In this simulation, a horizontal initial velocity of one direction is given as initial data. Different wave propagations of two wave types are observed. The P (pressure, primary) wave propagates horizontally and S (shear, secondary) wave propagates vertically. We can see S wave is slower than P wave.
In this simulation, a horizontally bumping initial velocity is given as initial data. The S wave propagation is very different from the first simulation. (technical note)