"soon thereafter" is a correct and usable phrase in written English.
It is often used to indicate an event that happened shortly after something else. Example Sentence: The two moons of Saturn were discovered soon thereafter.
As for Ms. O'Connor, she was spotted in a London department store in 1996, and was soon thereafter cast by Tom Ford for a Gucci runway show.
When Robert revolted against the English and claimed the Scottish throne (1306), Randolph joined the insurgency, but he was soon thereafter taken prisoner at the Battle of Methven.
The word American was soon thereafter appended to Indian to differentiate the indigenous peoples of these regions from those of South Asia.
The town is the site of Tonbridge Castle, which was originally constructed as an earth-and-timber fort by Norman invaders shortly after their arrival in 1066 but was soon thereafter converted to stone.
After the Israelite conquest of Canaan, the Tabernacle and the Ark of the Covenant were installed in Shiloh until the Ark was captured by the Philistines (c. 1050 bc) in a battle with the Israelites at Ebenezer (site unknown), and Shiloh was soon thereafter destroyed.
Poincaré married Louise Poulain d'Andecy on April 20 , 1881and was soon thereafter put on the faculty of sciences at the University of Paris.
On the day of the battle, March 19 , 1865 Foraker was promoted to brevet captain, and was soon thereafter made aide-de-camp to General Slocum.
"What's meant by direct, it may not be tomorrow, but the fear is it could be soon thereafter … The emphasis should not be on the word direct; the emphasis should be on the word threat".
