Site response study in Abruzzo (Central Italy): underground array versus surface stations   总被引：1，自引：1，他引：0  

G. De Luca  E. Del Pezzo  F. Di Luccio  L. Margheriti  G. Milana  R. Scarpa 《Journal of Seismology》1998,2(3):223-236

In this site response study we examined local earthquakes recorded at surface stations of a local seismic network and at a temporary underground seismic array installed in a tunnel underneath the Gran Sasso Massif in Abruzzo (central Italy). This allowed us to compare the seismic site response beneath the mountain and on the surface in similar geological environment (soft rock sites). We applied spectral ratios method on different segments of the seismograms and used different reference spectra in the 1–20 Hz frequency band. We found little or no amplification effects at most of the surface stations whereas site transfer functions evaluated with respect to underground sites show an amplification factor up to 6 in the 1–8 Hz frequency range. Coda spectral ratios estimated at soft rock sites are confirmed as good estimates of shear wave transfer function.  相似文献   

TCM-90现场试验台风能量频散波列特征   总被引：13，自引：5，他引：8  

徐祥德  陈联寿  解以扬  亢迪 《气象学报》1998,56(2):129-138

采用ＴＣＭ－９０（台风运动－９０）台风现场科学试验资料,对台风ＦＬＯ,ＥＤ个例进行了诊断分析,并做了有关数值试验研究。分析研究结论揭示了台风涡旋作为一动力、热力强迫源或ＣＩＳＫ不稳定结构,其与环境场相互作用可激发出动能频散波列;台风扰源通过频散机制可构成类似２维Ｒｏｓｓｂｙ波的经向波列;台风涡旋的移动路径与上述能量传播特征有一定的相关关系。  相似文献   

Preliminary Results from Paleomagnetic Records on Lake Sediments from South America     

Gogorza  C.S.G.  Di Tommaso  I.  Sinito  A.M.  Jackson  B.  Nuñez  H.  Creer  K.  Vilas  J.F. 《Studia Geophysica et Geodaetica》1998,42(1):12-29

The preliminary results of paleomagnetic and radiocarbon dating of late pleistocene-holocene sediments from two lakes of south-western Argentina (41°S, 71.5°W) are presented. The magnetic susceptibility, intensity and direction of the natural remanent magnetisation were measured. The stability of the natural remanent magnetisation was investigated by alternating field demagnetisation. The magnetic parameters allowed the cores within each lake to be correlated. ¹³ C analysis, total organic content measurements and C ¹⁴ dating were carried out. A model of sedimentation is suggested. Using this model and the correlation, curves of variations of magnetic inclination and declination in time are shown.  相似文献   

Human-induced sedimentological changes in Manzala Lagoon, Nile Delta, Egypt   总被引：1，自引：0，他引：1  

G. Randazzo  D. J. Stanley  S. I. Di Geronimo  C. Amore 《Environmental Geology》1998,36(3-4):235-258

 The Manzala Lagoon in Egypt's Nile Delta has become a sediment sink of reduced area and depth, with increased contaminant levels. Loss of much-needed fresh to brackish water reserves and decreased fish catches have serious ramifications. Herein, maps of temporal and regional sediment distributions in Manzala incorporate petrological and statistical analyses of 200 surficial and short core samples. These provide baseline information needed to help implement protection measures for this vital wetland. Four periods are considered: 1920s, 1940s, ∼1965, and 1990. Important depositional changes between 1940s and ∼1965 resulted from anthropogenic effects on this quasi-closed lagoon system, including industrial buildup, wetland conversion to agricultural land, and irrigation waterway development. Further modification from ∼1965 to 1990 is associated with closure of the Aswan High Dam, continued construction of waterways that discharge waste water into lagoon margins, and marine incursion into the northern lagoon. If current practices continue, the lagoon could be reduced to about one-third of its present area by 2050 AD. Received: 2 October 1997 · Accepted: 13 January 1998  相似文献   

Mineral magnetic record of paleoclimate variation in loess and paleosol from the Buenos Aires formation (Buenos Aires, Argentina)     

M. J. OrgeIra  A. M. Walther  C. A. Vsquez  I. Di Tommaso  S. Alonso  G. Sherwood  Hu Yuguan  J. F. A. Vilas 《Journal of South American Earth Sciences》1998,11(6):561-570

Environmental magnetic techniques were applied to a loess–paleosol sequence of the Chacopampean plain (Buenos Aires, Argentina). Mineral magnetic carriers and their grain size were identified in order to detect magnetic mineral fluctuations associated with climatic changes. Multidomain magnetite of detrital origin dominates the record. In paleosols, a high coercivity fraction was identified. Horizons with no visual evidence of pedogenesis, but showing magnetic behavior analogous to that of paleosols were observed and are thought to represent environmental conditions similar to those prevailing during paleosol formation.The results suggest that the magnetic signal yielded by paleosols in these South American loess deposits is different from that in the Chinese loess. This may be due to differences in parent materials, diagenetic processes and/or differences in paleoclimatic conditions in both regions.  相似文献   

地质成分数据统计分析   总被引：5，自引：0，他引：5  

周蒂 《地球科学》1998,23(2):28

地质学研究中遇到大量成分数据,其各行之和相同,因而组分相关性中含由闭合效应引起的伪相关,而且不服从正态分布,给统计分析带来了很大困难．分析了前人提出的一些识别成分数据中伪相关的方法的缺欠,提出对数比变换作为成分数据统计分析的基本步骤的依据、优越性及存在问题;指出闭合造成的信息损失包括基的相关结构的信息,是任何方法都找不回来的．今后应着重分析有哪些信息还保留在成分数据中,并有针对性地寻找萃取这些信息的方法．  相似文献   

万维网上地球科学信息源的搜寻     

周蒂 《物探化探计算技术》1998,20(4):289-292

信息时代呼啸而至,给科学工作者带来了极大的机遇和挑战。能否及时掌握最新信息,能否以最快速度得到所需的特殊信息,成了能否取得前沿成果的关键之一。本文主要根据Ｓｃｈｉｍｍｒｉｃｈ的文章［１］作一些补充,简要介绍在万维网上搜寻地球科学信息源的一些知识。  相似文献   

Magnetic reconnection: flares and coronal heating in active galactic nuclei     

T. Di Matteo 《Monthly notices of the Royal Astronomical Society》1998,299(1):L15-L20

A magnetically structured accretion disc corona, generated by buoyancy instability in the disc, can account for observations of flare-like events in active galactic nuclei. We examine how Petschek magnetic reconnection, associated with MHD turbulence, can result in a violent release of energy and heat the magnetically closed regions of the corona up to canonical X-ray emitting temperatures. X-ray magnetic flares, the after effect of the energy released in slow shocks, can account for the bulk of the X-ray luminosity from Seyfert galaxies and consistently explain the observed short-time-scale variability.  相似文献   

Fourteen years of multifrequency-coordinated observations of the X-ray/Be system A 0535+26/HDE 245770     

F. Giovannelli  C. Bartolini  A. Guarnieri  A. Piccioni  M. Burger  E. L. Van Dessel  V. G. Kurt  E. K. Sheffer  D. De Martino  R. Waters  I. Gonzalez Martinez-Pais  Yu. N. Gnedin  V. M. Larionov  N. I. Shakovskaya 《Astrophysics and Space Science》1990,169(1-2):139-145

Within the framework of a very long multifrequency campaign of coordinated, and very often simultaneous, observations of the transient X-ray/Be system A 0535+26/HDE 245770, we present a summary of this large collection of data taken with IUE and ASTRON satellites as well as with many ground-based telescopes in optical and IR regions.In this paper we emphasize the study of the physics and dynamics of the mass transfer at periastron and subsequent X-ray flaring, which is a typical problem of the X-ray/Be binary system class.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

Limitations of an Eddy-Covariance System in Measuring Low Ammonia Fluxes     

Ferrara  Rossana Monica  Di Tommasi  Paul  Famulari  Daniela  Rana  Gianfranco 《Boundary-Layer Meteorology》2021,180(1):173-186

Green manuring of legume crops can improve soil fertility and sustainability. To evaluate its agronomic and environmental effectiveness, gaseous losses of ammonia (NH₃) in the surface layer need to be quantified by direct measurements in the field. However, the application of the eddy-covariance technique to atmospheric NH₃ is challenging: its high reactivity, water solubility, and low background concentrations all hinder the response time of closed-path sensors for fast measurements of NH₃ concentration. Ammonia emissions following green manuring were measured for 21 days using a flux system equipped with a fast-pulsed quantum-cascade tunable-infrared-laser spectrometer. The noisy cross-covariance function for this configuration indicates flux measurements are close to the limit of detection; the low signal-to-noise ratio further increases the uncertainties, introducing a mirroring effect on the fluxes, which results in the rapid alternation between emission and deposition, within the limit of detection (around 13 and 20 ng m^?2 s^?1, at the 95 and 99% confidence limits, respectively). An evaluation of the measurement errors is presented, focussing on three technical aspects of the eddy-covariance system: (1) time lag, (2) random error, and (3) limit of detection. The NH₃ fluxes measured by the spectrometer are close to its limit of detection, with a random error of the same order as the flux.

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