Living with Earthquakes - Earthquake Engineering for Structural Design - page 40

In the following, the main earthquakes that occurred in the last century are
commented on in order to identify their influence on the main advances in seismic
design.
The first very important seismic event produced in the 20 th Century is the 1906
US San Francisco earthquake (Fig. 2.5) (USGS, nd, Wikipedia, nd) . A break 430
km long along the San Andreas Fault initiated an earthquake of 7.8 magnitude and
sparked widespread fire in the San Francisco area. The earthquake damaged large
portions of the city, especially the older buildings, which were not structurally
sound, and caused large sections of the city which had been built upon filled land
to resettle and sink. A horizontal displacement of 6.4 m was measured and in many
places broke fence lines and split roadways. Since that day, this earthquake
remains one of the most devastating to hit the San Francisco area. The main shock
epicenter occurred about 3 km from the city, being the first case when an
earthquake occurred close to a very urbanized area. At the same time, the resulting
fire after the earthquake shows the damaging effects of the out of control
subsequent fires. It has been estimated that about 90% of the total destruction was
a consequence of the subsequent fires. The destruction that resulted from this
earthquake opened the eyes of many people to the hazards of living in an
earthquake-prone zone. At the same time, the importance of this earthquake for
seismic design was the establishment of the relation between faults and
earthquakes, being the start of a scientific conception, for structural design. After
this earthquake, the Seismological Society of America was established, being
considered like the birth date of Earthquake Engineering in US.
The second very important event was the Messina earthquake. On December
28, 1908 a strong earthquake (M 7.5) hit Messina in Sicily, as well as Reggio
Calabria (Wikipedia, nd). The earthquake arose in the Messina Strait, which
separates Sicily from Calabria. After the earthquake, a tsunami was formed striking
many coastal habitats with 15m waves and causing even more destruction than the
earthquake itself. This is one of the largest tsunami ever to have occurred. The
cause of this earthquake was due to the existing fault system, resulting from the
subduction of the African tectonic plate under the Eurasian one. With 83,000
deaths, the Messina earthquake is, until today, the most murderous among the
European earthquakes. According to Housner (2002), this earthquake can be
considered the origin in Italy of practical earthquake engineering, because the
Commission report appears to be the first engineering recommendation for the
design of earthquake-resistant structures, by using the equivalent static method of
analysis.
The third very important earthquake of the beginning of the 20 th Century was
the 1923 Japan Kanto (Tokyo) earthquake (Fig. 2.6), (Wikipedia, nd), produced in
the area around Sagami Bay with a magnitude of 8.3. The origin of this earthquake
was the presence of a fault system associated to the existence of four tectonic
plates (Pacific, Philippine, North American and Eurasian plates) near the Japan
Isles. In the frame of this fault system, the Pacific plate subducted under the other