Real‐time testing of the on‐site warning algorithm in southern California and its performance during the July 29 2008 Mw5.4 Chino Hills earthquake

The real‐time performance of the τ c ‐ P d on‐site early warning algorithm currently is being tested within the California Integrated Seismic Network (CISN). Since January 2007, the algorithm has detected 58 local earthquakes in southern California and Baja with moment magnitudes of 3.0 ≤ M w ≤ 5.4. Combined with newly derived station corrections the algorithm allowed for rapid determination of moment magnitudes and Modified Mercalli Intensity (MMI) with uncertainties of ±0.5 and ±0.7 units, respectively. The majority of reporting delays ranged from 9 to 16 s. The largest event, the July 29 2008 M w 5.4 Chino Hills earthquake, triggered a total of 60 CISN stations in epicentral distances of up to 250 km. Magnitude predictions at these stations ranged from M w 4.4 to M w 6.5 with a median of M w 5.6. The closest station would have provided up to 6 s warning at Los Angeles City Hall, located 50 km to the west‐northwest of Chino Hills.