Here's why a tsunami warning was sent after the 7.0 earthquake in Northern California
Last Thursday's Tsunami Warning was scary for everyone who received the alert along the West Coast. Luckily, the warning was canceled, but many people are still wondering — Why was it issued in the first place?
A 7.0 magnitude earthquake occurred at 10:44 a.m. right off the coast of Northern California. Just five minutes later, the National Tsunami Warning Center issued a Tsunami Warning for coastal communities spanning from Oregon to Santa Cruz, California including the Bay Area.
Tsunamis are triggered by the upward or downward motion of the Earth's surface under the ocean. Normally, tsunamis are triggered by underwater earthquakes at a subduction zone, where tectonic plates move up or down on top of each other.
However, the earthquake last Thursday occurred on the San Andreas fault, which is a different type of zone known as a strike-slip fault, where the tectonic plates slide next to each other, not up and down.
Although an earthquake occurring on this kind of fault is unlikely because there is no inherent up or down motion to create the tsunami, it's not impossible. While about 80% of tsunamis are caused by underwater subduction zone earthquakes, there is still a 20% chance that it could be caused by something else.
In this case, the San Andreas earthquake could have triggered an underwater landslide which could have displaced enough water to create a tsunami. Since this earthquake occurred close to land, and tsunami waves can travel at up to 500 mph, the weather service did not have the luxury to wait for observation and buoy data, which can take up to an hour to collect.
Again although unlikely, this was one of those better safe than sorry situations. Hopefully, you now know your evacuation route if you didn't already, because next time we might not be as lucky.
