The 1923 Great Kanto Earthquake

1
(No Transcript)
2
The 1923 Great Kanto Earthquake
Introduction
Located on top of several converging tectonic
plates, Japan is deemed one of the most
earthquake-prone countries in the world (1). It
lies at the junction of the Eurasian, Pacific,
and Philippine Sea plates, one of the most
seismically active areas of the world (2). Among
the cities of Japan, the Kanto district in
central Japan has the most frequent occurrence of
earthquake activities. A recent study indicates
that there are numerous repeating earthquake
activities happening in the Kanto area due to the
Philippine Sea plate subduction (3). (see figure
1) The last devastating earthquake happened in
this region occurred in 1923, known as the Great
Kanto earthquake.
Figure 1 repeating earthquakes in The Kanto
region
Source Tectonophysics (3)
3
The 1923 Great Kanto Earthquake
Introduction (cont)
In this major event, a great number of people
lost their lives and many left homeless. It is
claimed as one of the worlds most destructive
earthquakes ones with 50,000 or more deaths
(4). It took a long time for the government to
rebuild the region because the damage caused by
the event was too great to recover in a short
period of time.
Figure 2 cities are destroyed
Source SiberHegner
Figure 3 many people left homeless
Source SiberHegner
4
The 1923 Great Kanto Earthquake
September 1, 1923
Two minutes before noon, an earthquake with
magnitude 7.9 stroke the Kanto district on the
first day of September, 1923. Official records
claimed 10 minutes of felt vibration and up to
two and a half hours of constant motion (5). The
event caused 142,800 deaths and firestorms that
burned about 381,000 houses in Tokyo and
Yokohama. It also caused nearly 2 meters of
permanent uplift on the north shore of Sagami Bay
and a horizontal displacement of 4.5 meters on
the Boso Peninsula (5). A tsunami followed the
earthquake with a substantial wave up to 39.5
feet stroke along the north shore of Oshima
Island, yet little damage was done (5). Most of
the damage was caused by the firestorms that
broke out throughout residential areas in Tokyo
and Yokohama (6).
Figure 4 Aerial view of earthquake fires
Source J. B. Macelwane Archives
Figure 5 damage caused by tsunami
Source SiberHegner
5
The 1923 Great Kanto Earthquake
Figure 6 Epicenter of the Kanto Earthquake
Source The 1923 Tokyo Earthquake website
What caused it?
As introduced in previous paragraphs, Japan
locates on top of the Eurasian, Pacific, and
Philippine Sea plates. According to a study done
by Sato et al, the Philippine Sea plate subducts
northwestward under the Kanto region at a rate of
about 30 to 40 mm per year. When the Philippine
Sea plate subducted beneath the Tokyo
metropolitan region in 1923, the Great Kanto
earthquake happened. The fault beneath the Kanto
area was the source of the event. The epicenter
was in the Sagami Bay (figure 6), near the
junction of the Philippine Sea plate and the
Eurasian plate.
6
The 1923 Great Kanto Earthquake
What caused it? (cont)
According to James (5), the degree of shaking
felt in the affected regions varied greatly
because of soil structures. He claimed that the
epicenter of the largest quake was close to
Oshima Island. However, the area consisted mostly
of lava and scoria and thus experienced
relatively little shaking. Compare to Oshima
Island, Tokyo and Yokohama areas located on soft
river deposits. Therefore, both cities suffered
heavier shaking.
Figure 7 ocean trench earthquakes
Source Tokyo Metropolitan Government
7
The 1923 Great Kanto Earthquake
Damages caused by fire
When the earthquake happened, most of the
residents in the Kanto region were preparing for
lunch. Therefore, many households were lighting
their stoves when the earthquake hit the area.
Natural gas lines spouted fire and cooking fires
spilled their coals across wooden kitchen areas.
Houses were built of wooden materials and crowded
together.
Figure 8 crowded residential area
Source J. B. Macelwane Archives
Figure 9 Ratio of the total collapse of wooden
houses
Source J. B. Macelwane Archives
8
The 1923 Great Kanto Earthquake
Figure 9 Ratio of the total collapse of wooden
houses
Source Matsuzawa
Damages caused by fire (cont)
Soon the residential areas were covered in fires.
Putting out the fires became a tough job for
firemen since most of the water mains were cut
due to the earths movement. The fires spread and
joined, creating a virtual firestorm that
consumed all oxygen and flammable materials. 71
of people in Tokyo and 86 of people in Yokohama
lost their homes because of the fires. The
official figure for the property damage caused by
fire was over 5 billion yen about US 2.5
billion (7). Damages caused by the firestorms
were far more severe than the ones caused by the
earthquake itself. Since most buildings were made
of wood, they were exposed to greater danger in
this kind of devastating event. Figure 9 shows
the ratio of the total collapse of wooden houses
due to the earthquake. The number of houses
partially or completely destroyed totaled in
excess of 694,000, with 381,000 burned and 83,000
collapsed (5).
9
The 1923 Great Kanto Earthquake
Minor damages landslides and tsunami
There was an unusual characteristic of the
earthquake. A dramatic uplifting and depression
of the ground resulted in thousands of
landslides. Nevertheless, there were no official
data reporting damages caused by those
landslides. Following the earthquake, there were
several tsunamis in Sagami Bay. Tsunami waves
along the north shore of Oshima Island reached 12
meters and ones on the Izu and Boso Peninsulas
reached 6 meters, but little damage was done (4).
Figure 10 Nihonbashi district, before / after
earthquake
Source J. B. Macelwane Archives
10
The 1923 Great Kanto Earthquake
Other damages
Figure 11 - Destroyed city street
The earthquake also destroyed telephone and
telegraph systems, leaving the residents
completely cut off from the outside world.
Therefore, it was impossible for them to contact
their families or to know how bad the situation
was in other cities. Travel was also made
impossible due to the destruction of railroad
tracks, damaged bridges, loss of power to
electric tramways and roads choked with rubbles
(5). (figure 11 and 12)
Source SiberHegner
Figure 12 Collapsed street
Source SiberHegner
11
The 1923 Great Kanto Earthquake
Lessons learned
Since Japan is sitting on top of several
converging tectonic plates, numerous earthquakes
happen annually. After the devastating event of
the Kanto earthquake, new buildings are designed
to withstand the strongest tremors. Wood
materials that were used to build houses are now
replaced by steel materials (2). (see figure 13)
The local government of Tokyo even offers all of
its citizens a structural health check on their
homes. However, the engineering work to
strengthen the buildings is not cheap. Thus, not
everyone can afford to strengthen them (1).
Figure 13 Building materials
Source Risk Management Solutions
12
The 1923 Great Kanto Earthquake
Lessons learned (cont)
Figure 14 Earthquake drill in Japanese schools
Source BBC News
After the most devastating natural disaster, the
Ministry of Education published a collection of
stories about the earthquake in a three-volume
series titled Education Materials Related to the
Earthquake. The volumes were later distributed
to schools throughout Japan for use as
supplementary materials in the national education
curriculum (10). Living in one of the most
earthquake-prone countries in the world, citizens
should definitely be well-educated on this
natural disaster in order to react properly in
such an event. Drills are held in Japanese
schools regularly to educate children on
earthquake knowledge, like shown in figure 14.
The army and emergency services in Japan also go
through elaborate drills every year on the
anniversary of the Great Kanto earthquake to be
better prepared for unexpected events like the
1923 earthquake (1).
13
The End