From the same article:
Among the sensors cited by Hayoun was an array installed about 70 km (43 miles) off Lebanon’s coast by the international geological project IRIS - which cast doubt on his conclusions.
IRIS said its sensors picked up more than five “small bursts” at intervals of around 11 seconds before the main Beirut explosion, a sequence that continued after the incident.
“I do not believe that they are associated with the large explosion in Beirut,” Jerry Carter, director of IRIS data services, told Reuters.