ANCHORAGE, Alaska — A significant earthquake occurred in Northern California on Thursday, leading to a temporary tsunami warning that impacted around 5 million residents along the West Coast, stretching from Northern California to Oregon. Fortunately, the alert was eventually lifted. Here’s a closer look at what tsunamis are and their frequency.
Tsunamis, derived from Japanese characters meaning harbor and wave, are massive waves generated by the abrupt movement of oceanic water, as explained by the National Weather Service. The majority of these waves, especially the most powerful ones, stem from earthquakes that occur on reverse faults. Such earthquakes typically happen in subduction zones, where tectonic plates interact, causing one plate to be pushed under another, which can lead to sudden shifts in the ocean floor.
When the earthquake’s magnitude is sufficiently strong and its epicenter is deep near the ocean floor, the resulting energy may trigger a swift rise or drop of the ocean bed. This rapid vertical movement is what primarily initiates a tsunami, according to the National Oceanic and Atmospheric Administration (NOAA). Tsunamis propagate outward in all directions from where they start and can traverse entire ocean basins.
Upon reaching land, tsunamis can lead to significant coastal flooding, with currents capable of persisting for hours or even days. The weather service refers to tsunamis as one of nature’s most formidable and destructive forces.
In terms of occurrence, tsunamis that result in damage or casualties near the earthquake source happen roughly twice a year, based on data from the Global Historical Tsunami Database. Conversely, events causing destruction or fatalities over distances greater than 620 miles (1,000 kilometers) are recorded about twice every decade.
Tsunamis can arise in any ocean, sea, or large body of water. However, specific regions are more susceptible to such events due to their proximity to earthquake sources and additional factors like ocean depth and the topography of the seafloor. From 1900 to 2015, there were 754 confirmed tsunami events, with approximately 78% occurring in the Pacific Ocean. Japan has experienced the highest number of tsunamis since 1900, followed by Russia and Indonesia.
A notable example of destructive tsunamis includes the magnitude 9.2 earthquake in 1964, which resulted in extensive devastation in the Anchorage area and claimed the lives of 131 individuals, including fatalities in Oregon and California due to the subsequent tsunami.
In 2004, a catastrophic magnitude 9.1 earthquake was recorded off the coast of Sumatra, Indonesia, unleashing a tsunami that reached heights of 167 feet (51 meters) and resulted in an estimated 230,000 deaths. Furthermore, a magnitude 9.1 earthquake in Japan in 2011 also generated a devastating tsunami, with waves measuring 127 feet (39 meters), leading to approximately 18,000 deaths and triggering a nuclear power plant disaster.
