geringem Theile dem Umstände zuzuschreiben sein, dass die zuletzt genannten Forscher die Diagramme nicht nach dem astronomischen, sondern nach dem magnetischen Meridian orientirt haben. In Folge dessen lassen sich aber die Componenten X und Y nicht unmittelbar aus ihnen entnehmen. Auch verhüllen sich dadurch recht wesentliche Eigenthümlichkeiten derselben, so z. B. die Thatsache, dass unter der Annahme eines in sich gleichbleibenden, im Laufe des Tages die Erde umkreisenden Systems von Kräften diese Diagramme für alle Punkte eines und desselben Parallelkreises dieselbe Gestalt und Lage haben müssen. Das Gleiche gilt von dem Zusammenhange zwischen der mittleren Zeit des Durchganges des Vectors durch den magnetischen Meridian und der mittleren Declination, u. s. w.
Einige Gesichtspunkte für die Einrichtung erdmagnetischer simultanbeobachtungen zur Erforschung der Ursachen der erdmagnetischen Störungen
Authors: Schmidt Von Ad.
Published: February 2008

Die bekannten characteristischen Eigentümlichkeiten der erdmagnetischen Störungen oder Ungewitter weisen darauf hin, dass man in diesen vorwiegend lokale Vorgänge als nächste Ursache anzunehmen hat, die—in ihrem Verlaufe schnell wechselnd—zwar stets gleichzeitig auf der ganzen Erde magnetische Wirkungen hervorrufen, aber meistens nur auf einem beschränkten Gebiete einen starken Einfluss ausüben. Unter der zur Zeit wahrscheinlichsten Voraussetzung, dass diese ursächlichen Vorgänge ihrer physikalischen Natur nach electrische Strömungen in den oberen Schichten des festen Erdkörpers oder der Atmosphäre seien, führt jene zuvor erwähnte Schlussfolgerung dazu, diese Strömungen näher als wandernde Stromwirbel zu characterisieren, und die synoptische Darstellung der während einer Störung an verschiedenen Orten beobachteten ablenkenden Kräfte beweist, dass es sich in der That so verhält. Genauere Betrachtungen, welche neben den horizontalen auch die verticalen Störungskräfte in Betracht ziehen, führen weiter zu dem Schlüsse, dass jene electrischen Wirbelströme ihren Sitz vorzugsweise in der Atmosphäre haben, und dass die gleichzeitig im Erdkörper auftretenden Strömungen wahrscheinlich vollkommen durch Inductionserscheinungen zu erklären sind.

Eine nähere Begründung und weitere Ausführung der im Vorstehenden kurz geschilderten Folgerungen ist von mir vor einigen Monaten in der Meteorologischen Zeitschrift (September 1899) veröffentlicht worden. Meine Absicht bei dieser Veröffentlichung, die bei dem verhältnissmässig geringen Umfange des darin verwerteten Beobachtungsmaterials natürlich keinerlei abschliessende Resultate bieten konnte, war es hauptsächlich, darauf hinzuweisen, dass sich aus den mitgeteilten Ergebnissen bestimmte Gesichtspunkte für die weitere Erforschung der Ursache der magnetischen Störungen eröffnen. Vor allem tritt, wie mir scheint, danach die Notwendigkeit eines fortgesetzten, planmässigen Zusammenwirkens möglichst zahlreicher Observatorien so deutlich hervor, dass man wohl hoffen darf, dieses schon wiederholt angeregte und vorübergehend auch erzielte Zusammenwirken werde in nicht zu ferner Zeit zu einer dauernden Einrichtung werden.
A comparison of the isogonic charts for the year 1900, issued by the “Deutsche Seewarte” the United States Hydrographic Office, and the United States Coast and Geodetic Survey
Authors: Fleming J. A.
Published: February 2008

The basis of this comparison was the declination values scaled from the charts for some 2,900 stations, distributed over the entire Earth. These stations are ports for which the tidal constants are given by the tidal division of the United States Coast and Geodetic Survey. For the sake of general information it has been customary to give in the annual “Tide Tables,” published by the Survey, the approximate magnetic declination. The preparation of this data for the 1901 tables gave a splendid opportunity for comparing the most recent charts. The isogonic chart of the British Admiralty, being for the year 1895, was only made use of occasionally.
Summary of the results of recent investigations in atmospheric electricity
Authors: Exner Franz
Published: February 2008

Complaints can be made with justice at present that, although in every year new theories of atmospheric electricity are brought forth, the amount of useful observational data, however, increases very slowly. This is largely due to the difficulty experienced in measurements in atmospheric electricity, a difficulty greatly increased by the numerous disturbing influences encountered because of the impurities of the air in cities and in their vicinity.

A further difficulty is due to the large variations in atmospheric electricity concomitant with the prevailing meteorological conditions of the atmosphere, in consequence of which it has been found necessary to separate the phenomena observed in clear, normal weather entirely from, those obtained during disturbed weather conditions, such as cloudiness, rain, snow, etc. The latter phenomena are to be regarded as disturbances of the usual normal electric field which prevails during fine weather.
Note on the secular motion of the earth's mean magnetic axis
Authors: Bauer L. A.
Published: February 2008

In 1897 the writer presented before the American Association for the Advancement of Science a preliminary communication in which the attempt was made to determine the secular change in the position of the Earth's magnetic axis during the past two or three centuries. This is a problem which can be solved without a knowledge of the horizontal intensity. The necessary formulæ for the solution of the problem, a, depending on inclination data alone, b, on declination data, and c, on both declination and inclination data, were established, and some applications to observational data were made; notably, to the inclination data for 1780 (Hansteen's chart), and for 1885 (Neumayer's chart). I have already had occasion to refer to the results obtained,2 and in No. 2 of my series of papers, “On the Physical Decomposition of the Earth's Permanent Magnetic Field,” I have compared my former results with those derived more recently.
Verteilung der electrischen ionen in den höheren schichten der atmosphäre
Authors: Ebert Von H.
Published: February 2008

Durch die wichtigen Untersuchungen der Herren J. Elster und H. Geitel1 scheint es ausser Zweifel gestellt zu sein, dass die schon früher bemerkte und namentlich von Herrn Linss2 eingehender studierte electrische Leitfähigkeit der natürlichen atmosphärischen Luft auf dem Vorhandensein von frei beweglichen, electrisch geladenen Teilchen ,,Ionen“ beiderlei Vorzeichens beruhe. Die genannten Forscher benutzen zur Reduction der Angaben des von ihnen zur genaueren Prüfung dieser Erscheinung construierten Zerstreuungsapparates das von Coulomb aufgestellte Zerstreuungsgesetz, wonach der Electricitätsverlust eines geladenen, in der Luft aufgestellten, gut isolierten electrischen Conductors proportional der Oberflächen dichte ist.

Der Gedankengang, auf welchem Coulomb zu seinem Gesetze gelangte, weicht aber weit von der Vorstellung ab, welche wir uns heute auf Grund der Ionentheorie der Gasleitung von dem Vorgangezu machen haben ; denn diese ist ein Ergebnis der allerneuesten Forschungen, namentlich des Herrn J. J. Thomson in Cambridge und seiner Schüler. Es entsteht also die Frage, ob die Annahme jenes Zerstreuungsgesetzes auch von diesem Standpuncte aus berechtigt ist. Wir wollen zunächst zeigen, dass dieses in der That der Fall ist.
Report on the magnetic observations made during the total solar eclipse May 17–18, 1901, at the magnetic observatory, Wilmelmshaven, Germany
Authors: Börgen C.
Published: February 2008

I take pleasure in making report herewith on the magnetic observations made by us during the recent total solar eclipse in response to the appeal in Vol. V, p. 166. Readings of the unifilar and bifilar magnetometers were made from minute to minute for the time interval 14h to 21h, May 17, 1901, Greenwich mean astronomical time; the observers were my assistant, Mr. E. Stück, Captain Capelle, Computer Sperling and Chief Pilot Tietz. The latitude of the Observatory is 53° 31′ 52.2″ N., and the longitude 0h 32m 35.2s east of Greenwich. The values of the magnetic elements on January 1, 1901 were : D = 12° 26.1′ W, I = 67° 45.8′ and H = 18128.0γ.
Report on the magnetic observations made at Dehra Dún, India, during the total solar eclipse of May 17–18, 1901
Authors: Fraser H. A. Denholm
Published: February 2008

The observations were carried out in accordance with the instructions given in “Terrestrial Magnetism” of December, 1900.

Changes in the declination and horizontal intensity were recorded photographically on the magnetographs installed in the new underground room, whilst eye readings of the declination were taken every minute with unifilar magnetometer No. 2, by Cooke & Sons, described in the July issue (Vol. VI, p. 65).
Report on the magnetic observations made in Christchurch, New Zealand, during the total solar eclipse, May 17–18, 1901
Authors: Farr C. Coleridge
Published: February 2008

The observations—viz., declinations—were made May 17d 14h 8m to 17d 21h Greenwich mean time (astronomical), corresponding to 18d 1h 39m to 18d 8h 31m New Zealand mean time, in a tent set up in approximate latitude 43° 31′ 17″ S. and in longitude 172° 38′ 06″ E, The instrument used was a Kew Magnetometer “N. A. Bc.,” the property of the National Physical Laboratory Committee of the Royal Society. A new thread previously soaked in glycerine had been inserted and the plummet suspended for twenty‐four hours. The twist in the thread had all disappeared after the plummet had been suspended for about three hours, and none was found in the thread either immediately before or immediately after the observations were made.
Notice of magnetic disturbance during eruption of Mont Pelée, Martinique
Authors: Bauer L. A.
Published: February 2008

On May 8, 1902, at 11.59 A.M., Greenwich mean time, a magnetic disturbance occurred which began simultaneously at the two Coast and Geodetic Survey magnetic observatories in the United States, viz: at Cheltenham, Maryland, and Baldwin, Kansas. Taking the longitude of Mont Pelée, Martinique, as 4.04.6 W. of Greenwich or of St. Pierre 4.04.7, this magnetic disturbance began at 7.54 A.M., St. Pierre (or Mont Pelée) local mean time. The newspaper reports, in general, agree that the first eruption of Mont Pelée occurred at about 8 A.M. May 8th and it has been reported that the town clock of St. Pierre was found stopped at 7.50.

The reports received thus far from other observatories, viz: Honolulu (Hawaiian Islands), Toronto (Canada), Stoneyhurst (England), Val Joyeux (France), Potsdam (Germany), and Pola (Austria) show that this disturbance was quite general, and that it began practically simultaneously at all of them. The horizontal intensity was the element principally disturbed.
Magnetic deflection of long steel wire plumb lines
Authors: Hallock W.
Published: February 2008

The Portage Lake Mining Gazette, in its issue of October 10, 1901, gave a very complete and interesting account of some recent operations in the very deep shaft of the Tamarack Mining Company, on Lake Superior. It became necessary to plumb down two points to a depth of 4,250 feet, and for this purpose the plumb lines were made of No. 24 piano wire carrying a 50‐pound iron weight. At first the two lines were 16.33 ft. apart at the top, but were afterward moved to a distance of 17.58 ft. It was thought that possibly these plumb lines, over 4,000 feet in length, might show the convergence of the Earth's radii, or possibly the Newtonian attraction between the two 50‐pound masses of iron.
Die beabsichtigte Norwegische Expedition nach dem magnetischen Nordpol
Authors: Amundsen Roald
Published: February 2008

Wenn ich dem für mich so ehrenvollen Ersuchen der Gesellschaft für Erdkunde, über meine beabsichtigte Reise einige Angaben zu machen, gern und mit bestem Danke Folge leiste, so geschieht dies in dem Bewusstsein, dass es für mich nur von dem grössten Nutzen sein kann, vor so hervorragenden Fachleuten meine Pläne zu entwickeln. Ich möchte deshalb die Herren bitten, mir jedes Bedenken gegen das Eine oder das Andere in meinem Vorhaben rückhaltslos zu äussern.

In schwierigen Verhältnissen kann oft ein guter Rath von weittragender Bedeutung sein. Meine Theilnahme an der antarktischen Expedition der Belgica gab mir die erste Veranlassung zu dem Projekt.
Results of harmonic analysis of the diurnal variation at the Cape of Good Hope and at Hobart
Authors: Heimbrod G.
Published: February 2008

The reduction by harmonic analysis of the observations made at Cape Town and at Hobart under the direction of Sabine, has been undertaken by me in conjunction with the plan formulated by Dr. A. Nippoldt, of the Potsdam Magnetic Observatory. The steps by which the analysis is carried out, have been explained by him in a paper published in the “Annalen der Hydrographie und Maritimen Meteorologie” No. 2, 1899.1

The data for the present investigation have been taken from the published results of the observations. The first volume of each observatory contains a table which gives the mean hourly position for each month relatively to the general mean position for the month. A minus sign denotes that the mean declination at that hour is west of the mean for the month, a plus sign east of the monthly mean. These tables contain the quantities on which the harmonic analysis is based.
Variation diurne de la déclinaison en Chine
Authors: de Moidrey J.
Published: February 2008

Nous ne pensons pas qu'aucune observation aît encore été faite en Chine, sauf à Zi‐ka‐wei, qui puisse donner une idée de la variation diurne de la déclinaison: cet élément, essentiel cependant à la réduction des mesures, est complètement inconnu.

L'été dernier, M. M. Shinjō, Ōtani et Yamakawa, de l'Université de Tōkyō, au cours d'une expédition géodésique,1 ont fait aussi des observations magnétiques notamment à Hong‐kong, à Han‐k'eou et à Cha‐che, un peu plus en amont sur le Fleuve Bleu. La méthode de ces Messieurs est de multiplier en chaque station les mesures de manière à obtenir au moins une courbe diurne complète : c'est ainsi qu'à Cha‐che, ils ont fait 21 observations de la déclinaison en 33 heures, ce qui leur a donné deux maximums et un minimum. Ce procédé est laborieux, mais les séries ainsi exécutées, et dont ces savants nous ont‐obligeamment donné communication, sont fort instructives. Elles nous montrent ce que peut être la variation diurne en ces trois stations et nous permettent aussi de nous rendre un peu compte de l'approximation que l'on pourrait espérer, en réduisant une observation isolée de la déclinaison, au moyen des enregistreurs de Zi‐ka‐wei.
A direct‐recording magnetic variometer
Authors: Cady W. G.
Published: February 2008

The construction of the instrument described below was undertaken in the hope of providing a means for ascertaining at a glance the magnetic character of the day. The great accuracy attainable with modern magnetic instruments often renders the fickleness of the Earth's field a serious source of error. If it were possible to observe the “magnetic weather” conditions whenever desired, much time would be saved, and better results obtained in the comparison of instruments, determination of constants, etc. Moreover, it is of well recognized importance for certain investigations to make especially accurate records of the magnetic variations at times of disturbance; hence, an instrument giving some intimation of the presence of a magnetic storm would be valuable as a warning to make eye‐reading observations or to start the magnetograph at high speed.
Appeal for co‐operation in magnetic and allied observations during the total solar eclipse of August 29–30, 1905
Authors: Bauer L. A.
Published: February 2008

Those who are in position to take part in above co‐operative work are earnestly requested to make the necessary preparations and to put themselves in communication with the undersigned.

As this will be the best opportunity for some time to come to further test and observe the magnetic and electric phenomena which have been found to occur in connection with total solar eclipses, and as these phenomena are destined to play an important rôle in the theory of the variations of the Earth's magnetism and electricity, ascribed to outside forces, it is very much hoped that all countries through which or near which the belt of totality passes will organize and send in the field observing parties.
Ueber den Einfluss der Torsion bei den Ablenkungen eines hängenden magneten
Authors: Bidlingmaier Friedrich
Published: February 2008

In der einschlägigen Literatur herrscht eine irrige Auffassung über den Einfluss der Torsion bei dem Ablenkungsversuch nach der Sinusmethode, welcher zur Ermittlung der Horizontal‐Intensität angestellt wird. Lamont sagt in §90 seines “Handbuches des Erdmagnetismus” (Berlin, 1849), “dass im Resultate der Einfluss der Torsion gänzlich ausfällt;” Maxwell in seinem “Treatise on Electricity and Magnetism” (Oxford, 1892), §455: “In this method there is no correction of the torsion of the suspended fibre, since the relative position of the fibre, telescope and magnet is the same at every observation,” und Mascart in §76 seines “Traité de Magnétisme Terrestre” (Paris, 1900): “Dans ce cas, la torsion du fil n'intervient plus, puisqu'il reste toujours dans le même état.”

Zweck dieser Zeilen ist es, darauf hinzuweisen, dass dieser Einfluss auf das Resultat thatsächlich besteht und in welcher Weise derselbe ermittelt und eliminiert werden kann.
Proposed magnetic survey of the North Pacific Ocean by the Carnegie Institution
Authors: Bauer L. A. , Littlehales G. W.
Published: February 2008

While the state of our knowledge of the distribution of the Earth's magnetic forces over oceanic areas, owing to the paucity of precise data, is in general exceedingly unsatisfactory, this is especially true for that great body of water—the Pacific Ocean—rapidly developing in great commercial importance.

Except for data from occasional expeditions and such as were acquired in wooden vessels a long time ago, the present magnetic charts used by the navigator over this region depend largely upon the observations on islands and along the coasts. Such land observations, however, are rarely representative of the true values because of prevalent local disturbances. It is, therefore, impossible to make any statement as to the correctness of the present charts.
On the electric charge of the sun
Authors: Arrhenius Svante A.
Published: February 2008

The chief forces which determine the motions of celestial bodies are due to the gravitation of their masses, according to the law of Newton. But besides these forces, which tend to concentrate matter, there exist others of a repulsive nature, as Kepler already observed regarding the comets' tails. As no other repelling forces were known than those between similarly electrified bodies, it was supposed that these forces were of electric origin, and especially Zöllner worked out this theory for explaining the form of the tails of the comets.

These electric forces were nevertheless of a highly hypothetical nature, because no reason could be found why the Sun and the particles of the comets' tails should be charged electrically. Therefore the astrophysicists were gratified when a new repelling force, namely, that of the pressure of radiation, which is a consequence of the theories of Maxwell and Bartoli, was introduced for the explanation of the observed repulsions between celestial bodies. According to these theories, the radiation from the Sun would be sufficient to exert a pressure against a totally reflecting spherical drop of 1.5 μ diameter, which would balance its gravity if the drop had a specific weight like that of water. Drops of this magnitude ought, therefore, to swim in the atmosphere of the Sun, just as if they had no weight at all. Bigger drops ought to fall down to the Sun, whereas smaller ones ought to be repelled from it.