The Inconvenient Truth about Tsunamis

For a tsunami to occur, an earthquake must exceed a certain threshold. The 8.9-magnitude (on the Richter Scale) of Japan's earthquake was enough to trigger a tsunami, and the magnitude-7.7 earthquake that struck Indonesia in October 2010 only just surpassed the threshold for causing a tsunami. Earthquakes below 7.5 or 7.0 usually do NOT trigger tsunamis. A 7.1 or a 7.4 will not do it. In our whole history of colonial settlement post 1840, only 2 earthquakes have exceeded 7.7mag, and that occurred in 1855, in Lake Wairarapa, a 8.2mag. (ref: https://en.wikipedia.org/wiki/List_of_earthquakes_in_New_Zealand) and 2017, in Kaikoura.

Even that is uncertain, because the Richter Scale was only developed in 1935. So magnitude of seismic events prior to that is only estimation. The fact remains that in our nearly 200 year history of settlement, over 2 million earthquakes have been recorded, and from them less than a single handful of tsunami scares, with little or no loss of life. Compare that to the annual tragic road toll of several hundred lives lost. It is disproportionate. We have extensive tsunami alarm systems in place costing ratepayers thousands of dollars e.g along the Kaikoura coastline, but there are few road risk alarm systems in place.

Therefore NZ very seldom, and in truth almost never, gets events large enough. On the other hand, Japan, which is the world's most active earthquake region regularly gets such larger events. Once a tsunami reaches shallow water near the coast, it is slowed down, yet NZ is almost surrounded by a shallow shelf. e.g. an underwater layer that is the edge of the plate on which Australia and NZ sits extends out to the east at Wairarapa by about 200miles before dropping off into the deep Pacific. In comparison, Japan quite quickly drops into the deep Pacific.

In the Pacific Islands the currents go east, so higher waves from the Samoa tsunami could not threaten NZ. Earthquakes that occur around our coast are not able to threaten to travel inland with any destructive force. The speed of tsunami waves (and therefore the destructive power) depends on ocean depth rather than the distance from the source of the wave. One that is 55kms deep (Friday's event) is even less likely to cause harm. To get some perspective on this, consider that the 2004 Indian Ocean event was 10kms down, the Samoan tsunami (magnitude 8.0) was at a depth of 18 km, and the 11 March 2011 Japanese tsunami was an 9-mag at the depth of 32kms.

Tsunami scares are part of the funding industry that makes up alarmist scenarios to achieve research funding. They are alongside other scams like global warming, climate change and rising sea levels. The media have now created widespread public panic that every earthquake is a potential tsunami, every summer warm spell is the result of runaway global warming, and every dry season is proof of climate change. I believe that this is irresponsible science, and should be condemned as child abuse, for children have now been whipped into a state of permanent fear.

When I was a child I did not ever hear the word 'tsunami'. But it was probably not that they did not occur then. We might reflect that tsunami is a Japanese word, and was only applied to events in Japanese waters. In a similar way, only the northern hemisphere gets "hurricanes", and only the Asian countries get "typhoons". Down here we call them cyclones. And in Japan they have always had tsunamis associated with large earthquakes because the depth of the Pacific juxtaposing with the largest land mass; Eurasia, causes them. So why have they apparently become more frequent worldwide in more recent years?