ALBERT

Description: Cruise M160 is part of concerted MOSES/REEBUS Eddy Study featuring three major research expeditions (M156, M160, MSM104). It aims to develop both a qualitative and quantitative understanding of the role of physical-chemical-biological coupling in eddies for the biological pump. The study is part of the MOSES “Ocean Eddies” event chain, which follows three major hypotheses to be addressed by the MOSES/REEBUS field campaigns: (1) Mesoscale and sub-mesoscale eddies play an important role in transferring energy along the energy cascade from the large-scale circulation to dissipation at the molecular level. (2) Mesoscale and sub-mesoscale eddies are important drivers in determining onset, magnitude and characteristics of biological productivity in the ocean and contribute significantly to global primary production and particle export and transfer to the deep ocean. (3) Mesoscale and sub-mesoscale eddies are important for shaping extreme biogeochemical environments (e.g., pH, oxygen) in the oceans, thus acting as a source/sink function for greenhouse gases. In contrast to the other two legs, MOSES Eddy Study II during M160 did not include any benthic work but focused entirely on the pelagic dynamics within eddies. It accomplished a multi-disciplinary, multi-parameter and multi-platform study of two discrete cyclonic eddies in an unprecedented complexity. The pre-cruise search for discrete eddies suitable for detailed study during M160 had already started a few months prior to the cruise. Remote sensing data products (sea surface height, sea surface temperature, ocean color/chlorophyll a) were used in combination with eddy detection algorithms and numerical modelling to identify and track eddies in the entire eddy field off West Africa. In addition, 2 gliders and 1 waveglider had been set out from Mindelo/Cabo Verde for pre-cruise mapping of the potential working area north of the Cabo Verdean archipelago. At the start of M160, a few suitable eddies – mostly of cyclonic type – had been identified, some of which were outside the safe operation range of the motorglider plane. As technical problems delayed the flight operations, the first eddy (center at 14.5°N/25°W) for detailed study was chosen to the southwest of the island of Fogo. It was decided to carry out a first hydrographic survey there followed by the deployment of a suite of instruments (gliders, waveglider, floats, drifter short-term mooring). Such instrumented, we left this first eddy and transited – via a strong anticyclonic feature southwest of the island of Santiago – to the region northeast of the island of Sal, i.e. in the working range of the glider plane. During the transit, a full suite of underway measurements as well as CTD/RO section along 22°W (16°-18.5°N) were carried in search for sub-surface expressions of anticyclonic eddy features. In the northeast, we had identified the second strong cyclonic eddy (center at 18°N/22.5°W) which was chosen for detailed study starting with a complete hydrographic survey (ADCP, CTD/RO, other routine station work). After completion of the mesoscale work program, we identified a strong frontal region at the southwestern rim of the cyclonic eddy, which was chosen for the first sub-mesoscale study with aerial observation component. There, the first dye release experiment was carried out which consisted of the dye release itself followed by an intense multi-platforms study of the vertical and horizontal spreading of the initial dye streak. This work was METEOR-Berichte, Cruise M160, Mindelo – Mindelo, 23.11.2019 4 – 20.12.2019 supported and partly guided by aerial observation of the research motorglider Stemme, which was still somewhat compromised by technical issues and meteorological conditions (high cloud cover, Saharan dust event). Nevertheless, this first dye release experiment was successful and showed rapid movement of the dynamic meandering front. After completion of work on this second eddy and execution of a focused sampling program at the Cape Verde Ocean Observation, RV METEOR returned to the first eddy for continuation of the work started there in the beginning of the cruise. This was accompanied by a relocation of the airbase of Stemme from the international airport of Sal to the domestic airport of Fogo. The further execution of the eddy study at this first eddy, which again included a complete hydrographic survey followed by a mesoscale eddy study with dye release, was therefore possible with aerial observations providing important guidance for work on RV METEOR. Overall, M160 accomplished an extremely intense and complex work program with 212 instrument deployments during station work, 137 h of observation with towed instruments and a wide range of underway measurements throughout the cruise. Up to about 30 individually tracked platforms (Seadrones, glider, wavegliders, drifters, floats) were in the water at the same time providing unprecedented and orchestrated observation capabilities in an eddy. All planned work components were achieved and all working groups acquired the expected numbers of instrument deployments and sampling opportunities.

Description: Zur Bestimmung des Weges und der Fortpflanzungsgeschwindigkeit der Erdbebenwellen im Erdinneren lassen sich zwei Methoden anwenden. Entweder wird unter Zugrundelegung von Annahmen über Wellengeschwindigkeiten innerhalb einzelner Erdschichten versucht, gegebene Laufzeitkurven zu approximieren, oder man schließt aus den Laufzeitkurven direkt auf den Weg der Erdbebenwellen im Erdinnern. Gerade die zweite direkte Methode zur Strahlberechnung, die Herglotz-Wiechertsche Methode, die sich auf die Theorie der Abelschen Integralgleichung stützt, hat außerordentlich viel Verwendung gefunden. Jedoch ergaben die neuesten Erfahrungen, dass in manchen Fällen das zuerst von E. Wiechert angegebene Näherungsverfahren vorzuziehen ist…Aus dieser Erwägung heraus erhebt sich jetzt die Frage nach dem Aufbau der Erdrinde. Welche von den Ergebnissen sind für Untersuchungen des Verlaufes der Erdbebenwellen bei Fernbeben zu berücksichtigen. In den Bearbeitungen des Materials der Oppau-Katastrophe treten bei 0. Hecker und De Quervain nicht unerhebliche Abweichungen auf. Es wird daher eine neue Berechnung der Stationsentfernungen durchgeführt und die Laufzeitkurve neu bestimmt (v= 5,66 km/sec).

Description: research

Description: DFG, SUB Göttingen

Description: Am Donnerstag den 28. Januar 1926 um 5 Uhr 58 Min. MEZ nachmittags erschütterte ein Erdbeben mäßiger Stärke den östlichen Teil des Thüringer Beckens, die sogenannte Saaleplatte zwischen Saale und Elster; am kräftigsten wirkte es in Stadtroda. Seismometrisch registriert wurde es zu Jena (Epizentralentfernung ∆ = 13 km), Plauen (∆ = 50 km), Leipzig (∆ = 73 km) und Göttingen (∆ = 146 km), am zuletzt genannten Orte allerdings nur noch mit dem zweitausendfach vergrößernden Siebzehntonnenpendel von WIECHERT. Trotz der Unbedeutendheit dieses Bebens erschien seine Untersuchung geboten, um so mehr als Erdbeben thüringischen Ursprunges zu den Seltenheiten gehören.

Description: research

Description: DFG, SUB Göttingen

Description: We develop empirical relationships between the surface wave magnitude MS and macroseismic data, i.e. the epicentral intensity I0, isoseismal radii R(I) of different intensities I and the focal depth h. The basis of this study is formed by carefully selected instrumental parts (since 1900) of 2 earthquake catalogues: Kárník 1996 (Europe and the Mediterranean), and Shebalin et al. 1998 (Central and Eastern Europe). We use the orthogonal regression because we presume that all parameters are in error and because it has the advantage to provide a reversible regression equation. From Shebalin et al.1998 catalogue we obtain MS = 0.65 I0 + 1.90 log(h) – 1.62 with equivalent error δMS = ±0.21. In order to establish a relationship between MS and isoseismal radii we apply a theoretically based model which takes into account both exponential decay and geometrical spreading. From Shebalin et al. 1998catalogue we find MS = 0.673 I + 2.44 log (S(I)) + 0.00163 S(I) – 2.48 with δMS = ±0.28. Here I is the macroseismic intensity (I = 3…9) of the isoseismal in the focal distance S(I) [km]. Kárník 1996 gives isoseismal radii for I = 3 and 5. We obtain: MS = 0.808 I + 2.84 log (S(I)) + 0.00190 S(I) – 3.71 with δMS = ±0.65. These equations make possible reliably estimates of MS . We recommend them for application. The use of high quality data only as input in the regression analysis provides reliable relationships to estimate magnitudes. The magnitude estimation of a historical earthquake from the epicentral intensity gives reliable results only if the focal depth is known well enough. The relationship using isoseismal radii is of greater practical importance as it allows more reliable magnitude estimations of historical earthquakes. We observe regional variations in the relationships which need further investigation.

Description: poster

Description: Die vorliegende Bearbeitung fasst die instrumentellen Aufzeichnungen zum Erdbeben vom 26. Juni 1926 zusammen. Dazu wurden von den seismischen Stationen die Originalkurven (O) oder Kopien (K) erbeten. Wo diese nicht zur Verfügung standen, wurden die Berichte (S. B.) und auch die Angaben im International Summary (I. S.) verwertet. In der folgenden Tabelle wurden die Stationen nach Herdentfernungen geordnet. Hinzugefügt wurden Angaben über die Instrumente und deren Konstanten, um einen Vergleich zwischen den einzelnen Registrierungen zu ermöglichen. Fehlten im Bericht die Konstanten, wurden mittlere Daten mitgeteilt, wie sie aus der Aufstellung im „Bulletin of the National Research Council Nr. 82“ hervorgehen. In den in 24 Tafeln zusammengestellten Wiedergaben der Seismogramme sind nach Möglichkeit die Stationen nach Herdentfernungen geordnet. Als Arbeitsmaterial enthalten die Kurven nur Angaben über die Zeiten, zur Erleichterung meist von 2 zu 2 Minuten hinzugesetzt, über die Richtung der Bodenbewegung, sowie in manchen Fällen auch über die einzelnen Instrumente. Es ist dann möglich, unabhängig von dieser Bearbeitung das Kurvenmaterial anderweitig zu verwerten. Andererseits aber erlaubt die genaue Zeiteinteilung bei den Kurven die im Teil I enthaltenen Auswertungen sehr bequem zu vergleichen.

Description: report

Description: DFG, SUB Göttingen