bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismicity and focal mechanisms of the Arctic region and the North American plate boundary in Asia
Authors: Fujita Kazuya , Cook David B. , Hasegawa Henry , Forsyth David , Wetmiller Robert 
Published: April 2015

Abstract
Although Arctic earthquakes have been recorded since 1908, detailed study of them has been hampered due to the lack of seismograph stations and the infrequent occurrence of large earthquakes north of the Arctic Circle. Detailed analysis of Arctic earthquakes began during the International Geophysical Year (IGY, 1957–1958), and subsequent studies have been facilitated by the development of the World-Wide Standardized Seismograph Network (WWSSN) starting in 1963.
Many authors have published summaries of Arctic seismicity. The pre-IGY state of knowledge is summarized by Hodgson and others (1965), and epicentral coordinates and magnitude estimates of pre-WWSSN seismicity are given in Gutenberg and Richter (1954), Linden (1961), Hodgson and others (1965), and Rothe (1969). Overview summaries of the distribution and magnitude of Arctic seismicity are presented by Sykes (1965) and Wetmiller and Forsyth (1978). Numerous maps of Arctic seismicity have been published (e.g., Veis-Ksenofontova, 1962; Sykes, 1965; Barazangi and Dorman, 1970; Tarr, 1970; Wetmiller, 1978; Avetisov and Sokolova, 1980). Additional details about Arctic seismicity are given in international bulletins, national seismicity summaries, and annual reports.
In this chapter we summarize the development of seismograph stations in the Arctic, the distribution of seismicity in the Arctic, focal mechanisms that have been determined for the Arctic seismic zone, including northeastern Siberia and Baffin Bay, and the implications of the seismic data for plate tectonic models of the region. In addition, we summarize inferences on crustal structure of the Arctic region based on the propagation characteristics of earthquake waves.
Perspectives on the geology of the North Atlantic Ocean
Authors: Tucholke Brian E. , Vogt Peter R. 
Published: April 2015

Abstract
This volume deals with the geology and geophysics of the western North Atlantic, the basin between the Mid-Atlantic Ridge and the eastern margin of North America. Although the book’s focus is on the “North American Basin” (Fig. 1), individual chapters and charts extend the bounds beyond the “western North Atlantic.” These extensions were dictated by the geology, which cannot be synthesized meaningfully if constrained by artificial geographic or political boundaries. Generally speaking, the content of this volume is contained within the region surrounded by the continental margins of the Antilles, eastern North America, Greenland, and Iceland in the west and north, the Mid- Atlantic Ridge crest on the east, and approximately 10°–15° N latitude to the south. However, in dealing with the Mid-Atlantic Ridge, plate kinematic models, and Atlantic paleogeography, we have extended our scope north into the Arctic region and east into the eastern Atlantic in order to present a complete synthesis of this major plate boundary and its evolution through time. The significance of Iceland for oceanic geoscience often has been overlooked or underrated; to help remedy this, two chapters deal mainly with this remarkable subaerial exposure of the Mid-Atlantic Ridge. One topic, mid-plate seismicity and stress, also demanded a plate-wide treatment covering the entire “stable” lithosphere from the Mid-Atlantic Ridge to the western Cordillera. Placing this treatment in the North Atlantic synthesis presumes that mid-plate stress is closely related to absolute plate motion (which is calculated largely from oceanic data) and/or to “ridge-push” forces from the
Geochemical and isotopic variation along the Mid-Atlantic Ridge axis from 79°N to 0°N
Authors: Schilling Jean-Guy 
Published: April 2015

Abstract
The first hint of the existence of the Mid and how gradually its topographic definition and latitudinal extent were made known in the 1850 to 1900 period. In the summary volumes of the “Challenger Reports,” the MAR is shown to be continuous from 50°N southward throughout the South Atlantic. The widest part of the Mid-Atlantic Ridge, between 30°N and 50°N, was referred to as the Dolphin Plateau. The narrow portion south of 30°N was named the Connecting Plateau, as it was thought to connect the Dolphin Plateau to the Challenger Plateau running down the center of the South Atlantic; but Murray and Peake (1904) pointed out that this connection is broken for a short interval at the Equator, because of deep soundings found there (evidently a first hint of the Equatorial Fracture Zones). The name of the Mid-Atlantic Ridge seems to first appear in Murray and Hjort’s (1912) classic book, The Depths of the Ocean, and was probably coined in the 1904–1912 period. the
Atlantic Ridge occurred in the period of 1849-1853 after soundings were made by US Navy Ships under the direction of USN Lieut. M. F. Maury. Congress had authorized the effort to assist Maury in his study of winds and currents and apparently also in the preparation of laying the first Trans-Atlantic cable. It was first called the Telegraphic Plateau. Murray and Peake (1904) gave a detailed account and colorful anecdotes surrounding the initial discovery of the Mid-Atlantic Ridge, Only in the 1950s was it discovered that
The geology of North Atlantic transform plate boundaries and their aseismic extensions
Authors: Fox Paul J. , Gallo David G. 
Published: April 2015

Abstract
By the late 1960s the morphotectonic character (Menard and Dietz, 1952; Menard, 1955, Heezen and others, 1964a,b) and kinematic significance (Wilson, 1965; Sykes, 1963, 1965, 1967; Stover, 1966; McKenzie and Parker, 1967; Morgan, 1968; LePichon, 1968) of fracture zones had been established and it was generally accepted that fracture zones are comprised of two principal tectonic elements; a seismically active zone of strike-slip tectonism linking two offset ridge axes called the transform fault or ridge-transform-ridge (RTR) plate boundary, and two aseismic limbs, continuous with each end of the transform fault, that represent the fossil trace of the transform. With this basic tectonic framework developed, investigators turned their attention to elucidating the details about how RTR plate boundaries behave in time and space and how this fundamental plate boundary conditions the accretion of oceanic lithosphere. There are important kinematic and geometric variables that are likely to condition and govern the structural and petrologic processes operating along a RTR plate boundary. These variables will be reviewed before we summarize the salient properties of the slowly-slipping RTR plate boundaries found in the North Atlantic.
Kinematic considerations of the plate tectonic hypothesis mandate that strike-slip motion must occur along an oceanic transform fault at a rate equal to the rate of plate separation of the associated ridge segments. The total opening rates of the ridge segments comprising the mid-oceanic ridge system vary from less than 1.7 cm/yr (Arctic Ridge) to approximately 18 cm/yr southern
The present plate boundary configuration
Authors: Vogt Peter R. 
Published: April 2015

Abstract
The discovery of an elongated geological feature is soon followed by studies of how the feature varies along its length. This is true of the Mid-Oceanic Ridge (MOR), the longest feature on our planet, although there has been far more work done on transverse than on longitudinal variations. Since the MOR accreting plate boundary (the zero-age isochron) and older isochrons are offset by many transform faults, a precise longitudinal profile must be assembled from numerous detached segments. In practice such profiles are generally constructed from transverse crossings. By contrast, long continuous transverse profiles can be obtained (e.g., Klitgord and Schouten, this volume) by following flowlines of plate motion, keeping a constant distance from adjacent fracture zones (FZ). Early ignorance of the existence of fracture zones led to misinterpretation of transverse bathymetric profiles across the Mid-Atlantic Ridge (MAR), e.g., in terms of spurious elongated terraces (the “Upper,” “Middle,” and “Lower Step” of Heezen and others, 1959). Even the later TransAtlantic Geotraverse (TAG) profiles (Rona, 1980) were collected without knowledge of the late Cretaceous/early Tertiary FZ bend, and consequently cross fracture zones at low angles and jump from one flowline to another.
The first longitudinal profile of the MAR (both North and South Atlantic) showed regional variations in minimum crestal depth (Stocks and Wï¿½st, 1935). Later, Heezen and others (1959) plotted rift valley depth, west and east rift mountain heights, and other bathymetric parameters from 14°N to 55°N. Heirtzler and LePichon (1965) examined the along-strike amplitude variation of the central
Geoid undulations mapped by spaceborne radar altimetry
Authors: Vogt P. R. 
Published: April 2015

Abstract
Were the ocean and atmosphere at rest, the sea surface would describe a surface of constant gravitational potential. This equipotential surface is called the geoid. Removal of a simple reference surface (spheroid or ellipsoid) leaves geoid anomalies, or undulations of various wavelengths. Geoid undulations range in amplitude from many tens of meters for the broad high in the Azores-Iceland area (Fig. 1) down to a few centimeters for the local effect of a small seamount or minor fracture valley. The positive density anomaly (mass excess) represented by a seamount acts as a small “moon” on the ocean floor by pulling the sea towards itself, producing a bump (undulation) on the ocean surface. Conversely a sea-floor valley produces a dimple on the ocean surface.
The gravity field is the normal component of the gradient of the potential. Thus, gravity anomalies (Rabinowitz and Jung, this volume) are a measure of the spacing between the geoid and neighboring potential surfaces. The slope of the geoid is described by the Vertical Deflection (V.D.), a small angle (rarely more than 0.5′ arc) between the normal to the reference ellipsoid (a function of latitude only) and the normal to the geoid (the local astronomic vertical). Both geoid and V.D. can be calculated from gravity data (Rice, 1952; Brammer, 1979). Using a gyro- stabilized telescope, von Arx (1966) measured a V.D. of 60 to 90 (±12) arc sec over the Puerto Rico Trench. This pioneering work in direct measurement of V.D. was supplanted by
Magnetic anomalies and crustal magnetization
Authors: Vogt Peter R. 
Published: April 2015

Abstract
The study of geomagnetism is, after geodesy, the oldest of the geophysical sciences and, with the advent of plate tectonics, perhaps the most important. European mariners were using compasses, probably of the “floating lodestone” type, by no later than the treatise by Alexander Neckam in the year 1187. The GSA centennial thus also marks eight centuries of geomagnetic measurement. When Columbus measured magnetic declination (variation) at several points on his 1492 voyage, he made the first “geophysical transect” across the Atlantic Ocean, some 3½ centuries before the first bathymetric profile was drawn. Of course, Columbus was actually prospecting the earth’s core, not the oceanic crust. Geomagnetic field strength was first measured by Gauss in 1832, but continuous, accurate measurement suitable for mapping magnetic anomalies of geologic origin was only achieved a century later. However, the first magnetic chart detailed enough to resolve magnetic anomalies of geologic origin in the western Atlantic (Bermuda; Cole, 1908) depicted anomalies of declination, not intensity. Cole referred to the anomalies merely as “sources of considerable local disturbance.” Declination anomalies measured already in 1786 in Icelandic harbors by P. Lövenörn (published in 1799) were correctly attributed to magnetic effects of iron-rich minerals in nearby basalts (Kristjánsson, 1982).
Continuous magnetic field strength measurements began after the end of World War II, which had stimulated the development of airborne magnetometers to detect submarines. In 1948 a U.S. Navy self-orienting fluxgate magnetometer was converted to a “towed fish” at Lamont Observatory (Heezen and others, 1953). That year the
Petrologic and geochemical evolution of pre-1 Ma western North Atlantic lithosphere
Authors: Bryan W. B. , Frey F. A. 
Published: April 2015

Abstract
The Mid-Atlantic Ridge in the central North Atlantic was the source of the first deep-sea basement rocks to be studied in detail (Nicholls and others, 1964; Muir and Tilley, 1966; Miyashiro and others, 1969). The historical background and compositional details of basalts recovered from the modern Mid-Atlantic Ridge are discussed by Schilling and by Melson and O’Heara in other chapters in this volume. Some of the first recoveries of Old oceanic basement rocks were obtained by drilling in the western North Atlantic (Ayuso and others, 1976; Bryan and others, 1977). In this paper we summarize (1) the characteristics of pre-1 Ma lithosphere in the western North Atlantic and (2) inferences about its geologic evolution during the past 200 m.y. Such a review is subject to some serious limitations. Very large areas of the North Atlantic remain unsampled by drilling, and many crustal rocks that have been recovered may be too altered to yield definitive information about their magmatic geochemistry. Also, the deepest crustal penetrations in the North Atlantic have failed to reach the base of layer 2, which is composed almost entirely of extrusive basalts. The nature of the deeper levels of layer 2 and of the (presumably) gabbroic layer 3 must be inferred from samples recovered from a few holes apparently drilled in anomalously thin layer 2, from dredged samples recovered in fracture zones, or by extrapolation of observations at site 504 which was drilled into the deeper levels of layer 2 near the
Mid-plate stress, deformation, and seismicity
Authors: Zoback Mary Lou , Nishenko Stuart P. , Richardson Randall M. , Hasegawa Henry S. , Zoback Mark D. 
Published: April 2015

Abstract
The state of stress in the lithosphere is the product of a variety of forces that act on the plates. The interior region of a plate may be stressed by large-scale plate-driving forces, local density contrasts in'the plate, regional thermal anomalies, the residual effects of past tectonic events, or load redistribution caused by glaciation, volcanism, or erosion/sedimentation. Investigation of the tectonic in-situ stress field can enhance our understanding of mid-plate deformation and may also elucidate the relative importance of the various forces acting on the plates.
To this end we have assembled deformation, seismicity, and stress data for the mid-plate region of the North American plate. Our area of study covers continental North America and the oceanic portions of the North American plate, excluding zones of deformation along the plate boundaries. Excluded are the Mid- Atlantic Ridge and the shear and subduction boundaries associated with the Caribbean plate (covered by other chapters in this volume) and the entire western Cordillera of Canada and the United States (from the eastern Rocky Mountains front to the Pacific coast). The state of stress in the broad, intensely deformed western part of the North American plate is considered to be influenced primarily by local processes related to Pacific-North American plate interaction.
Numerous techniques and stress indicators provide information on the principal tectonic stresses in the crust and, for the oceans, the mantle lithosphere. Compilations of available data show that stress orientations inferred from different methods or techniques quite often agree within the accuracy
Seismic structure of the ocean crust
Authors: Purdy G. M. , Ewing John 
Published: April 2015

Abstract
Several notable papers have been published recently that review our knowledge of the seismic structure of oceanic crust (e.g. Christensen and Salisbury, 1975; Tréhu and others, 1976; Kennett, 1977; Lewis, 1978; Ewing and Houtz, 1979; Spudich and Orcutt, 1980a; Houtz, 1980; White, 1984). To reduce duplication of those previous efforts, this paper will emphasize evaluation of the resolving power of existing seismic data in the Western Atlantic Ocean and will compare this evaluation with the scale of local and regional variations in crustal structure predicted by reasonable geological models. We shall not focus attention on the relationship between the seismic and petrological structure of the crust and will use the terms Layer 2, Layer 3, and Moho only in their original seismic sense. Layer 2 is a region of high velocity gradients (perhaps as high as 3s−1 at its upper surface), with velocities in the range 3 to 6.5 km/s that extends from the seafloor to depths of 2–3 km. (We neglect sediments in this chapter, restricting ourselves to the igneous crustal column.) Layer 3 is typically about 4 km in thickness, has velocities of 6.7 to 7.2 km/s, and is characterized by low velocity gradients, generally less than 0.1 s−1. The Mohorovicic discontinuity (Moho) is actually a transition zone varying in thickness from a few hundred meters (or less) to 1–2 km and is almost always the most prominent seismic characteristic of the ocean crust. Velocities increase by about 1 km/s
Plate kinematics of the North Atlantic
Authors: Srivastava S. P. , Tapscott C. R. 
Published: April 2015

Abstract
The problem of determining the past relative positions of continents now situated around the North Atlantic has been a challenge to geologists and geophysicists for many years. Yet a solution acceptable to all does not exist. Since the acceptance of the idea of continental drift, a number of reconstructions has been published. The earlier reconstructions, prior to the birth of the plate tectonic theory, were done qualitatively in order to match morphological features of the continental margins (Choubert, 1935) or geological boundaries on land. The first quantitative fit of the North Atlantic was published by Bullard and others (1965) who described the motion between continents or plates as angular rotation about a set of poles. Since then a number of papers have been published showing reassembly of continents during various stages of evolution of the North Atlantic using magnetic anomalies in the oceanic regions as isochrons or plate boundaries and fracture zones as the direction of motion between plates. The most notable of these are by Pitman and Talwani (1972), Laughton (1971, 1972), Williams (1975), LePichon and others (1977), Sclater and others (1977), Kristoffersen and Talwani (1977) , Talwani and Eldholm (1977), Kristoffersen (1978), Srivastava (1978, 1985), Olivet and others (1981), Unternehr (1982), Nunns (1983), and Vink (1982, 1984).
Most of these reconstructions are based on a limited amount of geophysical information from one or more regions of the North Atlantic available at the time of publication. Thus different criteria and assumptions had to be made
Plate kinematics during the last 20 m.y. and the problem of “present” motions
Authors: Vogt P. R. 
Published: April 2015

Abstract
While increasingly precise plate reconstructions are being made at intervals of the order 10 m.y. for times corresponding to well-defined magnetic lineations (Klitgord and Schouten, this volume; Srivastava and Tapscott, this volume), much less is known about possible irregularities in plate motions over shorter time scales. Obviously the most recent geologic past offers the best hope for detecting any “kinematic fine structure.” This paper discusses the last 10–20 m.y., with special emphasis on the “present,” which, of course, is not an instant but involves a finite averaging interval, whether several years for geodetic or earthquake measurements, or several million years for a measurement based on magnetic anomalies. The chapter begins with Wegener’s attempts to measure continental drift, reviews the geodetic measurements on Iceland where the MAR (Mid-Atlantic Ridge) plate boundary is exposed, and discusses the latest attempts to measure plate motions over the “historical” present (several years time scale). The latter field is just being launched (see Anderle, this volume), and whatever is written today will soon be outdated. The main part of this paper is devoted to the question of relative and absolute plate motions over the “geological” present (m.y. time scale) resolved by magnetic lineations, transform faults, and hotspot traces. There is very little information about variability of plate motion over time scales intermediate between the “historical” and “geological” present. A case is made for significant geologically “short-period” (a few m.y.) global fluctuations in rates of plate motions over the last 10–20 m.y. The latest episode began
Surficial sedimentary processes revealed by echo-character mapping in the western North Atlantic Ocean
Authors: Laine E. P. , Damuth J. E. , Jacobi Robert 
Published: April 2015

Abstract
The development of high-resolution precision depth recorders (PDR) in the 1950s (Luskin and others, 1954; Knott and Hersey, 1956) not only permitted continuous and accurate measurement of ocean depths, but also provided a new tool for the study of deep-sea sedimentation processes. Changes in acoustic reflectivity and microtopography of the seafloor as observed on these early 12-kHz PDR records were found in many cases to be caused by erosional/depositional processes (Heezen and others, 1959). One of the first studies helped to confirm the existence of the Western Boundary Undercurrent (WBUC), a thermohaline, contour-following bottom current which is important in shaping the continental rise off eastern North America (Heezen and others, 1966; see also McCave and Tucholke, this volume). As part of this study, Hollister (1967) constructed an “echo character” map of the continental rise off Nova Scotia by classifying and mapping the regional changes of acoustic reflectivity observed on 12-kHz echograms. This map suggested that certain types of echoes (e.g. hyperbolae and prolonged echoes) were apparently reflected from sand waves or other depositional bedforms created by the WBUC. Regionally, these echo types were thought to be aligned parallel to bathymetric contours beneath the WBUC axis (Heezen and others, 1966; Hollister, 1967; Hollister and Heezen, 1972). Although subsequent and more detailed studies using much better quality 3.5-kHz echograms have shown that the regional pattern of echo character along the Nova Scotian margin is primarily downslope rather than along slope, this pioneering work by Hollister