Spectrogram - Regional Earthquake
These are quakes that occur outside the PNSN area but less than 1,000 km away. These include events from California, British Columbia, Idaho and Montana and from the Juan de Fuca plate offshore. Regional events will usually be recorded by most stations within several geographical areas. Usually two very distinctly different phases (bursts of energy) can be seen from 10s of seconds to two minutes apart. The first phase (P-wave) usually will have a slightly higher frequency content than the second phase (S-wave), which may be stronger.