The travel velocity of these two wave types is not the same (P-waves are faster than S-waves). Thus, if there is an earthquake somewhere, the first waves that arrive are P-waves. In essence, the gap in P-wave and S-wave arrival gives a first estimate of the distance to the earthquake.
With the mysterious U.S. Senator Eddie Morra (Bradley Cooper) providing him with a second drug to counteract NZT's deadly side effects, Brian uses his enhanced abilities to help FBI agent Rebecca Harris (Jennifer Carpenter).
The film is still shooting in Bavaria but the first image has just been revealed, seen partially above, as well as a bunch of new cast additions including Felicity Huffman (Transamerica, Desperate Housewives), Victor Garber (Alias, Argo) and Ted Levine (Silence of the Lambs).