Qualla: 1703 Genroku Earthquake

1703 Genroku Earthquake: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Amojo Enite James, CC BY-SA 4.0. At two o'clock in the morning on December 31, 1703, the ground beneath Edo -- the city that would become Tokyo -- began to shake with a violence that would not be matched for over two centuries. The Genroku earthquake ruptured along the Sagami Trough, where the Philippine Sea Plate grinds beneath the Eurasian Plate, releasing energy equivalent to a magnitude 8.1 to 8.4 event across at least two and probably three fault segments. Within minutes, fires erupted in the darkness. Within hours, a tsunami was racing toward coastlines from the Izu Peninsula to the Boso Peninsula. By the time the sea retreated, at least 5,233 people were dead -- some estimates push the toll as high as 200,000.

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Image: Amojo Enite James | CC BY-SA 4.0

1703 Genroku Earthquake: The Last Night of Genroku

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Kalabarian, CC BY-SA 3.0. The earthquake struck during the Genroku era, a culturally significant period spanning 1688 to 1704 that marked a golden age of arts, commerce, and urban life in Edo-period Japan. The timing could hardly have been worse: the middle of a winter night, when residents were asleep in...

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Image: Kalabarian | CC BY-SA 3.0

1703 Genroku Earthquake: The Sea Arrives

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Alexrk2, CC BY-SA 3.0. The tsunami generated by the Genroku earthquake swept across a staggering 400 kilometers of coastline. Run-up heights exceeded 5 meters over wide stretches, with the waves reaching 10.5 meters at Wada on the Boso Peninsula and 10 meters at both Izu Oshima island and Ainohama. Dea...

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Image: Alexrk2 | CC BY-SA 3.0

1703 Genroku Earthquake: The Trough Beneath

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Pekachu, CC BY-SA 3.0. Modern seismology has revealed the Genroku earthquake's mechanism with unsettling clarity. The Sagami Trough, running offshore of the Kanto region, marks the boundary where the Philippine Sea Plate subducts beneath the continental plate at a rate of several centimeters per year. ...

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Image: Pekachu | CC BY-SA 3.0

1703 Genroku Earthquake: Echoes in the Modern City

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit As6022014, CC BY-SA 3.0. The 1703 Genroku earthquake matters today because the same fault system remains active beneath one of the most densely populated regions on Earth. Greater Tokyo's 37 million residents live above the convergence zone of three tectonic plates, and the Sagami Trough continues to acc...

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Image: As6022014 | CC BY-SA 3.0