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Earthquakes! 8 Facts

A slow-shutter photo of a taxi and Nagoya Towers in 2018. Nagoya Japan.

Melbourne has experienced three significant earthquakes in the last two years. So, some people here are freaked out. But they needn’t be. The most seismically active place on earth is probably Hualien Taiwan having nearly daily tremors. I’ve visited there probably on the most stable three days in it’s history. I’ve got used to living with earthquakes having lived in Taiwan and Japan. But to experience them here in Melbourne is very unexpected. Here are eight facts that Australian media should talk about, but because they have limited knowledge, they don’t.

Entrance to the Hualien National Park, Taiwan in 2003. Digitised from film.
Hualien National Park entrance in 2003. Digitised from film. Hualien Taiwan.

Shallow earthquakes waves usually don’t travel very far. Deeper earthquakes can have a wider area of impact. An earthquake is a sudden shift in the ground columns, but is transmitted through the earth in a similar way to waves in a pond.

Most small earthquakes are releasing stress. It’s better for us when this happens. Otherwise, a build-up of pressure will eventually lead to very large and sudden movements that can be devastating to humans. The Tibetan earthquake in 2015 is an example of this.

If an earthquake happens at sea it can still be felt on land. However, if it’s stronger than 7 magnitude on the Japanese scale of measurement, then a tsunami is likely. A tsunami of about 50cm is strong enough to knock a human over, which often results in being caught up in debris, consequently serious injuries and death. This is why Japan has concreted seawalls over most of their coastline.

A low amplitude earthquake (long times between earthquake waves) tend to cause taller buildings to sway more, and be felt by people on the street as if they’re suddenly feeling a bit woozy. Low amplitude earthquake waves tend to travel further. High amplitude earthquakes (short times between wave peaks) tend to shake shorter buildings and feels more violent to anyone standing on the street. High amplitude earthquake waves then to dissipate quickly.

Slow-shutter photography of a taxi and Nagoya Towers in Japan.
Slow-shutter photograph of a taxi and Nagoya Towers in 2018. Nagoya Japan.

Some people can hear earthquakes. There are two earthquake waves, the alpha and the beta. Animals, and some humans can hear alpha waves, when are usually a seconds to tens of seconds ahead of the beta waves that we feel. For people who can hear the alpha waves, there are two types, those who can consciously hear the alpha wave, and those who don’t consciously hear it, but report that they “know” an earthquake is about to happen. Alpha wave sounds are so low, that they are below the normal hearing range of most people.

What do you do during an earthquake? The standard recommendation is to flee the building. If you don’t have time, hide in the doorway, where there is less risk of things like bookcases, shattered window glass, the ceiling, and other things falling on you. If you’re in the CBD, keep well clear of buildings, as exterior windows can break loose and fall. There can be a lot of shattered class falling.

Mobile phone networks in Japan and Taiwan have earthquake backup systems. If the tower is shaken too much, or the power cuts out, the computer will restart, and has it’s own battery that can support communications for hours. Does Australian telcos have such a system? I don’t know.

The Melbourne earthquake appears to be releasing stresses, which is different to aftershocks. An aftershock is the continued release of pressure after a major seismic event. Aftershocks can echo for days, weeks, months, sometimes hundreds of years after an event. There can be pre-shocks. Before Japan’s 11th March 2011 earthquake, there were a series of earthquakes of increasing intensity in the three days before.

Finally, yes. I was there in Japan on the 11th March 2011 at 2.44pm on the Friday afternoon. I experienced it all and saw live footage of the tsunami sweeping in over people.

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