The 1762 earthquake was born from one of the planet's most complex tectonic boundaries. Eastern Bangladesh and southwestern Myanmar sit along the oblique convergent zone where the Indian plate grinds northward into the Eurasian plate. Unlike a simple head-on collision, the motion here is diagonal, producing a mix of forces: thrust faulting where the plates compress against each other, and strike-slip faulting where they slide laterally past one another. The Western Burma Scarp accommodates some of this sideways motion, while the Indo-Burmese Wedge, a fold and thrust belt to the north, absorbs the compression. Major faults like the Kabaw and Sagaing slice through the region farther east. This is not a single fault line but a broad zone of deformation, and when it ruptures, it does so on a scale that reshapes geography.

In Chittagong, the shaking lasted approximately four minutes -- an eternity for an earthquake. The exact epicenter remains uncertain; researchers have placed it anywhere from near Chittagong to along the Arakan coast of modern Myanmar. The rupture may have extended hundreds of kilometers along the plate interface, with displacements estimated at 9 to 16 meters. The sheer scale of the event is debated among seismologists. Some estimates, based on the extent of coastal uplift recorded from Foul Island to Ramree Island and subsidence around Chittagong, place the magnitude as high as 8.8. Others argue the evidence is ambiguous and suggest a magnitude between 7 and 8. What is not debated is the destruction. At Bar Chara, just north of Cox's Bazar, the land sank and 200 people died. Chittagong, the region's major port, "suffered severely" -- the ground split open, sand volcanoes erupted through fissures, and the soil itself liquefied beneath buildings.

The earthquake triggered a tsunami in the Bay of Bengal. It was a local event -- no effects were recorded on the bay's western shores in India -- but along the coastline nearest the rupture, the ocean surged inland across land that was simultaneously sinking. Near Chittagong, approximately 60 square miles of coastal territory permanently subsided beneath the waves. Entire stretches of shoreline that had been dry land on the morning of 2 April were underwater by evening, and they remain underwater today. The uplift along the Arakan coast told the opposite story: sections of seabed rose above the waterline from Foul Island to Ramree Island, reshaping the coastline in the other direction. The earthquake did not merely shake the ground. It redrew the boundary between land and sea along hundreds of kilometers of coast.

Perhaps the earthquake's most extraordinary consequence was its effect on the Brahmaputra, one of Asia's great rivers. Before 1762, the Brahmaputra flowed east of Dhaka along what is now called the Old Brahmaputra River. The earthquake's tectonic disruption -- the uplift, subsidence, and tilting of the landscape -- redirected the river 150 kilometers to the west, where it carved a new channel now known as the Jamuna River. The Jamuna today is a braided river over 10 kilometers wide in places, one of the largest rivers in the world by discharge. Every monsoon flood, every silt deposit, every riverbank erosion along its course traces back to an afternoon in 1762 when the earth moved and a river was forced to find a new way to the sea. The Old Brahmaputra still exists as a smaller channel east of Dhaka, a geographical ghost of the river's former self.

The 1762 Arakan earthquake matters today because the tectonic forces that produced it have not gone away. The Indian plate continues its northward push at roughly 50 millimeters per year. Stress accumulates along the same faults and plate boundaries that ruptured in 1762. Modern researchers studying the event have debated its true size precisely because understanding it bears directly on estimating the risk of future earthquakes and tsunamis in the Bay of Bengal -- a body of water now bordered by some of the most densely populated coastlines on Earth. Chittagong, Cox's Bazar, and Dhaka are orders of magnitude more populous than they were in 1762. A repeat event of similar magnitude would affect tens of millions of people. The subsided coastline, the rerouted river, the uplifted coral reefs along the Arakan shore -- these are not just historical curiosities. They are evidence of what this stretch of earth is capable of.