This is a very interesting research prospect and perhaps can be tested in earthquake prone areas, for example Indonesia regions near the fault lines.

Using the Android smartphone existing sensors (e.g. accelerometer), probably it can easily detect earthquake once it has happened. Japan has similar existing alarm system where they send SMS alerts to the residents of affected cities once any earth quake incident is detected, but not really sure where and how they put the sensors.

The more interesting approach is a system for prior alert of earthquakes. It is for predicting soon to happen earthquake, moments (or better several minutes or hours) before the incident. This is probably feasible due to many reports that mentioned animals got alarmed and look for cover themselves moments before the earthquake events[1].

For this prior alert detection maybe a more accurate front-end sensors are required for example, ADI's AD7768 sensor and connected them to a powerful cloud based earthquake detection back-end engine [2].

[1]https://www.discovermagazine.com/planet-earth/animals-sense-...

[2]https://www.analog.com/en/analog-dialogue/articles/understan...