Earthquakes

English: Quake epicenters. Română: Epicentre a...
English: Quake epicenters. Română: Epicentre ale cutremurelor produse în intervalul de ani 1963–1998. (Photo credit: Wikipedia)

This week’s subject pretty much suggested itself. There I was, sitting at my desk, and suddenly I felt this rolling, shaking sensation. Well, I feel it every time a truck goes past, but this time the shaking continued and it became apparent that this was an earthquake. It measured 6.6 on the earthquake scale and was the biggest one I can remember for a long time. Fortunately we were not at the epicentre and no one was killed. Those living close to the epicentre had a rougher time than we did and many houses were damaged, though only one appears to have been severely damaged.

(Note: Images in this post are not from the Wellington earthquakes that I am talking about in this post).

Since we are prone to earthquakes here the children in school are drilled in what to do when an earthquake strikes. I particularly like the idea expressed by one child that “earthquakes cause salamis”. (See the second video on the page that is linked to above.)

Earthquake Drill
Earthquake Drill (Photo credit: Benjamin Chun)

The previous earthquake happened when I was at home. Instinctively my wife ran for the door. I equally instinctively rushed to stop the TV from toppling! It’s funny what you do in an emergency.

Luckily no one was seriously hurt in the earthquakes though people in lifts (elevators) and at the top of high buildings were shaken about a bit. Apparently lifts (elevators) are designed to stop moving if there is a big quake.

In the city nothing much was damaged, although a lift (elevator) shaft which was damaged in an earlier quake is scheduled to be removed and one ‘lane’ (pedestrian access between buildings) in the city centre was taped off by authorities. Last time there was a certain amount of damage but nothing significant, though people were sent home so that the buildings could be checked. A rugby test match between New Zealand and Australia may be cancelled. That’s classified as a Big Thing round here.

Footbridge over Avon river following both Sept...
Footbridge over Avon river following both September and February earthquakes. (Photo credit: Wikipedia)

All in all, people have taken the earthquake in their stride, though news pictures showed some people who appeared to be in shock. The one injury that I heard of was one woman who tried to dive under her desk and missed cracking her head against it. I saw a picture of two girls hiding under a desk with a bottle of wine. That’s apparently what they had been doing all afternoon. One guy texted from the airport and said that he would be glad to get up into the air. (As it happens the airport stopped flights in and out for a while, but they soon caught up with the backlog).

Naturally people wanted to go home to be with their families and to check that their houses had not been damaged. This led to the roads out of and around the city becoming gridlocked. I didn’t want to get caught up in that so I hung around until just before the time that rush hour usually happens  and my trip home was in fact easier than usual. I did wonder what would happen if a significant earthquake or after shock happened while I was travelling at 100kph on the motorway! Also, there is a part of my route that lies under a motorway bridge, and there was a chance that I’d get stuck at the traffic lights. Fortunately they were showing green so I did not have to stop under the heavy concrete spans of the motorway. That would have been scary.

Footbridge over Avon river following both Sept...
Footbridge over Avon river following both September and February earthquakes. (Photo credit: Wikipedia)

The thing about earthquakes is that you don’t know how powerful they are going to be. You don’t know if it is going to be a jiggle and a roll or whether it is going to rip the building apart underneath you. I find them scary and exhilarating. After one is over people are often more relaxed than before it, and gather to exchange news and ‘war stories’. At least, that is so in the earthquakes that I have so far experienced. But they have been relatively benign.

Unfortunately this was not true nearer the epicentre where almost all the houses had some damage, though no serious injuries have been suffered and no fatalities have happened.

Wellington office after earthquake.

Summer, Autumn, Winter and Spring

Revolving earth at winter solstice on the nort...
Northern winter solstice

On 21st June we in the Southern Hemisphere get our shortest day of the year. This corresponds to the longest day in the Northern Hemisphere of course, and my wall calendar, which originates from the Northern half of the planet says that 21st June is the start of summer. I believe that the official start of winter, here in New Zealand, is 1st June.

That started me thinking. One would expect that 21st June, the southern winter solstice, would be the middle on winter, since the earth is tilted furthest away from the sun in southern latitudes at that date, and that the seasons would change mid way between the solstices and the equinoxes in both hemispheres for similar reasons. The equinoxes are the days when the night and days are the same length in both the northern and southern hemispheres. (Pedants will notice that I’m not being precisely correct in my explanations of equinoxes and solstices, but that doesn’t matter for my purposes.)

English: Two equinoxes are shown as the inters...
Equinoxes

It is obvious to anyone who has reached a sufficient age that the warmest and coldest parts of the year don’t correspond to the solstices and that the change from higher than average temperatures to lower than average temperatures and vice versa don’t happen at the equinoxes, though these latter events are probably not that noticeable. There is obviously some seasonal lag.

Image representing Wikipedia as depicted in Cr...

So I browsed to Wikipedia, which is a useful place to start, even if some people question its accuracy and veracity. I’ve not found it too bad, myself. Sure enough, there is an article on seasonal lag, and I’ve no reason to doubt the information there. To summarise, the authors of the article attribute the lag to the oceans which, because of the latent heat of their water absorb heat energy and release energy as the seasons change. I’m not sure that I completely understand the reasons for this, but there are undoubtedly deeper analyses on the Internet. The Wikipedia article contains one reference.

Apparently the seasonal lag is different in each half of the year. I believe that means that the four seasons are not all equal in length. Hmm, summer does seem shorter than the other seasons, but that may be only subjective. However, our shortest day is only four weeks away, so we will at least be seeing more daylight each day from then on. We will be on the upwards slide to Spring and Summer, even though Winter will not have bottomed out, and we can look forward to barbecues and a summertime Christmas!

Pohutakawa
Pohutakawa flowers. They bloom at Christmas, in early summer.