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| Titel |
Seismic activity waves in the Earth's lithosphere |
| VerfasserIn |
Shamil Mukhamediev, Andrey Grachev |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095220
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| Publikation (Nr.) |
 EGU/EGU2014-10670.pdf |
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| Zusammenfassung |
| The plot of temporal variation in the seismic activity level of the 40°–80°N segment of the
Mid-Atlantic Ridge over the period from 1917 through 1987 is rather similar in
shape with an analogous plot for Fennoscandia (Skordas et al., 1991) and, as is
shown in the present work, for the eastern part of the North American platform
(NAP). However, the characteristic features of the Mid-Atlantic Ridge plot are
repeated with an ~3-yr delay in Fennoscandia and with a 4–8-yr delay in the NAP.
This positive phase shift is consistent with the hypothesis on significant dynamic
control of a mid-ocean ridge (MOR) over seismic activity in adjacent platforms. This
control is realized via the MOR push force. Variations in this force induced by the
nonstationary process of dike intrusion in the axial zone of the ridge bring about migration
of perturbations in the stationary stress–strain state of the lithosphere away from
the MOR and induce seismic activity variations in platform regions adjacent to
the MOR. The positive time shift in plots of platform seismic activity relative to
the corresponding MOR plot is explained in terms of the delay in the arrival of
the stress wave at the platform; due to energy dissipation in the asthenosphere,
the amplitude of the wave significantly attenuates during its propagation from the
MOR. Using the Elsasser model and the observed time shift, an estimate of η = 1017
Pa s accurate to within ±30% is obtained for the asthenosphere viscosity in the
case under consideration. Such values of the viscosity are sufficient to bring about
the triggering effect of stress–strain state perturbations on platform seismicity. An
increase in the obtained value of η by a few times would lead to overly large travel
times of the stress wave, so that seismic activity would remain unaffected by such
a wave at distances of the order of 2000 km. The examined numerical model is
indirectly supported by the variation amplitude of seismic activity: as compared
with Fennoscandia, this amplitude is lower in the central and eastern NAP, located
farther from the Mid-Atlantic Ridge. On the other hand, the stationary seismicity
level on the NAP is higher than in Fennoscandia, which can explain the difference
between stationary values of shear stress intensities Ï in the regions considered. The
smaller stationary values of Ï in Fennoscandia are due to the higher curvature of the
Mid-Atlantic Ridge encompassing this region. The results of this work not only confirm the
idea previously proposed by the authors according to which the MOR push force
affects the stationary level of seismic activity in adjacent platform regions but also
provide new insights into the mechanism of this effect in a nonstationary state. |
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