SURFACE DEFORMATION DUE TO A STRIKE-SLIP-FAULT IN AN ELASTIC GRAVITATIONAL LAYER OVERLYING A VISCOELASTIC GRAVITATIONAL HALF-SPACE

We extend a technique previously used to model surface displacements r esulting from thrust faulting in an elastic-gravitational layer over a viscoelastic-gravitational half-space to the case of strike-slip faul ting. The method involves the calculation of the Green's functions for a strike-slip point source contained in an elastic-gravitational laye r over a viscoelastic-gravitational half-space. The correspondence pri nciple of linear viscoelasticity is applied to introduce time dependen ce. The resulting Green's functions are then integrated over the sourc e region to obtain the near-field displacements. Several sample calcul ations are presented involving 90 degrees and 30 degrees dipping fault s and ruptures completely and partially through the elastic layer, We also illustrate the time dependent deformation due to a buried fault. Results show that the use of a viscoelastic half-space underlying an e lastic layer introduces a long wavelength component into the deformati on field [Cohen and Kramer, 1984], even in cases of non vertical strik e-slip fault and inclusion of gravitational effect, that cannot be mod eled by purely elastic techniques. Calculations have shown that vertic al postseismic displacement is insignificant and that the horizontal m ovement is about the same magnitude as the coseismic strike-slip displ acement. The inclusion of gravity affects the horizontal displacement due to vertical strike-slip faulting in far field and the vertical dis placement for dipping strike-slip faulting in near-field. The computed results have been fit to the Global Positioning System measurements o f the Landers earthquake taken shortly after the main shock, assuming a relaxation time of the order of days, This relaxation time is consid erably shorter than times of the order of years to decades found in pr evious studies. The major differences between this detailed three-dime nsional and simplified two-dimensional model are the decay of magnitud e in displacement field and the distinct displacement pattern in the r egions beyond the fault tip, The displacement field due to the cyclic earthquakes was constructed by considering the finite fault length and inclusion of gravity. It is found that the displacement field is domi nated by the plate motion in the case of short recurrence time. On the other hand, a ''looping'' and migrating pattern in the displacement f ield is found in the case of very long recurrence time, which is not s een in those 2D simplified models.