Since 1800, California has felt (MMI IV+) 392 earthquakes during the month of October.

Most shocks have fallen in the M 4.0 - M 5.0 range (182) or in the <M 4.0 range (165). Of those in the potentially damaging M 5.0 - M 6.0 range, there have been 32 quakes, with the greatest concentration on October 1 (5) or on the 22nd, 23rd, and 24th (10 total).

Still, at the M6 or stronger, there have been 13 events, including two shocks hitting on the 21st; the Hayward earthquake (Mw 6.8 1868); the Fish Creek Mountains earthquake (Mw 6.0, 1942), and 3 events striking on October 22nd, the San Emidigo Canyon earthquake (Mw 6.0, 1916) and the twin Monterey Bay quakes (Mw 6.1, 1926).

Of other interest, the years 1940 and 1942 were the busiest with 12 and 14 shocks, respectively, during October.

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