The Flores back-arc thrust fault runs just off Bali's northern coast, stretching east through the Banda Sea from Bali to the island of Wetar. It formed from the slow collision between the Sunda and Australian tectonic plates, which converge northward in a grinding process that has produced at least 26 earthquakes of magnitude 6.0 or greater since 1960. The same fault would rupture again in 1992, killing thousands in Flores, and again in 2018 during the devastating Lombok earthquake sequence. In 1815, the fault delivered a shallow magnitude 7.0 shock directly beneath the mountainous terrain above the Buleleng coast. The shallowness of the rupture amplified the shaking intensity to IX on the Mercalli scale, meaning structures were violently thrown apart. Tremors reached Surabaya on Java and the island of Lombok, but the worst destruction was concentrated along the narrow strip of coast where mountains meet the sea.

Heavy rainfall in the days before the earthquake had destabilized the steep slopes above Singaraja. When the shaking began, the saturated mountainsides collapsed in what must have sounded, in the darkness, like artillery fire. The landslide carried boulders and debris down the Banyumala River, growing in volume as it gathered river sediment and vegetation. Dutch colonial official Bloemen Waanders later documented the scale of the flow. According to his reports, seventeen villages were engulfed entirely. Gusti Panji Sakti, a local Balinese authority, provided his own account of the flow depth, though the exact figures in both reports have been lost to incomplete transcription. What is certain is the death toll: at least 10,253 people died beneath the landslide alone, buried as they slept. A fissure opened from Buleleng all the way to Tabanan, agitating Lake Tamblingan and causing flooding far from the epicenter. The landscape of northern Bali was remade in a single hour.

The landslide debris did not stop at the shoreline. Massive flows of rock and sediment poured into the sea along Bali's northern coast, displacing enough water to generate a destructive tsunami. The wave killed an additional 1,200 people and swept away the coastal buildings of Buleleng harbor in Pabean District. Gusti Panji Sakti recorded the tsunami's run-up height, though the specific measurement is not preserved in surviving translations. What makes this tsunami unusual is its origin: it was not triggered directly by the seafloor displacement of the earthquake, but by the secondary effect of landslide material entering the ocean. This mechanism made the wave intensely local. No tsunami was reported on nearby Lombok or Java, despite both islands having felt the earthquake's shaking. The destruction was concentrated exactly where it could do the most harm, along the densely settled coast of the Bali Kingdom's northern capital.

Singaraja, the seat of power in northern Bali, was devastated. The earthquake struck at the worst possible hour. Families were indoors, asleep, in structures that offered no protection against both violent shaking and the wall of debris that followed. Aftershocks continued for at least an hour after the initial rupture, preventing any organized response in the darkness. The Bali Kingdom, which had governed the island's northern coast, suffered a blow from which recovery would take decades. The event unfolded six months after the eruption of Mount Tambora on nearby Sumbawa, which in April 1815 had produced the largest volcanic eruption in recorded history. For the people of the Lesser Sunda Islands, 1815 was a year of compounding catastrophe. The earthquake's destruction of Buleleng's political and economic infrastructure left northern Bali vulnerable during a period when colonial pressures from the Dutch were steadily increasing.

Modern seismologists have modeled what a magnitude 7.3 earthquake on the Flores back-arc thrust would produce today, and the results are sobering. The models predict shaking intensities of VIII to IX across northern and eastern Bali, the same levels that destroyed Buleleng in 1815. Bali's northern coast remains directly above the fault, and the intervening two centuries have added population, infrastructure, and tourism to the equation. The 1992 Flores earthquake and the 2018 Lombok sequence both demonstrated that this fault system remains active and capable of generating major tsunamis. What happened in 1815 was not an anomaly. It was the expected behavior of a tectonic boundary that will rupture again. The ruins of old Singaraja lie beneath the modern city, a reminder that geology operates on timescales that outlast both kingdoms and memories.