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| Titel |
Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes |
| VerfasserIn |
W. Friederich, L. Lambrecht, B. Stöckhert  , S. Wassmann, C. Moos |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 5, no. 1 ; Nr. 5, no. 1 (2014-03-12), S.141-159 |
| Datensatznummer |
250115260
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| Publikation (Nr.) |
 copernicus.org/se-5-141-2014.pdf |
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| Zusammenfassung |
Return flow in a deep subduction channel (DSC) has been proposed to explain rapid exhumation of high pressure–low temperature metamorphic
rocks, entirely based on the fossil rock record. Supported by thermo-mechanical models, the DSC is envisioned as a thin layer on top of the
subducted plate reaching down to minimum depths of about 150 km. We perform numerical simulations of high-frequency seismic wave propagation
(1–5 Hz) to explore potential seismological evidence for the in situ existence of a DSC. Motivated by field observations, for modeling
purposes we assume a simple block-in-matrix (BIM) structure with eclogitic blocks floating in a serpentinite matrix. Homogenization calculations
for BIM structures demonstrate that effective seismic velocities in such composites are lower than in the surrounding oceanic
crust and mantle, with nearly constant values along the entire length of the DSC. Synthetic seismograms for receivers at the surface
computed for intermediate depth earthquakes in the subducted oceanic crust for models with and without DSC turn out to be markedly
influenced by its presence or absence.
While for both models P and S waveforms are dominated by delayed high-amplitude guided waves,
models with DSC exhibit a very different pattern of seismic arrivals compared to models without DSC.
The main reason for the difference is the greater length and width
of the low-velocity channel when a DSC is present. Seismic velocity heterogeneity within the DSC or oceanic crust
is of minor importance.
The characteristic patterns allow for definition of
typical signatures by which models with and without DSC may be discriminated.
The signatures stably recur in slightly modified form for earthquakes at different
depths inside subducted oceanic crust. Available seismological data from intermediate depth earthquakes recorded in the
forearc of the Hellenic subduction zone exhibit similar multi-arrival waveforms as observed in the synthetic seismograms for models with DSC.
According to our results, observation of intermediate depth earthquakes along a profile across the forearc may allow to test the hypothesis
of a DSC and to identify situations where such processes could be active today. |
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