Coherent Event Research Articles

Slow earthquakes and great earthquakes along the Nankai trough

We have reexamined reports indicating that slow deformation occurred before the great Japan earthquakes of 1944 (Tonankai) and 1946 (Nankaido) and find that the observations are well founded. Although no quantitative models have previously been proposed to explain all of the relevant data we show that they are satisfied by a simple model for both earthquakes. The model, based on known properties of subduction zones, has slow slip on the subduction interface in an area deeper than the seismic rupture. If this model is correct and a similar physical situation holds for an anticipated Tokai earthquake, existing instruments will be able to reveal the pre-slip in real time. While differences among the deformation time series at different sites will provide strong constraints on the slow rupture propagation, these differences could result in delaying the recognition of a coherent event.

Spatio-temporal development of streamflow droughts in north-west Europe

Abstract. This paper examines the spatial and temporal development of streamflow droughts in Europe over the last 40 years, differentiating the climatic factors that drive drought formation from catchment controls on drought manifestation. A novel approach for quantifying and comparing streamflow and precipitation depletion is presented. This approach considers atypical flow or rainfall events, as well as more severe droughts, regardless of the season in which they occur (although unlikely to constitute drought in an operational sense, sustained atypical flows are important with regard to understanding how droughts arise and develop). The amount of flow depletion is quantified at daily resolution based on the standardised departure from the mean day d flow, or flow anomaly. The index was derived for 2780 gauging points within north-west Europe using data from the FRIEND European Water Archive for the 1960-1995 period. Using a simple interpolation procedure these data were used to produce a time-series of grids, with a cell size of 18 km2, showing the spatial distribution of flow anomaly over the study area. A similar approach was used to characterise monthly precipitation anomalies, based on existing grid data (see New et al., 2000). The grids were analysed chronologically to examine the spatial and temporal coherency of areas showing large flow and/or precipitation anomalies, focussing on drought development during the 1975-1976 and 1989-1990 periods. Using a threshold approach, in which an anomaly of 2 standard deviations represents the onset of drought conditions, indices were developed to describe the time-varying extent and areal-severity (flow deficit) of streamflow and precipitation drought. Similar indices were used to describe how the magnitude and temporal variation of flow depletion varied spatially. In terms of streamflow depletion, the 1976 drought was found to be a highly coherent event, having a well defined start (in January 1976) and end (in September 1976). The worst and most persistent streamflow droughts occurred in southern England and northern France. Central parts of Europe experienced only severe streamflow depletion during the ‘height’ of the drought in June, July and August when there was negligible precipitation across large areas of Europe. In contrast, the 1989/90 period was characterised by a series of shorter and less severe droughts, with much greater variability over time. The relationship between precipitation drought and streamflow drought was less clear, which might have resulted from periods of precipitation depletion occurring randomly in time. Particularly high levels of streamflow drought were again observed in southern England and northern France. Several possible explanations for the increased drought occurrence over southern England and northern France were investigated using data from the 1976 event. However, immediately antecedent precipitation deficits could not explain the level of streamflow depletion which appears to have been enhanced by decreased discharge of groundwater into the river networks in this region. This can probably be attributed to large precipitation deficits during autumn 1975 and spring 1976: the consequent reduction in groundwater recharge ultimately led to depressed groundwater levels. Keywords: drought, streamflow depletion, streamflow drought, low-flow regimes, Drought Index

Migration velocity analysis from locally coherent events in 2‐D laterally heterogeneous media, Part I: Theoretical aspects

We present a new method based on migration velocity analysis (MVA) to estimate 2‐D velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field. Classical approaches using picking on common image gathers (CIGs) must consider continuous events over the whole panel. This interpretive step may be difficult—particularly for applications on real data sets. We propose to overcome the limiting factor by considering locally coherent events. A locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube.In the prestack depth‐migrated volume obtained for an a priori velocity model, locally coherent events are picked automatically, without interpretation, and are characterized by their positions and slopes (tangent to the event). Even a single locally coherent event has information on the unknown velocity model, carried by the value of the slope measured in the CIG. The velocity is estimated by minimizing these slopes.We first introduce the cost function and explain its physical meaning. The theoretical developments lead to two equivalent expressions of the cost function: one formulated in the depth‐migrated domain on locally coherent events in CIGs and the other in the time domain. We thus establish direct links between different methods devoted to velocity estimation: migration velocity analysis using locally coherent events and slope tomography.We finally explain how to compute the gradient of the cost function using paraxial ray tracing to update the velocity model. Our method provides smooth, inverted velocity models consistent with Kirchhoff‐type migration schemes and requires neither the introduction of interfaces nor the interpretation of continuous events. As for most automatic velocity analysis methods, careful preprocessing must be applied to remove coherent noise such as multiples.

Long-Period wind oscillations in the mesosphere and lower thermosphere at Yamagawa (32°N,131°E), Pontianak (0°N,109°E) and Christmas Island (2°N,157°W)

From daily mean winds observed with the MF radar in the mesosphere and lower thermosphere (80– 100 km ) at Yamagawa (32°N,130°E) in 1996–1997, we have analyzed periodic oscillations of zonal and meridional wind velocity with a period of 4–10 days and 12–20 days. These oscillations are interpreted as planetary wave or Rossby normal mode. Such oscillations have also been observed by other MF radars located in equatorial regions: Pontianak (0°N,109°E) and Christmas Is. (2°N,157°W). Enhanced wave activity sometimes continued simultaneously a few tens of days at three sites: moreover, the envelope of the intensity of these waves was generally similar among the different coordinates. Therefore, these oscillations are interpreted as global scale planetary waves, several of which have the characteristics of Rossby normal modes. In order to identify the zonal wave number and latitude structure for each wave event, we have analyzed the coherence and phase difference of wind oscillations with periods of 4–10 days among the three radar sites. Oscillations at the period of 4–10 days are explained by 5-day and 4-day waves which are the equatorially symmetric first mode having zonal wave number 1 and 2, respectively. In particular, a coherent wave event was identified in three observation periods. From the middle of April to the middle of May, 1996, the 4–10 day oscillation can be interpreted as the 5-day wave of the Rossby normal mode. However, from the middle of July to the end of August, 1996, the oscillation seems to be a manifestation of the 4-day wave. On the other hand, from the end of September to the end of October 1996, the oscillation could not be simply explained as a normal mode. A similar analysis was applied to 12–20 day wind oscillations. The latitude and longitude structure of the 12–20 day oscillation from the middle of January to the end of March, 1996, seems to be explained by that for a 16-day wave, having zonal wave number 1, which is called the equatorially symmetric second Rossby normal mode. From July to the middle of October, 1996, we were unable to clearly identify a specific mode for the 12–20 day oscillations. Amplitudes of the 12–20 day oscillation were large during days 185–285, 1996, at Yamagawa when these waves were enhanced at Pontianak and Christmas Is. This result suggests that an interhemispheric penetration of the 16-day wave occurred through a weak mean wind region over the tropics.

A blind interpretation of drill‐bit signals

The role of kurtosis in evaluating the quality of vertical seismic profiling (VSP) drill‐bit data is investigated. The calculations show how kurtosis depends on the dominant frequency, bandwidth, and phase content of a seismic signal. This analysis is applied to synthetic and real common‐offset and common‐shot drill‐bit seismograms to evaluate the prominence and quality of the first arrival and other coherent events. High values of kurtosis correspond to an isolated first arrival or to a compressed coherent noise event, while low values are typical of low S/N (distributed) ratio traces. Kurtosis analysis applied to drill‐bit VSP data while drilling proved to be successful at identifying high‐quality traces with little interpretational input.

Deep seismic structure of the continental margin in the Gulf of Guinea: a summary report

Abstract Post-stack reprocessing of the PROBE seismic data set has resulted in a refined tectonic model of the continental margin between Cameroon and southern Gabon. The margin is divided into the North Douala and Gabon Basins by the Kribi Fracture Zone, a 75 km wide transform fault zone that trends northeast-southwest and intersects the coastline between 2 and 3°N. North of the Kribi Fracture Zone, oceanic crust extends essentially to the coastline and floors the narrow margin off Cameroon. Little or no offshore rift margin exists in the northern Douala Basin. Reflection Moho beneath oceanic crust is relatively weak but continuous throughout the northern Douala Basin. Oceanic crustal thickness is extremely uniform in the North Douala Basin, averaging c. 1.75 s in two-way travel time. A distinct northeast-southwest trending structural grain at both basement and reflection Moho levels occurs within the Kribi Fracture Zone. Much of the margin off Equatorial Guinea is influenced or controlled by fracture zone tectonics. South of the Kribi Fracture Zone, oceanic crust is offset c. 350 km to the southwest, resulting in a broad rift margin off Gabon that is unaffected by major-offset fracture zones. This margin seems to have evolved by a form of imperfect pure shear, involving brittle, upper continental crustal sheets overlying a series of ductile lower sheets that generally dip easterly to southeasterly. The ductile sheets may unroof at outer highs, which mark the boundary between oceanic and continental lithosphere. Dominant reflection events are often associated with the ductile shear zones that define the lower sheets, but a regionally coherent event representing reflection Moho cannot be delineated. The concept of reflection Moho beneath rifted continental crust may be invalid. The tectonic and rheological models presented here can be used to frame hydrocarbon exploration tactics and strategies along this passive margin. In a broader context, elucidation of margin architecture may be a cost-effective way to approach frontier passive margins in the next century.

Multiwavelength Observations of Collisional Ring Galaxies. III. Oxygen/Nitrogen Abundances and Star Formation Properties of Ring Knots

This is the third paper in a series examining the multiwavelength properties of a sample of northern ring galaxies, in which we present optical long-slit spectra and broadband BVR and JHK colors of individual star-forming knots embedded in the ring. We present the oxygen and nitrogen abundances of the starburst knots and compare the reddening-corrected colors of individual star clusters with recent models of stellar evolution. We also present kinematic data for one system, LT 41. The star-forming knots in the rings have very similar colors, which implies similar ages in the range 4–80 Myr. These ages are less than the dynamical ages of the rings, which are typically 100–300 Myr. The fact that the implied ages of knots within individual ring galaxies cluster around the same age argues that their formation is recently triggered by a coherent event all around the ring. This strongly supports the triggering of the star formation as being due to the propagation of a radial density wave, as in the classical picture. The ring galaxies are found to have subsolar metallicities in the range one-half to one-fifth solar in [O/H] and [N/H] ratios. There is a suggestion of an increase in the mean nitrogen abundance for the rings of larger linear size, but oxygen abundances show no trend with ring diameter. The uniformity of the oxygen abundances over the sample is consistent with their rather narrow range of K-band luminosities, which suggests that even in strongly disturbed galaxies, when prompt local enrichment is expected to be important, the primary factor governing oxygen metallicity is total luminosity.

Seismic reflection and ground‐penetrating radar imaging of a shallow aquifer

In 1995 and 1996, researchers associated with the US Air Force’s Phillips and Armstrong Laboratories took part in an extensive geophysical site characterization of the Groundwater Remediation Field Laboratory located at Dover Air Force Base, Dover, Delaware. This field experiment offered an opportunity to compare shallow‐reflection profiling using seismic compressional sources and low‐frequency ground‐penetrating radar to image a shallow, unconfined aquifer. The main target within the aquifer was the sand‐clay interface defining the top of the underlying aquitard at 10 to 14 m depth. Although the water table in a well near the site was 8 m deep, cone penetration geotechnical data taken across the field do not reveal a distinct water table. Instead, cone penetration tests show a gradual change in electrical properties that we interpret as a thick zone of partial saturation. Comparing the seismic and radar data and using the geotechnical data as ground truth, we have associated the deepest coherent event in both reflection data sets with the sand‐clay aquitard boundary. Cone penetrometer data show the presence of a thin lens of clays and silts at about 4 m depth in the north part of the field. This shallow clay is not imaged clearly in the low‐frequency radar profiles. However, the seismic data do image the clay lens. Cone penetrometer data detail a clear change in the soil classification related to the underlying clay aquitard at the same position where the nonintrusive geophysical measurements show a change in image character. Corresponding features in the seismic and radar images are similar along profiles from common survey lines, and results of joint interpretation are consistent with information from geotechnical data across the site.

Global Pc5 geomagnetic pulsations of March 24, 1991, as observed along the American Sector

Analysis of the globally coherent Pc5 geomagnetic pulsation event of March 24, 1991, from a chain of stations extending from the auroral oval to the equatorial region along the American sector, has shown unequivocal evidence on the enhancement of pulsation amplitude in the narrow equatorial band centered at the dip equator. The fine spatial structure of this equatorial enhancement, documented observationally for the first time, emphasizes the importance of an ionospheric component associated with enhanced Cowling conductivity. The presence of an ionospheric component is also indicated at mid‐latitudes by the sharp increase in the amplitude of pulsations, more dominantly in the Y than in the X component, on the sunward side of the dawn terminator. The sunrise effect also causes a reversal of the sense of rotation of the wave polarization across the dawn terminator. Propagation of the magnetospheric inducted polar electric field to low and equatorial latitudes through the ionosphere is invoked to account for the equatorial enhancement and the sunrise effect seen in these Pc5 pulsations.

Regional Seismic Evaluation of Basement Control on Paleozoic Sedimentation in Ohio and West Virginia: ABSTRACT

Paleozoic sediments of the central Appalachian lie upon a complexly deformed basement that continued to deform during the Paleozoic. In West Virginia basement is cut by an aulocogen known as the Rome trough. Seismic data reveal that the Rome Trough is an asymmetrical graben with a faulted eastern margin, and generally rotational western margin. Differential subsidence across the western margin decreases exponentially following the early Cambrian inception of the Trough. Displacement of the East Margin fault appears coupled to west-flank rotation. Minor inversion of Trough structure is also observed following the initial phase of rapid subsidence. Inversion influences local sedimentation patterns and results in minor structures that may influence hydrocarbon distribution. Regional seismic evaluation has been extended further west into Ohio to define regional scale subsidence history and local structural reactivation. Three seismic lines have been analyzed in Ohio that extend northwest from West Virginia to the Ohio COCORP line. Seismic expressions of the basement is marked by a relatively coherent reflection event. The basement faults in the distal part have similar offsets and therefore less influence on the sedimentary features. This analysis evaluates the structural affects of Coshocton zone, Cambridge Arch and Burning Spring anticline on the depositional historymore » of Paleozoic sedimentation in Ohio.« less

Evidentiality in ritual discourse: The social construction of religious meaning

ABSTRACTThe communal creation of religious meaning is here examined in the context of an Irish Catholic Charismatic prayer meeting. Through a micro-analysis of the “spontaneous” ritual language of one such meeting, various discursive strategies are revealed which function to create for the participants an experience of divine/human communication. These include an explicit effort on the part of speakers to construct a thematically consistent and coherent ritual event out of a sequence of apparently spontaneous individual speech acts, as well as a marked use of evidentials to attribute spiritual authorship and authority to personal speech acts. In contrast to what has been suggested as the self-evident nature of ritual speech, the frequent use of evidentials is related to the relatively recent emergence of the movement, its ideology, and its emphasis on the personal narrative as the central form of religious discourse. (Ritual language, evidentials, Catholic religion, charismatic religion, religious movements, authority in discourse)

Coherent multiple Pc1 pulsation bands: possible evidence for the ionospheric Alfvén resonator

Abstract. A fair fraction of Pc1 pulsation events observed on the ground includes more than one simultaneous pulsation band. In most such multiband events the bands display different characteristics and, therefore, come from different source regions via horizontal ducting in the ionosphere. However, in this report we identify a new "coherent" subclass of multiband Pc1 events where the pearls of the simultaneous bands have the same group velocities (repetition rates) as well as dispersion and other properties, thus implying that the bands are produced by the same source. Studying one example of such a coherent multiband event in more detail, we argue that these events defy an explanation in terms of band splitting by magnetospheric heavy ions because the observed frequency gap between the bands is smaller than would result in such a case. We interpret these events to be due to the frequency dependence of the ionospheric reflection coefficient of Alfvén waves. An oscillatory frequency dependence of the coefficient is a natural consequence of the idea that the ionosphere acts as a resonator for Alfvén waves. We also discuss other predictions of this interpretation.

Distribution of magma beneath the East Pacific Rise near the 9°03′N overlapping spreading center from forward modeling of common depth point data

We have reprocessed six cross‐axis and three along‐axis common depth point (CDP) profiles near the 9°03′N overlapping spreading center (OSC) to understand the relationship between axial magma chamber (AMC) width and seafloor morphology. Travel time modeling of the AMC reflector reveals an asymmetric distribution of melt across the 9°03′N OSC. The variation of modeled AMC width beneath either OSC limb is minimal, but the width increases nearly fourfold across the offset attaining an estimated maximum width of 4.15 km near the 9°17′N ridge axis discontinuity. Additionally, melt distribution underlying the eastern rise limb is not symmetric with respect to the rise axis/neovolcanic zone but is displaced toward the western rise flank. Depth migration, based on a continuum velocity model consistent with postcritical reflections from the base of layer 2A, places the skewed AMC reflector beneath a nearly constant thickness sheeted dike section which dips ∼ 10° away from the rise axis. To confirm AMC continuity beneath the western rise flank, we use the Maslov synthetic seismogram method to show that amplitude enhancement of the AMC reflector is consistent with a continuous melt body underlying a thickening extrusive layer. Analysis of along‐strike CDP profiles indicates an AMC which is neither overlapping nor discontinuous when projected onto the along‐strike plane. Identifying intracrustal events on along‐axis CDP lines, however, requires extreme caution; we have modeled out‐of‐plane scattering using a Kirchhoff formulation, and we show that a coherent event identified beneath the overlap basin results from diffraction off the AMC which lies nearly 3 km to the west of the profile. We attribute the asymmetric pattern of melt to a decoupling of melt supply from preexisting weaknesses in the brittle upper crust. In this model, melt ascends upward (buoyancy forces) until deflected by the impermeable sheeted dike complex; melt then migrates updip, beneath the base of the sheeted dikes, toward the neovplcanic zone where fissuring produces a temporary conduit for emplacement. Discrete jumps in modeled AMC width toward the overlap basin represent a further displacement/defocusing of melt supply (western AMC edge) relative to the neovolcanic zone (eastern AMC edge). The asymmetric pattern of melt therefore represents a gradual, en‐echelon accommodation of melt supply across the 9 km of ridge axis offset at 9°03′N. Thus for asymmetric configurations, AMC width may not correlate solely with magmatic robustness but may signify the amount of decoupling which exists between melt supply and extrusive emplacement within the neovolcanic zone. Here we present a new model for OSC development which invokes a significant component of cross‐axis melt migration. Moreover, abrupt changes in AMC width near ridge axis discontinuities (e.g., 9°17′N deviation in axial linearity) suggest that any along‐axis melt migration is confined to subsegments of the ridge and seem to preclude the segment length migration of melt proposed in some current models. The transition of melt supply beneath the overlap basin might favor a continuous low‐velocity zone underlying this feature; if true, basin development may be related to the subsidence of a mechanically weak crustal lid. The proposed model for OSC development therefore views ridge axis discontinuities as the surficial response of misalignment and/or defocusing of melt supply in the uppermost mantle.

Multi-Component Seismic event Correlation in Coherent Noise

A new correlation and picking algorithm has been developed which uses multi-component seismic data from two stations. A conventional single-station covariance matrix analysis is well known to provide polarization estimates of the particle motion at a given point in space. This single-station technique is successful if any noise present on the data is purely random. However, in the presence of coherent noise, the single-station analysis breaks down. A two-station (binocular) covariance matrix provides similar information at two points in space, as well as indicating the correlation between the two stations. The major advantage of the procedure is that it can successfully identify overlapping arrivals (in the time domain) where a single-station analysis fails. The binocular analysis may be sequentially applied to a multi-station seismic gather using the same reference signal to identify a coherent event. The technique was applied to synthetic data and then successfully used to pick overlapping events on data acquired in a physical scale-model experiment.

Early Late Cretaceous-early Tertiary gold mineralization; a galena lead isotope study of the Bridge River mining camp, southwestern British Columbia, Canada

The Bridge River gold camp, 180 km north of Vancouver, Canada, produced more gold than any other camp in British Columbia over its 70 years of operation (130 metric tons or 4 million oz), mainly from the Bralorne and Pioneer deposits. A compilation of new and existing lead isotope ratios from 20 widespread and diverse deposits in the Bridge River camp shows a distinct clustering of data. This is interpreted to be the expression of a single protracted but episodic mineralizing event coinciding with the emplacement of the Coast Plutonic Complex during early Late Cretaceous to early Tertiary time (90-45 Ma). The timing of this event is constrained at Bralorne by a premineral albitite dike set (91.4 + or - 1.4 Ma by U-Pb on zircon) and a late intramineral hornblende porphyry dike set (85.7 + or - 3 Ma by K-Ar on hornblende). Late lamprophyre dikes that crosscut the mineralized veins, dated at 43.5 + or - 1.5 Ma by K-Ar on biotite, set a lower age limit for the mineralization. The host rocks, the Bralorne intrusions, have no genetic relation to the mineralization since they are Early Permian (270 + or - 5 Ma by U-Pb on zircon).The conclusion that all mineralization is related to a coherent event is in accord with recognition of a districtwide mineral zoning scheme by Woodsworth, Pearson, and Sinclair. In this scheme, a sequence from high-temperature Au-As-W-Mo through intermediate Sb-Ag-Au-As to low-temperature Sb-Hg vein assemblages as generated from southwest to northeast within the thermal aureole of the Coast Plutonic Complex. Stable isotope and temperature data from other workers support this northeastly decreasing gradient in mineralization temperature.Clustered lead isotope data define a trend that plots between model Pb isotope curves of Doe and Zartman for the upper crust and the mantle. This trend is interpreted to be a mixing line, between primitive mantle-type lead and more radiogenic lead, by one or a combination of two postulated processes: between two groups of rocks (more primitive oceanic volcanics and more radiogenic upper crustal volcanic arc-clastic rocks) by a meteoric thermal system generated by the emplacement of the Coast Plutonic Complex, or between less and more radiogenic magmas during the emplacement of the Mesozoic-Cenozoic volcanics and intrusion hosting the deposits. The accreted nature of the host oceanic and arc terranes is emphasized by the differences between the model proposed and the upper crustal shale curve model of Godwin and Sinclair, which represents much of the locally adjacent autochthonous portion of the Canadian Cordillera.

Beyond bartlett: Narratives and remembering

This paper explores some of the ways in which narratives can shed light on mental processes, particularly those involved in remembering. Information appears to be stored in the mind in the form of minimal ‘ideas’ of referents, events, and states. At a particular time during the production of a narrative a particular idea may be active, semi-active, or inactive in the mind of the speaker. Ideas that are already active are typically verbalized with pronouns and low pitch, newly activated ideas with full noun or verb phrases and intonation peaks. Combinations of ideas appear linguistically as intonation units, whose properties are discussed. The typical intonation unit in English has the form of an independent clause which is linked to the preceding intonation unit with ‘and’, and ends with a clause-final intonation. When sentence-final intonation occurs, it typically signals the boundary of a coherent sequence of intonation units. Often the coherence is that of a paragraph-like unit, distinguished by a coherent location, coherent temporal sequence, coherent character configuration, and coherent event structure. Just as intonation units shed light on the capacity of the mind to handle active information, so these paragraph-like units help us to understand the nature of peripheral memory.

Timing of emplacement of the Muskox intrusion: constraints from Coppermine homocline cover strata

The Muskox intrusion is a Middle Proterozoic shallow-level mafic–ultramafic layered intrusion in the northwest corner of the Bear Province of the Canadian Shield. The intrusion was emplaced into the Lower Proterozoic Akaitcho Group and Hepburn metamorphic–plutonic complex of the Wopmay orogen and overlying Middle Proterozoic Coppermine homocline strata. To date, radiometric, paleomagnetic, and geochemical evidence has produced only equivocal results concerning the age of the Muskox intrusion relative to overlying Coppermine River Group basalts and Mackenzie diabase dykes. Stratigraphic redefinition of and structural relationships to the cover sequence of the intrusion provide the best available evidence for the age of the Muskox intrusion.Although previously inferred to be a pre-Dismal Lakes Group structure, the Canoe Lake Fault is here shown to cross-cut Dismal Lakes strata with west-side-down displacement equivalent to that documented to the south where it offsets the intrusion. This relationship, supported by detailed mapping that shows that the Muskox intrusion intrudes units 11 and 12 of the Dismal Lakes Group, demonstrates a post-Dismal Lakes age for the intrusion. This conclusion strongly supports the contention that the Muskox intrusion and Coppermine River Group are coeval and comagmatic.Syndepositional uplift and normal faulting within uppermost Dismal Lakes Group strata were most pronounced near the exposed roof of the intrusion, and are interpreted to have been related to emplacement of a small sill-like body that probably was the precursor to the main intrusive event. At least 70 m of sediments was deposited after this initial disturbance, but before extrusion of the Coppermine River Group basalts (which heralded the main emplacement event). This thickness of sedimentary strata implies a period of several hundred thousand years between the two igneous events.These results support earlier contentions that the Mackenzie igneous event, comprising emplacement of Mackenzie dykes, Coppermine River Group basalts, and the Muskox intrusion, was a coherent mafic igneous event that occurred approximately 1200 Ma ago, with the Muskox intrusion as a locus.

Interplanetary pitch angle scattering and coronal transport of solar energetic particles: New information from Helios

Solar particle data from the Kiel experiment on Helios 2 at 0.5 AU were compared with the predictions of a model which includes the effect of a postulated temporal profile of injection and which describes the coherent interplanetary transport of energetic particles. During an event on March 28, 1976, good agreement between observations and predictions was obtained for 5 MeV protons and for ∼0.5 MeV electrons. For both species, this correspondence led to a mean free path of 0.7±0.1 AU, independent of rigidity, and a focusing length of 0.86±0.1 AU. The latter value is substantially larger than the value of ∼0.25 AU, which is expected if the large‐scale interplanetary magnetic field has its nominal spiral pattern. The large‐scale dependence of scattering was investigated with the aid of a least squares criterion for agreement between the data and the model. The strongly anisotropic pitch angle distributions that were recorded throughout this nearly coherent event were most accurately described when the rate of scattering was assumed to go through a minimum centered at 90° pitch angle. Coherent interplanetary propagation and close proximity of Helios to the sun made it possible to derive reliable temporal profiles of particle injection at the coronal footpoint of the interplanetary field line through the spacecraft. Within the uncertainties, the injection of electrons had the same temporal dependence as the flux of 7‐GHz radio noise had during the rising phase of the ‘great burst’ that accompanied the flare. After the radio maximum, the radio intensity decayed more rapidly than the electron injection. The injection of protons took place later and on a slower time scale than that of electrons.

Crustal studies in the La Malbaie Region, Quebec

The results of three seismological investigations of the crust in the seismically active La Malbaie Region are reported. First arrivals from a reversed reflection–refraction profile within the Charlevoix structure indicate a uniform Pg velocity of 6.08 ± 0.04 km/s. Secondary arrivals forming discontinuous, sometimes arcuate segments on the record sections are interpreted as subcritical reflections from structural contortions related to impact of the Charlevoix meteorite. A coherent event at 14 s may signal reflection from the M-discontinuity near 45 km depth.Analysis of travel times from calibration shots recorded by a network of stations spanning the St. Lawrence River in terms of time–distance profiles, travel time residuals, and numerical models provides excellent support for a model of the Precambrian–Paleozoic contact striking along the north shore and dipping to the southeast about 20° beneath the wedge of 5.5 km/s sediments.Unreversed profiles obtained by recording timed Thetford Mines blasts across a similar network suggests a comparable deep structure beneath the north and south shores, with average crustal velocities of 6.8 and 6.7 km/s, respectively. A minor mid-crustal discontinuity is suggested, and Moho depth is estimated at 42–43 km.The 6.2 km/s upper crustal velocity found for the crater and immediately surrounding area is anomalously low compared to the 6.4–6.5 km/s reported for the eastern shield region. Structural lineations gleaned from satellite imagery suggest an elongated area of impact-related disruption much larger than previously recognized. This expanded area of crustal weakening encompasses and may partially explain the zone of continuing microseismic activity, as well as the low upper crustal velocity of the La Malbaie Region.

Ritual Performance and Religious Experience: A Service for the Gods in Southern Haiti

Offertory ritual in Haitian voodoo is examined from the point of view of the participants. The implications of the structure and the organization of worship for the subjective experience of the devotes is explored. Such a view highlights spirit possession and acoustic/kinetic performance as the most salient features of ritual within this religious system. The design and the success of ritual are predicated on the articulation of basic theological tenets with an aesthetic principle for collective participation in song and dance. It is argued that previous analyses of voodoo tend to fragment and/ or objectify this fundamental ritual process. A perspective which confronts the act of worship on its own terms, as a coherent and meaningful event in the religious lives of the faithful, leads to a reformulation of some traditional anthropological questions concerning the culture-history, function, and psychological significance of Haitian voodoo.