TY - JOUR A1 - Fischer, Tomáš A1 - Hrubcova, Pavla A1 - Dahm, Torsten A1 - Woith, Heiko A1 - Vylita, Tomáš A1 - Ohrnberger, Matthias A1 - Vlček, Josef A1 - Horalek, Josef A1 - Dedecek, Petr A1 - Zimmer, Martin A1 - Lipus, Martin P. A1 - Pierdominici, Simona A1 - Kallmeyer, Jens A1 - Krüger, Frank A1 - Hannemann, Katrin A1 - Korn, Michael A1 - Kaempf, Horst A1 - Reinsch, Thomas A1 - Klicpera, Jakub A1 - Vollmer, Daniel A1 - Daskalopoulou, Kyriaki T1 - ICDP drilling of the Eger Rift observatory BT - magmatic fluids driving the earthquake swarms and deep biosphere JF - Scientific drilling : reports on deep earth sampling and monitoring N2 - The new in situ geodynamic laboratory established in the framework of the ICDP Eger project aims to develop the most modern, comprehensive, multiparameter laboratory at depth for studying earthquake swarms, crustal fluid flow, mantle-derived CO2 and helium degassing, and processes of the deep biosphere. In order to reach a new level of high-frequency, near-source and multiparameter observation of earthquake swarms and related phenomena, such a laboratory comprises a set of shallow boreholes with high-frequency 3-D seismic arrays as well as modern continuous real-time fluid monitoring at depth and the study of the deep biosphere. This laboratory is located in the western part of the Eger Rift at the border of the Czech Republic and Germany (in the West Bohemia–Vogtland geodynamic region) and comprises a set of five boreholes around the seismoactive zone. To date, all monitoring boreholes have been drilled. This includes the seismic monitoring boreholes S1, S2 and S3 in the crystalline units north and east of the major Nový Kostel seismogenic zone, borehole F3 in the Hartoušov mofette field and borehole S4 in the newly discovered Bažina maar near Libá. Supplementary borehole P1 is being prepared in the Neualbenreuth maar for paleoclimate and biological research. At each of these sites, a borehole broadband seismometer will be installed, and sites S1, S2 and S3 will also host a 3-D seismic array composed of a vertical geophone chain and surface seismic array. Seismic instrumenting has been completed in the S1 borehole and is in preparation in the remaining four monitoring boreholes. The continuous fluid monitoring site of Hartoušov includes three boreholes, F1, F2 and F3, and a pilot monitoring phase is underway. The laboratory also enables one to analyze microbial activity at CO2 mofettes and maar structures in the context of changes in habitats. The drillings into the maar volcanoes contribute to a better understanding of the Quaternary paleoclimate and volcanic activity. Y1 - 2022 U6 - https://doi.org/10.5194/sd-31-31-2022 SN - 1816-8957 SN - 1816-3459 VL - 31 SP - 31 EP - 49 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Kieling, Katrin A1 - Rößler, Dirk A1 - Krüger, Frank T1 - Receiver function study in northern Sumatra and the Malaysian peninsula JF - Journal of seismology N2 - In this receiver function study, we investigate the structure of the crust beneath six seismic broadband stations close to the Sunda Arc formed by subduction of the Indo-Australian under the Sunda plate. We apply three different methods to analyse receiver functions at single stations. A recently developed algorithm determines absolute shear-wave velocities from observed frequency-dependent apparent incidence angles of P waves. Using waveform inversion of receiver functions and a modified Zhu and Kanamori algorithm, properties of discontinuities such as depth, velocity contrast, and sharpness are determined. The combination of the methods leads to robust results. The approach is validated by synthetic tests. Stations located on Malaysia show high-shear-wave velocities (V (S)) near the surface in the range of 3.4-3.6 km s (-aEuro parts per thousand 1) attributed to crystalline rocks and 3.6-4.0 km s (-aEuro parts per thousand 1) in the lower crust. Upper and lower crust are clearly separated, the Moho is found at normal depths of 30-34 km where it forms a sharp discontinuity at station KUM or a gradient at stations IPM and KOM. For stations close to the subduction zone (BSI, GSI and PSI) complexity within the crust is high. Near the surface low V (S) of 2.6-2.9 km s (-aEuro parts per thousand 1) indicate sediment layers. High V (S) of 4.2 km s (-aEuro parts per thousand 1) are found at depth greater than 6 and 2 km at BSI and PSI, respectively. There, the Moho is located at 37 and 40 km depth. At station GSI, situated closest to the trench, the subducting slab is imaged as a north-east dipping structure separated from the sediment layer by a 10 km wide gradient in V (S) between 10 and 20 km depth. Within the subducting slab V (S) a parts per thousand aEuro parts per thousand 4.7 km s (-aEuro parts per thousand 1). At station BSI, the subducting slab is found at depth between 90 and 110 km dipping 20A degrees +/- 8A degrees in approximately N 60A degrees E. A velocity increase in similar depth is indicated at station PSI, however no evidence for a dipping layer is found. KW - Receiver functions KW - Absolute shear-wave velocity KW - Sumatra KW - Subduction zone structure Y1 - 2011 U6 - https://doi.org/10.1007/s10950-010-9222-7 SN - 1383-4649 VL - 15 IS - 2 SP - 235 EP - 259 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Hannemann, Katrin A1 - Krüger, Frank A1 - Dahm, Torsten T1 - Measuring of clock drift rates and static time offsets of ocean bottom stations by means of ambient noise JF - Geophysical journal international N2 - Marine seismology usually relies on temporary deployments of stand alone seismic ocean bottom stations (OBS), which are initialized and synchronized on ship before deployment and re-synchronized and stopped on ship after recovery several months later. In between, the recorder clocks may drift and float at unknown rates. If the clock drifts are large or not linear and cannot be corrected for, seismological applications will be limited to methods not requiring precise common timing. Therefore, for example, array seismological methods, which need very accurate timing between individual stations, would not be applicable for such deployments. We use an OBS test-array of 12 stations and 75 km aperture, deployed for 10 months in the deep sea (4.5-5.5 km) of the mid-eastern Atlantic. The experiment was designed to analyse the potential of broad-band array seismology at the seafloor. After recovery, we identified some stations which either show unusual large clock drifts and/or static time offsets by having a large difference between the internal clock and the GPS-signal (skew). We test the approach of ambient noise cross-correlation to synchronize clocks of a deep water OBS array with km-scale interstation distances. We show that small drift rates and static time offsets can be resolved on vertical components with a standard technique. Larger clock drifts (several seconds per day) can only be accurately recovered if time windows of one input trace are shifted according to the expected drift between a station pair before the cross-correlation. We validate that the drifts extracted from the seismometer data are linear to first order. The same is valid for most of the hydrophones. Moreover, we were able to determine the clock drift at a station where no skew could be measured. Furthermore, we find that instable apparent drift rates at some hydrophones, which are uncorrelated to the seismometer drift recorded at the same digitizer, indicate a malfunction of the hydrophone. KW - Time-series analysis KW - Interferometry KW - Broad-band seismometers Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggt434 SN - 0956-540X SN - 1365-246X VL - 196 IS - 2 SP - 1034 EP - 1042 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hannemann, Katrin A1 - Krüger, Frank A1 - Dahm, Torsten A1 - Lange, Dietrich T1 - Oceanic lithospheric S-wave velocities from the analysis of P-wave polarization at the ocean floor JF - Geophysical journal international N2 - Our knowledge of the absolute S-wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S-wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P-wave polarization (apparent P-wave incidence angle) of teleseismic events to investigate the S-wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P-wave incidence angle at the ocean bottom dependent on the half-space S-wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBSs) to derive apparent S-wave velocity profiles. These profiles are dependent on the S-wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P-wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S-wave-velocity-depth models by a three-step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S-wave velocities. The apparent S-wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 and 0.9 km with S-wave velocities between 0.7 and 1.4 km s(-1). The estimated total crustal thickness varies between 4 and 10 km with S-wave velocities between 3.5 and 4.3 km s(-1). We find a slight increase of the total crustal thickness from similar to 5 to similar to 8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S-wave velocities decrease from values around 5.5 to 4.5 km s(-1) towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S-wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P-wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S-wave velocities for real and synthetic data to estimate S-wave velocity-depth models. KW - Time-series analysis KW - Body waves KW - Theoretical seismology KW - Oceanic transform and fracture zone processes Y1 - 2016 U6 - https://doi.org/10.1093/gji/ggw342 SN - 0956-540X SN - 1365-246X VL - 207 SP - 1796 EP - 1817 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hannemann, Katrin A1 - Krüger, Frank A1 - Dahm, Torsten A1 - Lange, Dietrich T1 - Structure of the oceanic lithosphere and upper mantle north of the Gloria Fault in the eastern mid-Atlantic by receiver function analysis JF - Journal of geophysical research : Solid earth N2 - Receiver functions (RF) have been used for several decades to study structures beneath seismic stations. Although most available stations are deployed on shore, the number of ocean bottom station (OBS) experiments has increased in recent years. Almost all OBSs have to deal with higher noise levels and a limited deployment time (approximate to 1year), resulting in a small number of usable records of teleseismic earthquakes. Here we use OBSs deployed as midaperture array in the deep ocean (4.5-5.5km water depth) of the eastern mid-Atlantic. We use evaluation criteria for OBS data and beamforming to enhance the quality of the RFs. Although some stations show reverberations caused by sedimentary cover, we are able to identify the Moho signal, indicating a normal thickness (5-8km) of oceanic crust. Observations at single stations with thin sediments (300-400m) indicate that a probable sharp lithosphere-asthenosphere boundary (LAB) might exist at a depth of approximate to 70-80km which is in line with LAB depth estimates for similar lithospheric ages in the Pacific. The mantle discontinuities at approximate to 410km and approximate to 660km are clearly identifiable. Their delay times are in agreement with PREM. Overall the usage of beam-formed earthquake recordings for OBS RF analysis is an excellent way to increase the signal quality and the number of usable events. KW - receiver function KW - oceanic lithosphere and mantle KW - ocean bottom seismology Y1 - 2017 U6 - https://doi.org/10.1002/2016JB013582 SN - 2169-9313 SN - 2169-9356 VL - 122 SP - 7927 EP - 7950 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Fischer, Tomas A1 - Hrubcova, Pavla A1 - Dahm, Torsten A1 - Woith, Heiko A1 - Vylita, Tomas A1 - Ohrnberger, Matthias A1 - Vlcek, Josef A1 - Horalek, Josef A1 - Dedecek, Petr A1 - Zimmer, Martin A1 - Lipus, Martin P. A1 - Pierdominici, Simona A1 - Kallmeyer, Jens A1 - Krüger, Frank A1 - Hannemann, Katrin A1 - Korn, Michael A1 - Kämpf, Horst A1 - Reinsch, Thomas A1 - Klicpera, Jakub A1 - Vollmer, Daniel A1 - Daskalopoulou, Kyriaki T1 - ICDP drilling of the Eger Rift observatory BT - magmatic fluids driving the earthquake swarms and deep biosphere JF - Scientific Drilling N2 - The new in situ geodynamic laboratory established in the framework of the ICDP Eger project aims to develop the most modern, comprehensive, multiparameter laboratory at depth for studying earthquake swarms, crustal fluid flow, mantle-derived CO2 and helium degassing, and processes of the deep biosphere. In order to reach a new level of high-frequency, near-source and multiparameter observation of earthquake swarms and related phenomena, such a laboratory comprises a set of shallow boreholes with high-frequency 3-D seismic arrays as well as modern continuous real-time fluid monitoring at depth and the study of the deep biosphere. This laboratory is located in the western part of the Eger Rift at the border of the Czech Republic and Germany (in the West Bohemia-Vogtland geodynamic region) and comprises a set of five boreholes around the seismoactive zone. To date, all monitoring boreholes have been drilled. This includes the seismic monitoring boreholes S1, S2 and S3 in the crystalline units north and east of the major Novy Kostel seismogenic zone, borehole F3 in the Hartousov mofette field and borehole S4 in the newly discovered Bazina maar near Liba. Supplementary borehole P1 is being prepared in the Neualbenreuth maar for paleoclimate and biological research. At each of these sites, a borehole broadband seismometer will be installed, and sites S1, S2 and S3 will also host a 3-D seismic array composed of a vertical geophone chain and surface seismic array. Seismic instrumenting has been completed in the S1 borehole and is in preparation in the remaining four monitoring boreholes. The continuous fluid monitoring site of Hartousov includes three boreholes, F1, F2 and F3, and a pilot monitoring phase is underway. The laboratory also enables one to analyze microbial activity at CO2 mofettes and maar structures in the context of changes in habitats. The drillings into the maar volcanoes contribute to a better understanding of the Quaternary paleoclimate and volcanic activity. Y1 - 2022 U6 - https://doi.org/10.5194/sd-31-31-2022 SN - 1816-8957 SN - 1816-3459 VL - 31 SP - 31 EP - 49 PB - Copernicus CY - Göttingen ER - TY - GEN A1 - Lipke, Katrin A1 - Krüger, Frank A1 - Rößler, Dirk T1 - Subduction zone structure along Sumatra from receiver functions N2 - Receiver functions are a good tool to investigate the seismotectonic structure beneath the a seismic station. In this study we apply the method to stations situated on or near Sumatra to find constraints on a more detailed velocity model which should improve earthquake localisation. We estimate shallow Moho-depths (~ 21 km) close to the trench and depths of ~30 km at greater distances. First evidences for the dip direction of the slab of ~60° are provided. Receiver functions were calculated for 20 stations for altogether 110 earthquakes in the distance range between 30° and 95° from the receiver. However the number of receiver functions per station is strongly variable as it depends on the installation date, the signal-to-noise-ratio of the station and the reliability of the acquisition. N2 - Receiver Funkttion stellen eine gut Methode zur Untersuchung von Seismotektonischen Strukturen unterhalb einer seismischen Station dar. In dieser Arbeit wenden wir die Methode auf Station auf oder nahe Sumatra an um Hinweise für ein detaillierteres Geschwindigkeitsmodell zu erhalten, welches die Lokalisierung von Erdbeben verbessern sollte. Wir ermitteln flache Moho-Tiefen (~21 km) in der Nähe des Trenchs und Tiefen um die 30 km in größeren Distanzen. Erste Hinweise für eine Einfallsrichtung des Slabs von ~60° konnten gefunden werden. Receiver Funktionen wurden für 20 Stationen für insgesamt 110 Erdbeben im Distanzbereich zwischen 30° und 95° berechnet. allerdings ist die Anzahl von Receiver Funktionen pro Station sehr variabel, da sie vom Installationszeitpunkt, dem Signal-Rausch-Verhältnis und der Zuverlässigkeit der Datenaufnahme an der Station abhängt. KW - Receiver Funktionen KW - Sumatra KW - Seismologie KW - Subduktion KW - Receiver Functions KW - Sumatra KW - Seismology KW - Subduction Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18260 ER - TY - JOUR A1 - Lipke, Katrin A1 - Zitzmann, Max A1 - Amberger, Manuel A1 - Ehlert, Carsten A1 - Rößler, Dirk A1 - Krüger, Frank A1 - Ohrnberger, Matthias T1 - Traveltime residuals at regional and teleseismic distances for SE-Asia N2 - Traveltime residuals for worldwide seismic stations are calculated. We use P and S waves from earthquakes in SE-Asia at teleseismic and regional distances. The obtained station residuals help to enhance earthquake localisation. Furthermore we calculated regional source dependent station residuals. They show a systematic dependence of the locality of the source. These source dependent residuals reflect heterogenities along the path and can be used for a refinement of earthquake localisation. N2 - Laufzeitresiduen für weltweite seismische Stationen werden berechnet. Wir nutzen P - und S-Wellen von Erdbeben in Südostasien in teleseismischen und regionalen Distanzen. Die so erhaltenen Stationsresiduen helfen, die Lokaliesierung von Erdbeben zu verbessern. Außerdem berechnen wir regional quellabhängige Stationsresiduen. Diese zeigen eine systematische Abhänbgigkeit vom Ort der Quelle. Sie spiegeln Heterogenitäten entlang des Strahlweges wieder und können für eine Verfeinerung der Ersbebenlokaliesierung genutzt werden. KW - Seismologie KW - Südostasien KW - Laufzeitresiduen KW - GITEWS KW - Wellengeschwindigkeiten KW - seismology KW - Southeast Asia KW - traveltime KW - residuals KW - GITEWS Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14117 ER - TY - JOUR A1 - Krüger, Frank A1 - Dahm, Torsten A1 - Hannemann, Katrin T1 - Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array JF - Geophysical journal international N2 - A mid-aperture broad-band test array (OBS array DOCTAR) was deployed from June 2011 to April 2012 about 100 km north of the Gloria fault in the Eastern North Atlantic in about 5000 m water depth. In addition arrays were installed on Madeira Island and in western Portugal mainland. For the first time in the Eastern North Atlantic, we recorded a large number of high frequency Po and So waves from local and regional small and moderate earthquakes (M-L < 4). An incoherent beamforming method was adapted to scan continuous data for such Po and So arrivals applying a sliding window waveform migration and frequency-wavenumber technique. We identify about 320 Po and 1550 So arrivals and compare the phase onsets with the ISC catalogue (ISC 2015) for the same time span. Up to a distance of 6 degrees to the DOCTAR stations all events listed in the ISC catalogue could be associated to Po and So phases. Arrivals from events in more than 10 degrees distance could be identified only in some cases. Only few Po and/or So arrivals were detected for earthquakes from the European and African continental area, the continental shelf regions and for earthquakes within or northwest of the Azores plateau. Unexpectedly, earthquake clusters are detected within the oceanic plates north and south of the Gloria fault and far from plate boundaries, indicating active intraplate structures. We also observe and locate numerous small magnitude earthquakes on the segment of the Gloria fault directly south of DOCTAR, which likely coincides with the rupture of the 25 November 1941 event. Local small magnitude earthquakes located beneath DOCTAR show hypocentres up to 30 km depth and strike-slip focal mechanisms. A comparison with detections at temporary mid-aperture arrays on Madeira and in western Portugal shows that the deep ocean array performs much better than the island and the continental array regarding the detection threshold for events in the oceanic plates. We conclude that sparsely distributed mid-aperture seismic arrays in the deep ocean could decrease the detection and location threshold for seismicity with M-L < 4 in the oceanic plate and might constitute a valuable tool to monitor oceanic plate seismicity. KW - body waves KW - earthquake source observations KW - seismicity and tectonics Y1 - 2020 U6 - https://doi.org/10.1093/gji/ggaa054 SN - 0956-540X SN - 1365-246X VL - 221 IS - 2 SP - 1055 EP - 1080 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Jeltsch, Florian A1 - Blaum, Niels A1 - Brose, Ulrich A1 - Chipperfield, Joseph D. A1 - Clough, Yann A1 - Farwig, Nina A1 - Geissler, Katja A1 - Graham, Catherine H. A1 - Grimm, Volker A1 - Hickler, Thomas A1 - Huth, Andreas A1 - May, Felix A1 - Meyer, Katrin M. A1 - Pagel, Jörn A1 - Reineking, Björn A1 - Rillig, Matthias C. A1 - Shea, Katriona A1 - Schurr, Frank Martin A1 - Schroeder, Boris A1 - Tielbörger, Katja A1 - Weiss, Lina A1 - Wiegand, Kerstin A1 - Wiegand, Thorsten A1 - Wirth, Christian A1 - Zurell, Damaris T1 - How can we bring together empiricists and modellers in functional biodiversity research? JF - Basic and applied ecology : Journal of the Gesellschaft für Ökologie N2 - Improving our understanding of biodiversity and ecosystem functioning and our capacity to inform ecosystem management requires an integrated framework for functional biodiversity research (FBR). However, adequate integration among empirical approaches (monitoring and experimental) and modelling has rarely been achieved in FBR. We offer an appraisal of the issues involved and chart a course towards enhanced integration. A major element of this path is the joint orientation towards the continuous refinement of a theoretical framework for FBR that links theory testing and generalization with applied research oriented towards the conservation of biodiversity and ecosystem functioning. We further emphasize existing decision-making frameworks as suitable instruments to practically merge these different aims of FBR and bring them into application. This integrated framework requires joint research planning, and should improve communication and stimulate collaboration between modellers and empiricists, thereby overcoming existing reservations and prejudices. The implementation of this integrative research agenda for FBR requires an adaptation in most national and international funding schemes in order to accommodate such joint teams and their more complex structures and data needs. KW - Biodiversity theory KW - Biodiversity experiments KW - Conservation management KW - Decision-making KW - Ecosystem functions and services KW - Forecasting KW - Functional traits KW - Global change KW - Monitoring programmes KW - Interdisciplinarity Y1 - 2013 U6 - https://doi.org/10.1016/j.baae.2013.01.001 SN - 1439-1791 VL - 14 IS - 2 SP - 93 EP - 101 PB - Elsevier CY - Jena ER -