Beirut, Lebanon – The first time Eliah Kaylough, 26, heard the thunderous blast, he was so terrified, he instinctively ran for cover. On Tuesday this week, he had just started his shift as a waiter at a restaurant on bustling Gemmayze Street in east Beirut when he was suddenly startled by the sound of a major blast.

For Kaylough, it immediately triggered memories of the massive port explosion in 2020 and he was terrified the city was either experiencing a new explosion or that it was under attack.

But as he was racing out of the restaurant, a man from a nearby shop stopped him and explained that Beirut wasn’t being bombed. The sound, Kaylough discovered, was a sonic boom, a thunderous noise caused by an object moving faster than the speed of sound.

Israeli jets have been increasingly triggering these sonic booms over Lebanon since October 7 last year, following the attack on southern Israel by Hamas. But the booms which sounded over Beirut on Tuesday were the loudest that had been heard in the city, several residents told Al Jazeera.

Kaylough said that it was the first time that he had heard one since Israel tends to launch sonic booms in other parts of the country and city.

“The sound was terrifying and I really thought we were under attack,” Kaylouh told Al Jazeera on Thursday evening at the restaurant, where he was back working a shift. “I remember putting on my hat and grabbing my bag and I was ready to close up shop.”

Since October, the Lebanese armed group, Hezbollah, and Israel have been engaged in a low-level conflict. On Friday, Israel stepped up its attacks, killing Hamas official Samer al-Hajj in a drone attack on the coastal city of Sidon, about 50km (30 miles) from Lebanon’s southern border.

Throughout the Gaza war, however, Israel has been launching sonic booms by flying jets at low altitudes over Lebanon in an apparent effort to intimidate and terrify the population, analysts and residents told Al Jazeera.

“We are concerned about the reported use of sonic booms by Israeli aircrafts over Lebanon that has caused great fear among the civilian population,” said Ramzi Kaiss, a Lebanon researcher for Human Rights Watch. “Parties in armed conflict should not use methods of intimidation against a civilian population.”

Indeed, sonic booms heard earlier this week occurred just two days after the anniversary of the August 4, 2020 Beirut-port explosion, which devastated large swaths of Beirut, killed more than 200 people and injured thousands. The blast was caused by a fire in a warehouse where a stockpile of highly combustible ammonium nitrate was being stored.

Tuesday’s sonic boom was triggered just moments before Hezbollah’s Secretary-General Hassan Nasrallah was about to begin a speech. Last month, tensions between the foes escalated after Israel assassinated Hezbollah’s senior commander, Fuad Shukr, in Lebanon and Hamas’s political leader Ismail Haniyeh in Iran’s capital Tehran.

Systematic use of ‘sound terror’

The use of sonic booms is part of a broader trend of psychological warfare that Israel wages against the Lebanese population, according to Lawrence Abu Hamdan, a sound expert and the founder of Earshot, a nonprofit that conducts audio analysis to track human rights abuses and state violence.

Abu Hamdan said that since the 2006 Hezbollah-Israel war, which lasted 34 days and left 1,100 Lebanese nationals and 165 Israelis dead, Israel has routinely violated Lebanese airspace with its fighter jets to scare civilians.

“Since the truce of 2006, there have been more than 22,000 Israeli air violations of Lebanon. In 2020 alone, there were more than 2,000 [air violations] with no response from Hezbollah, Abu Hamdan told Al Jazeera.

Abu Hamdan believes that, since last October, Israel has also been using sonic booms as an “acoustic reminder that [Israel] can turn Lebanon into Gaza at any point”.

He said Israel’s increasing use of sonic booms reflects the escalation in conflict with Hezbollah over the past several months.

“There is an escalation and we are seeing that escalation in sound. The next phase to the escalation is, of course, material destruction,” Abu Hamdan said.

Beirut resident Rana Farhat, 28, said Israel’s scare tactics are having the desired effect. She heard the August 6 sonic booms while having dinner with her family at a restaurant in a town north of Beirut.

They were startled when they heard the sound of an explosion, but her parents tried to reassure her and her siblings that Beirut was not being attacked. Everyone quickly checked their phones to find out what was going on.

“We were all checking the news to see if it was an explosion or not,” Farhat, 28, said, while smoking shisha in a Beirut cafe on Thursday night. “There were little children in the restaurant and they were clearly scared. They don’t understand what such sounds mean.”

Recurring trauma

The murmur of fighter jets and other blast-like noises can re-traumatise populations that have survived previous explosions and wars, Abu Hamdan said.

Over the long term, recurring jet and blast sounds can even increase the risk of stroke and deplete calcium deposits in the heart, according to medical studies he cited.

“Once you have been exposed to [jet or blast] sounds that have produced the sort of fear that they have in this country, then whenever you hear it – even quietly – it will produce the same stress response [in an individual],” Abu Hamdan explained.

Kaylough said that the sonic booms he heard on Tuesday this week transported him back to the Beirut port explosion. That day, he was working in a mall when a sudden blast shattered the glass around him and blew the doors off the hinges of the store he was working in.

“The sound was so loud. I remember people were screaming, but I couldn’t hear them,” he told Al Jazeera.

After the initial shock, Kaylough felt a sudden pain and realised that a large piece of metal was wedged into his lower leg. He was rushed to hospital and eventually treated by doctors.

While Kaylough suffered no long-term physical injuries, he says the sonic booms are triggering the trauma he experienced that day.

“The [sound from] the sonic boom did take me back to the moment of the blast, but I’m just trying not to think about it,” he said.

Farhat said the sonic booms also remind her of the 2006 war.

At the time, her neighbourhood was not directly being hit,  but she remembers watching coverage of the war on television with her parents. As a 10-year-old, she realised that the scenes of collapsed buildings and rubble she was seeing were being filmed just a short drive from her home.

She also recalls hearing the sound of Israeli fighter jets flying over Beirut to bomb the southern suburbs. While Farhat does not know if another war is looming over Beirut right now, she insisted that Israel’s scare tactics won’t compel her to leave her beloved city.

“They are just trying to scare us, but I take it as a sign of weakness,” she told Al Jazeera. “Whatever happens, I don’t want to leave home and I won’t. I was born here, raised here and I will stay here.”