Earth Physics Branch Research Articles

Jesuit Seismological Award Citation for Henry Hasegawa

Throughout his career with the Earth Physics Branch and the Geological Survey of Canada, Henry Hasegawa has been a major contributor to Observational Seismology in eastern North America. He is well known for his important contributions to the understanding of eastern North American seismicity. Very few seismologists have studied so many seismic areas, considered so many different seismological sources, and had such an impact on research in Canada while maintaining such high standards of quality research. Henry Hasegawa has devoted most of his professional life working on Canadian seismicity, …

New Seismic Hazard Assessment for Canada

INTRODUCTION The Seismology Program of the Geological Survey of Canada (GSC) and its predecessor agencies (Dominion Observatory and Earth Physics Branch) have prepared seismic hazard assessments for input to seismic zoning maps for the National Building Code of Canada (NBCC) since the first zoning map appeared in the Code in 1953 (Hodgson, 1956). Subsequent updates to this early map have appeared in the NBCC in 1970 (Whitham et al. , 1970) and 1985 (Basham et al. , 1985). A recent review of this history of three generations of seismic zoning maps can be found in Basham (1995). A fourth generation is now justified because there is sufficient new information available to improve the hazard estimates (Adams et al. , 1995; Basham, 1995). The principal document describing the new seismic hazard model and results is GSC Open File 3283 (Adams et al. , 1996), prepared to present the new results to the Canadian National Committee...

An assessment of long-wavelength magnetic anomalies over Canada

The reliability of the long-wavelength portion (> 300 km) of the magnetic field over Canada, as represented by the national aeromagnetic anomaly database compiled by the Geological Survey of Canada (GSC), is assessed by comparison with two independent data sets: a high-altitude country-wide survey carried out by the former Earth Physics Branch (EPB) and data from the MAGSAT and POGO satellite missions. The different altitudes at which each data set was measured (300 m, ~4 km, and ~400 km), and their different resolution and time span of observations allow a determination of the integrity of selected wavelength bands in each data set. The (upward-continued) EPB and MAGSAT–POGO fields compare well for wavelengths of 300–2500 km. The GSC data show significant differences to the former, indicating that the levelling and merging of several hundred individual surveys has degraded the longer wavelength components of the magnetic field. Replacing the GSC wavelength components >300 km with those from the EPB field produces a magnetic data set containing more dependable information within the largest possible waveband.

A historical summary of Geological Survey of Canada studies of earthquake seismology and geomagnetism

The solid-earth geophysical sciences of seismology and geomagnetism have roots in Canada that predate the founding of the Geological Survey of Canada (GSC) in 1842. These sciences matured in the Dominion Observatory, which was formed in 1904, and came to the GSC when it merged with the Earth Physics Branch in 1986. For most of the past three decades, these two sciences have been closely linked in the federal government by a common administration and by jointly housed and staffed observatories.Knowledge of Canadian earthquakes dates from the time of first European settlement, in the 17th century in eastern Canada and in the 19th century in western Canada. Instrumental recording began at the end of the 19th century, but the early instruments were unable to detect most of the earthquakes occurring in Canada. An ability to locate and study Canadian earthquakes followed the installation of sensitive seismograph stations in the east in the late 1920's and in the west in the early 1950's; the impetus for these installations came from large damaging earthquakes in both regions. Assessments of seismic hazards were first made in the 1940's, were displayed on three successively more detailed seismic zoning maps up to 1985, and are currently under revision for 1995. The Standard Seismograph Network, installed in the 1960's as the Canadian contribution to a worldwide program and supplemented by regional station networks in the 1970's and 1980's, has greatly advanced our understanding of Canadian earthquakes. These networks are now being refurbished to form a modern, satellite-based, digital network that should stand the GSC s seismology program in good stead into the next century.Magnetic observations in Canada date from the time of the earliest European explorers, Cartier and Champlain. Other explorers made measurements of magnetic declination during expeditions in search of the Northwest Passage. A Toronto magnetic observatory was established in 1840, and the observations begun there started a series of secular change measurements that continues today as part of the repeat station network. Major magnetic surveys made by the Toronto observatory staff formed the basis of the magnetic charts of British North America until the 20th century. Shortly after its founding, the Dominion Observatory began a comprehensive magnetic survey of Canada, which has evolved into the 60-station repeat station program in the GSC today. The Dominion Observatory also expanded the permanent magnetic observatory network to a total of 13 stations by the late 1970's, which, under the current GSC program, are being refurbished with the latest generation of digital technology. A breakthrough in regional magnetic field modelling was made in the 1980's with the development of spherical cap harmonic analysis, which is now used for revisions of the Canadian Geomagnetic Reference Field. Magnetic disturbance forecasting was begun in the 1970's, and has recently taken on greater importance as the complexity of the technology at risk has increased.

The founding of the Canadian Geophysical Union

This article is adapted from the speech John Hodgson gave May 9, 1988, at the 15th Annual Meeting of the Canadian Geophysical Union in Saskatoon, Saskatchewan, on the occasion of the adoption of the constitution that makes CGU an independent organization. Hodgson, retired Director General of the former Earth Physics Branch of the Department of Energy, Mines, and Resources of Canada, was a founder of the original CGU and is a historian of geophysics.

An intercomparison of LaCoste and Romberg Model-D gravimeters: results of the International D-meter Campaign 1983

Summary. The LaCoste and Romberg Model-D gravimeter has found many applications in studies of geophysical processes around the world. To assist in evaluating the results of these studies the performance of 13 Model-D gravimeters from seven countries was determined during a two-week observing campaign in 1983 on calibration ranges in the Federal Republic of Germany. Independent analyses of the data were carried out by the Institute of Physical Geodesy (IPG), Federal Republic of Germany, the Earth Physics Branch (EPB), Canada, and the International Latitude Observatory of Mizusawa (LOM), Japan. All instruments were found to have significant non-linear calibration functions (1 0-60 pGal corrections) and periodic error terms (2-7 pGal amplitudes). Calibration functions for most gravimeters were expressible in terms of third-order polynomials but a few instruments exhibited shorter wavelength structure. The calibration results appear to be similar to those obtained by the manufacturer's laboratory method, Cloudcroft Junior. Redundant observations taken at different reset-screw positions were used to estimate the uncertainties of the calibration functions. It is shown that the accuracy of a D-meter can be expressed in terms of the repeatability of readings and the uncertainty of its calibration function. For the average D-meter the present calibration error exceeds that associated with repeatability when gravity differences are greater than about 26 mGal. Although variations in precision and residual drift of the D-meters could not be clearly linked to environmental factors, the best results were obtained by D21 which was distinguished from the other gravimeters by having an extra thermostatized enclosure. Instruments transported in the manufacturer's cases without a special suspension system tended to give inferior precision. It

In Canada: Possible changes in geophysics programs

The Earth Physics Branch of the Canadian Department of Energy, Mines, and Resources (formerly the Dominion Observatory) has been the primary government agency for geophysics in Canada since the turn of the century. It has operated the national observatories for seismology and geomagnetism and has established and maintained national networks, surveys, and standards in gravity, geodynamics, and geothermics. A reassessment of the role of federal government agencies now underway by the current Conservative administration in Canada is examining the question of whether the Earth Physics Branch should be combined with the Geological Survey of Canada in one agency that would carry the issue is expected within the next few out all federal geoscience activities. The opinion that such a merger would adversely affect the future of solid earth geophysics in Canada has been expressed by the Canadian Geophysical Union in a letter to the Minister of Energy, Mines, and Resources. Resolution of the issue is expected within the next few months.

Deep Geology from Seismic Reflection Studies in Canada

In 1964, the Department of Physics at the University of Alberta initiated a programme to explore the feasibility of recording reflected seismic energy from boundaries within the lower crust and from the Mohorovičić discontinuity. This was the first attempt by a North American institute to systematically develop and apply industry-type seismic reflection techniques for investigations of the deep crust. For the first study a modification of the expanding spread technique was applied to an area of southern Alberta, where the general crustal layering was known from the results of reversed seismic refraction profiling. Kanasewich and Cumming (1965) reported on the success of this study by providing convincing evidence that reflections from the deep crust had been recorded. In particular, a strong lower crustal reflector at a two-way travel time of 11.4 sec was phase correlated over a distance of about 13 km, enabling the compilation of a T2-X2 plot and the determination of an average vertical velocity and depth to the reflector. Within experimental error, the 34 km depth to the reflector (later named the Riel discontinuity) matched the results from an earlier seismic refraction survey along the same line (Cumming and Kanasewich 1966). Encouraged by this initial success the group at the University of Alberta expanded its programme and by the late 1960s to the mid-1970s seismologists at three other institutes (University of Saskatchewan, University of Manitoba and the Earth Physics Branch of the Federal Department of Energy, Mines and Resources) were shooting short seismic reflection profiles across various parts of western Canada. It was during this period, in 1973, that Mair and Lyons (1976) recorded the first strong evidence that Vibroseis was a viabie source for probing the deep crust. They recorded a relatively continuous reflection from the Mohorovičić discontinuity along a 20 km line in the Cordilleran Orogen. In 1975, in an effort to consolidate funding and pool the limited human resources and recording/processing capabilities available in Canada, crustal seismologists from across the country joined together to form the Consortium for Crustal Reconnaissance Using Seismic Techniques (COCRUST). Since its inception most major crustal seismic surveys on the Canadian landmass have been conducted under the COCRUST umbrella. Unfortunately, due to a continued low level of funding,COCRUST has yet to capitalise fully on the earlier successes in Canadian reflection seismology. To date, most of the COCRUST funding has been directed to regional refraction surveys; accompanying short reflection profiles have been obtained only at critical locations. In this paper we review briefly, in chronological order, some of the important results of the pre-COCRUST era and then we present the conc1usions obtained from two COCRUST sponsored seismie reflection surveys and a recent government/industry sponsored intermediate depth reflection survey. Finally, we describe briefly the latest Canadian initiatives (LITHOPROBE) for mapping the third dimension of geology during the 1980s and beyond.

Comment and Reply on ‘Coal Creek serpentinite, Llano Uplift, Texas: A fragment of an incomplete Precambrian ophiolite’

Research Article| August 01, 1982 Comment and Reply on ‘Coal Creek serpentinite, Llano Uplift, Texas: A fragment of an incomplete Precambrian ophiolite’: COMMENT M. D. Thomas M. D. Thomas 1Gravity and Geodynamics Division, Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Ontario K1A 0Y3, Canada Search for other works by this author on: GSW Google Scholar Geology (1982) 10 (8): 440–441. https://doi.org/10.1130/0091-7613(1982)10<440:CAROCC>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. D. Thomas; Comment and Reply on ‘Coal Creek serpentinite, Llano Uplift, Texas: A fragment of an incomplete Precambrian ophiolite’: COMMENT. Geology 1982;; 10 (8): 440–441. doi: https://doi.org/10.1130/0091-7613(1982)10<440:CAROCC>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Eastern Canadian Earthquakes - 1979

Research Article| April 01, 1981 Eastern Canadian Earthquakes - 1979 R. J. Wetmiller; R. J. Wetmiller Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Canada, K1A 0Y3 Search for other works by this author on: GSW Google Scholar A. J. Wickens A. J. Wickens Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Canada, K1A 0Y3 Search for other works by this author on: GSW Google Scholar Seismological Research Letters (1981) 52 (2): 32–39. https://doi.org/10.1785/gssrl.52.2.32 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation R. J. Wetmiller, A. J. Wickens; Eastern Canadian Earthquakes - 1979. Seismological Research Letters 1981;; 52 (2): 32–39. doi: https://doi.org/10.1785/gssrl.52.2.32 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietySeismological Research Letters Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

The map of contemporary vertical crustal movements in Canada

For years, the IUGG Interunion Commission on Recent Crustal Movements, voicing the wishes of various groups of geoscientists, has been urging its member countries to produce maps of geologically contemporary (i.e., at most, 100 years in the past) vertical movements in regions under their jurisdiction. In Canada, the work on such a map began early in 1977 in the form of a cooperative project between the Earth Physics Branch of the Department of Energy, Mines and Resources and the Department of Surveying Engineering, University of New Brunswick. It had been well known, from previous projects, that data from repeated geodetic levelings in Canada were very sparse, except for those from a few fairly heavily inhabited regions. Thus the main expectation for this project was as complete as possible an inventory of existing releveled segments, tide gage records, and lake level differences.

The Lomonosov ridge experiment: “Lorex 79”

In the spring of 1979 the Department of Energy, Mines and Resources (EMR) undertook a large‐scale, multidisciplinary project to study the nature and origin of the Lomonosov Ridge. The scientific program was planned and coordinated by the Earth Physics Branch, and the logistic support was provided by the Polar Continental Shelf Project/Scientists from other branches of EMR, from the Department of Fisheries and Oceans (DFO), and from a number of universities in Canada and the U.S.A. took part in the project code named Lorex 79.The Lomonosov Ridge is an aseismic submarine mountain range that bisects the Arctic Ocean into the Amerasia and Eurasia Basins (Figure 1). It rises sharply to a height of some 3 km above the adjacent abyssal plains, the Makarov Basin to the west, and the Fram Basin to the east. It is close to 200 km wide where it approaches the North American and Eurasian continental shelves but narrows to 25 km at its midpoint near the North Pole. Its relatively flat top, the steepness of its flanks, and results from previous geophysical measurements indicate that it may be a sedimentary structure of continental origin rather than a structure of oceanic origin [Sweeney et al., 1978]. In this context it has been suggested on several occasions that it is a rafted fragment split off the Eurasian continental shelf at the time of the opening of the North Atlantic and the Eurasia Basin in Early Tertiary times. However, since the available geophysical, geological, and bathymetric data are relatively sparse and often of doubtful quality (because of the enormously difficult operating conditions), the continental nature of the Lomonosov Ridge has never been unambiguously demonstrated.

Seismological service of Canada: Instrumentation and data processing

The Earth Physics Branch of the Department of Energy, Mines and Resources operates a variety of seismological installations throughout Canada including nineteen Standard and fourteen Regional Stations. At Yellowknife there is an 18-element short-period medium-aperture array with on-site processing which produces a daily detection bulletin. At Ottawa and Victoria, regional telemetered networks have been established which employ wide dynamic range digital data transmission and on-line event detectors. A six-element transportable array employing FM telemetry in the UHF band is used for local seismicity studies. Microprocessor-controlled event-triggered casette recorders are being developed as a further aid to regional seismicity studies. On the West Coast the Branch operates a strong-motion network that includes 28 accelerometers. At Ottawa, the data management group controls the flow of data and arranges for the distribution of seismograms, tape recordings, phase data and other derived information to Branch seismologists and other outside agencies.

THEORY AND EVALUATION OF THE LACOSTE AND ROMBERG THREE‐AXIS INERTIAL PLATFORM FOR MARINE GRAVIMETRY

In 1972, the Earth Physics Branch of the Canadian Department of Energy, Mines and Resources acquired a LaCoste and Romberg Inc. air/sea gravimeter complete with three‐axis inertial platform. Since then, in cooperation with the manufacturer, a thorough evaluation of this system for regional applications has been undertaken over two field seasons. In 1972, the instrument was operated over the Halifax Test Range where direct comparisons with the underwater measurements indicated that the system as constituted gave results which were accurate from ±5 to ±10 mgal (±1σ), with position updates at about two hour intervals. In general, the errors were greatest when the gyro precession rates were large and hardware modifications were made to reduce this effect. A second survey in Queen Charlotte Sound was made in 1973 to evaluate improvements designed to reduce the gyro precession rates. An analysis of crossover differences indicated that accuracies in measuring gravity of 3 mgal (±1σ) using the inertial platform under open sea conditions is achievable. The accuracy of the Eötvös correction determined from inertial data is intermediate between that obtained using Loran‐C in the rho‐rho mode and hi‐fix.

Seismic Ground Motion and Residual Deformation near a Vertical Fault

Ground motion and residual ground deformation at strategic points in the epicentral region of an idealized, vertical shear fault that may correspond to an intermediate magnitude (6–6½) earthquake are displayed and analyzed. For analytical purposes, Haskell's expressions for the elastic displacements near a propagating fault are separated into two parts, the near-field and the far-field terms. The distance from the fault at which the far-field terms are sufficient to describe the total field varies, depending upon the orientation of particle motion relative to that of the dislocation (slip) vector. For the component of particle motion parallel to the dislocation vector, this distance is comparatively greater than that for the perpendicular component. The Earth Physics Branch strain gauge, which has a threshold sensitivity of about 5 × 10−10, has the capability of detecting residual strain at least as far as 100 km from the hypothetical fault. The Earth Physics Branch tiltmeter, which can detect a step change in tilt in the range 5 × 10−9 to 5 × 10−10 radians, can detect residual tilt at least as far as 50 km from the causative fault.The high-frequency slope of the theoretical Fourier amplitude spectrum of ground acceleration (FS), is not appreciably steepened by the addition of the near-field to the far-field terms. The implication of this observation is that the steep slope observed at high frequencies on FS curves of predominantly California earthquakes cannot be attributed, even in part, to the source mechanism assumed but must be attributed entirely to travel path effects such as attenuation and scattering.

Seismic Refraction Measurements in Southeast Alaska and Western British Columbia

Crustal thickness determinations were made from seismic refraction measurements along two profiles extending north–northwest along the Inside Passage of Southeast Alaska and western British Columbia. The source for the seismic waves was a series of 10 explosions detonated by personnel of the Earth Physics Branch, Department of Energy, Mines and Resources of Canada. Arrivals recorded in Southeast Alaska from explosions in Bird Lake on Graham Island indicate a 26 km thick crust over a mantle with a Pn velocity of 7.9 km/s. Measurements of Pn wave attenuation suggest that the uppermost mantle has a Q value of 650 ± 120. Arrivals recorded along the mainland coast of British Columbia from explosions in Ripley Bay indicate a 30 km thick crust over a mantle with a Pn velocity of 8.1 km/s. On the basis of compiled gravity and seismic refraction data, the crust of the Inside Passage region from Queen Charlotte Sound to Cross Sound is believed to be anomalously thin. Crustal thickening from ocean to continent appears to occur in a stepwise, rather than continuous, fashion in the vicinity of the Inside Passage.

Storage and retrieval of gravity data

At the Earth Physics Branch in Ottawa, storage and retrieval of gravity data has progressed from the pencil and paper system used until the late 1950’s to the current file-oriented gravity library operated on a large, high speed computer. The main impetus for the development of this computer library has been the requirements of the petroleum and mineral exploration industry, but military requirements and those of physical geodesy, geology and geophysics have had a large influence on the system at some or all stages of its development. The current system is user-oriented and tends to be complex internally to preserve a simple and convenient interface to the user.

The statistics of the time-term method

Letter| December 01, 1971 The statistics of the time-term method K. G. Barr K. G. Barr Seismology Division Earth Physics Branch Department of Energy, Mines and ResourcesOttawa, Canada Search for other works by this author on: GSW Google Scholar Bulletin of the Seismological Society of America (1971) 61 (6): 1853–1854. https://doi.org/10.1785/BSSA0610061853 Article history received: 01 Jun 1971 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation K. G. Barr; The statistics of the time-term method. Bulletin of the Seismological Society of America 1971;; 61 (6): 1853–1854. doi: https://doi.org/10.1785/BSSA0610061853 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

A Canadian Network of Gravity Measurements with Pendulums

Summary From 1968 to 1970, the Canadian pendulum apparatus of the Earth Physics Branch (formerly Dominion Observatory) was used to establish a network of gravity stations within Canada to provide scale control for the Canadian gravimeter net. The pendulum network, adjusted by the method of least squares, has a standard deviation of 0.12mgal. Agreement with Faller's absolute apparatus to - 23 ppm in scale is noted.