Examining ambient noise using colocated measurements of rotational and translational motion

In the past decade, a number of studies have reported the observation of rotational motion associated with seismic events. We report a first observation of rotational motion in the microseismic ambient noise band. A striking feature of rotational motion measurements is that the information about the seismic phase velocity and source back azimuth is contained in the amplitude ratio of a point measurement of rotation rate and transverse acceleration. We investigate the possibility of applying this method to ambient noise measured with a ring laser and a broadband seismometer at the Wettzell Geodetic Observatory in Germany. Using data in the secondary microseismic band, we recover local phase velocities as well as the back azimuth of the strongest noise source for two different time periods. In order to confirm these findings, we additionally compare the results with classical array processing techniques of the Gr?fenberg array located nearby.     

Geotektonische Verknüpfung von Plutonismus und Vulkanismus im südwestdeutschen Variscicum

Zusammenfassung Die variscische Orogenese wurde in Südwestdeutschland von einem intensiven palingenen Magmatismus begleitet. Dabei folgte der Vulkanismus als eigenständige Entwicklung den granitischen Intrusionen in einem Abstand von ca. 20 Ma. In den felsischen Vulkaniten läßt sich das Auftreten von primärem Tiefquarz als Geobarometer verwenden und spricht für eine besonders große Bildungstiefe der Magmen. Sie setzen damit die Entwicklungsreihe der granitischen Schmelzen fort, die zunehmend aus größerer Tiefe kamen. Als heißeste und trockenere Bildung entstanden die Vulkanite im Zuge der stärksten Krustenverkürzung und damit-verdickung und stiegen nach dem Durchlaufen der orogenen Einengungswelle zur Erdkruste auf.

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A widespread palingenetic magmatism accompanied Hercynian orogenesis in SW-Germany. Thereby, felsic volcanism occupied a specific place in the tectonic evolution of the Hercynian orogen following about 20 m. y. after the granitic plutonism. The finding of primary low quartz as intratelluric phenocrysts in these volcanics can be used for geobarometry and demonstrates a rather deep origin of the melt. They continue the development of the granitic melts which originated from a progressively deeper and hotter source. The felsic volcanics represent the hottest and driest crustal magmatism which originated in areas of strong crustal shortening and reached the surface after the Hercynian orogenic compressional wave had passed the region.

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Résumé L'orogenèse hercynienne dans le sud-ouest de l'Allemagne a été accompagnée d'un magmatisme palingénétique intense. Dans le développement de ce processus, le volcanisme felsitique a succédé aux intrusions granitiques après un intervalle de 20 Ma. La présence de quartz alpha primaire dans les volcanites peut être utilisée comme géobaromètre et indique que les magmas ont été engendrés à grande profondeur dans des conditions de plus en plus profondes et de plus en plus chaudes au cours du temps. Les volcanites felsitiques représentent le magmatisme le plus chaud et le plus sec, qui a été engendré consécutivement au raccourcissement et à l'épaississement de la croûte et qui est monté dans l'écorce terrestre après le passage de l'onde compressive orogénique hercynienne.

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Modelling the responses of mature forest trees to air pollution

Systems analysis of the responses of forest trees to air pollutants led to mathematical models which represent the essential life processes of mature trees (photosynthesis, respiration, growth etc.) under ‘normal’ conditions and — especially — under pollution strees. Computer simulations using these models have made it possible to test and analyse the consequences of — known or hypothetical — pollution effects. The simulation runs have led to the identification of three distinct behavioural modes (growth, stagnation, breakdown) and corresponding stable and unstable system states. The results have produced new insights and contributed to the understanding of the dieback process of spruce and beech trees. The presentation will concentrate on the most recent and most complex of the hitherto existing models, theBeech model.     

Strain rotation coupling and its implications on the measurement of rotational ground motions

Spatial derivatives of the seismic wave field are known to be sensitive to various site effects (e.g., cavity effects, topography, and geological inhomogeneities). In this study, the focus is on strain rotation coupling that can cause significant differences between point measurements compared to array-derived rotational motions. The strain rotation coupling constants are estimated based on finite element simulations for inhomogeneous media as well as for the 3D topography around Wettzell, Germany (the location of the G ring laser). Using collocated array and ring laser data, the coupling constants of the ring laser itself are shown to be small. Several examples are shown to illustrate the order of magnitude that strain-induced rotation might have on the seismograms in the near field of volcanoes as well as in the far field and in the low-frequency spectrum (free oscillations).     

Simulation of SH- and P-SV-wave propagation in fault zones

Seismic fault-zone (FZ) trapped waves provide a potentially high-resolution means for investigating FZ and earthquake properties. Seismic waves emitted within and travelling along low-velocity FZ layers may propagate many kilometres within the low-velocity structure associated with the fault. Waveform observation of FZ trapped waves can be modelled in terms of FZ layer velocities, thicknesses and attenuation coefficients. This can greatly improve the resolution of imaged FZ structure and microearthquake locations. At present, broad-band theoretical seismograms are restricted to plane-parallel layers of uniform properties. However, it is not clear how realistic these models are compared with actual fault structures which could, for example, flare outwards near the surface, have irregular boundaries, interior heterogeneities, etc. To address these interpretational uncertainties, we perform finite-difference simulations for irregular FZ geometries and non-uniform material properties within the layers. The accuracy of the numerical solutions are verified by comparison with the analytical solution of Ben-Zion & Aki (1990) for plane-parallel structures. Our main findings are: (1) FZs can widen at the ctustal surface only slightly modifying the trapped waves; (2) velocity variations with depth destroy trapped wave propagation at all wavelengths; (3) FZ trapped waves can be obscured by the presence of a low-velocity surface layer; (4) models with short-scale random structures suggest that trapped waves average out irregular FZ geometries, and hence can be effectively modelled by average-property plane-layered media for the observed range of wavelengths.     

Seismic imaging of the laterally varying D" region beneath the Cocos Plate

We use an axisymmetric, spherical Earth finite difference algorithm to model SH -wave propagation through cross-sections of laterally varying lower mantle models beneath the Cocos Plate derived from recent data analyses. Synthetic seismograms with dominant periods as short as 4 s are computed for several models: (1) a D" reflector 264 km above the core–mantle boundary with laterally varying S -wave velocity increases of 0.9–2.6 per cent, based on localized structures from a 1-D double-array stacking method; (2) an undulating D" reflector with large topography and uniform velocity increase obtained using a 3-D migration method and (3) cross-sections through the 3-D mantle S -wave velocity tomography model TXBW. We apply double-array stacking to assess model predictions of data. Of the models explored, the S -wave tomography model TXBW displays the best overall agreement with data. The undulating reflector produces a double Scd arrival that may be useful in future studies for distinguishing between D" volumetric heterogeneity and D" discontinuity topography. Synthetics for the laterally varying models show waveform variability not observed in 1-D model predictions. It is challenging to predict 3-D structure based on localized 1-D models when lateral structural variations are on the order of a few wavelengths of the energy used, particularly for the grazing geometry of our data. Iterative approaches of computing synthetic seismograms and adjusting model characteristics by considering path integral effects are necessary to accurately model fine-scale D" structure.     

The development of forest damage — control and prognosis on the basis of remote sensing data

Forest damage can be caused by three types of stress which exercise their influence by predisposing, causative and contributory factors. Predisposing factors, above all permanent immision stress, cause the general diminishing of the trees' vitality. Causative fators such as long and extreme periods of dryness cause a fast and evident deterioration of the forest stand, contributory factors as eg pest attacks cause their mortification. When using remote sensing data to monitor the development of forest damage it is necessary therefore not only to pay attention to spectral signatures characterizing the degree of green space and thus the information of the canopy but also to spectral signs showing the water supply of the stands. This has not been done so far though nowadays the necessary multispectral satellite data are on regular offer. For this reason it may be suggested that the existing possibilities to predict the development of forest damage on the basis of remote sensing data have not yet been fully used.In order to examine these possibilities, in the environs of Berlin, ie in the east and south of the Land of Brandenburg both the vegetation index which has been known from literature for a long time and an index for the difference in remission identifying the water bands in the short-wave infrared have been calculated on the basis of Landsat-TM data. A multi-temporal comparison shows that despite the bad conditions of the forest in 1991 on the test site located north-east of Berlin due to a relatively good water supply in that year the pine forest damage had not progressed in 1992. This allows to draw the conclusion that at least in the pine forests of the East German interior lowland the development of forest damage is essentially determined by dryness stress. In this way on the basis of 1992 Landsat-TM data there was not only an inventory made of the actual condition of the forest on the east and south-east of the Land of Brandenburg but also trends of damage progress shown. The damage classification of pine stands be completed by a prognosis as to the development of damage.     

On the Aerosol factor in the twilight method)

Summary It is proved by means of measuring series for skylight polarization during twilight carried out at different places that the zenith polarization is affected by the tropospheric turbidity still during the middle phase of twilight. This result is important for the inverse problem of the twilight theory. 3 approaches which explain this effect are examined. — Aerosol in the mesopause region is the cause for the well-known dip in the polarization curve during the middle phase of twilight. This interpretation can be supported by the distinct spectral differences.

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Zusammenfassung An Meßreihen der Himmelslicht-Polarisation in der Dämmerung von verschiedenen Meßorten wird nachgewiesen, daß die Zenitpolarisation von der troposphärischen Trübung noch in der mittleren Dämmerungsphase beeinflußt wird. Dieses Ergebnis ist für die inverse Aufgabe der Dämmerungstheorie wichtig. 3 Möglichkeiten der Erklärung dieses Effekts werden untersucht. —Aerosol im Mesopausenbereich ist die Ursache für die bekannte Stufe in der Polarisationskurve während der mittleren Dämmerungsphase. Diese Deutung kann durch die deutlichen spektralen Unterschiede gestützt werden.

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This work has been presented at the IUGG/WMO Symposium on Radiation including Satellite Techniques (Bergen/Norway, August 22–28, 1968).     

Solifluction meets vegetation: the role of biogeomorphic feedbacks for turf‐banked solifluction lobe development

Vegetation is an important factor influencing solifluction processes, while at the same time, solifluction processes and landforms influence species composition, fine‐scale distribution and corresponding ecosystem functioning. However, how feedbacks between plants and solifluction processes influence the development of turf‐banked solifluction lobes (TBLs) and their geomorphic and vegetation patterns is still poorly understood. We addressed this knowledge gap in a detailed biogeomorphic investigation in the Turtmann glacier foreland (Switzerland). Methods employed include geomorphic and vegetation mapping, terrain assessment with unmanned aerial vehicle (UAV) and temperature logging. Results were subsequently integrated with knowledge from previous geomorphic and ecologic studies into a conceptual model. Our results show that geomorphic and vegetation patterns at TBLs are closely linked through the lobe elements tread, risers and ridge. A conceptual four‐stage biogeomorphic model of TBL development with ecosystem engineering by the dwarf shrub Dryas octopetala as the dominant process can explain these interlinked patterns. Based on this model, we demonstrate that TBLs are biogeomorphic structures and follow a cyclic development, during which the role of their components for engineer and non‐engineer species changes. Our study presents the first biogeomorphic model of TBL development and highlights the applicability and necessity of biogeomorphic approaches and research in periglacial environments. Copyright © 2016 John Wiley & Sons, Ltd.     

Multiple drivers of Holocene lake level changes at a lowland lake in northeastern Germany

Many German lakes experienced significant water level declines in recent decades that are not fully understood due to the short observation period. At a typical northeastern German groundwater‐fed lake with a complex basin morphology, an acoustic sub‐bottom profile was analysed together with a transect of five sediment cores, which were correlated using multiple proxies (sediment facies, μ‐XRF, macrofossils, subfossil Cladocera). Shifts in the boundary between sand and mud deposition were controlled by lake level changes, and hence, allowed the quantification of an absolute lake level amplitude of ~8 m for the Holocene. This clearly exceeded observed modern fluctuations of 1.3 m (AD 1973–2010). Past lake level changes were traced continuously using the calcium‐record. During high lake levels, massive organic muds were deposited in the deepest lake basin, whereas lower lake levels isolated the sub‐basins and allowed carbonate deposition. During the beginning of the Holocene (>9700 cal. a BP), lake levels were high, probably due to final melting of permafrost and dead‐ice remains. The establishment of water‐use intensive Pinus forests caused generally low (3–4 m below modern) but fluctuating lake levels (9700–6400 cal. a BP). Afterwards, the lake showed an increasing trend and reached a short‐term highstand at c. 5000 cal. a BP (4 m above modern). At the transition towards a cooler and wetter late Holocene, forests dominated by Quercus and Fagus and initial human impact probably contributed more positively to groundwater recharge. Lake levels remained high between 3800 and 800 cal. a BP, but the lake system was not sensitive enough to record short‐term fluctuations during this period. Lake level changes were recorded again when humans profoundly affected the drainage system, land cover and lake trophy. Hence, local Holocene water level changes reflect feedbacks between catchment and vegetation characteristics and human impact superimposed by climate change at multiple temporal scales.