While I don’t see any connection between the 2 events, I’d surmise the crater might have been caused by a ruptured fire main, which might have given a volume of reactant to a larger chemical reaction. The explosion might have consumed much of the product and left a sink hole in its wake.
Unless there were UG storage tanks of some reactants which were also consumed by the event.
I suspect a lot of information isn’t being accurately reported,...e.g. from http://www.scmp.com/news/china/society/article/1849892/blast-survivor-found-shipping-container-chinese-city-tianjin
“Han Fengqun, 56, was found at 2pm in a shipping container 50 metres from the centre of the blast area, according to state broadcaster CCTV.
He was found by troops trained in chemical defence and warfare under a pile of shipping containers that had been buckled by the force of the blasts on Wednesday night.
They had been searching through the containers by torchlight before they found him, the report said.
He was still conscious and able to say a few words before he was taken to a military hospital.”