Earthquake recurrence of a particular type

The recurrence relation for Turkish earthquakes, expressed as the single-frequency versus magnitude dependence, exhibits significant maxima and minima, reflecting true physical conditions. Various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity. The results may be applicable to regions with high seismicity.     

Regional seismic discrimination

The discrimination of various phenomena, such as frost effects, sonic booms and explosions, from regional earthquakes is investigated on the basis of observations in Sweden. Explosions represent the greatest problem in this respect, for whose solution the short-period Rayleigh wave Rg provides the most reliable method. Its presence indicates an artificial origin, practically without exception.     

T-phases from Atlantic earthquakes

Summary Underwater sound waves from earthquakes or so-calledT-waves are investigated for the Atlantic-Arctic area for the years 1953–1968, mainly from Swedish seismograph records, and for comparison also from an earthquake in the equatorial Atlantic withT-waves recorded on both sides of the ocean. The waves travel as sound waves through water, and asPg, Sg andRg over the land path. The North Atlantic source area of theT-waves, recorded at Scandinavian stations, is very well limited in extent with a strong concentration northeast of Jan Mayen, probably due to favourable bottom topography. The calculated sound velocities in water are 1.43 km/sec for the Arctic case and 1.52 km/sec for the equatorial one. TheT-waves exhibit a clear inverse dispersion. The dispersion explains their long duration. The duration of theT-phase increases logarithmically with the maximum amplitudes within theT-wave group and decreases linearly with distance over the land path, corresponding to a quality factor of about 700. Propagation across the ocean by multiple reflections between surface and bottom appears as the most probable mechanism. The particle motion ofT Sg is dominantly transverse horizontal, which is explained by refraction when the waves are transmitted to land. TheT-wave spectra at two different localities show clear relations, depending upon the ocean depths.     

Ultra-long-period motions from the Alaska earthquake of July 10, 1958

Summary Ultra-long-period motions from the Alaska eerthquake of July 10, 1958, have been studied on records at Uppsala. Mantle Rayleigh waves with up to six passages around the earth were recorded. The dispersion curve for the period range 100–400 sec was deduced, showing a minimum group velocity of 3.56 km/sec at a period of 225 sec, thus confirming earlier results byEwing & Press. A value of the internal friction in the mantle of 480×10^–5 for the period range 120–260 sec was obtained. The particle motion of the mantle Rayleigh waves is retrograde elliptical in the plane of propagation, the vertical axis being 0.68 of the horizontal axis. A transverse horizontal wave motion is observed on theE-component. Both its period (12 min 10 sec) and the delay of its onset (8 hours after the earthquake) confirm the hypothesis that it represents a free torsional vibration of the whole earth, apparently observed for the first time.

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Zusammenfassung Bewegungen mit ultra-langen Perioden von dem Alaska-Beben am 10. Juli 1958 wurden mittels Registrierungen in Uppsala studiert. Mantel-Rayleigh-Wellen, die die Erde sechsmal umkreist haben, wurden registriert. Die Dispersionskurve für den Periodenbereich 100–400 Sek wird bestimmt; sie zeigt ein Minimum der Gruppengeschwindigkeit von 3.56 Km/Sek bei einer Periode von 225 Sek, womit frühere Resultate vonEwing & Press bestätigt werden. Ein Wert der inneren Reibung im Mantel von 480×10^–5 für den Periodenbereich 120–260 Sek wird abgeleitet. Die Partikelbewegung der Mantel-Rayleigh-Wellen ist retrograd elliptisch in der Ausbreitungsebene und die Länge der vertikalen Achse ist 0.68 der horizontalen Achse. Eine transversale, horizontale Wellenbewegung ist auf derE-Komponente registriert. Sowohl ihre Periode (12 Min 10 Sek) wie die Verzögerung ihres Auftretens (8 Stunden nach dem Beben) bestätigen die Hypothese, dass es sich um eine freie Torsionsschwingung der ganzen Erde handelt, die wahrscheinlich zum ersten Mal beobachtet ist.

     

Pa andSa waves and the upper mantle

Summary This investigation is based on records of 96 earthquakes withPa andSa written by the Press-Ewing instruments at Uppsala in the interval June 1961–December 1962.Pa andSa waves are observed for all earthquake regions, irrespective of distance, focal depth or path properties. They have significantly higher velocities under continents than under oceans, which demonstrates corresponding differences in the upper mantle. Continental velocities are 8.35 km/sec (Pa) and 4.56 km/sec (Sa), oceanic velocities 8.01 km/sec (Pa) and 4.45 km/sec (Sa). The most frequent periods are 10 sec (Pa) and 20 sec (Sa). They are independent of distance forPa but increase with distance forSa. The best developedPa andSa are obtained for earthquakes at focal depths less than about 60 km. The particle motion ofSa may be anything from pureSV to pureSH motion and has high correlation to the particle motion ofS. The apparent angles of emergence (in average 51° forPa and 54° forSa) vary with distance. On the basis of our observations it is suggested thatPa andSa propagate by multiple reflections under grazing incidence under the Moho discontinuity.

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Zusammenfassung Die vorliegende Untersuchung gründet sich auf die Registrierungen von 96 Erdbeben mitPa- undSa-Wellen, die mit Hilfe der Press-Ewing Instrumente zu Uppsala im Zeitraum Juli 1961–Dezember 1962 aufgenommen wurden. DiePa- undSa-Wellen sind für alle seismischen Regionen beobachtet worden, unabhängig von Entfernung, Herdtiefe oder Wellenweg. Sie haben bedeutend höhere Geschwindigkeiten unter den Kontinenten als unter den Ozeanen, was einen entsprechenden Unterschied im oberen Erdmantel beweist. Die kontinentalen Geschwindigkeiten betragen 8.35 km/sec (Pa) und 4.56 km/sec (Sa), die ozeanischen Geschwindigkeiten 8.01 km/sec (Pa) und 4.45 km/sec (Sa). Die am häufigsten vorkommenden Perioden betragen 10 sec (Pa) und 20 sec (Sa). Sie sind unabhängig von der Entfernung fürPa aber wachsen mit der Entfernung fürSa. Die am besten entwickeltenPa- undSa-Wellen werden für Erdbeben mit kleinerer Herdtiefe als rund 60 km beobachtet. FürSa wird jede beliebige Orbitalbewegung zwischenSV undSH beobachtet. Sie hat eine hohe Korrelation mit der Orbitalbewegung vonS. Die scheinbaren Emergenzwinkel (durchschnittlich 51° fürPa und 54° fürSa) variieren mit der Entfernung. Auf Grund unserer Beobachtungen wird die Hypothese aufgestellt, dass sich diePa-undSa-Wellen durch Mehrfachreflexionen, bei tangentialem Einfall, unter der Moho-Diskontinuität ausbreiten.

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Resumen La presente investigación está basada en los sismogramas de 96 terremotos, que muestranPa ySa, registrados por los sismógrafos de Uppsala (Press-Ewing), durante el periodo Junio 1961 a Diciembre 1962. Las fasesPa ySa se observan en todas las regiones sismicas, independientemente de la distancia, de la profundidad focal ó de las propiedades de la trayectoria. Tienen velocidades significativamente mayores bajo continentes que bajo los océanos, lo que demuestra la existencia de diferencias en el manto superior. Las velocidades continentales son 8.35 km/seg (Pa) y 4.56 km/seg (Sa) y las oceánicas 8.01 km/seg (Pa) y 4.45 km/seg (Sa). Los periodos mas frecuentes son 10 segundos paraPa y 20 segundos paraSa. Tales periodos son independientes de la distancia en el caso dePa pero crecen con ella paraSa. Las fasesPa ySa mejor desarrolladas se obtienen para terremotos cuya profundidad focal es inferior a los 60 kilómetros. El movimiento de la particula del suelo debido aSa puede ser de cualquier tipo, desde puroSV a puroSH, y muestra gran correlación con el movimiento de la particula deS. Los ángulos de emergencia aparentes (de promedio 51° paraPa y 54° paraSa) varian con la distancia. Basándonos en nuestras observaciones sugerimos quePa ySa se propagan por reflexión múltiple, bajo incidencia rozante bajo la discontinuidad de Mohorovii.

     

The dehydration process in the zeolite laumontite: a real-time synchrotron X-ray powder diffraction study

The dehydration process of the natural zeolite laumontite Ca₄Si₁₆Al₈O₄₈ · 18 H₂O has been studied in situ by means of powder diffraction and X-ray synchrotron radiation. Powder diffraction profiles suitable for Rietveld refinements were accumulated in time intervals of 5 minutes using a position sensitive detector (CPS-120 by INEL), while the temperature increased in steps of about 5 K. The synchronization of accumulation time and temperature plateau allowed collection of 62 temperature-resolved powder patterns in the range 310–584 K, whose analysis produced a dynamic picture of the laumontite structure response to dehydration. The first zeolitic water molecules diffusing out of the channels are those not bonded to the Ca cations and located in the W(1) site, whose occupancy drops smoothly to 10% during heating to 349 K, while the sample in the capillary is still submerged in water. The remaining W(1) and 60% of W(5) water molecules are expelled rather sharply at about 370 K. At this temperature all remaining water submerging the powder crystallites is lost, the structure contains about 13 water molecules/cell, and the crystal structure is that of leonhardite. On continued heating 80% of the water molecules from the W(2) site are lost between 420 and 480 K, while a small amount of the diffusing water is reinserted in the W(5) site. The occupancy factor of the W(8) site decreases starting at 480 K, and reaches a maximum loss of 20% at 584 K. The combined occupancy of the Ca-coordinated W (2) and W (8) water sites never falls much below two, so that the Ca cations in the channels, which are bonded to four framework oxygen atoms, are nearly six-coordinated in the explored temperature range. The water loss is accompanied by large changes in the unit cell dimensions. Except at 367 K, where the excess surrounding water is leaving, all changes in cell dimensions are gradual. The loss of the hydrogen bonded W(1) and W(5) water molecules is related to most of the unit cell volume reduction below 370 K, as shown by the contraction of the a-, b- and c-axes and the increase in the monoclinic angle. Loss of the Ca-coordinated W(2) and W(8) water molecules has a small effect on the unit cell volume as the continued contraction of the a- and c-axes is counter-balanced by a large expansion in the b-axis and a decrease in the monoclinic β angle.     

The Kråkenes late-glacial palaeoenvironmental project

Kråkenes is the site of a small lake on the west coast of Norway that contains a long sequence of late-glacial sediments. The Younger Dryas is well represented, as a cirque glacier developed in the catchment at this time. This site offers unique opportunities to reconstruct late-glacial environments from independent sources of evidence; physical evidence (glacial geomorphology, sedimentology, palaeomagnetism, radiocarbon dating), and biological evidence from the remains of animals and plants derived from both the terrestrial and aquatic ecosystems. This report describes the background to the site, and the international multidisciplinary project to reconstruct late-glacial and early Holocene environmental and climatic changes at Kråkenes.     

Queens as Mothers: the role of the traditional safety net of care and support for HIV/AIDS orphans and vulnerable children in Ghana

The paper examines the significance of the traditional safety net to provide security and help to orphans and vulnerable children (OVC). (Abbreviation OVC, as conceptualised by UNICEF (2001)). It questions the scenario of societal breakdown due to HIV/AIDS by asking how the traditional safety net operates, nature of solutions to the OVC problem it provides and its sustainability. No geographical region in Ghana has been so affected by the HIV/AIDS pandemic than the Manya Krobo District in Ghana. While analysing the role of the work of the Manya Krobo Queen Mothers’ Association (QMA) and five private caregivers, the perceptions of three OVC are presented: on how it is to be an OVC, what their dreams and hopes are for the future, and their awareness of HIV/AIDS. It is observed that even though the QMA serves as a good role model for how to address the OVC problem, it has its limitations. The traditional extended family system is under pressure, but not about to break down. As the effectiveness of its support will depend on the contribution of the wider Ghanaian society, localised solutions have to be scaled up to make an impact. Thus, the breakdown scenario needs to be nuanced and contextualised. The vulnerability of the local place under study relates to unemployment and migration, economic poverty and social–cultural marginalisation. These factors are intertwined with the HIV/AIDS epidemic.     

Barite and barium in sediments and coral skeletons around the hydrocarbon exploration drilling site in the Træna Deep,Norwegian Sea

Barite and barium concentrations in bottom sediments and coral skeletons from the vicinity of the hydrocarbon exploration well drilled in 1992–1993 in the Træna Deep, Norwegian Sea have been studied to assess the spreading of the drilling mud and related ecological effects on Lophelia petrusa coral reefs. Sand size barite crystals derived from the drilling mud and elevated Ba concentrations in surface (0–2 cm) sediments were found up to 4 km from the exploration drilling site. ²¹⁰Pb-dating results on sediment cores indicate that Ba-rich surface intervals (0–2 cm) record ca. 20 years of sedimentation history, and connect Ba enrichment with exploration drilling. The geographic distribution of Ba contents in sediments allowed the reconstruction of the drilling mud dispersal pattern showing transport eastward from the drilling site, consistent with the prevailing current directions. The presence of relatively coarse-grained sediments and barite crystals trapped in coral polyps, ca. 500 m down current from the drilling site, reflects the elevated turbulence and sediment supply during the drilling activity. This elevated sediment dispersion likely placed a stress upon the coral reefs, but due to strong currents that effectively dilute episodic drilling waste and sediment discharges, the damage does not appear significant.