That is why scientists from China and Pakistan have teamed up to survey the trench and assess the dangers lurking in the deep.

The trench is a seismically active zone in the Arabian Sea where one plate is inching beneath the other in a “subduction zone”. The last major earthquake was a magnitude 8.1 quake in 1945, which triggered a tsunami that battered Iran, Pakistan, Oman and India, and killed around 4,000 people. And last year a 6.3-magnitude quake hit the area.

Despite the damage, not much is known about the zone.

Seismologist Yang Hongfeng, from Chinese University of Hong Kong, said scientific expeditions in this part of the ocean were quite rare.

“A lot of important scientific questions remain unanswered,” Yang said. “The results will definitely advance our understanding … [while] providing critical data to reduce the risk in the region.”

The quest is to get a better understanding of the subduction zone, which scientists say is unusual in part because it has a deposit of soft sediment several kilometres thick.

To find answers, roughly 40 researchers from the two countries boarded the Experimental 3 vessel for the trench last month, lowering instruments into the waters to do a “CT scan” of the Earth’s structure.

The expedition was a joint effort by the South China Sea Institute of Oceanology in Guangzhou and the National Institute of Oceanography in Pakistan. It was funded largely by the Chinese government-funded Chinese Academy of Sciences, according to Asif Inam, NIO director general.

“The information and data being collected during the expedition would make a significant contribution to … coastal developers and planners,” Inam said.

The threat of an earthquake near the port is a big concern for both countries.

The facility gives China access to waterways through which about 40 per cent of the world’s oil passes and is the centrepiece of the US$62 billion China-Pakistan Economic Corridor linking Gwadar to Xinjiang in China.

The corridor is also part of Beijing’s sprawling “Belt and Road Initiative”, a vast infrastructure and trade programme to project China’s influence abroad.

“There’s a whole lot at stake,” Michael Kugelman, a senior associate for South Asia at the US-based think tank Wilson Centre, said. “The port, if fully developed and operationalised, can be a critical asset for Pakistan, and there’s no nation that Pakistan would be more comfortable entrusting it to than its close friend China.”

But Kugelman said the destructive impact that an earthquake or tsunami could have on the operations of the port should not be overstated, given that actual operations were still limited.

“Still, given issues of proximity and general vulnerability – Pakistan doesn’t cope or respond well to natural disasters, given a lack of resources and incapacity – there’s certainly reason to believe that intense earthquake activity would pose a clear and present danger to Gwadar,” he said.

Developments at the port have caused unease in neighbouring India, especially with reports that Gwadar will be the site for Beijing’s second overseas military base.

“China, India, and Pakistan are on a collision course,” Kugelman said. “This isn’t to say we’re about to see conflict, but escalations in tensions are highly likely as China steps up its activities in the region, and particularly in Pakistan.”

If China built a naval base in Gwadar, as reports had suggested, it could trigger even greater tensions with India, he said.

But Zhang Jiadong, director of South Asian studies at Fudan University in Shanghai, said China’s focus should not be on India, but on solidifying its relationship with Pakistan and ensuring the success of their joint projects.

“India feels that all countries in South Asia need to listen to India,” Zhang said. “If China worries about India, it will not be able to do anything.”