J.H. Hagedoorn – inventing the Hapa: A review of a geophysicist's 'other' work and how it inspired others

This paper describes J.G. Hagedoorn's work on 'ultimate sailing'– the combination of a manned kite and a water kite called a Hapa, constituting a minimal sailing system – and the way others have taken up his challenge to sail while suspended from a kite. Hagedoorn's goal has not been entirely achieved, but 'near' and partial solutions have been reached. Kite-Hapa-sailing continues to pose a 'Holy Grail' type challenge to many kite-sailors.     

Influence of a cyclic and dynamic loading history on dynamic properties of dry sand, part II: cyclic axial preloading

Initial fabric of a soil induced by its cyclic strain history is an important parameter among others like void ratio, state of stress and amplitude concerning the further accumulation of deformations under cyclic loading. It is of high importance to determine methods in order to estimate the initial fabric of the grain skeleton or the cyclic loading history of the soil. An attempt is made in this paper to correlate small strain stiffness of non-cohesive soil with its cyclic loading history. For this purpose several cyclic triaxial tests with specimens subjected to cyclic axial loading were performed and changes of small strain soil properties due to this cyclic loading were studied. All these tests showed only moderate changes of small strain stiffnesses independently of the different boundary conditions. Thus, a correlation between fabric or strain history and small strain stiffnesses seems not to be possible.     

PART I: Theoretical Site Response Estimation for Microzoning Purposes

— We estimate the theoretical site response along seven cross sections located in the city of Thessaloniki (Greece). For this purpose the 2-D structural models used are based on the known geometry and the dynamic soil properties derived from borehole measurements and other geophysical techniques. Several double-couple sources have been employed to generate the seismic wavefield, and a hybrid method that combines the modal summation with finite differences, has been deployed to produce synthetic accelerograms to a maximum frequency of 6 Hz for all components of motion. The ratios between the response spectra of signals derived for the 2-D local model and the corresponding spectra of signals derived for the 1-D bedrock reference model at the same site, allow us to estimate the site response due to lateral heterogeneities. We interpret the results in terms of both geological and geometrical features of the models and of the characteristics of the wave propagation. The cases discussed confirm that the geometry and depth of the rock basement, along with the impedance contrast, are responsible for ground amplification phenomena such as edge effects and generation and entrapment of local surface waves. Our analysis also confirms that the peak ground acceleration is not well correlated with damage and that a substantially better estimator for possible damage is the spectral amplification.     

Tectonic stages along a traverse cross cutting the Rhodopian zone (Greece)

In a cross section along the Rhodopian zone from the Greece/Bulgarian border through the postalpine basins in the Xanthi area to Thasos island detailed structural mapping and collection of field data enable us to determine a sequence of tectonic stages that affected this area. This allows us to propose a model of continental collision.During the early Eocene, NE-SW directed movements produced a southwest facing pile of crystalline nappes with internal deformation comprising NW and NE trending isoclinal folds and a NE-SW trending stretching lineation. After a short time interval, nappe movements started again under brittle deformation conditions and produced composite thrust sheets, WNW- and NNE trending chevron folds and thick cataclasite. Late erogenic uplift and extension caused the formation of NW- and NE trending normal faults. These faults bounded the Oligocene flysch- and molasse basins and provided pathways for voluminous magmatic suites. This tectonic process was interrupted at the Oligocene/Miocene boundary by a late orogenic compression reflected in NW open folds and dissolution cleavages. Subsequently, differential uplift and subsidence associated with NW- and NE trending normal faults has continued up to the present time. From the early Pliocene new fragmentation and thinning of the crust reflected in WNW listric faults and NNE transfer faults has affected the southern parts of the Rhodopian zone.Nappe forming movements are the result of a progressive collisional process involving a Kimmerian microcontinent lying between the Eurasia and Apulia continents. In the final stages of this collision, uderplating processes led to regional uplift and extension. Additional extensional movements were related to the formation of the Aegean back arc basin caused by the Late Cenozoic Hellenic subduction zone.

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Zusammenfassung Durch Gefügedatensammlung und strukturelle Kartierung in einer Geotraverse durch die Rhodopische-Zone von der griechisch-bulgarischen Grenze, die sich über das postalpine Becken der Xanthi-Gegend bis zur Insel Thassos hinzieht, wurde sowohl die Zeitabfolge der tektonischen Ereignisse definiert als auch ein Kontinental-Kollisionsmodel aufgestellt.Während dem unteren Eozän haben NE-SW streichende Bewegungen einen südwestlich vergenten kristallinen Deckenstappel gebildet, der von NW- und NE streichenden Isoklinalfalten und einer SW streichenden Strekkungslineation innendeformiert wurde. Nach einer kurzen Zeitspanne haben Deckenbewegungen unter Bruchbedingungen wiederbegonnen. Dadurch wurden zusammengesetztes Deckenstappel, WNW and NNE streichende Knickfalten und mächtige Kataklasite gebildet. Postorogenetisches Aufsteigen des Gebirges wird von NW- und NE streichenden Abschiebungen gekennzeichnet. Diese Verwerfungen begrenzen Oligozäne Flysch- und Molassebecken und stellen Aufstiegswege von magmatischen Produkten dar, die stellenweise die Erdoberfläche erreichten. An der Grenze Oligozän-Miozän zeigt eine postorogene Kompression NW gerichtete geöffneteFalten und eine begleitende Lösungsschieferung. Nach dieser kurzen Unterbrechung setzt sich das Aufsteigen des Gebirges bis heute fort bei gleichzeitigen NW- und NE gerichteten Abschiebungen. Seit dem unteren Pliozän wird eine Zerspaltung und Ausdünnung der Kruste sowohl durch WNW gerichtete-listrische-Abschiebungen als auch durch NNE gerichtete »Transfer«-Verwerfungen hervorgerufen.Deckenbewegungen sind das Ergebnis eines kontinuierlichen Kollisionsprozesses, der einen Kimmerischen Mikrokontinent miteinbezieht, welcher zwischen dem Eurasischen- und dem Apulischen Kontinent lag. In den letzten Stadien der Kollision führte Plattenverdickung zu einem Aufsteigen des Gebirges, das von regionaler Ausdehnung begleitet wird. Eine weitere Ausdehnung bezieht sich auf die Bildung des Ägäischen »black arc basin« das durch die rezente Hellenische Subduktionszone hervorgerufen wurde.

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Résumé Dans une géotraverse de la zone du Rhodope, depuis la frontière gréco-bulgare, à travers les bassins post-alpins de la région de Xanthi et jusqu'à l'île de Thasos, on a effectué une cartographie structurale de détail et diverses observations de terrain. Cette investigation a permis de définir la succession des événements tectoniques et de proposer un modèle de collision continentale.Pendant l'Eocène inférieur, des mouvements de direction NE-SW ont engendré un empilement de nappes cristallines à vergence SW dont les structures de déformation interne comprennent des plis isoclinaux de directions NW et NE ainsi qu'une linéation d'étirement NE-SW. Après une courte pause, le mouvement des nappes a repris dans des conditions de déformation cassante, avec production de lames charriées composites, de plis en chevrons orientés WNW et NNE et de zones cataclasitiques épaisses. Un soulèvement orogénique tardif accompagné d'une extension crustale a ensuite engendré des failles normales de directions NW et NE. Ces failles ont délimité les bassins oligocènes de flysch et de molasse et ont ouvert la voie à de volumineuses venues magmatiques qui, par endroits, ont atteint la surface. Ces processus tectoniques ont été interrompus à la limite Oligocène-Miocène parune compression tardi-orogénique responsable de plis ouverts orientés NW et d'une schistosité de dissolution. Par la suite, des mouvements de soulèvement et de subsidence différentiels se sont poursuivis jusqu'aujourd'hui. A partir du début du Pliocène, les parties méridionales de la zone du Rhodope ont été le siège de nouveaux processus de fragmentation et d'amincissement de la croûte, qui se sont traduits par des failles listriques WNW et par des décrochements.La genèse des nappes résulte d'un processus progressif de collision impliquant un microcontinent kimmérien compris entre les continents eurasien et apulien. Lors des stades finals de cette collision, des phénomènes d' «underplating» ont provoqué un soulèvement de l'ensemble accompagné d'une extension à l'échelle régionale. Des mouvements d'extension ultérieurs sont en relation avec la formation du bassin d'arrière-arc égéen engendré par la zone de subduction hellénique au Cénozoïque supérieur.

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A tectono-stratigraphic record of an extensional basin: the Lower Jurassic Ab-Haji Formation of east-central Iran

The Lower Jurassic Ab-Haji Formation consists of siliciclastic strata which are widespread and superbly exposed across the Tabas and Lut blocks of east-central Iran. The formation records the geodynamic history of central Iran during the Early Jurassic in the aftermath of the main Cimmerian event (near the Triassic–Jurassic boundary) through its sedimentary facies and stratigraphic architecture and allows palaeogeographic and palaeoenvironmental reconstructions. We measured and studied three well-exposed outcrop sections and identified lithofacies and facies associations (fluvial plain, delta plain, delta front, prodelta, and shallow-marine siliciclastic shelf). The integration of all geological, stratigraphic, and sedimentological data shows a west-to-east continental-to-marine gradient within the Ab-Haji Formation. Based on thickness variations, lateral facies changes, palaeocurrent patterns, and changes in the nature of the basal contact of the Ab-Haji Formation on the Tabas and Lut blocks, we locate the fault-bounded Yazd Block in the west and the Shotori Swell at the eastern edge of the Tabas Block as provenance regions. The pattern of thickness variations, rapid east–west facies changes, and provenance is best explained by a tectonic model invoking large tilted fault blocks in an extensional basin. The basal unit shows distinct increase in grain size at the base of the Ab-Haji Formation, similar to the Shemshak Group of the Alborz Mountains (the base of the Alasht Formation) and the non-marine time-equivalent succession of the Binalud Mountains of northeastern Iran. This grain size pattern may have been caused by rapid source area uplift due to slab break-off of the subducted Iran plate in the course of the Cimmerian collision in east-central Iran.     

Flow rule in a high-cycle accumulation model backed by cyclic test data of 22 sands

The flow rule used in the high-cycle accumulation (HCA) model proposed by Niemunis et al. (Comput Geotech 32: 245, 2005) is examined on the basis of the data from approximately 350 drained long-term cyclic triaxial tests (N = 10⁵ cycles) performed on 22 different grain-size distribution curves of a clean quartz sand. In accordance with (Wichtmann et al. in Acta Geotechnica 1: 59, 2006), for all tested materials, the “high-cyclic flow rule (HCFR)”, i.e., the ratio of the volumetric and deviatoric strain accumulation rates \(\dot{\varepsilon}_{\rm{v}}^{{\rm acc}}/\dot{\varepsilon}_{\rm{q}}^{{\rm acc}}\) , was found dependent primarily on the average stress ratio η ^av = q ^av/p ^av and independent of amplitude, soil density and average mean pressure. The experimental HCFR can be fairly well approximated by the flow rule of the modified Cam-clay (MCC) model. Instead of the critical friction angle \(\varphi_{\rm{c}}\) which enters the flow rule for monotonic loading, the HCA model uses the MCC flow rule expression with a slightly different parameter \(\varphi_{\rm{cc}}\) . It should be determined from cyclic tests. \(\varphi_{\rm{cc}}\) and \(\varphi_{\rm{c}}\) are of similar magnitude but not always identical, because they are calibrated from different types of tests. For a simplified calibration in the absence of cyclic test data, \(\varphi_{\rm{cc}}\) may be estimated from the angle of repose \(\varphi_{\rm{r}}\) determined from a pluviated cone of sand (Wichtmann et al. in Acta Geotechnica 1: 59, 2006). However, the paper demonstrates that the MCC flow rule with \(\varphi_{\rm{r}}\) does not fit well the experimentally observed HCFR in the case of coarse or well-graded sands. For an improved simplified calibration procedure, correlations between \(\varphi_{\rm{cc}}\) and parameters of the grain-size distribution curve (d ₅₀,   C _u) have been developed on the basis of the present data set. The approximation of the experimental HCFR by the generalized flow rule equations proposed in (Wichtmann et al. in J Geotech Geoenviron Eng ASCE 136: 728, 2010), considering anisotropy, is also discussed in the paper.