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On 11 March 2011 at 14:46 local time (JST), a magnitude Mw 9.1 earthquake struck off the northeast coast of Honshu, Japan's largest island. The Tohoku earthquake (officially the Great East Japan Earthquake) was the most powerful earthquake ever recorded in Japan and the fourth largest globally since 1900. The subsequent tsunami killed the vast majority of victims and triggered a nuclear disaster at Fukushima Daiichi. This case study addresses Edexcel A-Level Geography Enquiry Question 2 (EQ2) and provides essential comparative material with the Nepal 2015 case study.
Japan occupies one of the most tectonically complex locations on Earth, sitting at the junction of four tectonic plates:
| Plate | Type | Interaction with Japan |
|---|---|---|
| Pacific Plate | Oceanic | Subducts beneath the Okhotsk Plate at the Japan Trench |
| Philippine Sea Plate | Oceanic | Subducts beneath the Eurasian Plate at the Nankai Trough |
| Okhotsk (North American) Plate | Continental | Overrides the Pacific Plate in northeast Japan |
| Eurasian Plate | Continental | Overrides the Philippine Sea Plate in southwest Japan |
The 2011 earthquake occurred on the Japan Trench subduction zone, where the Pacific Plate subducts beneath the Okhotsk Plate at approximately 8–9 cm/year. This is one of the fastest convergence rates on Earth.
| Tectonic Detail | Information |
|---|---|
| Plate boundary | Oceanic-continental subduction (Pacific beneath Okhotsk) |
| Convergence rate | ~8–9 cm/year |
| Fault type | Megathrust (low-angle reverse fault) |
| Earthquake magnitude | Mw 9.1 |
| Depth | 32 km |
| Rupture area | ~500 × 200 km (100,000 km²) |
| Slip | Up to 50 m (one of the largest fault displacements ever recorded) |
| Duration of rupture | ~150 seconds (2.5 minutes) |
| Epicentre | 38.30°N, 142.37°E (130 km east of Sendai, 373 km NE of Tokyo) |
The earthquake released approximately 1.9 × 10¹⁷ joules of energy — equivalent to approximately 600 million times the energy of the Hiroshima atomic bomb. It shifted the Earth's axis by an estimated 10–25 cm and shortened the length of the day by approximately 1.8 microseconds.
Exam Tip: When describing the Tohoku earthquake, emphasise the unprecedented fault slip (up to 50 m) and rupture area (100,000 km²). These figures explain why the earthquake generated such a devastating tsunami — the massive vertical displacement of the seafloor displaced an enormous volume of water.
| Effect | Detail |
|---|---|
| Shaking intensity | JMA Intensity 7 (maximum on the Japanese scale) in Miyagi Prefecture |
| Duration of strong shaking | ~3–5 minutes in the Tohoku region (exceptionally long) |
| Shaking felt | Across virtually all of Japan's main islands |
| Building damage from shaking | Relatively limited — Japan's seismic building codes performed extremely well |
| Infrastructure | Some older buildings and bridges damaged; bullet train (Shinkansen) stopped automatically by earthquake early warning system |
Japan's seismic building codes (Building Standards Act, revised after the 1995 Kobe earthquake) ensured that most modern buildings withstood the shaking, even at MMI IX intensity. Base isolation, cross-bracing and damping systems proved effective. The Shinkansen (bullet train) was automatically stopped by the Earthquake Early Warning system — no derailments occurred despite several trains being in operation at the time.
GPS measurements revealed that parts of northeast Japan moved up to 5 m eastward and subsided by up to 1.2 m as a result of the earthquake. The city of Ishinomaki, for example, subsided by 78 cm, permanently increasing its flood risk.
The tsunami was by far the most destructive aspect of the 2011 disaster. The vertical displacement of the seafloor (up to 10 m uplift) generated a tsunami that crossed the Pacific Ocean.
| Property | Detail |
|---|---|
| Maximum run-up height | 40.5 m (Miyako, Iwate Prefecture — verified by field survey) |
| Maximum inland penetration | Up to 10 km in flat coastal areas (Sendai Plain) |
| Arrival time | First waves reached the Tohoku coast within 25–30 minutes |
| Warning | JMA issued tsunami warning within 3 minutes; initial estimate was 3 m (later upgraded to 6–10 m, then "immense") |
| Speed | ~700 km/h in the open Pacific; ~30–40 km/h at the coast |
| Wave period | ~30–60 minutes between successive waves |
Japan had the world's most extensive tsunami defence infrastructure:
| Defence | Performance |
|---|---|
| Tsunami seawalls | Many were overtopped — walls designed for 5–10 m waves were hit by 15–40 m waves. The Taro seawall (10 m high, built after 1933 tsunami) was overtopped and partially destroyed |
| Breakwaters | The Kamaishi breakwater (world's deepest at 63 m, cost $1.5 billion) was breached; it reduced tsunami height by approximately 40% but was insufficient |
| Tsunami gates | Some operated successfully; others failed mechanically or were overwhelmed |
| Evacuation routes | Many designated evacuation sites were in the inundation zone; some evacuation routes were flooded before people could reach safety |
| Historical stone markers | Ancient tsunami stones on the Tohoku coast warned: "Do not build below this point." Most were ignored in the post-war construction boom |
Exam Tip: Japan's tsunami defences represent a critical lesson: engineered defences can create a false sense of security. Communities behind seawalls believed they were safe and delayed evacuation. Some researchers argue that the seawalls increased mortality by encouraging complacency. This is a valuable evaluative point for 20-mark essays.
The tsunami flooded the Fukushima Daiichi Nuclear Power Plant, disabling the backup diesel generators that powered the cooling systems. Without cooling, three of the plant's six reactors experienced partial meltdowns. The nuclear disaster was rated Level 7 on the INES scale (the maximum), the same as Chernobyl (1986).
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