 The mainshock generated a small tsunami that was recorded by the National Oceanic and Atmospheric Administration's sea level gauge stations on the coasts of northern California, Oregon, and Hawaii. The series of waves first came ashore at the North Spit station in Eureka after a 26-minute travel time, but the largest surges were seen just to the north at Crescent City and arrived close to low tide, a condition that would have lowered the risk had the surges had a destructive capacity. The first packet of energy reached that location in 47 minutes and had a maximum wave height of 35 cm (14 in), and a second, larger packet arrived later with a maximum amplitude of 53 cm (21 in). The waves were also detected to the south in the interior of San Francisco Bay at Alameda, but with a considerable delay (135 minutes after the mainshock), due to the shallow waters of the bay and the shelf surrounding the bay's entrance. The speed a tsunami travels is directly related to the depth of the water in which it is traversing. The tsunami was detected farther to the south in Monterey, for example, after just a 64-minute travel time, due to the deeper offshore waters and those in the Monterey Bay.
