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51.
Summary A method is developed, which permits a rapid and reliable determination of the location of near epicenters (within about 10o) using the differences of arrival times of a common phase (usually Sg) to a net of three stations. The resulting equation for computation of epicentral distances is solved numerically once for all by an electronic computer for every station triangle and for all possible time differences for every wave used. The calculated epicentral distances and coordinates are arranged in tables with the two travel-time differences for each triangle as entries. Such tables permit an immediate solution of the problem in every special case. The accuracy of the method is investigated, and necessary precautions in its use are emphasized. Application is made to a few cases of Sg recorded at the Swedish stations.
Zusammenfassung Eine Methode wird entwickelt, die eine schnelle und zuverlässige Bestimmung der Lage von nahegelegenen Epizentren (innerhalb rund 10o) mittels der Laufzeitdifferenzen einer gegebenen Welle (gewöhnlichSg) in einem Netz von drei Stationen ermöglicht. Die erhaltene Gleichung für die Berechnung der Herdentfernungen wird mittels einer elektronischen Rechenmaschine für jedes Stations-dreieck und für alle möglichen Zeitdifferenzen für jede verwendete Welle ein für allemal numerisch gelöst. Die berechneten Herdentfernungen und-Koordinaten werden in Tabellenform dargestellt mit den beiden Laufzeitdifferenzen für jedes Dreieck als Eingangswerte. Solche Tabellen ermöglichen eine unmittelbare Lösung des Problems in jedem einzelnen Fall. Die Genauigkeit der Methode wird untersucht, und die notwendigen Vorsichtsmassregeln bei ihrer Verwendung werden hervorgehoben. Die Methode wird auf einige Registrierungen vonSg an den schwedischen Stationen angewendet.相似文献
52.
Markus Båth 《Pure and Applied Geophysics》1959,43(1):131-147
Summary By means of the long-period records at Uppsala and Kiruna of thirteen specially selected earthquakes, the Love and Rayleigh wave dispersion is determined for all oceans and all continents except for South America. The observations have given information on crustal structure along several paths, not investigated earlier; in other cases, they have confirmed earlier results. The methods are discussed. The results for oceanic areas are summarized in the following table:
The observations demonstrate the oceanic structure of the central Arctic area as well as the complete similarity of the Atlantic and Pacific bottom structure. Continental dispersion curves are determined for very long paths over Euro-Asia and for the hitherto longest path over North America as well as for a path crossing Africa. These observations indicate an average crust about 10–15 km thicker along the Euro-Asiatic path than along the North American path, whereas there is perfect agreement between the North American and the African continent. A shear-wave velocity of 4.3–4.4 km/sec is obtained for the upper part of the mantle under the continents. Further conclusions must await the computation of a greater number of theoretical dispersion curves.
Zusammenfassung Mittels der langperiodischen Registrierungen in Uppsala und Kiruna von dreizehn speziell ausgewählten Erdbeben ist die Dispersion der Love-und Rayleigh-Wellen für alle Ozeane und alle Kontinente mit Ausnahme von Süd-Amerika bestimmt worden. Die Beobachtungen haben in mehreren Fällen Auskunft über die Krusten-Struktur längs Wellenwege gegeben, die nie früher untersucht worden sind; in anderen Fällen haben sie frühere Resultate bestätigt. Die Methoden werden diskutiert. Die Resultate für ozeanische Gebiete sind in der folgenden Tabelle zusammengefasst: Die Beobachtungen beweisen sowohl die ozeanische Struktur des zentralen Teiles des arktischen Gebietes als auch die vollständige Gleichheit der atlantischen und pazifischen Krusten-Struktur. Kontinentale Dispersionskurven sind für sehr lange Wellenwege über Euro-Asien und für den bisher längsten Wellenweg über Nord-Amerika bestimmt worden. Diese Beobachtungen zeigen, dass die mittlere Krusten-Dicke 10–15 km grösser längs des euro-asiatischen Weges ist als längs des nordamerikanischen Weges; dagegen zeigen die Beobachtungen für Nord-Amerika und Afrika sehr gute Übereinstimmung. Eine Transversalwellen-Geschwindigkeit von 4.3–4.4 km/sek wird für den oberen Teil des Erdmantels unter den Kontinenten gefunden. Weitere Schlussfolgerungen müssen die Berechnung einer grösseren Anzahl theoretischer Dispersionskurven erwarten.相似文献
53.
Dr. Markus Bath 《Pure and Applied Geophysics》1957,38(1):19-31
Summary A study has been made of a new channel wave, denotedLi, using a total of 83 observations from the seismic records of Swedish stations, mainly from earthquakes at normal depth.Li resembles theLg waves in several respects: it propagates only through continental structures, it has a similar particle motion, i.e. mainly transverse horizontal, and only slightly larger period. ButLi has a higher velocity, 3.79±0.07 km/sec, and it is believed to propagate in the intermediate layer in the crust in a way similar to the propagation of theLg waves in the granitic layer.Li is identical withS
* in records of near-by earthquakes in the same way asLg2 is identical withSg. Li usually exhibits no clear dispersion.
Zusammenfassung Es wurden Untersuchungen angestellt über eine neue Kanalwelle, welcher die BezeichnungLi gegeben wurde, wobei insgesamt 83 Erdbebenregistrierungen von schwedischen Stationen Verwendung fanden. Hauptsächlich waren es Erdbeben mit normaler Herdtiefe. DieLi-Wellen haben in verschiedener Hinsicht Ähnlichkeit mit denLg-Wellen: Sie pflanzen sich nur im Bereich kontinentaler Struktur fort und sie haben eine ähnliche Partikelbewegung, d.h. hauptsächlich horizontaltransversal.Li hat eine nur unwesentlich höhere Periode als dieLg-Wellen. AberLi hat eine wesentlich höhere Geschwindigkeit, 3.79±0.07 km/sec, und es ist anzunehmen, dass sie sich in der Basaltschicht der Kruste in ähnlicher Weise fortpflanzt wieLg in der Granitschicht.Li ist identisch mitS * in Aufzeichnungen von Nahbeben, so wieLg2 identisch mitSg ist.Li weist gewöhnlich keine deutliche Dispersion auf.相似文献
54.
Summary If for a point on the earth's surface, the apparent (moveout) seismic velocities have been determined for a number of profiles in different directions, a possibility is offered to calculate true strike and dip of crustal boundaries. In the present paper the theory is developed, partly for a sloping Mohorovii discontinuity only, partly for sloping Conrad and Mohorovii discontinuities with parallel strikes. The theory for the sloping Mohorovii discontinuity is applied to field measurements at a place about 30 km west of Uppsala performed in June 1969. With a crustalP-wave velocity of 6.3 km/sec, a good fit to the observations is obtained for aPn-velocity of 8.55 km/sec and a downdip of Moho of 7.2° in the direction S 3.8° E. These numerical values are not the most important output of this paper. On the other hand, the testing of the method appears far more important, and also that improvements can be suggested in the experimental procedure in future applications of this method. 相似文献
55.
Cold seep deposits of Beauvoisin (Oxfordian; southeastern France) and Marmorito (Miocene; northern Italy): microbially induced authigenic carbonates 总被引:12,自引:0,他引:12
J. Peckmann V. Thiel W. Michaelis P. Clari C. Gaillard L. Martire J. Reitner 《International Journal of Earth Sciences》1999,88(1):60-75
The relation of two well-known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study. Archaea are
found to be associated with the formation of Oxfordian seep carbonates from Beauvoisin and with a Miocene limestone from Marmorito
("tube-worm limestone"). Carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative
δ13Ccarbonate values, respectively. Highly positive values (+15‰) reflect the use of 13C-enriched CO2 produced by methanogenesis. Low δ13C values of the Marmorito carbonates (–30‰) indicate the oxidation of seepage-derived hydrocarbons. Likewise, the δ13C content of specific tail-to-tail linked isoprenoids, biomarkers for archaea, was found to be strikingly depleted in these
samples (as low as –115‰). The isotopic signatures corroborate that archaea were involved in the cycling of seepage-derived
organic carbon at the ancient localities. Another Miocene limestone ("Marmorito limestone") shows a strong imprint of methanotrophic
bacteria as indicated by δ13C values of carbonate as low as –40‰ and biomarker evidence. Epifluorescence microscopy and field-emission scanning electron
microscopy revealed that bacterial biofilms were involved in carbonate aggregation. In addition to lucinid bivalves previously
reported from both localities, we infer that sponges from Beauvoisin and tube worms from Marmorito depended on chemosynthesis
as well. Low δ13C values of nodules related to sponge taphonomy (–27‰) indicate that sponges might have been linked to an enhanced hydrocarbon
oxidation. Tube worm fossils from Marmorito closely resemble chemosynthetic pogonophoran tube worms from Recent cold seeps
and are embedded in isotopically light carbonate (δ13C –30‰).
Received: 13 October 1998 / Accepted: 5 February 1999 相似文献
56.
ABSTRACTWe thank Allen and Berghuijs for continuing the discussion on field hydrology and data sharing and discuss two incentives to promote data collection and sharing in hydrological sciences: a collaborative attitude and additional funding to make data publicly available. 相似文献
57.
ABSTRACT Groundwater level fluctuations are caused by spatial and temporal superposition of processes within and outside the aquifer system. Most of the subsurface processes are usually observed on a small scale. Upscaling to the regional scale, as required for future climate change scenarios, is difficult due to data scarcity and increasing complexity. In contrast to the limited availability of system characteristics, high-resolution data records of groundwater hydrographs are more generally available. Exploiting the information contained in these records should thus be a priority for analysis of the chronical lack of data describing groundwater system characteristics. This study analyses the applicability of 63 indices derived from daily hydrographs to quantify different dynamics of groundwater levels in unconfined gravel aquifers from three groundwater regions (Bavaria, Germany). Based on the results of two different skill tests, the study aids index selection for different dynamic components of groundwater hydrographs. 相似文献
58.
59.
Amaelle Landais Valérie Masson-Delmotte Jean Jouzel Dominique Raynaud Sigfus Johnsen Christof Huber Markus Leuenberger Jakob Schwander Bénédicte Minster 《Climate Dynamics》2006,26(2-3):273-284
The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated
climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show
that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (∼123–100 kyears
BP) encompassing Dansgaard–Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out
disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of
10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of δ18O of O2 to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years,
and to examine the interhemispheric sequence of events over this period. After a synchronous North–South temperature decrease,
the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic
counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to
intermediate levels of CO2 and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24
and 23 appear similar to typical full glacial DO events. 相似文献
60.
Nikolaus Gussone Gerald Langer Markus Geisen Blair A. Steel Ulf Riebesell 《Earth and Planetary Science Letters》2007,260(3-4):505-515
Four species of marine calcifying algae, the coccolithophores Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 °C, and one species, C. leptoporus, under varying [CO32−], ranging from 105 to 219 μmol/kg. Calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e.g. Emiliania huxleyi (coccolithophores) and Orbulina universa (planktonic foraminifera) as well as inorganically precipitated CaCO3, but also reveal small species specific differences. In contrast to inorganically precipitated calcite, but similar to E. huxleyi and O. universa, the carbonate ion concentration of the medium has no statistically significant influence on the Ca isotope fractionation of C. leptoporus coccoliths; however, combined data of E. huxleyi and C. leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium. Since coccoliths constitute a significant portion of the global oceanic CaCO3 export production, the Ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the Ca sink of the ocean, one of the key parameters for modelling changes to the marine Ca budget over time. For the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic Ca sink (Δsed) of about − 1.3‰, but the observed inter- and intra-species differences point to possible changes in Δsed through earth history, due to changing physico-chemical conditions of the ocean and shifts in floral and faunal assemblages. 相似文献