The United States Geological Survey ruled out an earthquake in San Diego saying that there were no indications of shifts in the area. Their confirmation came in the wake of many people across the county reporting a ‘mysterious boom’ on Friday morning.

The San Diegans said on social media that a sound was heard From Mission Valley to El Cajon and north to Encinitas and speculation raged as to whether it was a sonic boom, an earthquake, or potential military activities in the area. Dissuading such speculations, some people also said that it was merely the thunder and lightning, given that a storm system is currently sweeping the county.

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The confirmation by the Geological Survey might have given relief to San Diegans, but the question mark around the mysterious sound still remains. News outlets reporting on the issue reached out to local law enforcement as well as the military seeking an explanation for what the sound could be. A definitive explanation has not been provided as yet.

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However, a Marine lieutenant at Camp Pendleton told FOX5 News that he cannot say for certain what the sound was of, but added that it could be “routine live-fire training with high explosive munitions” by the army.

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Meanwhile, on social media, users continued to look for answers to what they experienced.

“Alright so many people heard a boom, felt shaking, more than once and nothing is on @USGS in #SanDiego. If it wasn’t an #earthquake— what was it? @MCASMiramarCA @CBS8,” wrote one user.

“Earthquake in San Diego or sonic boom? Felt and heard in North county – any one in South county feel or hear that ?? 2 big shakes and 2 big booms,” another one said.