What is Nankai Trough Earthquake Extra Information?

If you have ever participated in a disaster preparedness workshop in Japan, you have probably heard about the possibility of a 'Tokai Earthquake'or 'Tonankai Earthquake' occurring at any time. Strong earthquakes originating in the Nankai Trough, i.e. the area between Suruga Bay (Shizuoka Prefecture) and the Hyūga Sea (off the eastern shore of Kyushu), have caused much damage and loss of life in the past.

The next Nankai Trough earthquake could cause extensive damage across a large area extending from the Kanto region westwards including the Tokai region, Shikoku and Kyushu. Tsunami caused by the earthquake could inflict tremendous damage and casualties on coastal areas. In areas estimated to be at risk of heavy damage and casualties, it is important that preparations are made to protect the lives of residents. One measure that could help to save lives is Nankai Trough Earthquake Extra Information (Nankai torafu jishin rinji jōhō / 南海トラフ地震臨時情報).

Large-scale earthquakes have occurred along the Nankai Trough at intervals of between 100 and 200 years. History has also shown that, rather than a single quake, a pair of magnitude 8-class quakes have occurred in succession in the eastern and western sections of the Nankai Trough area. For example, the Ansei Tōkai Earthquake of 1854 (magnitude 8.6, eastern section) was followed 32 hours later by the Ansei Nankai Earthquake (magnitude 8.7, western section); and the Shōwa Tōnankai Earthquake of 1944 (magnitude 8.2, eastern section) was followed around 2 years later by the Showa Nankai Earthquake (magnitude 8.4, western section) in 1946. (*Although in these cases the eastern section quake preceded that in the western section, it is possible that a quake could occur in the western section first.)

In situations such as an earthquake of a certain scale occurring along the Nankai Trough, when it is assessed that the possibility of a subsequent Nankai Trough megaquake occurring is higher than usual, the Japan Meteorological Agency will issue a bulletin called Nankai Trough Earthquake Extra Information, which serves as a warning that a megaquake may be imminent. The announcement will also include phrases such as Megaquake Alert (kyodai jishin keikai / 巨大地震警戒) or Megaquake Advisory (kyodai jishin chūi / 巨大地震注意) to clarify the need for authorities and residents to take measures to prepare for a possible quake.

It is important to understand that Nankai Trough Earthquake Extra Information is not like the Earthquake Early Warning System (kinkyū jishin sokuhō / 緊急地震速報), which notifies residents that an earthquake of seismic intensity 5 or higher is expected via mobile phones, TV, radio, etc., sometimes seconds before an earthquake occurs. Nankai Trough Earthquake Extra Information may be issued as early as 2 hours after an earthquake has occurred in one section (e.g. western section) of the Nankai Trough area, once the preceding earthquake has been analyzed and the probability of a megaquake in the other section (e.g. eastern section) assessed.

Given the intervals between the historical pairs of Nankai Trough earthquakes mentioned above (32 hours / 2 years), it may not be clear how much advance warning the Nankai Trough Earthquake Extra Information may provide. Once issued, it will be important to stay calm and prepare. In some parts of Nagoya City, residents may be required to evacuate once the Extra Information is issued.

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What to do when Nankai Trough Earthquake Extra Information is issued - Advance Evacuation Areas

Following the occurrence of an earthquake of magnitude 8 or higher in the western area of the Nankai Trough, if the possibility of a further Nankai Trough earthquake is assessed as being relatively higher than usual, the Japan Meteorological Agency will issue Nankai Trough Extra Information (Megaquake Alert). Areas expected to be inundated (by tsunami, etc.) after the occurrence of a subsequent earthquake, and where residents will not be able to evacuate before inundation occurs, have been designated Advance Evacuation Areas (jizen hinan taishō chiiki / 事前避難対象地域). When Nankai Trough Extra Information (Megaquake Alert) has been issued, residents in these areas will be requested to evacuate for one week.

Residents in Advance Evacuation Areas should evacuate in advance as directed to protect themselves.

Activities within Advance Evacuation Areas will be restricted (businesses will not be able to operate and public facilities will be closed for one week). In areas not designated Advance Evacuation Areas, normal activities will continue as residents reconfirm their earthquake preparedness measures.

Designated Advance Evacuation Areas in Nagoya City

Areas designated Advance Evacuation Areas are those where, due to the subsidence of embankments or levees as a result of seismic motion, inundation (due to tsunami, etc.) is expected to exceed 30cm within 30 minutes of the occurrence of an earthquake*. Parts of 21 school districts situated along waterways in 5 wards are designated Advance Evacuation Areas.
*These estimates are based on a worst-case scenario of a magnitude 9-class earthquake and the resulting liquefaction causing extensive damage to levees.

Ward	School districts in which Advance Evacuation Areas are located	Rivers of concern in each area
Atsuta(熱田)	Chitose (千年)	Hori-kawa (堀川)
Nakagawa(中川)	Shoshiki (正色), Gotanda (五反田), Toda (戸田), Haruta (春田), Toyoharu (豊治, map 1 / map 2), Nishimaeda (西前田)	Shonai-gawa (庄内川), Shin-gawa (新川), Fukuta-gawa (福田川)
Minato(港)	Higashitsukiji (東築地), Kosei (港西), Tochi (当知), Takagi (高木), Jinguji (神宮寺), Nanyo (南陽), Nishifukuta (西福田), Fukuta (福田)	Hori-kawa (堀川), Shonai-gawa (庄内川), Shin-gawa (新川)、Nikko-gawa (日光川), Fukuta-gawa (福田川), Kanie-gawa (蟹江川)
Minami(南)	Toyoda (豊田), Dotoku (道徳), Hakusui (白水), Chidori (千鳥), Shibata (柴田)	Yamazaki-gawa (山崎川), Tempaku-gawa (天白川)
Midori(緑)	Odaka (大高)	Tempaku-gawa (天白川)
Total	Areas in 21 school districts

To check the location of the designated Advance Evacuation Areas, click on the school district in the table above, or see the City of Nagoya website (Japanese).

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When Nankai Trough Earthquake Extra Information is issued, check again that your home is prepared

Earthquakes can occur at any time, so it's important to take measures in your day-to-day life to help yourself be better prepared for when an earthquake occurs. When Nankai Trough Earthquake Extra Information is issued, check your preparation once again.

1. Prepare for tremors

To prevent injury from furniture moving or toppling over, fix furniture in place using L-brackets (to attach furniture to walls), or adjustable struts (tsuppari-bō /突っ張り棒) between the top of the item and the ceiling.
You can also put protective film over windows and glass doors to reduce the potential hazard of broken glass.

2. Prepare for fires

To prevent electrical fires after an earthquake, you can install an earthquake-sensitive circuit breaker that stops the flow of electricity automatically when it detects a tremor.

3. Prepare for life as an evacuee

●Confirm where you should evacuate to, and a safe route to get there.

Together with your family, confirm how each of you should notify one another that you are safe if you become separated.

●Familiarize yourselves with how to use the Disaster Emergency Message

Dial 171 Telephone Service, Disaster Emergency Message Board web171 (NTT), or the disaster emergency message boards provided by your mobile phone service provider.

◆Disaster Emergency Message Dial 171 Telephone Service, Disaster Emergency Message Board web171 (NTT): https://www.ntt-west.co.jp/saun/english/

◆Mobile phone service provider Disaster Emergency Message Board services

• • • • • NTT docomo: http://dengon.docomo.ne.jp/top.cgi
        • KDDI (au): http://dengon.ezweb.ne.jp/
        • Softbank/Y!mobile: http://dengon.softbank.ne.jp/

●Stock up on water and food

Stockpile sufficient water, food, etc. for your family for one week. Keep 3 days' worth in backpacks as part of your emergency evacuation kit.

After Nankai Trough Earthquake Extra Information is issued, keep the potential risk in mind as you go about your everyday activities.

• Avoid areas that are at risk from tsunami, landslides, etc. as much as possible.
• Keep your living quarters in as safe a place as possible indoors.
• Don't keep objects above the head of your bed or in high spots from which they could fall and cause injury.
• Confirm how and where you should obtain reliable information in an emergency, e.g. radio, official SNS of municipal authorities, etc.
  (Don't trust or share SNS posts shared by friends if they are not from a reliable source.)

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★Nankai Trough Earthquake -Preparing for the next earthquake that may occur- (Cabinet Office, YouTube)