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  • 1
    Online Resource
    Online Resource
    Rotation, Strain, and Translation Sensors Performance Tests with Active Seismic Sources
    MDPI AG ; 2021
    In:  Sensors Vol. 21, No. 1 ( 2021-01-03), p. 264-
    Details
    In: Sensors, MDPI AG, Vol. 21, No. 1 ( 2021-01-03), p. 264-
    Abstract: Interest in measuring displacement gradients, such as rotation and strain, is growing in many areas of geophysical research. This results in an urgent demand for reliable and field-deployable instruments measuring these quantities. In order to further establish a high-quality standard for rotation and strain measurements in seismology, we organized a comparative sensor test experiment that took place in November 2019 at the Geophysical Observatory of the Ludwig-Maximilians University Munich in Fürstenfeldbruck, Germany. More than 24 different sensors, including three-component and single-component broadband rotational seismometers, six-component strong-motion sensors and Rotaphone systems, as well as the large ring laser gyroscopes ROMY and a Distributed Acoustic Sensing system, were involved in addition to 14 classical broadband seismometers and a 160 channel, 4.5 Hz geophone chain. The experiment consisted of two parts: during the first part, the sensors were co-located in a huddle test recording self-noise and signals from small, nearby explosions. In a second part, the sensors were distributed into the field in various array configurations recording seismic signals that were generated by small amounts of explosive and a Vibroseis truck. This paper presents details on the experimental setup and a first sensor performance comparison focusing on sensor self-noise, signal-to-noise ratios, and waveform similarities for the rotation rate sensors. Most of the sensors show a high level of coherency and waveform similarity within a narrow frequency range between 10 Hz and 20 Hz for recordings from a nearby explosion signal. Sensor as well as experiment design are critically accessed revealing the great need for reliable reference sensors.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s21010264
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2052857-7
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  • 2
    Online Resource
    Online Resource
    Creating an Online Video Course for Computational Wave Propagation
    Seismological Society of America (SSA) ; 2019
    In:  Seismological Research Letters ( 2019-07-24)
    Details
    In: Seismological Research Letters, Seismological Society of America (SSA), ( 2019-07-24)
    Abstract: Teaching and training using online video material in science is on the rise. Science students entering universities today are of a “YouTube generation,” most likely already having a history of accessing educational videos for learning at school. Here, we report on our experiences with preparing a Massive Open Online Course (MOOC) for the COURSERA platform in the area of computational wave propagation. We describe the complexity of the process but also highlight the opportunities that this form of training offers on state‐of‐the‐art e‐learning platforms. It is foreseeable that in the future universities will promote combinations of direct and supervised online course learning, allowing for more flexibility and variability of training content. We propose that Earth‐Science‐specific databases with links to online courses should be developed, making such courses more accessible to the research community.
    Type of Medium: Online Resource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220190054
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2019
    detail.hit.zdb_id: 2403376-5
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    Die Erdrotationsachse in einem Netz aus Licht : Geophysik
    Wiley ; 2020
    In:  Physik in unserer Zeit Vol. 51, No. 6 ( 2020-11), p. 269-270
    Details
    In: Physik in unserer Zeit, Wiley, Vol. 51, No. 6 ( 2020-11), p. 269-270
    Abstract: Die Rotation der Erde unterliegt vielfachen Einflüssen und ist deshalb keineswegs konstant. Die absolute Rotationsrate im Raum mit extremer Empfindlichkeit zu messen, stellt eine große Herausforderung dar. Geowissenschaftlern der TU und LMU München ist es kürzlich gelungen, in einem unterirdischen Labor in der Nähe von München mit einem vierkomponentigen, tetraedrischen Laserkreiselarray, das so groß wie ein fünfstöckiges Gebäude ist, den vollen Erdrotationsvektor mit einer Auflösung von unter einer Bogensekunde über einen Zeitraum von mehr als sechs Wochen zu messen.
    Type of Medium: Online Resource
    ISSN: 0031-9252 , 1521-3943
    URL: Issue
    URL: Article
    DOI: 10.1002/piuz.v51.6
    DOI: 10.1002/piuz.202070607
    RVK:
    UA 1000 ; UA 6520
    Language: German
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 208871-X
    detail.hit.zdb_id: 2006647-8
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  • 4
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    Online Resource
    Frequency-dependent effects on travel times and waveforms of long-period S and SS waves
    Elsevier BV ; 1997
    In:  Physics of the Earth and Planetary Interiors Vol. 104, No. 1-3 ( 1997-11), p. 229-246
    Details
    In: Physics of the Earth and Planetary Interiors, Elsevier BV, Vol. 104, No. 1-3 ( 1997-11), p. 229-246
    Type of Medium: Online Resource
    ISSN: 0031-9201
    URL: Article
    DOI: 10.1016/S0031-9201(97)00051-4
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1997
    detail.hit.zdb_id: 3901-9
    detail.hit.zdb_id: 1500666-9
    SSG: 16,13
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  • 5
    Online Resource
    Online Resource
    Frequency dependence of magnetic susceptibility as a proxy for fine-grained iron minerals and aggregate stability of south Chilean volcanic ash soils
    Elsevier BV ; 2017
    In:  CATENA Vol. 158 ( 2017-11), p. 46-54
    Details
    In: CATENA, Elsevier BV, Vol. 158 ( 2017-11), p. 46-54
    Type of Medium: Online Resource
    ISSN: 0341-8162
    URL: Article
    DOI: 10.1016/j.catena.2017.06.013
    RVK:
    RA 1595
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2017
    detail.hit.zdb_id: 1492500-X
    detail.hit.zdb_id: 519608-5
    SSG: 13
    SSG: 14
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  • 6
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    A COMPARATIVE STUDY OF EXPLICIT DIFFERENTIAL OPERATORS ON ARBITRARY GRIDS
    World Scientific Pub Co Pte Ltd ; 2001
    In:  Journal of Computational Acoustics Vol. 09, No. 03 ( 2001-09), p. 1111-1125
    Details
    In: Journal of Computational Acoustics, World Scientific Pub Co Pte Ltd, Vol. 09, No. 03 ( 2001-09), p. 1111-1125
    Abstract: We compare explicit differential operators for unstructured grids and their accuracy with the aim of solving time-dependent partial differential equations in geophysical applications. As many problems suggest the use of staggered grids we investigate different schemes for the calculation of space derivatives on two separate grids. The differential operators are explicit and local in the sense that they use only information of the function in their nearest neighborhood, so that no matrix inversion is necessary. This makes this approach well-suited for parallelization. Differential weights are obtained either with the finite-volume method or using natural neighbor coordinates. Unstructured grids have advantages concerning the simulation of complex geometries and boundaries. Our results show that while in general triangular (hexagonal) grids perform worse than standard finite-difference approaches, the effects of grid irregularities on the accuracy of the space derivatives are comparably small for realistic grids. This suggests that such a finite-difference-like approach to unstructured grids may be an alternative to other irregular grid methods such as the finite-element technique.
    Type of Medium: Online Resource
    ISSN: 0218-396X , 1793-6489
    URL: Article
    DOI: 10.1142/S0218396X01000838
    Language: English
    Publisher: World Scientific Pub Co Pte Ltd
    Publication Date: 2001
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  • 7
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    Online Resource
    The centennial of the Sagnac experiment in the optical regime: From a tabletop experiment to the variation of the Earth's rotation
    Elsevier BV ; 2014
    In:  Comptes Rendus Physique Vol. 15, No. 10 ( 2014-12), p. 859-865
    Details
    In: Comptes Rendus Physique, Elsevier BV, Vol. 15, No. 10 ( 2014-12), p. 859-865
    Type of Medium: Online Resource
    ISSN: 1631-0705
    URL: Article
    DOI: 10.1016/j.crhy.2014.10.003
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2014
    detail.hit.zdb_id: 2079167-7
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  • 8
    Online Resource
    Online Resource
    Six Degree-of-Freedom Broadband Ground-Motion Observations with Portable Sensors: Validation, Local Earthquakes, and Signal Processing
    Seismological Society of America (SSA) ; 2020
    In:  Bulletin of the Seismological Society of America Vol. 110, No. 3 ( 2020-06-01), p. 953-969
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 110, No. 3 ( 2020-06-01), p. 953-969
    Abstract: The additional observation of three components of rotational ground motions has benefits for tilt-seismometer coupling (e.g., ocean-bottom seismometry and volcano seismology), local site characterization, wavefield separation, source inversion, glacial and planetary seismology, as well as the monitoring of structural health. Field applications have been mostly hampered by the lack of portable sensors with appropriate broadband operation range and weak-motion sensitivity. Here, we present field observations of the first commercial portable broadband rotation sensor specifically designed for seismology. The sensor is a three-component fiber-optic gyro strictly sensitive to ground rotation only. The sensor field performance and records are validated by comparing it with both array-derived rotation measurements and a navigation-type gyro. We present observations of the 2018 Mw 5.4 Hualien earthquake and the 2016 central Italy earthquake sequence. Processing collocated rotation and classical translation records shows the potential in retrieving wave propagation direction and local structural velocity from point measurements comparable to small-scale arrays of seismic stations. We consider the availability of a portable, broadband, high sensitivity, and low self-noise rotation sensor to be a milestone in seismic instrumentation. Complete and accurate ground-motion observations (assuming a rigid base plate) are possible in the near, local, or regional field, opening up a wide range of seismological applications.
    Type of Medium: Online Resource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120190277
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2020
    detail.hit.zdb_id: 2065447-9
    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    Seismological Processing of Six Degree-of-Freedom Ground-Motion Data
    MDPI AG ; 2020
    In:  Sensors Vol. 20, No. 23 ( 2020-12-03), p. 6904-
    Details
    In: Sensors, MDPI AG, Vol. 20, No. 23 ( 2020-12-03), p. 6904-
    Abstract: Recent progress in rotational sensor technology has made it possible to directly measure rotational ground-motion induced by seismic waves. When combined with conventional inertial seismometer recordings, the new sensors allow one to locally observe six degrees of freedom (6DOF) of ground-motion, composed of three orthogonal components of translational motion and three orthogonal components of rotational motion. The applications of such 6DOF measurements are manifold—ranging from wavefield characterization, separation, and reconstruction to the reduction of non-uniqueness in seismic inverse problems—and have the potential to revolutionize the way seismic data are acquired and processed. However, the seismological community has yet to embrace rotational ground-motion as a new observable. The aim of this paper is to give a high-level introduction into the field of 6DOF seismology using illustrative examples and to summarize recent progress made in this relatively young field. It is intended for readers with a general background in seismology. In order to illustrate the seismological value of rotational ground-motion data, we provide the first-ever 6DOF processing example of a teleseismic earthquake recorded on a multicomponent ring laser observatory and demonstrate how wave parameters (phase velocity, propagation direction, and ellipticity angle) and wave types of multiple phases can be automatically estimated using single-station 6DOF processing tools. Python codes to reproduce this processing example are provided in an accompanying Jupyter notebook.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s20236904
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
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  • 10
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    Online Resource
    Rotaphone-CY: The Newest Rotaphone Model Design and Preliminary Results from Performance Tests with Active Seismic Sources
    MDPI AG ; 2021
    In:  Sensors Vol. 21, No. 2 ( 2021-01-14), p. 562-
    Details
    In: Sensors, MDPI AG, Vol. 21, No. 2 ( 2021-01-14), p. 562-
    Abstract: Rotaphone-CY is a six-component short-period seismograph that is capable of the co-located recording of three translational (ground velocity) components along three orthogonal axes and three rotational (rotation rate) components around the three axes in one device. It is a mechanical sensor system utilizing records from elemental sensors (geophones) arranged in parallel pairs to derive differential motions in the pairs. The pairs are attached to a rigid frame that is anchored to the ground. The model design, the latest one among various Rotaphone designs based on the same principle and presented elsewhere, is briefly introduced. The upgrades of the new model are a 32-bit A/D converter, a more precise placing of the geophones to parallel pairs and a better housing, which protects the instrument from external electromagnetic noise. The instrument is still in a developmental stage. It was tested in a field experiment that took place at the Geophysical Observatory in Fürstenfeldbruck (Germany) in November 2019. Four Rotaphones-CY underwent the huddle-testing phase of the experiment as well as the field-deployment phase, in which the instruments were installed in a small-aperture seismic array of a triangular shape. The preliminary results from this active-source experiment are shown. Rotaphone-CY data are verified, in part, by various approaches: mutual comparison of records from four independent Rotaphone-CY instruments, waveform matching according to rotation-to-translation relations, and comparison to array-derived rotations when applicable. The preliminary results are very promising and they suggest the good functionality of the Rotaphone-CY design. It has been proved that the present Rotaphone-CY model is a reliable instrument for measuring short-period seismic rotations of the amplitudes as small as 10−7 rad/s.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s21020562
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2052857-7
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