"Shallow‐focus earthquakes occur along transform boundaries where two plates move past each other. The earthquakes originate in the transform fault, or in parallel strike‐slip faults, probably when a frictional resistance in the fault system is overcome and the plates suddenly move."
https://www.cliffsnotes.com/study-guides/geology/earthquakes/earthquakes-and-plate-tectonics
<span>An air mass is a large body of air that have similar characteristics, such as pressure, temperature, and moisture. What determines its characteristics is the source region. The source region is the surface over which it is formed.</span>