Users who download the app will be sending data to scientists when an earthquake as small as a magnitude 5 hits. By harvesting information from hundreds of phones closest to the earthquake, scientists will be able to test a computer system that could, in the future, dispatch early warnings that shaking is seconds or minutes away to people farther away from the earthquake’s origin. For instance, if a quake started in San Bernardino, cell phones there could register the quake and quickly help send warnings to smartphone users in Los Angeles. "This is a citizen science project," said Richard Allen,...