When earthquake happens, P-wave (Primary wave : a relatively small vertical wave) reaches first, and then S-wave (Secondary wave: a larger horizontal wave) reaches. EEW (Earthquake Early Warning System),uses this time lag to detect when the S wave (stronger shake) arrives. Let’s have a look into P-wave and S-wave by creating your own earthquake wave experimental model.
![samnail](https://www.eri.u-tokyo.ac.jp/en/wp-content/uploads/sites/2/2020/06/4ca30fee806c7d1b207573ed5289a176.png)