Detailed 1×1° gravimetric Indian Ocean geoid and comparison with GEOS-3 radar altimeter geoid profiles     

Hans-Gert Kahle  Michael Chapman  Manik Talwani 《Geophysical Journal International》1978,55(3):703-720

Summary. A new set of 1×1° mean free-air anomalies in the Indian Ocean is determined on the basis of previously published free-air anomaly maps (Talwani & Kahle) and the most recent Lamont surface ship gravity measurements. The data are then used to compute a (total) 1×1° gravimetric Indian Ocean geoid. The computation is carried out by combining the Goddard Space Flight Center (GSFC) GEM-6 geoid and a difference geoid that corresponds to the differences between the set of 1×1° surface gravity values and the GEM-6 gravity anomalies. The difference geoid is highest over the Madagascar Ridge (+ 20 m) and lowest over the Timor Trough (-30 m). The total geoid is compared with GEOS-3 radar altimeter derived geoid profiles and geophysical implications are discussed.  相似文献   

Crustal strain in central Greece from repeated GPS measurements in the interval 1989–1997     

P. J. Clarke  R. R. Davies  P. C. England  B. Parsons  H. Billiris  D. Paradissis  G. Veis  P. A. Cross  P. H. Denys  V. Ashkenazi  R. Bingley  H.-G. Kahle  M.-V. Muller  & P. Briole 《Geophysical Journal International》1998,135(1):195-214

  相似文献   

Book reviews     

Dr. A. Piaget  B. Federer  H. -G. Kahle 《Pure and Applied Geophysics》1979,117(5):1070-1073

  相似文献   

Holocene displacement along branch and secondary faults in the San Andreas fault zone, southern California     

James E. Kahle  Allan G. Barrows  David J. Beeby 《Tectonophysics》1979,52(1-4)

Detailed geologic mapping of the San Andreas fault zone in Los Angeles County since 1972 has revealed evidence for diverse histories of displacement on branch and secondary faults near Palmdale. The main trace of the San Andreas fault is well defined by a variety of physiographic features. The geologic record supports the concept of many kilometers of lateral displacement on the main trace and on some secondary faults, especially when dealing with pre-Quaternary rocks. However, the distribution of upper Pleistocene rocks along branch and secondary faults suggests a strong vertical component of displacement and, in many locations, Holocene displacement appears to be primarily vertical. The most recent movement on many secondary and some branch faults has been either high-angle (reverse and normal) or thrust. This is in contrast to the abundant evidence for lateral movement seen along the main San Andreas fault. We suggest that this change in the sense of displacement is more common than has been previously recognized.The branch and secondary faults described here have geomorphic features along them that are as fresh as similar features visible along the most recent trace of the San Andreas fault. From this we infer that surface rupture occurred on these faults in 1857, as it did on the main San Andreas fault. Branch faults commonly form “Riedel” and “thrust” shear configurations adjacent to the main San Andreas fault and affect a zone less than a few hundred meters wide. Holocene and upper Pleistocene deposits have been repeatedly offset along faults that also separate contrasting older rocks. Secondary faults are located up to 1500 m on either side of the San Andreas fault and trend subparallel to it. Moreover, our mapping indicates that some portions of these secondary faults appear to have been “inactive” throughout much of Quaternary time, even though Holocene and upper Pleistocene deposits have been repeatedly offset along other parts of these same faults. For example, near 37th Street E. and Barrel Springs Road, a limited stretch of the Nadeau fault has a very fresh normal scarp, in one place as much as 3 m high, which breaks upper Pleistocene or Holocene deposits. This scarp has two bevelled surfaces, the upper surface sloping significantly less than the lower, suggesting at least two periods of recent movement. Other exposures along this fault show undisturbed Quaternary deposits overlying the fault. The Cemetery and Little Rock faults also exhibit selected reactivation of isolated segments separated by “inactive” stretches.Activity on branch and secondary faults, as outlined above, is presumed to be the result of sympathetic movement on limited segments of older faults in response to major movement on the San Andreas fault. The recognition that Holocene activity is possible on faults where much of the evidence suggests prolonged inactivity emphasizes the need for regional, as well as detailed site studies to evaluate adequately the hazard of any fault trace in a major fault zone. Similar problems may be encountered when geodetic or other studies, Which depend on stable sites, are conducted in the vicinity of major faults.  相似文献   

The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach   总被引：2，自引：1，他引：1  

Andrew Lorrey  Nicolas Fauchereau  Craig Stanton  Petra Chappell  Steven Phipps  Andrew Mackintosh  James Renwick  Ian Goodwin  Anthony Fowler 《Climate Dynamics》2014,42(11-12):3039-3060

Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of ?0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. Reconstructed geopotential height at 1,000 hPa (z1000) suggests enhanced southwesterly flow across New Zealand occurred during the LIA to generate the terrestrial temperature anomalies. The mean atmospheric circulation pattern for summer resulted from a crucial reduction of the ‘HSE’-blocking synoptic type (highs over and to the west of NZ; largely settled conditions) and increases in both the ‘T’- and ‘SW’-trough synoptic types (lows passing over NZ; enhanced southerly and southwesterly flow) relative to normal. Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Niño-Modoki in the tropical Pacific and negative Southern Annular Mode activity.  相似文献   

Deep seismic reflectivity patterns in specific tectonic units of Western and Central Europe   总被引：2，自引：0，他引：2  

Petra Sadowiak  Thomas Wever  Rolf Meissner 《Geophysical Journal International》1991,105(1):45-54

  相似文献   

Continuous GPS and broad-scale deformation across the Rhine Graben and the Alps     

Magdala Tesauro  Christine Hollenstein  Ramon Egli  Alain Geiger  Hans-Gert Kahle 《International Journal of Earth Sciences》2005,94(4):525-537

In order to study the ongoing tectonic deformation in the Rhine Graben area, we reconstruct the local crustal velocity and the strain rate field from GPS array solutions. Following the aim of this work, we compile the velocities of permanent GPS stations belonging to various networks (EUREF, AGNES, REGAL and RGP) in central western Europe. Moreover, the strain rate field is displayed in terms of principal axes and values, while the normal and the shear components of the strain tensor are calculated perpendicular and parallel to the strike of major faults. The results are compared with the fault plane solutions of earthquakes, which have occurred in this area. A broad-scale kinematic deformation model across the Rhine Graben is provided on the basis of tectonics and velocity results of the GPS permanent stations. The area of study is divided into four rigid blocks, between which there might be relative motions. The velocity and the strain rate fields are reconstructed along their borders, by estimating a uniform rotation for each block. The tectonic behaviour is well represented by the four-block model in the Rhine Graben area, while a more detailed model will be needed for a better reconstruction of the strain field in the Alpine region.

Magdala TesauroEmail:

  相似文献   

Freshwater geographies: Experimenting with knowing and doing geography differently   总被引：1，自引：0，他引：1  

Brendon Blue  Claire Gregory  Kiely McFarlane  Marc Tadaki  Petra van Limburg‐Meijer  Nick Lewis 《New Zealand geographer》2012,68(1):62-66

The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently.  相似文献   

Changes in ice-season characteristics of a European Arctic lake from 1964 to 2008     

Ruibo Lei  Matti Lepp?ranta  Bin Cheng  Petra Heil  Zhijun Li 《Climatic change》2012,115(3-4):725-739

The long-term ice record (from 1964 to 2008) of an Arctic lake in northern Europe (Lake Kilpisj?rvi) reveals the response of lake ice to climate change at local and regional scales. Average freeze-up and ice breakup occurred on 9 November and 19 June, respectively. The freeze-up has been significantly delayed at a rate of 2.3 d per decade from 1964 onward (P?<?0.05). No significant change has taken place in ice breakup. Annual average ice thickness has become smaller since the mid-1980s (P?<?0.05). Air temperature during the early ice season significantly affected the ice thickness. The freeze-up date exhibits the highest correlation with the 2-month average daily minimum air temperature centered at the end of October, while the ice breakup date exhibits the highest correlation with the 2-month average daily maximal air temperature centered in mid May. A 1°C increase in the surface air temperature corresponds to a freeze-up later by 3.4?days and an ice breakup earlier by 3.6?days. Snow cover is a critical factor in lake-ice climatology. For cumulative November to March precipitation of less than 0.13?m, the insulating effect of the snow dominated, while higher rates of precipitation favored thicker ice due to the formation of snow ice. Variations in ice records of Lake Kilpisj?rvi can serve as an indicator of climate variations across the northern Europe. The North Atlantic Oscillation (NAO) does not significantly affect the ice season there, although both the local air temperatures and winter precipitation contain a strong NAO signal.  相似文献   

Floods in the Sahel: an analysis of anomalies, memory, and anticipatory learning     

Petra Tschakert  Regina Sagoe  Gifty Ofori-Darko  Samuel Nii Codjoe 《Climatic change》2010,103(3-4):471-502

This study explores the implications of recent extreme rainfall and flood events in the Sahel and the wider West African region for climate change adaptation. Are these events merely a temporal nuisance as suggested by the lingering desertification discourse or will more climatic extremes characterize the region over the next century? After reviewing incidences of severe rainfall and projected future climate variability, the paper examines local flood knowledge and decision-making, drawing upon a case study in Ghana. The data demonstrate that a variety of response strategies to flooding exist; yet, knowledge of and access to climate forecasts and other learning tools are essentially absent. So far, floods have not triggered mass displacement although cumulative environmental deterioration is likely to cause environmental refugees. The paper recommends to lay to rest the desertification narrative, consider the possibility of both floods and droughts, and mobilize local memory for anticipatory learning and practical adaptation.  相似文献