Background and Scope - Tohoku, Japan Earthquake and Tsunami of 2011 - page 18

earthquake on the northern tip of Honshu caused over $170 million damage, injured
200 people, and killed three.

1.4.3GlobalContextoftheGreatEastJapanEarthquake
The Great East Japan earthquake, unprecedented in Japan's recorded history,
provides a useful comparison to other large magnitude events around the world.
Table 5 presents the magnitudes and focal depths for earthquakes with a moment
magnitude of 8.8 and above after 1900. The absence of modern recording equipment
and general availability of reliable records make prior large magnitude events harder
to quantify.

Table 5 lists events in order of descending moment magnitude, Mw, a measure of the
total amount of work done in the seismic rupture. Mw relates to the final static
displacement at the rupture interface. A metric more representative of the effect of the
earthquake on land is the energy magnitude, Me, which uses the velocities observed
at the land surface to assess the relative size of an earthquake. Energy magnitude,
derived from velocity power spectra (energy flux in the pressure waves), is a measure
of the earthquake's potential for damage to people and structures. For older
earthquakes, the surface wave magnitude, Ms was used to evaluate ground effects by
measuring the amplitude and period of Rayleigh surface waves, however, the energy
magnitude, Me, is considered to be more accurate for large events.

Table 5. Earthquakes of moment magnitude 8.8 and above since 1900 (Source:
NGDC Earthquake Database; Energy Magnitudes, Me, from USGS, Mt from Abe
2011)
Earthquake

Focal
Depth

Moment
Magnitude

Energy
Magnitude

Surface
Magnitude

Tsunami
Magnitude

(km) Mw Me Ms Mt

Chile,Valdivia(1960) 33 9.3

9.5 8.3

Alaska(1964) 33 9.1 9.2 8.4

Sumatra(2004) 30 9.0 9.1 8.5 8.8

32 9.1 Great East Japan

(2011)

9.0 8.9

Kamchatka(1952) 45 9.0 9.0 ‐ 8.5

Chile,Maule(2010) 23 8.8 8.8 8.2 8.5

Ecuador(1906) 25

‐

8.8 ‐ 8.6

Of note in Table 5, the energy magnitude of the Great East Japan event is quite large
compared with the energy magnitude calculated for the 2004 Sumatra earthquake, an
event of comparable seismic moment. The shaking energy released at the surface of a
seismic event is a very small percentage, about 10 -5 , of the work done during the
seismic rupture. The magnitude of Me = 8.9 represents a surface energy release, Es,
of 5.1 x 10 17 joules as reported by the USGS (2011). The surface energy reported by
Ide (2011) for the Great East Japan earthquake was even higher at 9.1 x 10 17 joules.