This app was mentioned in 10 comments, with an average of 2.50 upvotes
Android: https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android&hl=ja
iPhone: https://itunes.apple.com/us/app/yurekuru-call/id398954883?mt=8
(although it ought to "just work" on iPhone, even on MVNOs. you'll need the app if you're using a pocket wifi or something though)
Android: https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android&hl=ja
iPhone: https://itunes.apple.com/us/app/yurekuru-call/id398954883?mt=8
You'll need data (get a rental SIM)
Yurekuru Call warns you about earthquakes
Japanese Dictionary that is pretty good and available offline.
There's no way it will work if your phone is not connected to any network... And in Japan there are only Japanese networks...
It might work as long as you're connected to a japanese network (even roaming), but otherwise there are also apps that work via push notifications (you'll still need data for this):
Android: https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android&hl=ja
iPhone: https://itunes.apple.com/us/app/yurekuru-call/id398954883?mt=8
https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android
Now you can enjoy the alert on your phone!
The app was called Yurekuru call, and features an adorable catfish icon.
https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android
If your phone doesn't have built-in support, you can use this app: https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android&hl=ja
Check out https://earthquaketrack.com/p/japan/recent
Or get Yurekuru Call - iPhone: https://itunes.apple.com/jp/app/yurekuru-call/id398954883?l=en&mt=8 - Google store: https://play.google.com/store/apps/details?id=jp.co.rcsc.yurekuru.android
Enjoy. 🤗
Usually it is nothing to be worried about. Earthquakes happen all the time and people continue about their lives without caring about the earthquake. But I can sympathise with you, the first time it happened to me, I was shit scared but I got used to the earthquakes after some time. If you are still worried install the app based on whether you have Android or iOS phone. The app gives notification for an incoming earthquake based on the rating level you set for your location. The app(and Japan) follows a different rating system than the usual Richter scale. If I were you, I would set it for earthquakes which have a rating of 2 or more. Hope this help. Links are below