「Earthquake」カテゴリーアーカイブ

Day_83 : Tsunami – the words

80% ofall tsunamis occurring in the world are concentrated in the Circum-Pacific Belt.The leading countries researching the tsunami are Japan, the U.S., and Russia. The tsunami is originally a Japanese term that means a high tidal wave. The name was used by Japanese immigrants during a tidal wave caused by the 1946 Aleutian Islands earthquake (tsunami) hit in Hiro, Hawaii and it became an international word, especially an academic word, ”Tsunami”. The International Union of Geodesy and Geophysics (IUGG) is in charge of a tsunami session at the start of an international conference about tsunamis. Tsunami” became public after the 2004 Indian Ocean Tsunami disaster.

*The word “tsu is composed of the Japanese words “Tsu” (which means harbor) and “Nami” (which means “wave”)(ITIC)

The 1946 Aleutian Islands earthquake
Hiro, 1964

***Pacific Tsunami Museum in Hiro

Day_204 : The story of the Great Kanto Earthquake of 1923, which set the cities of Tokyo and Yokohama on fire

When an earthquake strikes, fires start simultaneously in many places. The combination of dispersed firefighters’ ability to extinguish fires, broken buildings and unusable roads, broken water supplies and water shortages, and congested roads with many cars makes it very difficult to extinguish fires. For these reasons, large-town fires are more likely to occur during earthquakes. This is especially true in wet areas like Japan, where buildings are mainly made of wood and fires can spread over them as they break down, causing more damage. In dry areas, many houses are made of brick or stone, which are often completely destroyed by earthquakes.

During the Great Kanto Earthquake of 1923, 320,000 houses, or about 62% of the houses in Tokyo, were burned down. There were 136 fires, 76 of which spread widely, burning as much as 44% of the city in three days. Almost all (95%) of the deaths were caused by fire. Almost the same proportion (63%) of houses burned down in Yokohama. History shows that every time there has been a major earthquake, there has also been a major fire. The basic measure against fires caused by earthquakes is to make the house earthquake-proof and prevent it from collapsing.

 

source:
https://dil.bosai.go.jp/workshop/2006workshop/gakusyukai11.html

Day_203 : Distant Tsunamis Triggered by Massive Earthquakes: The 1960 Chilean Earthquake and the 2004 Indian Ocean Tsunami

On the early morning of May 23, 1960, a massive earthquake, the largest ever recorded with a magnitude of 9.5, struck southern Chile. This earthquake unleashed a tsunami that swiftly crossed the Pacific Ocean, reaching the Japanese coast about 22.5 hours later. The tsunami, which surged up to 8 meters high, resulted in 139 deaths and caused the destruction or displacement of 2,830 buildings across Japan. Due to the geographical position of Chile opposite Japan, the tsunami’s impact was more pronounced upon reaching the Japanese shores. These distant tsunamis are particularly challenging to forecast since they occur without the preliminary tremors typically associated with earthquakes. Consequently, regions prone to seismic activity, particularly around the Pacific, including Hawaii, have established early warning systems.

Day_168 : Past Interview Records – PTWC (Pacific Tsunami Warning Center) in Hawaii (1)

 

In 2004, the Indian Ocean was struck by another significant earthquake, which triggered a devastating tsunami. At that time, the absence of a tsunami warning system in the Indian Ocean contributed to a staggering death toll of 300,000. The effectiveness of tsunami warnings is limited by their ability to reach extensive coastal areas promptly. Therefore, it is crucial for residents to be aware of their local environmental characteristics and rely on personal judgment and preparedness to mitigate the risks posed by tsunamis.

Day_201 : Ground conditions are a fundamental factor in determining the amplification of seismic motions at the ground surface and the magnitude of earthquake damage

The condition of the ground is an important factor in determining how strongly an earthquake will be felt. For example, in the 1891 Nobi earthquake (Japan), the 1923 Kanto earthquake (Japan), and the 1985 Mexico earthquake (Mexico), the softer the ground, the stronger the earthquake shaking. Especially in softer strata, seismic waves are slower, so the shaking is greater. This shaking is further intensified when the period of the strata coincides with the period of the earthquake or building. This is called resonance and is the cause of many building failures.

For example, in the 1891 Nobi Earthquake in Japan, most houses near the epicenter were destroyed, but the number of houses destroyed decreased as one moved farther away from the epicenter. At a distance of 50 km from the epicenter, few houses were broken in areas with hard ground, while many were broken in areas with soft ground; in the 1923 Kanto earthquake in Japan, few houses were broken on the Yamanote plateau in Tokyo, while many were broken in the Arakawa lowlands; in the 1985 Mexico earthquake, the collapse of tall buildings in particular was observed, but this was also caused by soft ground.

The destruction of homes by earthquakes has a major impact on human casualties, fires, and even society as a whole. Therefore, when considering earthquake countermeasures, it is very important to carefully examine the condition of the ground.

Source URL:https://dil.bosai.go.jp/workshop/2006workshop/gakusyukai19.html

Day_200 : High-Speed Tsunamis and Delayed Warnings: The Urgency of Evacuation during the 1896 Meiji Sanriku, 1933 Showa Sanriku, and 2011 Great East Japan Earthquake and Tsunamis

Large tsunamis are caused by major earthquakes of magnitude 8 or greater. In particular, such earthquakes frequently occur along the Pacific coast of Hokkaido and Tohoku in Japan. The Sanriku coast in this region has a special shape called a “rias coast,” which is prone to tsunamis. In the 1896 Meiji Sanriku tsunami, the tsunami reached a height of 38 meters and killed about 22,000 people. Thirty-seven years later, in 1933, another major tsunami, the Showa Sanriku tsunami, struck the region, killing approximately 3,000 people. 2011’s Great East Japan Earthquake and Tsunami did not fully apply the lessons of the past, leaving approximately 18,000 people dead or missing.

The time between an earthquake and a tsunami reaching the coast is very short, from 5 to 10 minutes. Running to higher ground within this short time is almost the only way to protect yourself from a tsunami. The tsunami will reach the coast where it is the highest, and the tsunami will also reach the coast the fastest. Therefore, instead of waiting for information from the outside, it is important to have your own knowledge about tsunamis, understand your surroundings, and act on your own judgment.

Contents (in Japanese)
Source: URL:https://dil.bosai.go.jp/workshop/2006workshop/gakusyukai21.html

Day_198 : Characteristics of Earthquake Disasters

In most cases, when a strong earthquake occurs, many people die as buildings collapse. For example, in the Kobe earthquake, more than 90% of the 5,000 people who died lost their lives within 15 minutes immediately after the quake. For this reason, it is very important to build buildings well in order to reduce the number of people who die in earthquakes. This will prevent fires, make it less likely that people will lose their homes and become permanent refugees, and reduce the problems of relief and rebuilding.

In developing countries, especially in arid and semi-arid regions, earthquakes cause many deaths. In such areas, sun-dried bricks called “adobe” are a common building material, and buildings made of these bricks often collapse easily in earthquakes, burying many people alive. In developing countries, for economic reasons, standards for making buildings earthquake-resistant are often low, and construction is often inadequate. Therefore, even earthquakes that are not that strong can easily cause serious damage. In addition, in regions with many wooden houses, such as Central America and Southeast Asia, not only can buildings collapse, but they can also catch fire.

Day_138 : Natural Disasters in Europe (1)

Natural disasters in Europe mainly consist of hydrological, meteorological, climatological, earthquake and volcano eruption disasters.

europe-pic
Figure   The Europe

Earthquake disasters mainly occur in the Aegean Sea, the south-western coast of Balkan Peninsula, and the southern part of Italy. Volcanoes are active in the central and southern parts of Italy, the southern Aegean Sea, and Iceland area.

Concerning hydrological, meteorological, and climatological disasters, heavy rain and storm disasters are caused by low  pressure in the Icelandic area developed in the winter season. A cold atmospheric current coming from Arctic gains a warmer vapor stream from the Gulf Stream and develops a strong atmospheric depression in the area. This causes the strong winds and high tidal waves along the coastal areas of the North Sea.

Netherlands and England can be highlighted. The Netherlands had storm surges in 1530 and 1570. The death tolls were approximately 400,000 (1530) and 70,000 (1570) for each. The 1953 depression took an 1800-person death toll. This disaster also reached England. England’s disasters were the 1703 Thames river flood and the 2003 Heatwave. The temperature was 8–10 over the average year in August 2003.

With regard to earthquake disasters, Italy, Greece, and Portugal are the main countries to be affected.

The following past article explains the recent earthquake cases in Italy.

To be continued…

Day_76 : 1995 Kobe Earthquake victims

The 1995 Kobe earthquake taught us a lot of lessons. Today I am going to give you the following two questions:.
1) Why were there so many early 20s victims?
2) Which floor is more dangerous, 1st or 2nd?

1) Please look at the following picture. You can see the victims’ age distribution. Females and elderlies are more likely to be victimized because of their lack of physical strength. However, why did so many people in their early 20s die? Yes, they were university students. There are many universities in Kobe. Students tended to be less rich. They tended to stay on the 1st floor in cheaper wooden apartments.

kobe victims age distributions

2) You already know the answer. Of course, the first floor is more dangerous, especially in a wooden house. 1981 is the year in which the Japanese government set the building code. So the buildings, apartments, etc. built after the year tended not to be destroyed by the earthquake, including the Kobe earthquake.

1stfloorKobe

Photo: Dr.Takashi Inokuchi

We should learn the lessons from the disaster; this is the best thing we can do for the victims.

 

Day_196 : The Matsushiro Earthquake Center

The following is a reprint of a column I once wrote:

The Matsushiro Earthquake Center, nestled in the historic town of Matsushiro within Nagano Prefecture, represents a pivotal chapter in Japan’s approach to seismic research and disaster mitigation. Established in February 1967 under the auspices of the Japan Meteorological Agency’s Seismological Observatory, this institution was born out of a critical period marked by intense seismic activity. Between August 3, 1965, and April 17, 1966, the region experienced a staggering 6,780 seismic events, ranging from imperceptible tremors to significant quakes measuring intensity 5 and 4 on the Japanese scale. This unprecedented series of earthquakes not only posed a major societal challenge but also catalyzed the center’s founding.

The initiative to establish the center was strongly influenced by the then-mayor of Matsushiro, Nakamura, who famously prioritized the pursuit of knowledge and research over material wealth. This sentiment laid the groundwork for what would become a crucial site for earthquake prediction and disaster preparedness efforts, situated on the historical grounds of the Imperial Headquarters.

Drawing from my experience at the Natural Disaster Information Office and in collaboration with the Precise Earthquake Observation Office of the Japan Meteorological Agency (now known as the Matsushiro Earthquake Observatory), I have had the unique opportunity to organize and delve into discussions from that era. Despite being born after the seismic events in Matsushiro, I find the archival records fascinating. They not only recount the collective efforts of Matsushiro’s residents to forge a disaster-resilient community in the aftermath of the earthquake but also highlight the comprehensive nature of the research conducted.

The inquiries extended beyond seismic analysis, encompassing a holistic examination of the earthquake’s impact on the community. Noteworthy is the health survey conducted on students from a local school, in collaboration with the Matsushiro Health Center and hospital, to assess the psychological and physical effects of the seismic swarms. Moreover, the scope of investigation included studies on earthquake-induced landslides and the repercussions on water infrastructure, showcasing the multifaceted response from various experts and frontline workers of the time.

This rich tapestry of collective memory and scientific inquiry underscores the enduring spirit of Matsushiro—a community united in its commitment to disaster resilience, informed by the lessons of its past.

Ref.

http://researchmap.jp/read0139271/%E7%A0%94%E7%A9%B6%E3%83%96%E3%83%AD%E3%82%B0/

Day_112 : The 1923 Great Kanto Earthquake and Disaster Prevention Day(Tentative)

September 1 is Disaster Prevention Day in Japan. This is because of the 1923 Great Kanto Earthquake. This quake caused over 105,000 casualties and had huge impacts on Japanese society. The Great Kanto Earthquake is the worst disaster in Japanese history. Here, some points are picked up. First, the quake directly attacks the capital city, Tokyo. Second, the disaster killed so many people mainly by fire, not objects falling. Third, rumors made the disaster worse. Fourth, Tokyo has recovered first and strongly.
With regard to the devastated areas, Tokyo and Kanagawa (Yokohama) populated areas were severely affected by the quake. The epicenter was located near Oshima Island in Sagami Bay, south of Tokyo. In Yokohama, 90 percent of all homes were damaged or destroyed. 60 percent of the city’s population became homeless (Brown University).
Concerning the fire, the time at which the earthquake hit was 11:58, so the families had prepared for their lunches. Many families’ cooking stoves were overturned by the quake, causing fires. The fire spread out with strong winds.
In respect of the rumors, the rumors, especially about Koreans, such as “Koreans do criminal activities and cause social confusion,” make the disaster more political. The Home Ministry declared martial law and ordered all sectional police chiefs to make maintenance of order and security top priorities. After the disaster, the radio became popular all over Japan. This is because of the disaster’s lessons.
Concerning the recovery, Shinpei Goto, Mayor of Tokyo, created and proceeded with a reconstruction plan for Tokyo to rebuild better. The basic infrastructure of today’s Tokyo was built during that time. 

*Death numbers were revised after the recent research from over 140,000 to 105,000 because there were several double countings.