Dead Sea Basin Imaged by Ambient Seismic Noise Tomography     

Jacek?StankiewiczEmail author  Michael?H.?Weber  Ayman?Mohsen  Rami?Hofstetter 《Pure and Applied Geophysics》2012,169(4):615-623

In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests.  相似文献   

The Effects of the Earth’s Curvature on Gravity and Geoid Calculations   总被引：1，自引：0，他引：1  

Hasan??av?akEmail author 《Pure and Applied Geophysics》2012,169(4):733-740

While it is obvious that large-scale gravity studies should account for the sphericity of the Earth, each case should be examined. If a geometry model is very large for the 3D-gravity calculation, it cannot be correctly defined in Cartesian coordinates. Because of the Earth’s curvature it is necessary to use spherical coordinates, the importance of which is shown in this paper. The calculation of the gravity for a cylinder reveals, 1 m above the center of the cylinder, a relative difference of 13% between the models with Cartesian and spherical coordinates.  相似文献   

Homogenization of Earthquake Catalog for Northeast India and Adjoining Region   总被引：1，自引：0，他引：1  

Ranjit?DasEmail author  H.?R.?Wason  M.?L.?Sharma 《Pure and Applied Geophysics》2012,169(4):725-731

A catalog for northeast India and the adjoining region for the period 1897–2009 with 4,497 earthquakes events is compiled for homogenization to moment magnitude M _w,GCMT in the magnitude range 3–8.7. Relations for conversion of m _b and M _s magnitudes to M _w,GCMT are derived using three different methods, namely, linear standard regression, inverted standard regression (ISR) and orthogonal standard regression (OSR), for different magnitude ranges based on events data for the catalog period 1976–2006. The OSR relations for M _s to M _w,GCMT conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported in other studies. Since the number of events with magnitude ≥7 for this region is scanty, we, therefore, considered whole India region to obtain the regression relationships between M _w,GCMT and M _s,ISC. A relationship between M _w,GCMT and M _w,NEIC is also obtained based on 17 events for the range 5.2 ≤ magnitude ≤ 6.6. A unified homogeneous catalog prepared using the conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast India and the adjoining region.  相似文献   

Joint inversion of teleseismic P waveforms and surface-wave group velocities from ambient seismic noise in the Bohemian Massif     

Bohuslav R??ek  Jaroslava Plomerová  Vladislav Babu?ka 《Studia Geophysica et Geodaetica》2012,56(1):107-140

Joint inversion of teleseismic P-waveforms and local group velocities of surface waves retrieved from ambient seismic noise has been performed to model velocity structure of the crust and uppermost mantle of the Bohemian Massif. We analysed P-waveforms of 381 teleseismic earthquakes recorded at 54 broadband seismic stations located on the territory of the Czech Republic and in its close surroundings. Group velocities of Rayleigh and Love surface waves were obtained by cross-correlating long-term recordings of seismic noise. The basis for waveform inversion is the well-known methodology of P-to-S receiver functions constructed from converted phases. Due to instabilities in direct inversion of receiver functions caused by the necessity of applying deconvolution, we propose an alternative formulation to fit observed and calculated radial components of P waveforms. The joint inversion is transformed into a search for the minimum of the cost function defined as a weighted sum of waveform and group velocity misfits. With the use of the robust stochastic optimizer (Differential Evolution Algorithm), neither derivatives nor a starting model are needed. The task was solved for 1D layered isotropic models of the crust and the uppermost mantle. We have performed a sequence of inversions with models containing one, two, three and four layers above a half-space. By using statistical criteria (F-test) we were able to select the simplest velocity models satisfying data and representing local geological structures. Complex crustal models are typical for stations located close to boundaries of major tectonic units. The relatively low average P to S wave-velocity ratio is in agreement with the generally accepted view that the BM crust is predominantly felsic.  相似文献   

Comparison of the FORT approximation of the coupling ray theory with the Fourier pseudospectral method     

Ivan P?en?ík  Véronique Farra  Ekkehart Tessmer 《Studia Geophysica et Geodaetica》2012,56(1):35-64

The standard ray theory (RT) for inhomogeneous anisotropic media does not work properly or even fails when applied to S-wave propagation in inhomogeneous weakly anisotropic media or in the vicinity of shear-wave singularities. In both cases, the two shear waves propagate with similar phase velocities. The coupling ray theory was proposed to avoid this problem. In it, amplitudes of the two S waves are computed by solving two coupled, frequency-dependent differential equations along a common S-wave ray. In this paper, we test the recently developed approximation of coupling ray theory (CRT) based on the common S-wave rays obtained by first-order ray tracing (FORT). As a reference, we use the Fourier pseudospectral method (FM), which does not suffer from the limitations of the ray method and yields very accurate results. We study the behaviour of shear waves in weakly anisotropic media as well as in the vicinity of intersection, kiss or conical singularities. By comparing CRT and RT results with results of the FM, we demonstrate the clear superiority of CRT over RT in the mentioned regions as well as the dangers of using RT there.  相似文献   

Sea level variability at Antalya and Mente? tide gauges in Turkey: atmospheric, steric and land motion contributions     

Mehmet Simav  Hasan Yildiz  Ali Türkezer  Onur Lenk  Emin ?zsoy 《Studia Geophysica et Geodaetica》2012,56(1):215-230

Sea level trends and interannual variability at Antalya and Menteş tide gauges are investigated during the 1985–2001 period, quantifying the roles of atmospheric, steric and local land motion contributions. Tide gauge sea level measurements, temperature/salinity climatologies and GPS data are used in the analyses and the results are compared with the output of a barotropic model forced by atmospheric pressure and wind. The overall sea level trends at two tide gauges collocated with GPS are in the range of 5.5 to 7.9 mm/yr during the study period, but showing different behaviour in the sub-periods 1985–1993 and 1993–2001 due to variations in the contributing factors both in space and time. After the removal of the atmospheric forcing and steric contribution from sea level records, the resulting trends vary between 1.9 to 4.5 mm/yr in Antalya and −1.2 to −11.6 mm/yr in Menteş depending on the period considered. Vertical land movement estimated from GPS data seems to explain the high positive residual trend in Antalya during the whole period. On the other hand, the source of the highly negative sea level trend of about −14 mm/yr in Menteş during 1985–1993 could not be resolved with the available datasets. Interannual variability of wind and atmospheric pressure appear to dominate the sea level at both tide gauges during the study period. Atmospheric and steric contributions together account for ∼50% of the total sea level variance at interannual time scales. Mass induced sea level variations which were not considered in this study may help to close the sea level trend budgets as well as to better explain the interannual sea level variance.  相似文献   

Emergence patterns and microhabitat preference of aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) on a longitudinal gradient of barrage lake system     

Marija Ivkovi?  Vlatka Mi?eti? Stankovi?Zlatko Mihaljevi? 《Limnologica》2012,42(1):43-49

Aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) are important components of freshwater assemblages, especially in running waters. They are predators as larvae and adults and thus essential for understanding aquatic food webs. This study was conducted in Plitvice lakes National Park (Croatia) representing a wide variety of freshwater habitats (springs, streams, lakes and tufa barriers). Adults were collected monthly from March 2007 until March 2009 using pyramid-type emergence traps at 13 locations. A total of 3865 specimens comprising 18 species were collected. The dominant genus was Chelifera, while the most abundant species was Hemerodromia unilineata. All species were univoltine except Chelifera precabunda, Chelifera pyrenaica and Chelifera stigmatica that were bivoltine. Considerable differences in composition and structure of aquatic dance flies assemblages were recorded along a longitudinal gradient of studied sites, primarily related to differences in physical and chemical parameters of water. Water temperature was the main factor influencing the timing of emergence. Hemerodromia species preferred variable water temperature throughout the year while the majority of the Chelifera species preferred stable water temperature characteristic of spring sites. Furthermore, discharge affected assemblage composition of aquatic dance flies. The highest abundance of aquatic dance flies was recorded in lotic habitats with fast water current over substrates of moss, gravel and particulate tufa with detritus. These results give a new insight on microhabitat preference and their distribution on unique karstic habitats.  相似文献   

Zero-order ray-theory Green tensor in a heterogeneous anisotropic elastic medium     

Luděk Klime? 《Studia Geophysica et Geodaetica》2012,56(2):373-382

Although synthetic seismograms can, in many cases, be generated by direct numerical methods, approximate analytical ray-theory solutions are often very useful in forward and especially inverse problems of seismic wave propagation in complex 3-D media. In this paper, the frequency-domain zero-order ray-theory Green tensor in a heterogeneous anisotropic elastic medium is derived from the zero-order ray-theory approximation using the representation theorem applied in ray-centred coordinates.  相似文献   

Analysis of the Characteristics of Low-Latitude GPS Amplitude Scintillation Measured During Solar Maximum Conditions and Implications for Receiver Performance   总被引：1，自引：0，他引：1  

Alison de Oliveira Moraes  Fabiano da Silveira Rodrigues  Waldecir Jo?o Perrella  Eurico Rodrigues de Paula 《Surveys in Geophysics》2012,33(5):1107-1131

Ionospheric scintillations are fluctuations in the phase and/or amplitude of trans-ionospheric radio signals caused by electron density irregularities in the ionosphere. A better understanding of the scintillation pattern is important to make a better assessment of GPS receiver performance, for instance. Additionally, scintillation can be used as a tool for remote sensing of ionospheric irregularities. Therefore, the study of ionospheric scintillation has both scientific as well as technological implications. In the past few years, there has been a significant advance in the methods for analysis of scintillation and in our understanding of the impact of scintillation on GPS receiver performance. In this work, we revisit some of the existing methods of analysis of scintillation, propose an alternative approach, and apply these techniques in a comprehensive study of the characteristics of amplitude scintillation. This comprehensive study made use of 32?days of high-rate (50?Hz) measurements made by a GPS-based scintillation monitor located in S?o José dos Campos, Brazil (23.2°S, 45.9°W, ?17.5° dip latitude) near the Equatorial Anomaly during high solar flux conditions. The variability of the decorrelation time (τ₀) of scintillation patterns is presented as a function of scintillation severity index (S ₄). We found that the values of τ₀ tend to decrease with the increase of S ₄, confirming the results of previous studies. In addition, we found that, at least for the measurements made during this campaign, averaged values of τ₀ (for fixed S ₄ index values) did not vary much as a function of local time. Our results also indicate a significant impact of τ₀ in the GPS carrier loop performance for S ₄?≥?0.7. An alternative way to compute the probability of cycle slip that takes into account the fading duration time is also presented. The results of this approach show a 38% probability of cycle slips during strong scintillation scenarios (S ₄ close to 1 and τ₀ near 0.2?s). Finally, we present results of an analysis of the individual amplitude fades observed in our set of measurements. This analysis suggests that users operating GPS receivers with C/N ₀ thresholds around 30?dB-Hz and above can be affected significantly by low-latitude scintillation.  相似文献   

The Water Vapour Continuum: Brief History and Recent Developments     

Keith P. Shine  Igor V. Ptashnik  Gaby R?del 《Surveys in Geophysics》2012,33(3-4):535-555

The water vapour continuum is characterised by absorption that varies smoothly with wavelength, from the visible to the microwave. It is present within the rotational and vibrational–rotational bands of water vapour, which consist of large numbers of narrow spectral lines, and in the many ‘windows’ between these bands. The continuum absorption in the window regions is of particular importance for the Earth’s radiation budget and for remote-sensing techniques that exploit these windows. Historically, most attention has focused on the 8–12?μm (mid-infrared) atmospheric window, where the continuum is relatively well-characterised, but there have been many fewer measurements within bands and in other window regions. In addition, the causes of the continuum remain a subject of controversy. This paper provides a brief historical overview of the development of understanding of the continuum and then reviews recent developments, with a focus on the near-infrared spectral region. Recent laboratory measurements in near-infrared windows, which reveal absorption typically an order of magnitude stronger than in widely used continuum models, are shown to have important consequences for remote-sensing techniques that use these windows for retrieving cloud properties.  相似文献