1944 Tōnankai earthquake
At 1:35 in the afternoon on December 7, 1944 -- exactly three years after Pearl Harbor -- the seafloor off Japan's Pacific coast lurched. The 1944 Tōnankai earthquake, magnitude 8.1, was the strongest earthquake anywhere in the world that year. Along the coast of the Kii Peninsula and the Tōkai region, the ground shook at intensities that would later be classified as severe on the Mercalli scale. Within minutes, the ocean drew back from the shore. Then it returned as a wall of water ten meters high. Japan was already reeling from the war. Now the earth itself had turned against it. By the time the shaking stopped and the waters receded, 1,223 people were dead and another 2,135 lay seriously injured.
The Trough That Never Sleeps
The southern coast of Honshū runs parallel to the Nankai Trough, a 700-kilometer-long submarine trench where the Philippine Sea plate dives beneath the Eurasian plate. This convergent boundary is one of the most seismically active zones on Earth. The Nankai megathrust has five distinct segments, labeled A through E, that can rupture independently or in combination. For at least 1,300 years, these segments have broken in a repeating pattern, often firing in pairs with a short gap between them. The 1944 Tōnankai event ruptured segments C and D. Two years later, in 1946, the neighboring segments A and B broke in the Nankai earthquake. The same paired pattern had occurred in 1854. Each time, the northeastern segment ruptured first, as if the earth follows its own grim choreography.
A Coastline Shattered
The eastern face of the Kii Peninsula bore the worst of the damage, particularly the cities of Shingū and Tsu. The shaking alone destroyed 26,146 houses. Eleven buildings burned to the ground. Then came the tsunami, which obliterated a further 3,059 homes. Nearly 47,000 additional houses suffered serious damage from the combined assault. The rupture area measured approximately 220 by 140 kilometers, with a maximum displacement of 2.3 meters along the fault. Scientists later determined that splay faults -- subsidiary fractures branching off the main plate interface -- likely played a critical role in generating the tsunami. These splay faults act as amplifiers, redirecting seismic energy upward to displace massive volumes of water in ways that a simpler fault geometry would not.
Waves Across the Pacific
The maximum recorded tsunami wave height was ten meters on the Kumano coast in Mie Prefecture. Run-ups exceeding five meters struck multiple locations along the coasts of both Mie and Wakayama Prefectures. But the tsunami did not stop at Japan's shores. It propagated across the entire Pacific basin, observed along Japan's coastline from the Izu Peninsula in the northeast all the way to Kyushu in the southwest, and detected by tide gauges as far away as Alaska and Hawaii. The wartime Japanese government, already struggling to control information about military setbacks, suppressed news of the earthquake's full devastation. The disaster remained poorly documented for years, its true scale emerging only in the postwar period when censorship lifted.
A Clock Still Ticking
The 1944 Tōnankai earthquake was not an isolated event but a chapter in a recurring saga. The segment of the Nankai megathrust immediately to the east of the 1944 rupture zone -- segment E -- has not broken since 1854, making it overdue by historical standards. Seismologists consider the likelihood of a future Tōkai earthquake along this segment to be high. There is no evidence that segment E has ever ruptured on its own; any break there could cascade into segments C and D as well, potentially replicating the devastating 1854 Tōkai earthquake. The Nankai Trough remains one of the most closely monitored seismic zones in the world, a place where the question is not whether the next great earthquake will come, but when.
From the Air
The earthquake's epicenter is located offshore at approximately 34.0N, 137.1E, in the Pacific Ocean south of the Tōkai coast of Honshū. From the air, the Nankai Trough runs roughly parallel to the southern coast of Honshū. The most heavily damaged areas -- Shingū, Tsu, and the Kumano coast -- are visible along the eastern Kii Peninsula. Nearest major airports: Chubu Centrair (RJGG) to the north, Nanki-Shirahama (RJBD) on the Kii Peninsula's southwest coast. The coastline shows modern tsunami defenses and seawalls in many areas. Recommended viewing altitude 5,000-10,000 feet for coastline perspective along the Kii Peninsula.