To demonstrate that the SEM is accurate, we benchmark SEM synthetics against normal-mode synthetics for the Preliminary Reference Earth Model (PREM, right). Mode synthetics are basically exact for spherically symmetric Earth models; of course for the same cost the SEM can calculate synthetics in fully 3-D Earth models

Effect of crustal thickness: Love wave in a model with the two-layer PREM crust (red curve) and in a model with a one-layer crust with the same thickness and the properties of the PREM upper crust (green curve). Clearly the surface wave is very sensitive to the details of the crustal model.

Anisotropy: Wave propagation in anisotropic crystals. Apatite (left) and Zinc (right) have highly anisotropic P- and S-wave fronts. The SEM synthetics are in excellent agreements with predictions based upon ray theory (orange dashed lines).

Anisotropy: Comparison between normal-mode synthetics for anisotropic PREM (red line) and isotropic PREM ( green line). The effect of the anisotropic asthenosphere is to significantly delay the Rayleigh wave (left, vertical component) and slightly speed up the Love wave (right, transverse component).

(to top)

Attenuation: To illustrate the effects of attenuation and physical dispersion associated with anelastic PREM, we compare vertical component mode synthetics for PREM with (red line) and without (green line) incorporating the effects of anelasticity. Note that elastic PREM is faster than anelastic PREM, and that in particular the S wave is significantly attenuated.

Attenuation: Vertical component SEM (green line) and mode (red line) synthetic seismograms for anelastic PREM for the great magnitude 8.2 Bolivia earthquake of June 9, 1994, recorded at TriNet station PAS in Pasadena, California. The depth of the event is 647 km.

Antipodal synthetic: Comparison between SEM (green line) and mode (red line) transverse component synthetics at the antipode. This is a difficult location because rays emanating from the source converge simultaneously from all directions, plus the epicentral distance is largest, leading to maximal numerical dispersion in a 90-minute record. Anisotropy and attenuation are included.

PKP Arrivals: Record section comparison of PKP phases calculated for anelastic, anisotropic PREM based upon the SEM (green lines) and modes (red lines) between 130 and 230 degrees along the Greenwich meridian. All PKP arrivals, including DF, which has traveled through the central cube in the mesh, are well reproduced. Note also a very weak Pdiff arrival in both synthetics between 130 and 170 degrees and between 190 and 230 degrees.

Gravity: Vertical component of displacement of the normal-mode solution for a shallow Irian Jaya event with the full implementation of gravity (red line) and the SEM solution without gravity (green line) at an epicentral distance of 100 degrees. The results have been lowpass-filtered at a corner period of 120 s. At these long periods there is a large effect due to gravity on the vertical and longitudinal components

Gravity: Vertical component of the PREM normal-mode solution in the Cowling approximation (red line) and the SEM displacement (green line) for a shallow Irian Jaya event at an epicentral distance of 100 degrees. This illlustrates that gravity is accurately incorporated in the SEM.

Multi-Orbit Love Waves: Transverse components of the PREM normal-mode solution in the Cowling approximation (red line) compared to the SEM displacement (green line) for a shallow Irian Jaya event at an epicentral distance of 100 degrees. One can observe the multi-orbit Love waves up to G5,and the SEM is in excellent agreement with the modes.

Oceans: Vertical component of displacement for a PREM normal-mode calculation with a 3 km-thick ocean layer (red line), and for the SEM without the ocean layer (green line). The results are for a shallow Irian Jaya earthquake recorded at an epicentral distance of 60 degrees. The oceans have a small effect on P and S multiples and a large effect on the Rayleigh wave, which is slowed down considerably. The Love wave is not affected by the presence of the oceans.

Oceans: Vertical components of displacement for a PREM normal-mode calculation with a 3 km-thick ocean layer (red line) and for the SEM with the same ocean layer (green line). The results are for a shallow Irian Jaya earthquake recorded at an epicentral distance of 60 degrees. The SEM implementation of the oceans is approximate, so the dispersion of the Rayleigh wave is not perfect.


(to top)

HOME | GLOBAL | REGIONAL | NORMAL MODES | GLACIAL REBOUND | BEOWULF | PEOPLE | REPRINTS | DOWNLOADS