"mostly occurs" is a perfectly valid phrase in written English and can be used in a variety of contexts.
For example: "The depletion of natural resources mostly occurs when resources are over-exploited."
Some of his characters are visionaries, others are technocrats; successful innovation mostly occurs when they team up.
"You probably need to increase blood flow, which mostly occurs during endurance training," she says.
Precipitation mostly occurs in the summer months in the form of high-energy thunderstorms.
While hip-hop and art have often intertwined, it mostly occurs on the fringes, not at Sotheby's.
In Indonesia, home to the world's largest Muslim population, the religious ferment mostly occurs between conservative and moderate Islam.
This mostly occurs in homogeneous image regions.
Torsional failure mostly occurs in seismic affected areas subjected to sudden failure.
In agricultural watersheds, pesticide contamination in surface water mostly occurs during stormflow events.
However, the peak traffic mostly occurs in only a small portion of the time.
Previous studies have noted that informal learning mostly occurs without a specific time and place.
In the area, rainfall mostly occurs in the monsoon period, June to September.
