Visit the NEIC website for more information. This is the time at which an earthquake begins. On a seismogram, the earthquake origin time can be determined by the P wave arrival. See also P Wave and NEIC . A P Wave is one of two types of body waves.
P stands for primary or pressure or push-pull.
It is similar to a sound wave. See also Body Waves , S Waves , Surface Waves . Go to What are Seismic Waves by UPSeis to learn more about P waves. This is the time at which the first phase, the P Wave arrives. It marks the beginning of the earthquake on the seismogram.