Living with Earthquakes - Earthquake Engineering for Structural Design - page 42

plates. The fault displacement under the bay was measured to be nearly 240 m. The
large movements of ground in the Tokyo-Yokohama area had catastrophic
consequences; more than half of the building stock in the two cities was severely
damaged or ruined completely. However, most of the damage was due to the
devastating fires, which followed after the earthquake. The earthquake generated a
tsunami measuring 12 m high at Atami. After this earthquake, the Earthquake
Research Institute of the Tokyo University was the first research group formed for
studying both seismology and earthquake engineering. These researches
significantly contributed to the progress of the earthquake knowledge in Japan.
The 1940 US El-Centro earthquake is very important in the history of the
development of seismic design, being the first time when an earthquake was
recorded in digital form which then could be used in structural analysis. But the
instrument, which recorded this accelerogram, was attached to the concrete floor of
the El Centro Terminal Substation Building and not in a free-field location, which
can give some doubts about the actual earthquake characteristics. The record may
have under-represented the high frequency motions of the ground, because of the
soil interaction of the massive foundation with the surrounding soft soil
(Vibrationdata, 2007). Unfortunately, due to the fact that the knowledge about the
actual characteristics of different types of earthquakes was limited for a long time,
this record was used for many years in areas and for structures where such type of
earthquake acceleration can never occur.
The world's largest ground motion was the 1960 Chile earthquake, which
occurred off the coast of central Chile (Fig. 2.7). The quakes, whose magnitude of
9.5 has never been reached up to now by other recorded ones, resulted from the
rupture along the boundary of the subduction between the Nazca and the South
American Plates, which was 1000 km long and 200 km wide. Its tremors caused
widespread destruction, changes in land formations and one of the largest tsunami
recorded in the Pacific region (Wikipedia, nd). The coastal mountains uplifted
about 2 m, the hills of the Andes about 0.5 m and some offshore islands about 6 m.
The cities of Valdivia, Conception and Puerto Mont suffered the heaviest
destruction, while many smaller villages were completely destroyed. The effects of
the tsunami produced important damage in Chile (the 25m high sea waves washed
along the coasts of Hawaii, Japan and Philippines). Although the earthquake
magnitude was very high, there was not an enormous number of victims because
the population was alerted that something was going to happen by previous shakes
and underground noise.
The great 1964 Great Alaskan earthquake (Fig. 2.8) (also called Good Friday
earthquake) (Wikipedia, nd), with magnitude 9.2, was the largest ground motion