Receiver function study of the Hellenic subduction zone: imaging crustal thickness variations and the oceanic Moho of the descending African lithosphere

We use data from recently installed broad-band seismographs on the islands of Crete, Gavdos, Santorini, Naxos and Samos in the Hellenic subduction zone to construct receiver function images of the crust and upper mantle from south of Crete into the Aegean Sea. The stations are equipped with STS-2 seismometers and they are operated by GFZ Potsdam, University of Chania and ETH Zürich. Teleseismic earthquakes recorded by these stations at epicentral distances between 35° and 95° have been used to calculate receiver functions. The receiver function method is a routinely used tool to detect crustal and upper-mantle discontinuities beneath a seismic station by isolating the P-S converted waves from the coda of the P wave. Converted P-S energy from the oceanic Moho of the subducted African Plate is clearly observed beneath Gavdos and Crete at a depth ranging from 44 to 69 km. This boundary continues to the north to nearly 100 km depth beneath Santorini island. Because of a lack of data the correlation of this phase is uncertain north of Santorini beneath the Aegean Sea. Moho depths were calculated from primary converted waves and multiply reflected waves between the Moho and the Earth's surface. Beneath southern and eastern Crete the Moho lies between 31 and 34 km depth. Beneath western and northern Crete the Moho is located at 32 and 39 km depth, respectively, and behaves as a reversed crust-mantle velocity contrast, possibly caused by hydration and serpentinization of the forearc mantle peridotite. The Moho beneath Gavdos island located south of Crete in the Libyan Sea is at 26 km depth, indicating that the crust south of the Crete microcontinent is also thinning towards the Mediterranean ridge. This makes it unlikely that part of the crust in Crete consists of accreted sediments transported there during the present-day subduction process which began approximately 15 Ma because the backstop, i.e. the boundary between the current accretionary wedge of the Mediterranean ridge and the Crete microcontinent, is located approximately 100 km south of Gavdos. A seismic boundary at 32 km depth beneath Santorini island probably marks the crustal base of the Crete microcontinent. A shallower seismic interface beneath Santorini at 20-25 km depth may mark the depth of the detachment between the Crete microcontinent and the overlying Aegean subplate. The Moho in the central and northern Aegean, at Naxos and Samos, is observed at 25 and 28 km depth, respectively. Assuming a stretching factor of 1.2-1.3, crustal thickness in the Aegean was 30-35 km at the inception of the extensional regime in the Middle Miocen

Lithospheric structure of the Aegean obtained from P and S receiver functions

Combined P and S receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the Aegean region are used to map the geometry of the subducted African and the overriding Aegean plates. We image the Moho of the subducting African plate at depths ranging from 40 km beneath southern Crete and the western Peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern Greece. However, the dip of the Moho of the subducting African plate is shallower beneath the Peloponnesus than beneath Crete and Rhodes and flattens out beneath the northern Aegean. Observed P-to-S conversions at stations located in the forearc indicate a reversed velocity contrast at the Moho boundary of the Aegean plate, whereas this boundary is observed as a normal velocity contrast by the S-to-P conversions. Our modeling suggests that the presence of a large amount of serpentinite (more than 30%) in the forearc mantle wedge, which generally occurs in the subduction zones, may be the reason for the reverse sign of the P-to-S conversion coefficient. Moho depths for the Aegean plate show that the southern part of the Aegean (crustal thickness of 20–22 km) has been strongly influenced by extension, while the northern Aegean Sea, which at present undergoes the highest crustal deformation, shows a relatively thicker crust (25–28 km). This may imply a recent initiation of the present kinematics in the Aegean. Western Greece (crustal thickness of 32–40 km) is unaffected by the recent extension but underwent crustal thickening during the Hellenides Mountains building event. The depths of the Aegean Moho beneath the margin of the Peloponnesus and Crete (25–28 and 25–33 km, respectively) show that these areas are also likely to be affected by the Aegean extension, even though the Cyclades (crustal thickness of 26–30 km) were not significantly involved in this episode. The Aegean lithosphere-asthenosphere boundary (LAB) mapped with S receiver functions is about 150 km deep beneath mainland Greece, whereas the LAB of the subducted African plate dips from 100 km beneath Crete and the southern Aegean Sea to about 225 km under the volcanic arc. This implies a thickness of 60–65 km for the subducted African lithosphere, suggesting that the Aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the Cyclades

Observations of rapid-fire event tremor at Lascar volcano, Chile

During the Proyecto de Investigaciòn Sismològica de la Cordillera Occidental (PISCO '94) in the Atacama desert of Northern Chile, a continuously recording broadband seismic station was installed to the NW of the currently active volcano, Lascar. For the month of April, 1994, an additional network of three, short period, three-component stations was deployed around the volcano to help discriminate its seismic signals from other local seismicity. During the deployment, the volcanic activity at Lascar appeared to be limited mainly to the emission of steam and SO2. Tremor from Lascar is a random, «rapid-fire» series of events with a wide range of amplitudes and a quasi-fractal structure. The tremor is generated by an ensemble of independent elementary sources clustered in the volcanic edifice. In the short-term, the excitation of the sources fluctuates strongly, while the long-term power spectrum is very stationary

Observations of rapid-fire event tremor at Lascar volcano, Chile

During the Proyecto de Investigaciòn Sismològica de la Cordillera Occidental (PISCO '94) in the Atacama desert of Northern Chile, a continuously recording broadband seismic station was installed to the NW of the currently active volcano, Lascar. For the month of April, 1994, an additional network of three, short period, three-component stations was deployed around the volcano to help discriminate its seismic signals from other local seismicity. During the deployment, the volcanic activity at Lascar appeared to be limited mainly to the emission of steam and SO2. Tremor from Lascar is a random, «rapid-fire» series of events with a wide range of amplitudes and a quasi-fractal structure. The tremor is generated by an ensemble of independent elementary sources clustered in the volcanic edifice. In the short-term, the excitation of the sources fluctuates strongly, while the long-term power spectrum is very stationary

Observations of rapid-fire event tremor at Lascar volcano, Chile

During the Proyecto de Investigaciòn Sismològica de la Cordillera Occidental (PISCO '94) in the Atacama desert of Northern Chile, a continuously recording broadband seismic station was installed to the NW of the currently active volcano, Lascar. For the month of April, 1994, an additional network of three, short period, three-component stations was deployed around the volcano to help discriminate its seismic signals from other local seismicity. During the deployment, the volcanic activity at Lascar appeared to be limited mainly to the emission of steam and SO2. Tremor from Lascar is a random, «rapid-fire» series of events with a wide range of amplitudes and a quasi-fractal structure. The tremor is generated by an ensemble of independent elementary sources clustered in the volcanic edifice. In the short-term, the excitation of the sources fluctuates strongly, while the long-term power spectrum is very stationary

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts

La sismicité naturelle a été observée au cours des mois d'août à octobre 1995 dans la région située au nord d'Antofagasta. Le réseau consiste en 35 stations à terre et en 9 OBS à proximité de la côte. La sismicité qui a suivi le grand tremblement de terre d'Antofagasta est extrêmement forte. Un catalogue contenant 4500 évènements enregistrés sur CD-ROM et les temps de propagation seront utilisés pour une étude de tomographie locale détaillée. (Résumé d'auteur

The transition of cancer patients from acute care to rehabilitation: results of the OPTIREHA study

Introduction: Multiple symptoms and functional restrictions might impair workability and participation. Rehabilitation for cancer patients aims to achieve improvement of reintegration, participation and quality of life. Studies show insufficient cooperation and flow of information regarding patients' individual condition and needs between primary care and rehabilitation. Method: The study aimed to develop and pilot-test a modular assessment tool based on standard nursing assessments and ICF criteria in order to optimize patient transition between acute care and rehabilitation. The qualitative dominant mixed methods study was carried out comprising 4 phases: 1st semi-structured survey of heads of German rehabilitation clinics (n=138), 2nd analysis of exemplary patient records and structured survey of health care professionals (HCP) with respect to care transition, 3rd development and consent (Delphi-survey) of optimization measures and 4th pilot-testing of developed material in order to obtain first results regarding feasibility and acceptance.Results: The first study phase indicated insufficient assessment, documentation and communication of functional impairments and partly insufficient patient information. Standardized patient-information and an assessment tool based on nurse routine documentation and ICF criteria were developed. The pilot-testing showed reasonable time frames for completing the OPTIREHA-Assessment. Rehabilitation experts valued the information summarized in the OPTIREHA-Assessment.Conclusion: First results indicate feasibility and possible benefit of the OPTIREHA-Assessment. Additional studies are needed to investigate further clinical benefit.Einleitung: Die Belastung onkologischer Patienten durch multiple Symptome und Funktionseinschränkungen als Folge der Erkrankung oder Therapie kann zu psychosozialen Folgen, Einschränkungen der Lebensqualität und der Teilhabe am gesellschaftlichen und beruflichen Leben führen. Ziele der onkologischen Rehabilitation bestehen in einer weitgehenden Reduktion dieser Beeinträchtigungen sowie einer Reintegration. Die Rehabilitation stellt daher ein wichtiges Element im Nachsorgeprozess dar. Aktuelle Studien und Gutachten zeigen jedoch eine mangelnde Vernetzung und Schnittstellenprobleme v.a. hinsichtlich der Gesundheitsinformation zwischen ambulanter und stationärer Akutbehandlung und Rehabilitation.Methoden: Das Ziel der Studie war die Entwicklung und Pilotierung eines modularen an der ICF orientierten Assessments auf Grundlage der bestehenden pflegerischen Routinedokumentation zur Optimierung der Überleitung onkologischer Patienten in die Anschlussrehabilitation. Das Assessment soll strukturierte Informationen für die behandelnden Ärzte, das Pflegepersonal und den Sozialdienst für eine gezielte Reha-Antragstellung und Überleitung zur Verfügung stellen und als Basis zur Verbesserung eines klinikübergreifenden Informationsaustausches zwischen Akutkrankenhaus und Rehabilitationseinrichtung dienen. Es wurde ein qualitativ dominanter Mixed-Methods-Ansatz gewählt. 1) Teilstrukturierte Querschnittsbefragung (n=138) leitender Ärzte deutscher Rehabilitationskliniken mit onkologischem Schwerpunkt, 2) Stichprobenartige Analyse relevanter Akten (n=12) an 2 Zentren bezüglich Erfassung und Weiterleitung Reha-relevanter Informationen, 3) Erarbeitung und Konsentierung (Delphi-Verfahren) von Optimierungsvorschlägen und 4) Pilot-Testung der entwickelten Materialien an 4 Zentren, um erste Ergebnisse bezüglich Anwendbarkeit, Akzeptanz und potentiellem Nutzen zu erhalten. Ergebnisse: Der erste Studienabschnitt ergab Hinweise auf eine teilweise ungenügende Erfassung und Weiterleitung Reha-relevanter Patienteninformationen sowie ungenügende Information der Patienten zu Inhalten und Zielen der Rehabilitation. Die Aktenanalyse ergab Anhaltspunkte für Optimierungsvorschläge, die im dritten Abschnitt in der Entwicklung einer patientengerechten Informationsbroschüre sowie eines Überleitungsbogens zur poststationären Behandlung (OPTIREHA ASSESSMENT) resultierten. Letzterer soll die systematische Erfassung des Reha-Bedarfs sowie die Weiterleitung Reha-relevanter Befunde unterstützen. Die Pilottestung der entwickelten Materialien an 4 Zentren ergab positive Rückmeldungen hinsichtlich Anwendbarkeit und potentiellem Nutzen.Fazit: Die Ergebnisse deuten auf gute Anwendbarkeit und potentiellen klinischen Nutzen des Überleitungsbogens zur poststationären Versorgung hin. Weitere Studien sollten durchgeführt werden, um den klinischen Nutzen zu prüfen und die Optionen für einen standardisierten Einsatz zu klären

The lithosphere–asthenosphere boundary in the North-West Atlantic region

A detailed knowledge of the thickness of the lithosphere in the north Atlantic is an important parameter for understanding plate tectonics in that region. We achieve this goal with as yet unprecedented detail using the seismic technique of S-receiver functions. Clear positive signals from the crust–mantle boundary and negative signals from a mantle discontinuity beneath Greenland, Iceland and Jan Mayen are observed. According to seismological practice, we call the negative phase the lithosphere–asthenosphere boundary (LAB). The seismic lithosphere under most of the Iceland and large parts of central Greenland is about 80 km thick. This depth in Iceland is in disagreement with estimates of the thickness of the elastic lithosphere (10–20 km) found from postglacial rebound data. In the region of flood basalts in eastern Greenland, which overlies the proposed Iceland plume track, the lithosphere is only 70 km thick, about 10 km less than in Iceland which is located directly above the proposed plume. At the western Greenland coast, the lithosphere thickens to 100–120 km, with no indication of the Iceland plume track identified. Below Jan Mayen the lithospheric thickness varies between 40 and 60 km