4D GPS water vapor tomography: new parameterized approaches   总被引：1，自引：1，他引：0  

Donat Perler  Alain Geiger  Fabian Hurter 《Journal of Geodesy》2011,85(8):539-550

Water vapor is a key variable in numerical weather prediction, as it plays an important role in atmospheric processes. Nonetheless, the distribution of water vapor in the atmosphere is observed with a coarse resolution in time and space compared to the resolution of numerical weather models. GPS water vapor tomography is one of the promising methods to improve the resolution of water vapor measurements. This paper presents new parameterized approaches for the determination of water vapor distribution in the troposphere by GPS. We present the methods and give first results validating the approaches. The parameterization of voxels (volumetric pixels) by trilinear and spline functions in ellipsoidal coordinates are introduced in this study. The evolution in time of the refractivity field is modeled by a Kalman filter with a temporal resolution of 30 s, which corresponds to the available GPS-data rate. The algorithms are tested with simulated and with real data from more than 40 permanent GPS receiver stations in Switzerland and adjoining regions covering alpine areas. The investigations show the potential of the new parameterized approaches to yield superior results compared to the non parametric classical one. The accuracy of the tomographic result is quantified by the inter-quartile range (IQR), which is decreased by 10–20% with the new approaches. Further, parameterized voxel solutions have a substantially smaller maximal error than the non parameterized ones. Simulations show a limited ability to resolve vertical structures above the top station of the network with GPS tomography.  相似文献   

Fault zone signatures from ambient vibration measurements: a case study in the region of Visp (Valais, Switzerland)     

Cyrill Baumann  Jan Burjánek  Clotaire Michel  Donat Fäh  Luis A. Dalguer 《Swiss Journal of Geoscience》2013,106(3):529-541

Investigations of tectonic features, such as faults, are important challenges for geologists and engineers. Although direct investigational methods, such as boreholes and trenches, have the potential to provide accurate data, these direct methods are usually expensive and time consuming, and give only punctual insights into subsurface structures. Geophysical methods, for example electric surveys and ground penetrating radar, are less expensive and faster to implement. However, these geophysical methods may be difficult or sometimes even impossible to apply in regions with rough topography or regions which are highly urbanized. In this study, we propose an easy-to-use and affordable method to detect fault zones based on ambient vibration observations. We apply this method in the region between Visp and Unterstalden (canton Valais, Switzerland) on a small fault branch, which has no explicit surface expression, and which is linked to a major fault zone, the Simplon Fault Zone. The assumption is that the fault of interest is surrounded by damage zone consisting of fractured rock, and that this results in lateral changes of both seismic velocity and attenuation. The objective was, first, to identify such lateral changes in the observed seismic wave-field, and second, to map any anomalies and combine them with the available geological information. In this way, we were able to follow the fault trace even without a clear surface expression of the fault. Our observations showed the existence of a signature in the power spectra of the seismic noise that may correspond to a damage zone. Such signature is observed along the trace of the expected fault.  相似文献   

Damage field and site effects: multidisciplinary studies of the 1964 earthquake series in Central Switzerland   总被引：1，自引：0，他引：1  

Stefan Fritsche  Donat Fäh  Brian Steiner  Domenico Giardini 《Natural Hazards》2009,48(2):203-227

Central Switzerland shows comparatively high seismic activity by Swiss standards. Many historical earthquakes are known and several of them caused damage. The last major event dates back to 1964 and has the characteristics of an earthquake swarm. Among dozens of felt shocks were two main shocks (Mw = 5 and 5.7) that moderately damaged a limited area with hundreds of buildings suffering loss. Our aim here was to reconstruct the damage field and to analyze whether it was influenced by site effects. Given the existence of a contemporary damage assessment and other historical sources, we could describe the damage field in detail. For about 95% of the affected buildings, we could reconstruct the location and extent of loss, using assessments from the European Macroseismic Scale (EMS 98). Spatial analysis of the resulting data showed that most losses were concentrated in the villages of Sarnen and Kerns. Damage to residential houses and barns was by far most frequent (90%), but expensive losses to the relatively few sacral buildings were responsible for almost 50% of the repair costs. We compared the damage data with deposit thickness and soil composition and carried out field experiments using H/V spectral ratios to measure the fundamental frequency of ground resonance at 75 sites to estimate the frequency band in which amplification occurs. Our results show that locations on both thick fluviatile sediments and large alluvial cones showed higher intensities than did other ground types. Moreover, at some sites, intensity was probably increased by a layer of weathered rock below thin deposits.  相似文献   

The 1946 magnitude 6.1 earthquake in the Valais: site-effects as contributor to the damage     

Stefan Fritsche  Donat Fäh 《Swiss Journal of Geoscience》2009,102(3):423-439

The January 25, 1946 earthquake in the central Valais region in southwest Switzerland was the strongest for the last 150 years. It reached an epicentral intensity Io of VIII in the area of Sierre. The Swiss Earthquake Catalogue (ECOS 2002) assigns a moment magnitude of Mw = 6.1 to the event. Assessment of recordings from European stations resulted in a moment magnitude of 5.8 (Bernardi et al. 2005). The earthquake caused moderate to high damage within a circle of about a 25 kilometer radius. Slight damage occurred up to a distance of 200 kilometers from the epicenter. The goal of this study was to reconstruct the damage field and consider its possible site-effects. We used an approach combining historical research with seismo-/geological investigation including a large number of experiments measuring the fundamental frequency of resonance and the shear-wave velocities of the sedimentary layers, using the characteristics of ambient vibration. This kind of research is relevant, since a huge alpine valley characterizes the Valais region, showing ground conditions that make site-effects likely for earthquakes. While we searched for damage in an unlimited area, our investigation of site-effects was limited to the Rhone valley and to Sion and Sierre in the central Valais region in particular.  相似文献   

Fermi acceleration and particle pitch angle scattering     

John S. Scott  W. J. Cocke  R. A. Chevalier  Donat G. Wentzel 《Astrophysics and Space Science》1978,53(2):421-427

We suggest that sharp velocity gradients will exist in fluid-like turbulence in nearly collisionless plasma. This implies effective quenching of Fermi acceleration of thermal particles, but the Fermi acceleration coefficient for relativistic particles remains essentially unchanged.  相似文献   

Historical seismicity in Central Switzerland     

Monika Gisler  Donat Fäh  Philipp Kästli 《Eclogae Geologicae Helvetiae》2004,97(2):221-236

  相似文献   

Wave reflection and wave disorder in the solar transition zone and corona     

Donat G. Wentzel 《Solar physics》1978,58(2):307-318

The reflection coefficient for sound or Alfvén waves reaching the transition zone is evaluated. A family of temperature profiles, including T ^5/2 dT/dz = constant, permits analytical solutions for the velocity and yields the reflection coefficient as a function of both the wavelength and the temperature jump across the zone. When the temperature jump is large, even waves appreciably shorter than the zone thickness are reflected efficiently.Wave reflection disorders the waves in and below the transition zone, because rising waves there interact with reflected waves in a manner more similar to turbulence than to shock steepening.The distribution in directions of hydromagnetic waves is determined by the non-uniformity of their sources. Most inhomogeneities in the wave source cause the waves to resemble isotropic fastmode waves more than Alfvén waves. This places severe restrictions on possible sources of Alfvén waves.  相似文献   

Earthquakes in Switzerland and surrounding regions during 2015 and 2016     

Tobias Diehl  John Clinton  Nicolas Deichmann  Carlo Cauzzi  Philipp Kästli  Toni Kraft  Irene Molinari  Maren Böse  Clotaire Michel  Manuel Hobiger  Florian Haslinger  Donat Fäh  Stefan Wiemer 《Swiss Journal of Geoscience》2018,111(1-2):221-244

This report summarizes the seismicity in Switzerland and surrounding regions in the years 2015 and 2016. In 2015, the Swiss Seismological Service detected and located 735 earthquakes in the region under consideration. With a total of 20 earthquakes of magnitude M_L ≥ 2.5, the seismic activity of potentially felt events in 2015 was close to the average of 23 earthquakes over the previous 40 years. Seismic activity was above average in 2016 with 872 located earthquakes of which 31 events had M_L ≥ 2.5. The strongest event in the analyzed period was the M_L 4.1 Salgesch earthquake, which occurred northeast of Sierre (VS) in October 2016. The event was felt in large parts of Switzerland and had a maximum intensity of V. Derived focal mechanisms and relative hypocenter relocations of aftershocks image a SSE dipping reverse fault, which likely also hosted an M_L 3.9 earthquake in 2003. Another remarkable earthquake sequence in the Valais occurred close to Sion with four felt events (M_L 2.7–3.2) in 2015/16. We associate this sequence with a system of WNW-ESE striking fault segments north of the Rhône valley. Similarities with a sequence in 2011, which was located about 10 km to the NE, suggest the existence of an en-echelon system of basement faults accommodating dextral slip along the Rhône-Simplon line in this area. Another exceptional earthquake sequence occurred close to Singen (Germany) in November 2016. Relocated hypocenters and focal mechanisms image a SW dipping transtensional fault segment, which is likely associated with a branch of the Hegau-Bodensee Graben. On the western boundary of this graben, micro-earthquakes close to Schlattingen (TG) in 2015/16 are possibly related to a NE dipping branch of the Neuhausen Fault. Other cases of earthquakes felt by the public during 2015/16 include earthquakes in the region of Biel, Vallorcine, Solothurn, and Savognin.  相似文献   

The false Basel earthquake of May 12, 1021   总被引：1，自引：0，他引：1  

Gabriela Schwarz-Zanetti  Virgilio Masciadri  Donat Fäh  Philipp Kästli 《Journal of Seismology》2008,12(1):125-129

The Basel (CH) area is a place with an increased seismic hazard. Consequently, it is essential to scrutinize a famous statement by Stumpf (Gemeiner loblicher Eydgnoschafft Stetten, Landen und Völckeren Chronikwirdiger thaaten beschreybung. Durch Johann Stumpffen beschriben, 1548) that allegedly a large earthquake took place in Basel in 1021. This can be disproved unambiguously by applying historical and philosophical methods.  相似文献   

Projections of global warming-induced impacts on winter storm losses in the German private household sector     

Hermann Held  Friedrich-Wilhelm Gerstengarbe  Tobias Pardowitz  Joaquim G. Pinto  Uwe Ulbrich  Kai Born  Markus G. Donat  Melanie K. Karremann  Gregor C. Leckebusch  Patrick Ludwig  Katrin M. Nissen  Hermann Österle  Boris F. Prahl  Peter C. Werner  Daniel J. Befort  Olaf Burghoff 《Climatic change》2013,121(2):195-207

We present projections of winter storm-induced insured losses in the German residential building sector for the 21st century. With this aim, two structurally most independent downscaling methods and one hybrid downscaling method are applied to a 3-member ensemble of ECHAM5/MPI-OM1 A1B scenario simulations. One method uses dynamical downscaling of intense winter storm events in the global model, and a transfer function to relate regional wind speeds to losses. The second method is based on a reshuffling of present day weather situations and sequences taking into account the change of their frequencies according to the linear temperature trends of the global runs. The third method uses statistical-dynamical downscaling, considering frequency changes of the occurrence of storm-prone weather patterns, and translation into loss by using empirical statistical distributions. The A1B scenario ensemble was downscaled by all three methods until 2070, and by the (statistical-) dynamical methods until 2100. Furthermore, all methods assume a constant statistical relationship between meteorology and insured losses and no developments other than climate change, such as in constructions or claims management. The study utilizes data provided by the German Insurance Association encompassing 24 years and with district-scale resolution. Compared to 1971–2000, the downscaling methods indicate an increase of 10-year return values (i.e. loss ratios per return period) of 6–35 % for 2011–2040, of 20–30 % for 2041–2070, and of 40–55 % for 2071–2100, respectively. Convolving various sources of uncertainty in one confidence statement (data-, loss model-, storm realization-, and Pareto fit-uncertainty), the return-level confidence interval for a return period of 15 years expands by more than a factor of two. Finally, we suggest how practitioners can deal with alternative scenarios or possible natural excursions of observed losses.  相似文献