Some background, planning and actions

Tsu (port) + Nami (wave)

The waves are caused by under sea landslides, landslides from land into water, but the largest tsunamis are caused by large underwater earthquakes (magnitude 8 or 9) in subduction zones.
Most of the large subduction zones are located around the Pacific Rim (called the Ring of Fire). There are many active earthquakes and volcanoes in this ring.
The Cascadia subduction zone is about 100 miles off the coast of Northern California, Oregon, Washington, and British Columbia. A tsunami would take 10 minutes to hit the coast after an earthquake from this zone.

Download the MyShake app. It will give you 10 - 30 seconds notice of an earthquake. Shaking for the Big One could continue for 3 to 6 minutes.
Planning ahead and knowing the signs to watch for will save lives. Always know where the closest high ground or tall, strong structure is so that you can head that direction as soon as you are warned or you identify the signs of a coming wave.
Try to get 100 feet above sea level to be safe. If this isn’t possible in a very flat area, you need to identify a tall strong structure that you can get to within 10 minutes of when the earthquake happened.

If you are at the beach and the water retreats away from the shore very far and very quickly, that’s a sign that there could be a tsunami coming. Do not wait to watch what happens. You have maybe minutes to escape.
If you feel an earthquake and you are close to the ocean start counting. If your counting reaches 20 and it’s still shaking. After 20 seconds the earthquake’s magnitude could be over 7 and you need to get to higher ground immediately.
Often the first wave is not the largest wave. The water may retreat again after the first wave and it will form a even larger wave on its way back into shore.
Do not attempt to evacuate in your car as the road may be overwhelmed by water. Many drownings occur this way during tsunami events. Even if you can break a window and escape your vehicle you may end up on top of your floating vehicle.