'relatively common occurrence' is correct and usable in written English.
You can use this phrase to express that an event is not particularly common, but it does happen from time to time. For example, "Power outages have become a relatively common occurrence in this area."
This is a relatively common occurrence.
In his testimony, given under penalty of perjury, Spangenberg also objected to Uber's protocols to deal with raids on its offices – a relatively common occurrence at the company, which has been frequently criticised for riding roughshod over local regulations.
When meetings or conferences are canceled — a relatively common occurrence in these financially difficult times — hotels collect a fraction of the money they were expecting, and participants lose the chance to network or gain knowledge about their industry.
If a seller, for example, is counting on the proceeds of the sale of an existing house to buy a new one -- a relatively common occurrence -- it might be important for the seller to have a firm closing date on the existing house so as not to risk violating the terms of the contract to buy the new one.
Deadly stampedes are a relatively common occurrence at temples in India, where large crowds — sometimes hundreds of thousands of people — congregate in small areas lacking facilities to control big gatherings.
From the late 19th until the late 20th Century, recessions were a relatively common occurrence.
Other relatively common occurrences of the mineral dolomite are in dolomite marble and dolomite-rich veins.
Researchers also theorize that when big galaxies collide--a relatively common occurrence--their central black holes eventually merge.
Threats against police officers tend to be relatively common occurrences, and according to Jim Pasco, executive director of the Fraternal Order of Police, like most threats they're often not credible or acted upon.
Today, the existence of heteroplasmy is understood to be relatively common, although occurrence at the specific 16169 position is itself rare [13].
Kijko and Hartnady believe that – unlike the 1969 Tulbagh earthquake – this event was a mining-related earthquake which is a relatively more common occurrence than a natural earthquake in South Africa.
