himu-em: The French Polynesian connection

himu, em i andem ii are three of the main geochemical mantle components that give rise to oceanic island basalts [1]. They represent the end members that produce the extreme isotopic compositions measured on intraplate volcanics. In French Polynesia, all three mantle components are represented in volcanic rocks. The characteristichimu signature is found in Tubuai, Mangaia and Rurutu,em i is present in the source of Rarotonga and Pitcairn volcanics andem ii dominates the composition of most Society Islands. Intermediate values between the three end members are found on most islands.We suggest that the three components are not independent but are physically related in the mantle. Thehimu component is thought to be recycled oceanic crust that lost part of its Pb through hydrothermal processes prior to and during subduction.em i andem ii are believed to acquire their isotopic and trace element characteristics through entrainment of sediments that were subducted together with the oceanic crust.The trace element pattern and the isotopic composition ofhimu lavas can be quantitatively modelled using a mixture of 25% old recycledmorb crust and 75% mantle peridotite. The extreme Pb composition is modelled assuming that Pb was lost from oceanic crust when hydrothermal alteration at the ridge leached Pb from the basalt to redeposit it as sulphides on top of and throughout the crust, followed by preferential dissolution of sulphides during dehydration in the subduction zone. These processes led to a drastic increase of theU/Pb ratio of the subducted material which evolved over 2 Ga to very radiogenic Pb isotopic compositions. Pb isotopic compositions similar to those ofem i andem ii are modelled assuming that sediments with average crustal Pb isotopic compositions were subducted and recycled into the mantle together with the underlyingmorb oceanic crust. Pelagic sediments (μ 5 andκ 6) account for the Pb isotopic composition ofem i whereas terrigenous sediments (μ 10 andκ 4.5) evolve towards theem ii end member. A few percent of sediment in the recycled crust-sediment mixture will destroy the characteristic Pb isotopic signature of thehimu component. This, together with the low probability of isolating oceanic crust in the mantle for 2 Ga, explains why the extremehimu composition, as seen on Tubuai and St Helena, is sampled so rarely by oceanic volcanism.     

Über den Einfluß von elektrischen Erdbodeneigenschaften und meteorologischen Parametern auf praktische Feldstärkeberechnungen bei Kurzwellenausbreitung

Zusammenfassung Der Einfluß elektrischer Erdbodeneigenschaften auf Sendeabstrahlung und Ausbreitung wird theoretisch untersucht und mit Hilfe von Feldstärkebilanzgleichungen auf praktische Feldberechnungen angewendet. Meteorologische Einwirkungen auf diese Werte und direkt auf den troposphärischen Ausbreitungsweg werden besprochen und rechnerisch analysiert, wo es das Ausmaß der Einwirkung notwendig erscheinen läßt.

---

Summary The effect of electrical ground characteristics on radiation transmitted and on propagation are investigated theoretically and applied to practical field calculations with the aid of field-strength balance equations. Meteorological effects upon these values and directly upon the tropospheric propagation path are discussed and analysed by calculations wherever the extent of the effect appeared to make it necessary.

---

Résumé L'auteur étudie théoriquement l'influence des propriétés électriques du sol sur l'émission et la propagation des ondes. Il applique ensuite ses conclusions au calcul pratique des champs grâce aux équations du bilan d'intensité de ceux-ci. Il discute et analyse par le calcul les influences météorologiques sur les valeurs obtenues et sur le chemin de propagation dans la troposphère et cela pour autant que la proportion de ces influences rende nécessaire leur prise en considération.

     

Technische Gesichtspunkte bei Ionosphärendatenauswertung und modernem Ionosondenaufbau

Zusammenfassung Unter Benutzung seiner früheren Untersuchungen über Geräteeinflüsse bei Ionosphärenmessungen behandelt der Verfasser in der vorliegenden Arbeit eine Erweiterung des theoretischen Ausgleichverfahrens. Mit Bezug auf diese Ergebnisse wird in den anderen Abschnitten die moderne technische Einrichtung von Ionosonden diskutiert.

---

Summary Using his previous investigations on instrument effects with ionosphere measurements the author deals, in the present paper, with an extension of the theoretical adaptation method. With reference to these results, the modern equipment of ionosphere stations is discussed in the other sections.

---

Résumé S'appuyant sur ses recherches antérieures relatives à l'effet instrumental lors des mesures ionosphériques, l'auteur expose ici une extension du procédé théorique de compensation. Puis se référant à ces résultats, il traite de l'aménagement technique des sondes ionosphériques.

---

---

Mit 3 Textabbildungen     

Further studies on the chordal-hop theory of ionospheric long-range propagation

Summary This paper presents new results of the author's investigations on ionospheric propagation in Australia from 1952 to 1957. Considerations on path attenuation are followed by a discussion on the propagation paths to North America and Western Europe. Conclusions are in agreement with the author's previous publications in this field.

---

Zusammenfassung In dieser Arbeit behandelt der Verfasser neue Ergebnisse seiner Untersuchungen über ionosphärische Ausbreitung in Australien von 1952 bis 1957. Auf eine Betrachtung über die Signalschwächung folgt eine Diskussion über die Ausbreitungswege nach Nordamerika und Westeuropa. Die Folgerungen stimmen mit den früheren Veröffentlichungen des Verfassers auf diesem Gebiet überein.

---

Résumé L'auteur expose les nouveaux résultats de ses recherches sur la propagation ionosphérique en Australie de 1952 à 1957; il considère l'affaiblissement de la propagation des signaux et les chemins suivis par les ondes vers l'Amérique du Nord et vers l'Europe occidentale. Ces résultats concordent avec ceux qu'il a publiés précédemment.

---

---

With 1 Figure     

Exploring the role of risk perception in influencing flood losses over time

ABSTRACT

What implications do societies’ risk perceptions have for flood losses? This study uses a stylized, socio-hydrological model to simulate the mutual feedbacks between human societies and flood events. It integrates hydrological modelling with cultural theory and proposes four ideal types of society that reflect existing dominant risk perception and management: risk neglecting, risk monitoring, risk downplaying and risk controlling societies. We explore the consequent trajectories of flood risk generated by the interactions between floods and people for these ideal types of society over time. The results suggest that flood losses are substantially reduced when awareness-raising attitudes are promoted through inclusive, participatory approaches in the community. In contrast, societies that rely on top-down hierarchies and structural measures to protect settlements on floodplains may still suffer significant losses during extreme events. This study illustrates how predictions formed through social science theories can be applied and tested in hydrological modelling.     

Determination of Porosity and Permeability out of Dispersion Analyses of Borehole Wall Displacements

Waves carried in the borehole can be measured by the use of controlled sources inside the borehole and receivers located in the same borehole as well. This article gives the theoretical background and develops a new method to determine rock-physical parameters out of such controlled measurements of waves carried inside the borehole. Theoretical dispersion curves of the group velocities are matched to dispersion analyses of registrations obtained in the borehole. This inversion process intends to determine the in situ porosity and permeability of the rock.