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Japan has more measurable #earthquakes than any other country. This is because #Japan is wedged among four major tectonic plates. (Thread) 
80% of earthquakes worldwide occur around the circum-Pacific region chiefly along the subduction-zone boundaries, known as the “Pacific Ring of Fire”, so named because of the more than 400 active volcanoes that occur there.
The earthquake and volcano belt sweeps through Japan where about 20% of worldwide measured earthquakes occur. There are more than 100,000 earthquakes recorded in Japan every year. Of those about 1,500 are strong enough for people to notice.
Over 100 major earthquakes of M7 or larger have occurred in the past century.
The Pacific Plate subducts beneath the Okhotsk Plate at the Japan Trench. The rate of convergence is ~8.3 cm/yr. The Philippine Sea Plate subducts beneath central and southwest Japan at the Sagami Trough, the Nankai Trough, and the Ryukyu Trench.
Geoscientists observed that the displacement between the Pacific & Okhotsk plates during #earthquakes of the past few centuries was less than the plate motion. They were concerned the subduction zone might be storing elastic energy that could be released in a big earthquake.
On March 11 2011, the Tohoku-oki M9 earthquake ruptured a 500-km-long by 200-km-wide area of the plate boundary over an interval of 3 minutes. Extreme ground shaking affected coastal towns of northeastern Honshu and strong shaking lasted for 6 minutes in Tokyo.
Superior construction practices and earthquake preparedness impressively mitigated damage from ground shaking during this earthquake confirming that Japanese cities often shake but they rarely topple.
Unfortunately, the #tsunami generated by the Tohoku-oki earthquake reached greater heights and much farther inland than had been anticipated for tsunamis in this area.
Rupture initiated at the hypocenter, 24 km beneath the seafloor, then propagated both up-dip to the E and down-dip to the W. Max fault displacement reached 40m at a location 50 km from the Japan trench then decreased to 20m at the trench.
These are the largest fault displacements documented for any earthquake in history.
Elastic rebound during the #earthquake caused stations along the coast nearest the epicenter to jump E by as much as 4.4m. Seafloor uplift reached 7m above the zone of max fault displacement while the seafloor dropped by 2 m between the epicenter and the coast.
Most of the coastal area subsided during the earthquake. That vertical displacement of the ocean floor produced the tsunami that rushed onshore within 20 minutes of the earthquake.
In coastal areas where seafloor bathymetry & onshore topography focused wave energy, the tsunami reached elevations of 40 m above sea level. Although 96% of citizens successfully evacuated the tsunami inundation zone, nearly 20k lives were lost.
This painful lesson taught us that the subduction zone between the Pacific and Okhotsk plates, and probably others worldwide, can store elastic energy over 1000-year intervals then release that energy in just a few minutes during massive #earthquakes.
As towns in northeast Honshu devastated by the 2011 tsunami are being rebuilt, changes in coastal land-use practices are being implemented to decrease the number of people living and working in vulnerable near-shore areas.
In this and many other ways, Japan continues to advance #earthquake and #tsunami preparedness. To learn more please watch this educational video on the Tectonics of Japan -
Another great animation (by @UNAVCO) compares the tectonic setting of the PNW to Japan by showing how the shallow portion of the Cascadia plate boundary is locked, compressing the NA Plate in a NE direction during subduction of the Juan de Fuca Plate. iris.edu/hq/inclass/ani…
