Caltech
Email:
jtromp@gps.caltech.edu
poster/oral: oral
| We use a spectral-element method to simulate seismic wave propagation throughout the entire globe. The method is based upon a weak formulation of the equations of motion and combines the flexibility of a finite-element method with the accuracy of a global pseudospectral method. The finite-element mesh honors all first- and second-order discontinuities in the Earth model. To maintain a relatively constant resolution throughout the model in terms of the number of grid points per wavelength, the size of the elements is increased with depth in a conforming fashion, thus retaining a diagonal mass matrix. In the Earth's mantle and inner core we solve the wave equation in terms of displacement, whereas in the liquid outer core we use a formulation based upon a scalar potential. The three domains are matched at the inner-core and core-mantle boundaries, honoring the continuity of traction and the normal component of velocity. The effects of attenuation, anisotropy, self-gravitation, rotation, and the oceans are incorporated. The method is implemented on parallel computers using a message-passing technique. We benchmark spectral-element synthetic seismograms against normal-mode synthetics for spherically symmetric reference model PREM. The two methods are in excellent agreement for all body- and surface-wave arrivals with periods greater than about 18 s. At long periods the effect of gravity on multi-orbit surface waves up to R4 is correctly reproduced. We subsequently present results of simulations for two real earthquakes in fully 3-D Earth models for which the fit to the data is significantly improved compared to classical normal-mode calculations based upon PREM. For example, we show that for trans-Pacific paths the Rayleigh wave can arrive more than 80 seconds earlier than in PREM, and that the Love wave is much shorter in duration. |