It has been observed that most shallow earthquakes occur in a seismogenic layer which extends to a depth of a few tens of kilometres, while at greater depths the relative plate motion must take place aseismically. Such behaviour is reproduced by a model where a wide, deformed fault region is encompassed by two transcurrent plates and subjected to a constant strain rate. The shear zone is treated as a viscoelastic body, for which a power-law constitutive relation is employed. Temperature and, therefore, rheology depend on depth z. Also rigidity depends on depth. The model determines a maximum depth H for earthquake nucleation on the faults in the shear zone, if a frictional resistance linearly increasing with depth is assumed. The interseismic shear stress evolution on a vertical fault is obtained analytically for n = 1,2,3 and 4, where n is the power-law exponent. It is found that the rate of stress increase does not change appreciably as a function of n for z < H, while the effect of non-linearity becomes more sensible at larger z. Moreover, for z < H, the state of stress as obtained from this model is very different from estimates obtained from purely viscous models even for much longer times than are considered in seismology.
A model of interseismic stress evolution in a transcurrent shear-zone / Dragoni M.. - In: TECTONOPHYSICS. - ISSN 0040-1951. - STAMPA. - 149:3-4(1988), pp. 265-273. [10.1016/0040-1951(88)90177-1]
A model of interseismic stress evolution in a transcurrent shear-zone
Dragoni M.
1988
Abstract
It has been observed that most shallow earthquakes occur in a seismogenic layer which extends to a depth of a few tens of kilometres, while at greater depths the relative plate motion must take place aseismically. Such behaviour is reproduced by a model where a wide, deformed fault region is encompassed by two transcurrent plates and subjected to a constant strain rate. The shear zone is treated as a viscoelastic body, for which a power-law constitutive relation is employed. Temperature and, therefore, rheology depend on depth z. Also rigidity depends on depth. The model determines a maximum depth H for earthquake nucleation on the faults in the shear zone, if a frictional resistance linearly increasing with depth is assumed. The interseismic shear stress evolution on a vertical fault is obtained analytically for n = 1,2,3 and 4, where n is the power-law exponent. It is found that the rate of stress increase does not change appreciably as a function of n for z < H, while the effect of non-linearity becomes more sensible at larger z. Moreover, for z < H, the state of stress as obtained from this model is very different from estimates obtained from purely viscous models even for much longer times than are considered in seismology.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.