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[SCG55-P13] Inelastic surface deformation during and immediately after greater earthquakes
Keywords:inelastic deformation, potential energy, unconsolidated sedimentary layers
Greater earthquake with M7 to M9 that occurs between or within tectonic plates can be understood as a temporary release of the "strain'' that has accumulated in the focal fault area and its vicinity.
However, in the surface area, around the epicenter, where unconsolidated sedimentary layers exist, (inelastic) secondary deformations such as “landslides", "slope collapses", “mountain slope tsunamis,” liquefaction in landfills, and regional or localized subsidence in landfills, etc. might be induced.
Deformation of these unconsolidated sedimentary layers occurs sometimes in the human living environment, providing a higher risk of human damage. Deformation in unconsolidated sedimentary layers can be primarily recognized as a "(partial) release of potential energy." This potential energy release phenomenon is not treated by elastic wave theory such as the fault dislocation model.
The state of excessive local disequilibrium, both isostatically and/or topographically, included in uplift or subsidence due to previous greater earthquakes or inelastic deformation.
Surface deformation with the horizontal wavelength than the value of "lithospheric effective elastic layer thickness" (Te or T'e ) in the depth direction will be eliminated by a long-time viscoelastic deformation process. The time constant (tv) of the viscoelastic deformation process here is at least tens of thousands of years.
"Surface deformation process around the fault plane” is composed of (1) Long-term, long-wavelength (λ>T'e ) relaxation deformation (on the order of ten thousand years or more) which mechanical background mainly due to relative plate motion and isostasy-like relaxation), and (2) temporary deformation associated with the greater earthquake.
The second term, (2), may include components of (a) elastic deformation due to fault movement, (b) temporary deformation (especially in unconsolidated sedimentary layers), (c) passive, post-seismic deformation, and (d) other(s).
Here, (c) is the viscoelastic relaxation process associated with temporal fault movement (a), whose main mechanical deformation zones would be the lithosphere and uppermost mantle layer. Regarding (c), for example, if active structures, active volcanoes, or geothermal zones are recognized in the overriding lithosphere of the island arc or continent, elastic constants such as rigidity may be non-uniform or heterogeneous, and a simple isotropic homogeneous elastic model cannot be applied.
The mathematical expression of local deformation of the unconsolidated sedimentary layers in plains and hilly regions must be treated separately from discussions involving the effective elastic layer thickness of the lithosphere.
In regions of oceans or lakes where the slope is covered by unconsolidated sedimentary layers, slope collapses and slope slides are considered to have the potential to occur just after the great earthquake.
Likewise, large-scale to small-scale collapses associated with the growth of depressions in seafloor-expanding axes and back-arc-expanding systems may also have similar inelastic collapses and other deformations.
However, in the surface area, around the epicenter, where unconsolidated sedimentary layers exist, (inelastic) secondary deformations such as “landslides", "slope collapses", “mountain slope tsunamis,” liquefaction in landfills, and regional or localized subsidence in landfills, etc. might be induced.
Deformation of these unconsolidated sedimentary layers occurs sometimes in the human living environment, providing a higher risk of human damage. Deformation in unconsolidated sedimentary layers can be primarily recognized as a "(partial) release of potential energy." This potential energy release phenomenon is not treated by elastic wave theory such as the fault dislocation model.
The state of excessive local disequilibrium, both isostatically and/or topographically, included in uplift or subsidence due to previous greater earthquakes or inelastic deformation.
Surface deformation with the horizontal wavelength than the value of "lithospheric effective elastic layer thickness" (Te or T'e ) in the depth direction will be eliminated by a long-time viscoelastic deformation process. The time constant (tv) of the viscoelastic deformation process here is at least tens of thousands of years.
"Surface deformation process around the fault plane” is composed of (1) Long-term, long-wavelength (λ>T'e ) relaxation deformation (on the order of ten thousand years or more) which mechanical background mainly due to relative plate motion and isostasy-like relaxation), and (2) temporary deformation associated with the greater earthquake.
The second term, (2), may include components of (a) elastic deformation due to fault movement, (b) temporary deformation (especially in unconsolidated sedimentary layers), (c) passive, post-seismic deformation, and (d) other(s).
Here, (c) is the viscoelastic relaxation process associated with temporal fault movement (a), whose main mechanical deformation zones would be the lithosphere and uppermost mantle layer. Regarding (c), for example, if active structures, active volcanoes, or geothermal zones are recognized in the overriding lithosphere of the island arc or continent, elastic constants such as rigidity may be non-uniform or heterogeneous, and a simple isotropic homogeneous elastic model cannot be applied.
The mathematical expression of local deformation of the unconsolidated sedimentary layers in plains and hilly regions must be treated separately from discussions involving the effective elastic layer thickness of the lithosphere.
In regions of oceans or lakes where the slope is covered by unconsolidated sedimentary layers, slope collapses and slope slides are considered to have the potential to occur just after the great earthquake.
Likewise, large-scale to small-scale collapses associated with the growth of depressions in seafloor-expanding axes and back-arc-expanding systems may also have similar inelastic collapses and other deformations.