SAN DIEGO — The San Diego County Office of Emergency Services, governor's Office of Emergency Services and the U.S. Geological Survey tested a wireless emergency alert system Thursday on mobile phones throughout San Diego County.

The test scheduled was sent out at 11 a.m. to all mobile phones in the county, regardless of whether they belong to a permanent resident or not. The standard test was intended to study the system's effectiveness in warning residents of impending earthquakes.

Mobile phones received a test alert and a loud tone was emitted to signal the test.

State and local officials have worked with the USGS to develop the so-called ShakeAlert system since 2006, using underground seismic activity censors to detect the first ripples from an earthquake.

The system's first phase went into effect last fall in California, Oregon and Washington. Eventually, USGS officials hope to continue expanding the alert system across the country with the ability to alert people of earthquakes of a magnitude of 5.0 and above.