A cryptic boom has shaken the US city of San Diego near the border with Mexico, prompting wild speculation among residents. Unlike two previous incidents, which occurred within 10 minutes after 5 pm (local time), the latest one occurred after sunset around 8:20 pm. According to social media users the loud noise prompted residents to rush to their neighbours, asking whether they also felt it.
A sonic boom, explosion, and earthquake were among the most popular "suspects".
The earthquake scenario was later dismissed by the US Geological Survey, which said that no tremors were recorded in the vicinity of San Diego.
One person suggested that the mysterious boom felt like a severe natural disaster.
Another suggested that the loud noise was likely made by the US Marine Corps, which previously warned residents about the live-fire training.
The mayor of San Diego also spoke about the incident and took the opportunity to remind residents to get jabs against COVID-19.