Did you feel that? It may be time to refresh your disaster kits — and vocabulary.

The ground shakes beneath you. Your body sways a little. An alert pops up on your phone. You turn to a friend and ask: 今揺れた？ (Ima yureta?, Was that a quake just now?)

On Aug. 8, the 気象庁 (kishōchō, Japan Meteorological Agency) issued its first-ever alert for a 南海トラフ巨大地震 (Nankai Torafu kyodai jishin, Nankai Trough megaquake) after a magnitude 7.1 temblor struck off the coast of Miyazaki Prefecture.

Again, that’s not a 地震 (jishin, earthquake) — that was a 巨大地震 (kyodai jishin, megaquake) alert.

The word 巨大 (kyodai) is used to mean “giant.” In business, you might see it in the words 巨大企業 (kyodai kigyō, corporate giant), 巨大銀行 (kyodai ginkō, megabank) or 巨大複合企業 (kyodai fukugō kigyō, large conglomerate). So by using the term at the front of its alert, the 気象庁 was signaling to us: We mean business.

What 気象庁 actually said, using such vocabulary as 想定 (sōtei, assumption) and 震源 (shingen, epicenter), was: 南海トラフ地震の想定震源域で大規模地震が発生する可能性が普段と比べて高まっている (Nankai Torafu jishin no sōtei shingen-iki de daikibo jishin ga hassei suru kanōsei ga fudan to kurabete takamatte-iru, the chances of a major earthquake occurring around the hypocentral region of the Nankai Trough are higher than usual).

Fortunately, the alert was lifted a week later after no unusual seismic activity was detected. But the experience left some people thinking about how the 南海トラフ巨大地震 is a “real” 可能性 (kanōsei, possibility) — and those fears seem to be lingering. The noticeable 米不足 (kome busoku, lack of rice) on supermarket shelves due in part to 買い占め (kaishime, hoarding) following the alert has pushed vendors to put up signs limiting how much rice one person can buy: お米はお一人様1点までとなっております (O-kome wa o-hitori-sama itten made to natte-orimasu, One bag of rice per person).

With Sept. 1 being 防災の日 (bōsai no hi, Disaster Prevention Day), now might be a good time to refresh your earthquake protocol and vocabulary.

With 地震, size matters. A temblor with a projected magnitude of 7.8 or above is considered a 巨大地震 or a 大規模地震 (daikibo jishin, large-scale earthquake), while a quake with a magnitude higher than 5 but lower than 7 is a 中地震 (chūjishin, moderate earthquake). A 小地震 (shōjishin, minor earthquake) refers to a jolt with a magnitude above 3 and under 5, while anything under 3 is a 微小地震 (bishōjishin, micro earthquake).

It’s also important to note that Japan has its own 震度 (shindo) system of measuring quakes, as opposed to using the Richter scale that expresses strength in マグニチュード (magunichūdo, magnitude). So while the Great East Japan Earthquake of 2011 was a magnitude 9.1, in Japan it was expressed as a 震度７.

The government estimates that there is a 70% to 80% chance of a 巨大地震 with a magnitude of 8 or 9 occurring in the 南海トラフ within the next 30 years. According to a 被害想定 (higai sōtei, damage estimate) from 2012 looking at the worst-case scenario, there could be up to 323,000 casualties in the event of such a disaster.

国は南海トラフ巨大地震で高さ3メートル以上の津波のおそれなどもあると指摘している (Kuni wa Nankai Torafu kyodai jishin de takasa san mētoru ijō no tsunami no osore nado mo aru to shiteki shite-iru, The government has also pointed out that a Nankai Trough megaquake could trigger a tsunami of 3 meters or more in height).

地震によって引き起こされる火災への備えも重要である (Jishin ni yotte hikiokosareru kasai e no sonae mo jyūyō de aru, It is also important to be prepared for fires caused by an earthquake).

The 南海トラフ is a 海溝 (kaikō, ocean trench) that runs along the Pacific Coast of Japan where the ユーラシアプレート (yūrashia purēto, Eurasian plate) and フィリピン海プレート (firipin-kai purēto, Philippine Sea plate) intersect.

歴史上、強度な地震が周期的に南海トラフで起きている (Rekishijō, kyōdo na jishin ga shūki-teki ni Nankai Torafu de okite-iru, Historically, strong earthquakes have occurred periodically in the Nankai Trough). The last one hit Western Japan in 1946, and was dubbed the 昭和南海地震 (Shōwa Nankai jishin, Showa Nankai Earthquake).

When the 巨大地震注意 (kyodai jishin chūi, megaquake alert) was first issued earlier this month, residents who live in areas encompassed by the warning were urged to 地震への備えを再確認する (jishin e no sonae o kakunin suru, double-check their earthquake preparedness).

That includes 家具を固定する (kagu o kotei suru, securing your furniture), 避難場所の確認 (hinan basho no kakunin, confirming the location of the evacuation site) and brushing up on 家族の安否確認の方法 (kazoku no anpi kakunin no hōhō, safety confirmation methods with family).

Making sure your 非常用持ち出し袋 (hijō-yō mochidashi-bukuro, to go bag) is fully stocked is important, too. Nonperishable foods and water are essential, but some other items to include are: 携帯トイレ (keitai toire, a portable toilet), 救急用品 (kyūkyū-yōhin, a first-aid kit) and some 現金 (genkin, cash) — as you never know when it might come in handy.

If an earthquake is imminent, a 緊急地震速報 (kinkyū jishin sokuhō, emergency earthquake alert) will warn you to 強い揺れに備えてください (tsuyoi yure ni sonaete kudasai, brace for strong shaking).

One verb that frequently pops up in earthquake preparedness articles is 備える (sonaeru, to prepare for), which can be turned into a noun, 備え (sonae, preparation). When disaster strikes, however, it is also good to know the verbs 走る (hashiru, to run), 助ける (tasukeru, to save/rescue) and 逃げる (nigeru, to escape) — specifically the imperative forms of those verbs: 走れ! (hashire!, run!), 助けて! (tasukete!, help!) and 逃げて! (nigete!, flee!).

Some useful phrases to know in the event of a strong quake include: 机の下にもぐって頭を守ってください (tsukue no shita ni mogutte atama o mamotte kudasai, please hide under a desk and protect your head) and 窓から離れてください (mado kara hanarete kudasai, please get away from the windows). But during an emergency, time is of the essence — not formalities — so saying, 机の下に隠れて! (Tsukue no shita ni kakurete!, Hide under a desk!) or 窓から離れて！ (Mado kara hanarete!, Get away from the windows!) would be more straight to the point. An extra tip? When learning these emergency phrases, practice saying them out loud so you can learn how to speak them clearly and quickly.

Once the shaking stops, you can say to everyone: 避難所へ向かいましょう (hinanjo e mukaimashō, Let’s head over to the evacuation site). It would also be good to know how to say things like, ケガした (kega shita, [I’m] hurt) or 家族が家の中に閉じ込められてしまった (kazoku ga ie/uchi no naka ni tojikomerarete shimatta, my family is trapped in [our] house).

Other than vocabulary and knowing what actions to take, another important 防災 measure to keep in mind is 近所の助け合い (kinjo no tasuke-ai, helping one’s neighbors).

In the aftermath of the 阪神・淡路大震災 (Hanshin-Awaji daishinsai, Great Hanshin Earthquake) of 1995, the strength of community bonds is said to have played a major role in rescues and evacuations — a good reason to start striking up conversations with your neighbors well before disaster hits. 積極的に声をかけ、みんなで助け合いましょう (Sekkyoku-teki ni koe o kake, minna de tasuke-aimashō, We should all actively reach out to one another and help each other out).