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  • 1
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (47 Seiten)
    Series Statement: GEOMAR Report N. Ser. 41
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
    Publication Date: 2021-03-29
    Description: In this study different full waveform techniques was developed for the investigation of seismic ocean bottom single station data. These techniques were applied to data obtained in a pilot ocean bottom experiment in the Tyrrhenian Sea/Italy (TySea experiment) from December 2000 to May 2001. A network of broadband seven ocean bottom seismometers and seven ocean bottom hydrophones was installed above the subducting Ionian plate which descends from Southeast to Northwest. Local and teleseismic earthquakes were recorded by the stations. The newly developed techniques produce very promising results in reconstructing the sea floor structure beneath the stations and in attenuating waveform effects generated by water layer multiples. Additionally the techniques offer a possibility to determine the orientation of free fall ocean bottom seismometers. The main results are: 1. The waveform recorded at the seafloor differs from waveforms recorded at land stations. This is primarily due to multiple reflections in the water layer. These multiple reflections show different patterns on seismometer and hydrophone recordings depending on the seafloor structure. This opens the possibility to constrain the P-wave velocity structure beneath the station by means of a full waveform inversion...
    Description: thesis
    Keywords: 550 ; TSZ 100 ; VAE 890 ; TQC 700 ; Atlantischer Ozean {Geophysik} ; Ozeanische Kruste {Tektonik} ; Seismische Verfahren zur Feststellung von Atomexplosionen {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
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  • 3
    Publication Date: 2021-10-01
    Description: Villarrica Volcano (Chile) is one of the most active volcanoes in South America. Its low-frequency (≤5 Hz) seismicity consists of a continuous tremor, overlain by impulsive transient events of higher amplitude in 60-s intervals. This signal was recorded in March 2012 by an extensive local network, comprising 75 stations and including 6 subarrays. It allowed us to apply and compare three techniques to locate the origin of the seismicity: intersection of propagation directions determined by array analysis, mapping amplitudes, and modeling of amplitude decay. All methods yield almost identical, temporally stable, epicenters inside the summit crater, which confirms earlier attributions of the seismicity to volcanic activity inside the conduit. The discrete transients and the interevent tremor share the same source location. From the dominance of surface waves and the obvious scattering, we infer a source near the surface. For two arrays at the northern and western flank, a dispersion relation was derived, which allowed for the determination of S wave velocity-depth functions. At both locations, the velocity structure can be modeled by three layers with interfaces at 100 and 400m depths. The velocities (300 to 3,000 m/s) correspond to pyroclastic material at different states of consolidation. The modeling of the amplitude decay reveals a quality factor around 50.
    Keywords: 551.22 ; volcano seismology ; beamforming ; amplitude decay ; source location ; scattering ; S wave velocity structure
    Language: English
    Type: map
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