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11.
Ida Bülow Gregersen Hjalte Jomo Danielsen Sørup Henrik Madsen Dan Rosbjerg Peter Steen Mikkelsen Karsten Arnbjerg-Nielsen 《Climatic change》2013,118(3-4):783-797
Climate change is expected to influence the occurrence and magnitude of rainfall extremes and hence the flood risks in cities. Major impacts of an increased pluvial flood risk are expected to occur at hourly and sub-hourly resolutions. This makes convective storms the dominant rainfall type in relation to urban flooding. The present study focuses on high-resolution regional climate model (RCM) skill in simulating sub-daily rainfall extremes. Temporal and spatial characteristics of output from three different RCM simulations with 25 km resolution are compared to point rainfall extremes estimated from observed data. The applied RCM data sets represent two different models and two different types of forcing. Temporal changes in observed extreme point rainfall are partly reproduced by the RCM RACMO when forced by ERA40 re-analysis data. Two ECHAM forced simulations show similar increases in the occurrence of rainfall extremes of over a 150-year period, but significantly different changes in the magnitudes. The physical processes behind convective rainfall extremes generate a distinctive spatial inter-site correlation structure for extreme events. All analysed RCM rainfall extremes, however, show a clear deviation from this correlation structure for sub-daily rainfalls, partly because RCM output represents areal rainfall intensities and partly due to well-known inadequacies in the convective parameterization of RCMs. The results highlight the problem urban designers are facing when using RCM output. The paper takes the first step towards a methodology by which RCM performance and other downscaling methods can be assessed in relation to the simulation of short-duration rainfall extremes. 相似文献
12.
Mathilde Bøttger Sørensen Peter H. Voss Jens Havskov Søren Gregersen Kuvvet Atakan 《Journal of Seismology》2011,15(4):599-611
The seismically active Skagerrak region in the border area between Denmark and Norway has traditionally been associated with
uncertain earthquake locations due to the limited station coverage in the region. A new seismic station in southern Norway
and a recent update of the earthquake database of the Danish National Network have led to a much more complete and homogeneous
data coverage of the Skagerrak area, giving the possibility of improved earthquake locations in the region. In this study,
we relocate earthquakes in the Skagerrak area to obtain a more exact picture of the seismicity and investigate well-recorded
events to determine the depth distribution. Hypocenter depths are found to be generally in the range 11–25 km. Furthermore,
new composite focal mechanisms are determined for clusters of events with similar waveforms. Results indicate that the Skagerrak
seismicity is associated with shallow, crustal faults oriented in the NS direction south of the Sorgenfrei–Tornquist Zone
(STZ) as well as with the STZ itself. Mainly reverse faulting mechanisms along NE–SW oriented faults indicate maximum horizontal
compression in the NW–SE direction. This is in agreement with World Stress Map generalizations, most likely associated with
ridge push forces from the mid-Atlantic ridge, though modified probably by local crustal weaknesses. 相似文献
13.
Sren Gregersen 《Tectonophysics》1982,89(1-3)
Earthquakes of local magnitudes between
and
have occurred in Greenland in the last few decades. Most of the earthquakes are located near the coasts. Some of the earthquake zones are connected to known tectonic features in and near Greenland.The magnitude determinations are based on Lg wave amplitudes and are calibrated using the mb determinations of the International Seismological Centre. The attenuation of the Lg waves differs from region to region. Along some paths crossing younger geologic features the attenuation is large compared to that in the paths of the old crystalline shield rocks. The Lg wave propagation is influenced by the Greenland ice cap. All the long paths go through the interior of Greenland with its 2–3 km ice cap thickness and they exhibit relatively large Lg wave attenuation. 相似文献
14.
A first detailed look at the Greenland lithosphere and upper mantle, using Rayleigh wave tomography 总被引:2,自引:1,他引:2
15.
Søren Gregersen 《Studia Geophysica et Geodaetica》1995,39(3):257-261
Summary The present state of knowledge on recent crustal movements, stresses and earthquakes around the Tornquist Zone has been collected. It is found that the Tornquist Zone is neither geodetically nor seismically active, but it separates regions of different earthquake activity.Members of the working group on recent crustal movements around the Tornquist Zone: H. Lykke Andersen, M.C. Oncescu, V. Mocanu, E. and P. Bankwitz, G. Grünthal, and S. Gregersen. 相似文献
16.
17.
Sren Gregersen 《Journal of Geodynamics》1986,6(1-4)
Some very pronounced crustal inhomogeneities have been found in the North Sea and in Greenland, in regions which were adjacent to each other before the opening of the North Atlantic Ocean by sea-floor spreading. Some of these regions of inhomogeneities are zones of relatively high seismicity, while others are aseismic. In the North Sea, the Viking Graben has earthquakes, while its southern continuation, the Central Graben, is almost aseismic. In eastern Greenland, there are only few earthquakes near the Mesozoic graben, while there is a prominent earthquake zone at the coast line in north-eastern Greenland. It is concluded that, superposed on the apparent similarities in the two regions, some differences in stress conditions or crustal weakness patterns must exist. 相似文献
18.
Sø;ren Gregersen 《Geophysical Journal International》1978,54(1):121-127
Summary. Mode conversion at a continental margin between normal modes of surface waves is investigated by theoretical calculations for oblique incidence for periods longer than 15 s. It is suggested that significant conversion takes place between the various modes of Love waves in the period interval between 15 and 40 s, while there is negligible mode conversion for longer periods. The largest mode conversion involves the lowest modes. In addition the calculations have revealed a small but significant conversion between Love and Rayleigh fundamental modes around 20-s period. Reflections of Love waves are found to be significant only for the continental fundamental mode. 相似文献
19.
M. Wilde-Piórko W. H. Geissler J. Plomerová M. Grad V. Babuška E. Brückl J. Cyziene W. Czuba R. England E. Gaczyński R. Gazdova S. Gregersen A. Guterch W. Hanka E. Hegedűs B. Heuer P. Jedlička J. Lazauskiene G. Randy Keller R. Kind K. Klinge P. Kolinsky K. Komminaho E. Kozlovskaya F. Krüger T. Larsen M. Majdański J. Málek G. Motuza O. Novotný R. Pietrasiak Th. Plenefisch B. Růžek S. Sliaupa P. Środa M. Świeczak T. Tiira P. Voss P. Wiejacz 《Studia Geophysica et Geodaetica》2008,52(3):439-448
20.