| An alarm would sound with the first P-waves, a few crucial moments before ground-shaking S-waves arrive. |
| He explained how progress towards the critical point where a stressed rock mass fractures and causes an earthquake can be monitored by analysing seismic shear, or S-waves. |
| These waves arrive at seismic stations before secondary waves, or S-waves, which shake molecules from side to side. |
| To be useful, the various packets of energy that can be seen on the seismogram must be identified as refractions, reflections, P-waves or S-waves, etc. |
| Alfaro shows his results on the application of a heuristic method for estimation of velocity structure for S-waves and compares his findings with existing PS-logging data. |
| The rumbling P-waves were followed immediately by the stronger and more complex S-waves. |
