The use of teleseismic P-wave complexity for seismic event screening – results determined from GRF and GERESS array data

Seismic data recorded at the broad-band teleseismic GRF array and theshort-period regional GERESS array, which is a designated IMS primarystation, are analyzed to determine the effectiveness of teleseismic P-wave complexity for the purpose of seismic event screening within theframework of Comprehensive Nuclear-Test-Ban Treaty verification. For theGRF array, seismic waveform data from nearly 200 nuclear explosions havebeen recorded since its installation in the late 1970's, which were studiedalong with several thousand earthquakes from the last few years.Additionally, we investigated teleseismic P wave complexity for a similarnumber of earthquakes recorded at GERESS. However, owing to itsoperation starting in 1991, only a limited number of nuclear explosionseismograms are available for study.For nuclear explosions, complexity does not exceed levels of 0.3 except fora number of events from the Nevada Test Site recorded only at the GRFarray and located at a large distance where PcP may interfere with the initialP wavelet. Since all events with complexity at GRF larger than 0.3 areexclusively located on Pahute Mesa within the Nevada Test Site,near-source geology or topography must play a dominant role for theseincreased complexity values, while PcP may not contribute significantly tothe high-frequency energy measured by the complexity parameter.Although many earthquakes show complexities below this level, for morethan 25% of the earthquakes investigated the complexities determined arelarger than 0.7, thus showing distinctly larger values than nuclearexplosions. Therefore, this percentage may be screened as earthquakes fromall seismic events detected. As currently only about half of the eventsdetected by the global IMS network are screened out based on focal depthand the m _b :M _s criterion, teleseismic P-wavecomplexity may contribute significantly to the task of seismic eventscreening.     

Neue Beobachtungen zur Paläogeographie des Devon auf dem brasilianischen Block

Zusammenfassung Neuere Beobachtungen im Jatobá-Becken (Pernambuco — Brasilien), dem nördlichsten Ausläufer der Reconcavo-Zone von Bahia haben überraschenderweise dort eine Vertretung von Unterdevon und unterstem Unterkarbon ergeben. Das Cariri-Konglomerat im Liegenden der kretacischen Araripe-Serie (West-Pernambuco) muß nach neuen Beobachtungen ebenfalls ins Unterdevon eingereiht werden. Gleiches gilt für den stratigraphisch bisher in der Luft hängenden Tombador-Sandstein im zentralen Bahia, dessen Profil weitgehend dem Unterdevon-Profil von Piaui entspricht. Die Devondecke auf dem nordöstlichen Teil des brasilianischen Blockes war ursprünglich viel ausgedehnter als bisher vermutet werden konnte. Eigenartig ist die auf die weiten Entfernungen gleichförmige grobklastische Fazies auch in offensichtlich küstenferneren Bereichen, die kaum eine andere Deutung als driftglaziale Einflüsse im Unterdevon-Meer zuläßt, was früher auch schonMaack für das Unterdevon in Paraná vermutet hatte. Die aus paläomagnetischen Messungen erschlossene Lage des brasilianischen Blockes während des Devon stimmt damit gut überein.

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Recent observations in the basin of Jatobá (Pernambuco — Brasil), the extreme northern end of the Reconcavo-Zone of Bahia, resulted in the surprising discovery of Subdevonian and lowest Carboniferous. Recent studies also found out that the Cariri-conglomerat in the underlying bed of the cretaceous Araripe-series (West-Pernambuco) must also be classified in the Subdevonian, as well as the Tombador sandstone in central Bahia, whose profil resembles that of the Subdevonian of Piaui. The Devonian nappe on the north-eastern part of the Brasilian block was originally much larger than it has been assumed. The clastic facies even in regions far from the coast, is very strange. It can only be interpreted as glacial deposits in the subdevonian ocean, a suggestion which has already been made byMaack for the Subdevonian in Paraná. This agrees with the situation of the Brasilian block during the Devonian, infered from paleomagnetic measurements.

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Resumen Conforme as observações mais recentes há uma representação do Devoniano inferior e do Carbonífere mais inferior na bacia de Jatobá (Pernambuco — Brasil), a extremidade setentrional da zone de Revoncavo. O conglomerado de Cariri na lapa da série Araripe, deve ser atribuido ao Devoniano inferior conforme observações recentes. O arenito Tombador da Bahia, cujo perfil corresponde muito bem ao do Devoniano inferior de Piaui, tern a mesma posição estratigráfica. No bloco brasileiro, a capa, devoniana era originalmente muito mais extensa do que se supôs até agora. A fácies clástica, muito monótona por todas estas amplas áreas, é um fenomeno muito estranho que pode ser interpretado só pela idéia que no mar devoniano houve gelo flutuante. No Devoniano do Paraná, R.Maack pronunciou a mesma idéia. As medições paleomagnéticas indicam uma posição do bloco brasileiro durante o Devoniano, que bem corresponde a esta interpretação.

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, (, ) . Araripe Tombador. , .

     

Die Verteilung des Yttriums und der Lanthaniden in einem Olivin-Alkali-Basalt mit Peridotit-Einschlüssen

Zusammenfassung In zwei Peridotit-Einschlüssen und dem sie umgebenden Olivin-Alkali-Basalt des Hirzsteins (Nordhessen) wurde die Verteilung des Yttriums und der Lanthaniden quantitativ bestimmt. Die Summe der Lanthaniden (La-Lu, einschließlich Y) beträgt für die Peridotit-Einschlüsse 10–20 ppm, für den Olivin-Alkali-Basalt 280–360 ppm. Die relative Verteilung der Lanthaniden in den Peridotit-Knollen, bezogen auf Chondrite, gibt keinen Hinweis auf große Unterschiede zwischen den leichteren (La-Sm) und schwereren (Eu-Lu) Elementen. Dagegen sind in dem Olivin-Alkali-Basalt die Lanthaniden La-Sm deutlich stärker angereichert gegenüber den Elementen Eu-Lu. Dieser Befund steht in Einklang mit der Vorstellung, daß die chemisch stärker fraktionierten Olivin-Alkali-Basalte eventuell aus weniger stark differenzierten primären Gesteinen (Eklogit, Granat-Peridotit, tholeiitischer Basalt) entstanden sind. In Übereinstimmung mit anderen Beobachtungen handelt es sich bei den Peridotit-Einschlüssen des untersuchten Vorkommens wahrscheinlich um Gesteinsstücke, die in keiner unmittelbaren genetischen Beziehung zu dem umgebenden Basalt stehen.

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The patterns of the relative distributions of the lanthanides have been determined in two lherzolite inclusions and their surrounding alkaline olivine basalt from a locality in Northern Hessia (Hirzstein), Germany. The total contents of Y, La-Lu in the lherzolite inclusions are 10–20 ppm and in the alkaline olivine basalt 280–360 ppm. There is no great difference in the ratios ppm Y, La-Lu in rocks/ppm Y, La-Lu in chondrites if we compare the light (La-Sm) and the heavier lanthanides (Eu-Lu) in the lherzolite inclusions. In the case of the alkaline olivine basalt however the related ratios increase from Sm to La to a maximum of about 250. These results correspond to an assumption that the alkaline olivine basalts with their higher degree of chemical fractionation are formed from less differentiated primary rocks (eclogite, garnet-peridotite, tholeiitic basalt). The lherzolite inclusions of the investigated locality have probably no direct genetic relation to the surrounding basalt.

     

Holocene glacial and tree-line variations in the White River Valley and Skolai Pass,Alaska and Yukon Territory

Complex glacier and tree-line fluctuations in the White River valley on the northern flank of the St. Elias and Wrangell Mountains in southern Alaska and Yukon Territory are recognized by detailed moraine maps and drift stratigraphy, and are dated by dendrochronology, lichenometry, ¹⁴C ages, and stratigraphic relations of drift to the eastern (1230 ¹⁴C yr BP) and northern (1980 ¹⁴C yr BP) lobes of the White River Ash. The results show two major intervals of expansion, one concurrent with the well-known and widespread Little Ice Age and the other dated between 2900 and 2100 ¹⁴C yr BP, with a culmination about 2600 and 2800 ¹⁴C yr BP. Here, the ages of Little Ice Age moraines suggest fluctuating glacier expansion between ad 1500 and the early 20th century. Much of the 20th century has experienced glacier recession, but probably it would be premature to declare the Little Ice Age over. The complex moraine systems of the older expansion interval lie immediately downvalley from Little Ice Age moraines, suggesting that the two expansion intervals represent similar events in the Holocene, and hence that the Little Ice Age is not unique. Another very short-lived advance occurred about 1230 to 1050 ¹⁴C yr BP. Spruce immigrated into the valley to a minimum altitude of 3500 ft (1067 m), about 600 ft (183 m) below the current spruce tree line of 4100 ft (1250 m), at least by 8020 ¹⁴C yr BP. Subsequent intervals of high tree line were in accord with glacier recession; in fact, several spruce-wood deposits above current tree line occur bedded between Holocene tills. High deposits of fossil wood range up to 76 m above present tree line and are dated at about 5250, 3600 to 3000, and 2100 to 1230 ¹⁴C yr BP. St. Elias glacial and tree-line fluctuations, which probably are controlled predominantly by summer temperature and by length of the growing and ablation seasons, correlate closely with a detailed Holocene tree-ring curve from California, suggesting a degree of synchronism of Holocene summer-temperature changes between the two areas. This synchronism is strengthened by comparison with the glacier record from British Columbia and Mt. Rainier, Likewise, broad synchronism of Holocene events exists across the Arctic between the St. Elias Mountains and Swedish Lappland. Finally, two sequences from the Southern Hemisphere show similar records, in so far as dating allows. Hence, we believe that a preliminary case can be made for broad synchronism of Holocene climatic fluctuations in several regions, although further data are needed and several areas, particularly Colorado and Baffin Island, show major differences in the regional pattern.     

Analogous method for interpretation of gravitational anomalies

Summary From a corollary ofGreen's theorem is derived, that a thin layer of variable density can produce the same gravitational effect as a certain mass distribution below this layer. To this thin layer of variable density is analogous a sheet illuminated of variable intensity. The intensity of illumination is detected with a Philips LDR (light dependent resistor) cell. It is pointed out further that the method can be applied to determine the vertical gravity gradient too.

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Zusammenfassung Aus einem Folgesatz des Green-Theorems wird abgeleitet, dass eine dünne Schicht mit veränderlicher Dichte die gleiche Gravitationswirkung verursacht wie eine bestimmte — unter dieser Schicht liegende — Massenverteilung. Zwischen dieser dünnen Schicht mit veränderlicher Dichte und einer beleuchteten Fläche mit veränderlicher Lichtstärke besteht eine Analogie. Die Intensität der Beleuchtung wird mit einer Philips-LDR-Zelle gemessen. Es wird weiter darauf hingewiesen, dass die Methode auch für Bestimmung des vertikalen Gravitationsgradienten anwendbar ist.

     

Isotopenuntersuchungen zum Kalkumsatz im Löß

The ratio of oxygen and carbon isotopes is a criterion for the carbonate-genesis with distinct differences between marine, freshwater, soil and loess carbonates. In addition it becomes clear that there is a number of carbonate soils within the loess of the mediterranean region with distinguishable isotopic compositions. The components affecting the relation of the isotopes in these loesses and the intercalated soils are discussed. The carbonate-turnover during the sedimentation of the loess with carbonate-precipitation from remnant solutions seems to be of some importance. The relatively small participation of biogenic CO₂ in the carbonate-turnover ist evident.