This article consists of three independent parts with the common purpose of filling some gaps in our knowledge about P wave generation and propagation. Section 1 gives a statistical and physical study of multiple, especially dou- ble, P waves generated by successive events. The frequency of occurrence of double P waves is independent of focal depth, of magnitude, and mostly of region. The time lag between the two arrivals is independent of focal depth, but it decreases with increasing magnitude. The amplitude ratio between the second, larger event and the first, smaller event is also independent of focal depth, but it increases with increasing magnitude