Tuesday, September 27, 2011

Out in the field - the perils of lightning!

Last week one of our Senior Technicians - Dan, went down to Wednesday Peak and Welcome Bay in Fiordland (here) to replace and upgrade some radio gear that had recently been damaged by lightning. These sites have the important task of transmitting data from the tsunami monitoring site PUYT (Puysegur) back to  HQ.
Wednesday Peak
Helicopter leaving the site


Dan then traveled to the other end of NZ, to North Cape (here) (along with a technician from Maritime NZ), to investigate an outage of the tsunami monitoring site NCPT (North Cape). When they arrived it was clear that the lighthouse next to the site had sustained a direct lightning strike and was effectively destroyed, the lightning had also destroyed all of the equipment for our tsunami gauge. Although lightning protection was installed, it was ineffective against such a large strike. Everything at the site was replaced, with divers traveling within the next week to replace the actual tsunami sensors in the water - as the lightening traveled all the way down (over 250m) to the sensors in the water!.  

North Cape

Lighthouse and GNS Site(right)

Lightning damage inside the cabinet

Although traveling to these remote locations involves long hours and hard work, the technicians do get to see some amazing views of our beautiful country, and occasionally some wildlife... 

This whale was spotted in Te Waewae Bay.

Thanks to Daniel for taking the pics and telling me what he got up to (and for putting up with my pestering)

Monday, September 19, 2011

Exploring the website - ShakeNZ

When you go to the GeoNet homepage you will see a map of NZ covered in small squares, this is 'ShakeNZ'.  Each one of the squares gets near real-time shaking (this means in a few minutes, not right away) from our instruments out in the field.   So within a few minutes of an earthquake, you can look at the map and get a rough idea of where it was and the intensity of the shaking.

The key thing here is actually to do with the key!   The pic on the right is the key for the map, which shows intensity, not magnitude!   So when there is an earthquake and you can see an area of coloured squares, they are showing the intensity of shaking not the size.

The numbers correspond to the Modified Mercalli Intensity Scale, this is a really handy way to describe the effects of an earthquake, and is generally better than using the magnitude alone (as a mag 4 quake at 5km depth will produce a higher shaking intensity than a mag 4 at 10km depth)  It goes from MM 1 (barely felt by a few people) to MM 12 (complete devastation).

<---  This is what the map looks like with no activity, small blue/purple squares (blank = no data)


This is the map after a mag 5.5 earthquake, 30km deep near Wellington. -->


Now occasionally when we have technical issues ( the instrument is having a bad day, or a tech is out fixing something)  there will be a 'rogue' square!  Its usually pretty easy to see that its an error and not a large earthquake as there is just one square showing a high intensity, and when there is an actual event multiple squares will be 'lit up' .  
The map on the left shows one station/square showing an orange square, or 7 intensity of shaking, if this was an actual event the squares close by would also show some level of intensity.  There are more examples here.

You can also use an interactive version here  and go from 60min to the present - a cool way at looking at the squares light up following an earthquake.   

Friday, September 2, 2011

Felt Reports: Then & Now

GeoNet collects earthquake data directly from the public via our website where people can answer questions about what they felt during an earthquake. We use this feedback to assist with mapping the distribution of shaking intensity of earthquakes(see here ) and with scenario planning for future earthquakes.

These days its a quick questionarre on our website, however, back in the early 1900s (pre-internet -shock horror) things were slightly different! There was no GeoNet and no network of instruments across New Zealand.

For many years dedicated volunteers completed reports, filling in paper questionnaires and sending them to the observatory in Wellington.  Pre-1930s these, along with newspaper clippings, were used by scientists to calculate where an earthquake was located.  This was difficult in NZ as most people lived by the coast, so not much was known about the effects of earthquakes further inland.
Christchurch 1921

We keep all of these old records here at GeoNet
and they can be quite amusing to read, i have scanned 3 examples of 'felt reports' and one old Press article for you to look at here -->

Christchurch 1921
So next time you feel an earthquake and are (very paitently of course) awaiting the details from GeoNet, think back to the earlier years - they never got to find out how big the earthquakes were! 

Palmerston North 1923