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  • 1
    Publication Date: 2021-07-21
    Description: The Yığma Tepe of Pergamon is one of the largest known burial mounds in the Eastern Mediterranean. Its internal structure, especially the existence and location of burials, remains unknown so far because its height of 32 m and the diameter of 158 m have restricted extensive excavations. To explore the interior of the Yığma Tepe, we applied shear wave reflection profiling and traveltime tomography, locally complemented by electrical resistivity tomography. Shear wave reflection imaging enabled us to identify the layering and localize structures down to the basal surface of the mound with a metre‐scale resolution. A grid of crossing SH‐wave profiles with 4‐m line spacing covered the central mound area. The Yığma Tepe can be subdivided into three stratigraphic layers representing different construction phases, each about 10 m thick. The deepest is a consolidated layer with a locally compacted surface. SH‐wave reflection imaging verified the collapsed remains of a tunnel system and a shaft at about 30‐m depth that had been dug into the mound at the level of the basal surface at the beginning of the 20th century. The tunnel collapse created a damage zone of decreased S‐wave velocity reaching up to the overlying middle layer, in which four seismic objects of interest (SOIs) were detected. The largest of these SOIs is a north–south‐oriented structure, about 15 m long and 4 m wide. SH‐viscoelastic forward modelling showed that it likely consists of a collapsed walled cavity with a zone of loosened soil above. The third layer covers the underlying two and is enriched with large stone packages as verified by local excavations. We show the capabilities of shear‐wave reflection seismic to image small‐scale structures under complicated topographic conditions and how characteristics of cavities and volumes of decompacted soil can be evaluated by wavefield modelling.
    Description: Agence nationale de la recherche (ANR) http://dx.doi.org/10.13039/501100001665
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: German Archaeological Institut (DAI)
    Keywords: 622.1592 ; 930.1 ; Pergamon ; Yı gma Tepe ; seismic investigations
    Type: article
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  • 2
    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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