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  • 1
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    Imaging of Small‐Scale Heterogeneity and Absorption Using Adjoint Envelope Tomography: Results From Laboratory Experiments (2022)
    Details
    Publication Date: 2024-04-03
    Description: To complement the information provided by deterministic seismic imaging at length scales above a certain resolution limit we present the first application of adjoint envelope tomography (AET) to experimental data. AET uses the full envelopes of seismic records including scattered coda waves to obtain information about the distribution of absorption and small‐scale heterogeneity which provide complementary information about the investigated medium. Being below the resolution limit this small‐scale structure cannot be resolved by conventional tomography but still affects wave propagation by attenuating ballistic waves and generating scattered waves. Using ultrasound data from embedded sensors in a meter‐sized concrete specimen we image the distribution of absorption and heterogeneity expressed by the intrinsic quality factor Q〈sup〉−1〈/sup〉 and the fluctuation strength ɛ that characterizes the strength of the heterogeneity. The forward problem is solved by modeling the 2‐D multiple nonisotropic scattering in an acoustic medium with spatially variable heterogeneity and attenuation using the Monte‐Carlo method. Gradients for the model updates are obtained by convolution with the back‐propagated envelope misfit using the adjoint formalism in analogy to full waveform inversion. We use a late coda time window to invert for absorption and an earlier time window to infer the distribution of heterogeneity. The results successfully locate an area of salt concrete with increased scattering and concentric anomalies of intrinsic attenuation. The resolution test shows that the recovered anomalies constitute reasonable representations of internal structure of the specimen.
    Description: Plain Language Summary; No matter how small the structures are that a seismic imaging method is able to resolve, there is structure with smaller length scale. On the one hand this small‐scale structure causes unwanted signals for conventional imaging approaches. But on the other hand it provides complementary information about the investigated medium. To turn this to our advantage we, for the first time, apply a new imaging method that uses the waves which are caused by the small‐scale structure. Using data of an experiment in a concrete block we demonstrate that we can identify areas of anomalous small‐scale structure. The results may help in the future to locate minute perturbations in the medium as they occur in the advent of volcanic eruptions or after earthquakes and to obtain new information about the geologic history of subsurface materials. The approach can be transferred to investigate man‐made materials and structures, such as deteriorating concrete constructions.
    Description: Key Points: Adjoint envelope tomography is for the first time applied to image the scattering and absorption structure with the real data. The iterative inversion uses envelopes of ultrasound signals from embedded transducers in a meter‐sized reinforced concrete specimen. We successfully image the distribution of statistical parameters characterizing the small‐scale heterogeneity and attenuation.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: https://doi.org/10.5281/zenodo.7152278
    Keywords: ddc:550.78 ; seismic tomography ; adjoint method ; small‐scale heterogeneity ; attenuation ; ultrasonic experiment ; reinforced concrete
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    PatachE Stress Observation (PESO) (2023)
    GFZ Data Services
    Details
    Publication Date: 2024-02-23
    Description: Abstract
    Description: The PESO array provides two weeks of local seismological observation in the vicinity of the IPOC (Plate Boundary Observatory Network Northern Chile) station Patache (CX.PATCX) to investigate the subsurface structure and the ambient seismic field. Waveform data is available from the GEOFON data centre, under network code 7F, and is fully open.
    Keywords: Broadband seismic waveforms ; Seismic monitoring ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 EARTHQUAKES ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 VOLCANIC ACTIVITY ; In Situ/Laboratory Instruments 〉 Magnetic/Motion Sensors 〉 Seismometers ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS 〉 SEISMOLOGICAL STATIONS
    Type: Dataset , Seismic Network
    Format: ~100G
    Format: .mseed
    Format: XML
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    DATA GFZ
  • 3
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    Eifel Large-N Seismic Network (ELSN) (2023)
    GFZ Data Services
    Details
    Publication Date: 2024-04-11
    Description: Abstract
    Description: The Eifel Large-N Seismic Network is a concentric network of about 80km aperture around the Laacher See. Instrumentation consists of broad band seismometers, short period instruments (1Hz eigenfrequency) and 4.5Hz geophones. While the broadband and short period stations cover the area rather homogeneously for about 12 month, the geophone stations were moved after 6 month from a layout focussed on the closer vicinity of the Laacher See onto a line crossing the network from south-west to north-east with a dense station spacing. The goal of the experiment is the structural investigation of the feeding system of the East Eifel and a detailed study of the tectonic and volcanic seismic activity in this area. Waveform data is available from the GEOFON data centre, under network code 6E.
    Keywords: EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 EARTHQUAKES ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 VOLCANIC ACTIVITY ; In Situ/Laboratory Instruments 〉 Magnetic/Motion Sensors 〉 Seismometers ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS 〉 SEISMOLOGICAL STATIONS ; Passive seismic ; Local network ; Temporary ; Large-N ; Volcano ; Velocity ; Seismometers ; MiniSEED
    Type: Dataset , Seismic Network
    Format: ~300G
    Format: .mseed
    Format: XML
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    DATA GFZ
  • 4
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    Mantle and Crustal Sources of Magmatic Activity of Klyuchevskoy and Surrounding Volcanoes in Kamchatka Inferred From Earthquake Tomography (2021)
    Details
    Publication Date: 2021-07-01
    Description: Klyuchevskoy and surrounding volcanoes in central Kamchatka form the Northern Group of Volcanoes (NGV), which is an area of particularly diverse and intensive Pleistocene‐Holocene volcanism. In this study, we present a new seismic tomographic model of the crust and uppermost mantle beneath NGV based on local earthquake data recorded by several permanent and temporary seismic networks including a large‐scale experiment that was conducted in 2015–2016 by an international scientific consortium. Having an unprecedented resolution for this part of Kamchatka, the new model reveals many features associated with the present and past volcanic activity within the NGV. In the upper crust, we found several prominent high‐velocity anomalies interpreted as traces of large basaltic shield volcanoes, which were hidden by more recent volcanic structures and sediments. We interpret the mantle structure to reflect asthenospheric flow up through a slab window below the Kamchatka‐Aleutian junction that feeds the entire NGV. The interaction of the hot asthenospheric material with fluids released from the slab determines the particular volcanic activity within the NGV. We argue that the eastern branch of the Central Kamchatka Depression, which is associated with a prominent low‐velocity anomaly in the uppermost mantle, was formed as a recent rift zone separating the NGV from the Kamchatka Eastern Ranges.
    Description: Key Points: We present a new high‐resolution seismic model of the crust and upper mantle beneath the Northern Group of Volcanoes in Kamchatka. The volcanoes of the Northern group are fed by an asthenosphere flow ascending from a slab window below the Kamchatka‐Aleutian junction. Eastern branch of the Central Kamchatka Depression is a rift separating the Northern Group of Volcanoes from the Eastern Ranges.
    Description: Russian Ministry of Science and Education http://dx.doi.org/10.13039/501100012190
    Description: Russian Science Foundation http://dx.doi.org/10.13039/100004111
    Description: RFBR http://dx.doi.org/10.13039/501100002261
    Description: European Union Horizon 2020 Research and Innovation Programme http://dx.doi.org/10.13039/501100012190
    Keywords: 551.2 ; seismic tomography ; subduction ; Klyuchevskoy Group of Volcanoes ; Shiveluch ; Kizimen ; Central Kamchatka Depression
    Type: article
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    CITATION GEO-LEO
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