Abstract

A hybrid deterministic-stochastic method (dsm) is developed to calculate synthetic time series of ground accelerations radiated from an extended source. The main goal of the proposed methodology is to include in the classical point-source stochastic method (pssm) the effects of the rupture propagation on a finite fault. This purpose is achieved through two important modifications of the pssm technique. First, the envelope does not have a predetermined functional form; rather, it is calculated deterministically following the isochron formulation with a kinematic rupture model. Second, we have generalized the various parameters of the point-source ground motion spectrum to account for the extended fault: corner frequency, distance from the fault, and radiation pattern are evaluated through the kinematic modeling. The guiding principal in all these modifications has been to develop a robust methodology capable of capturing the complexity of near-source ground motion even when input information about earthquake source, propagation medium, and site characteristics are of a very schematic nature.

We show that the synthetic envelope contains the required information on the rupture process on extended fault, such as directivity effects and azimuthal variations depending on the source-to-receiver geometry. The method’s capability is demonstrated by modeling strong ground motions of the 1992 Mw 7.3 Landers, California, earthquake and comparing them with the recorded accelerograms, which are clearly affected by directivity effects. The proposed technique reproduces the main characteristics of strong-motion recordings, and can be implemented using only a limited number of parameters to describe the source (dimension and geometry), the propagation medium (wave velocities and layers), and the site effects (transfer function). These characteristics are important for a methodology aimed to simulate ground-shaking scenarios for which a more complete description of the faulting process is not available.

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