Friday, October 3, 2014

Earthquakes - Where the biggest is not the best ...

I was asked the other day if i knew the worlds largest earthquake, it turned out i didn't as i thought it was the 1964 Alaska quake (i wasn't far off though). So i thought i would take a look at the largest quakes in the world, i settled for the top five. And to compare, the top 5 quakes in NZ.

The top five quakes in the world (since 1900)

1 - 1960, Chile. The largest recorded earthquake in the world, a magnitude 9.5 with thousands of people killed, injured and millions left homeless. Large tsunamis were generated and reached up to 10m in Hawaii.

2 -1964, Alaska. The 'Great Alaska Quake' was a magnitude 9.2 and generated a tsunami with a maximum wave height of 67 meters in the shallow Valdez Inlet. The tsunami caused 122 of the 131 deaths of the quake.

The location of the top 5 quakes in the world
3 - 2004, Northern Sumatra. The Banda-Aceh earthquake was magnitude 9.1 this and the 'Boxing Day Tsunami' caused the deaths of over 200,000 people and displaced millions over 14 countries

4 - 2011, Japan. The magnitude 9.0 Tohoku Earthquake and subsequent tsunami killed thousands of people. The tsunami waves traveled 10km inland and reached heights of 39m.

5 - 1952, Kamchatka, Russia. The magnitude 9.0 earthquake also caused a tsunami, with wave heights of up to 15m causing considerable loss of life and damage.

The Top Five in New Zealand

Although magnitude is our common gauge of earthquake size, intensity is a better indicator of how the quake was felt on the surface. The Modified Mercalli Intensity Scale, or MM, ranges from MM1 (unnoticeable) right up to MM12 (completely devastating). To make it easier we have these intensities on the earthquakes posted on GeoNet as words: weak, light, moderate, strong, severe. 


The location of the top 5 NZ quakes
1 - Our largest earthquake was in 1855, the magnitude 8.2-8.3 Wairarapa quake had an intensity of  MM10 and killed 7-9 people. It was also highly destructive in Wellington and generated a tsunami in Cook Strait and Wellington Harbour. It resulted in extensive uplift, including what is now the Hutt Road alongside Wellington Harbour and the Basin Reserve (which was originally part of a waterway that led into the harbour and was proposed as a shipping basin until the quake!)

A damaged road after the Hawkes Bay Quake
2 - 2009, Dusky Sound (Fiordland) magnitude 7.8, MM7.  Due to its isolated location only a few properties were damaged, though it did generate a small tsunami.



3 - 1931, Hawkes Bay,  Also magnitude 7.8, but with an intensity of MM10, this quake is New Zealand's most devastating quake. 256 were killed, thousands injured and it altered the landscape forever. It was followed by uncontrollable fires due to broken water mains, and  is recorded as having caused the largest loss of life in New Zealand’s history.

4 - 1929, Buller. Another MM10, this magnitude 7.8 quake killed 15 people, severely damaged many roads, buildings, and bridges. The massive rumbling of this quake was heard as far away as New Plymouth. It also created thirty-eight new lakes from blocked rivers and waterways. 21 still exist today.  

Ground rupture following the Buller quake
5 - 1934, Horoeka (Pahiatua). Magnitude 7.6. This event caused widespread damage especially in Pahiatua where a number of buildings collapsed.

Although not up there in size, the magnitude 6.3 Christchurch earthquake in 2011 had a MM9, and is our second most devastating quake with 185 deaths. This quake was so damaging due to its shallow (5km) depth and location within 10km of the city.

You can read more information on these, and other historic events here


It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage (USGS)




Info Sources:

USGS - United States Geological Survey
GA - GeoScience Australia 
GeoNet
Te Ara - The Encyclopedia of New Zealand

Wednesday, August 6, 2014

Earthquakes and Pancakes

I was on the WestCoast last week and decided to check out Punakaiki, which is about 40minutes North of Greymouth. As well as home to some amazing scenery, its famous for The Pancake Rocks!

They were formed around 35 million years ago when tiny bits of dead plant and sea creatures settled on the seabed along with mud and sand. This lovely mixture was then squished by the water pressure and turned into the hard and soft 'pancake' layers of  Limestone and siltstone. 

Then the earthquakes come in, and all of this land was folded and lifted above the seabed, where it was then 'sculpted' (especially the soft layers) by rain, wind and the pounding sea. (this occurred over a long time period!)

The path to the rocks




Stepping off the State Highway you are immediately transported into an amazing lush green sub-tropical forest with Nikau Palms standing above.
Amazing backdrop of misty hills







It wasn't long before i heard the roar of the first blowhole and looked up to see saltwater mist blowing around in the wind.  It was called 'sudden sound' and was very true to its name! (I thought it sounded like a dragon was breathing under the rocks - must watch too many movies)

Mist swirling in 'Putai'





The blowholes work when it is high tide and a rough sea, as the large waves surge into the rocks, seawater is forced under great pressure into the underground passages. The water follows these passages to the surface and then escapes as fine mist above your head. 




Waves crashing into the rocks

You then walk on to more exciting sights! I had stormy weather when i visited so the waves were going really high!


The rock has eroded into some really cool looking shapes and although my pancakes have never looked like that, i can see where it gets its name!





So if you are ever on the West Coast i recommend you stop in and have a look, its worth it. And the cafe next to the visitors centre sells pancakes ....


Beautiful views everywhere!






Tuesday, June 24, 2014

We can't feel your ghost quakes

Recent quakes close to Raoul Island
Today there was a large quake in the Kermadecs. This is thousands of kilometers North-East of New Zealand, not far off the volcano Raoul Island.

Unfortunately this quake, and a few other deeper distant events, cause our system some strife!  Our instruments are very sensitive and have no trouble recording distant quakes.

Now if we start with a wee earthquake 101: Earthquake waves are made up of P-waves and S-waves (amongst others). The P wave arrives first and and then the slower S-wave arrives, you can see this on the photo below.

M7.2 Japan Quake arriving on our stations

 The delay in the arrival of the S wave (as well as a few other depth related factors) causes our automated quake system SeisComP3 to think that there were actually multiple large quakes in New Zealand, as shown on our app below.

 
 
 We have nicknamed these events 'Ghost Quakes'.

Todays event even gave us "Ghost Aftershocks" with numerous mag 3 and 4 events being posted due to the aftershocks from the large Kermadec event.

We are always working on our automated system and are trying to teach the system to stop doing this, it is a tricky task however!  99% of the time our system works amazingly and you get good quake info really quickly.  If you do get alerted to a large quake the best thing to do it check our website and see if it has been reviewed by one of our team.  Another trick is to check the 'felt reports'  if a large quake has none, its a bit suspect!


Friday, May 23, 2014

Quakes, The Final Frontier ...

Here is something a wee bit odd for a Friday, someone asked me if there were quakes on Mars, would they be called Marsquakes? An interesting question! This led me to find the following article: 
So the moon gets Moonquakes!  

Now how do we know this? The same way GeoNet knows about quakes here in NZ, seismometers! 

Between 1969-1972 four seismometers were placed, by Apollo astronauts, at their landing sites around the moon. The data was radioed to earth until they were switched off in '77.

This data is still being looked at today, and using improved technology, now available, the data is increasing our knowledge of the moons core. 

Here's a pic of Buzz Aldrin deploying a seismometer on the moon! (NASA) 


 Now back to Mars ....

A seismometer was installed by one of the Viking landing probes in the '70s. Now it's a tad windy on the surface so the data has been noisy and no clear quake data has been obtained.

In 2016 there is a new Mars lander launch planned and this (as well as some other fancy toys) includes another seismometer. The InSight has equipment that will drill down so sensors will be placed away from the surface noise and will hopefully give clearer readings. Much like our borehole instruments in the Auckland CBD. 

And yes they will be called 'MarsQuakes'

Thursday, January 23, 2014

Eketahuna Earthquake Response

This week I got to go back to my old hometown, and visit my old school! 


 
Wednesday morning I traveled up to Eketahuna, the location of this weeks M6.2 earthquake, with Lara and Sam to install three temporary strong motion instruments around the earthquake epicenter. These will help us get better coverage over the aftershock area, as the more instruments you have, the better earthquake size/location information. 



Charlie beside the instrument




Our first stop was my old primary Eketahuna School, here we checked in on technicians Daniel and Charlie who had just finished upgrading the permanent strong motion site EKTS we have at the school. 




We then traveled out east  past Alfredton, towards the quake epicenter, where quite a few roads were damaged like the picture below.
SH53 had lots of damage


There wasn't a lot of cellphone coverage so it was tricky to find a place for our instruments, they also need power and to sit on a concrete pad. Lara had done a lot of prep beforehand and had narrowed down some ideal areas, but we still had to drive around a fair bit looking for houses that had both cellphone coverage, and an ideal area for the instrument.




The first farm we visited were happy to let us install some equipment, so our first strong motion site is in their chiller room.




Sam busy installing
The farm is on top of a small hill so one of the few places in the area with excellent cell phone signal, which we need as the data is sent back to us via the cellphone network.


Sam has to secure the cases to the concrete floor, he does this by drilling and using bolts, so we really appreciate the home-owners letting us take up power, space and drill holes!


The basalt then gets bolted into the case, this is the instrument which records the shaking of the earthquakes.


The Basalt







The sites all have external GPS which gives us accurate position and, more importantly, accurate timing of the quakes.

 

Epicenter just over there



On our way to the second site we drove right past the (rough) M6.2 quake epicenter location (beside Pa Valley Road)  just over in the paddock!  As you would expect there was a lot of road damage and slips around this area.




Our second spot was a tad south at Ihuraua, the farmer had some impressive cracking on his property, he kindly let us use a small room in one of his sheds. 







Sam drilling















After each site is installed Sam checks to make sure the GPS is talking to the satellites and then calls work to make sure the data is coming through.





 Although a large earthquake is not the most ideal time, it was quite neat to be in that area again, as its been some time since i was that far out of Eketahuna.  And two of our instruments ended up at homes of people that knew my family.

 


 Most of the people we had spoken to had some damage, things fall over and break in their houses, cracks in walls and paths etc.  Its important if this happens after a quake, to not just pick things back up and put them how they were. As we live in such a seismically active country, we always have to be prepared for earthquakes. 

So this is a good time to make sure heavy items are secured to the wall and wont fall over again, valuables on shelves wont fall off and break. And to check your chimneys and hot water cylinders for damage and protect them for the future.   EQC have a really handy website called Fix. Fasten, Don't Forget  which makes this process really simple, it has great information on how to protect all of these things and more.

Also to help get this important message across  GNS Science, MCDEM and EQC have gotten together to share a reminder on preparing for earthquakes

 A little effort now, will save a lot of heartache and nuisance later on!




And finally, its always important to wear appropriate
clothing ...






Wednesday, December 18, 2013

Out in the Field - Tagging along with the boys

Yesterday i went along with two of our technicians, Sam and Todd, they were out and about to fix some of our equipment out in the field.  Maintenance is an important job, as we have hundreds of stations all over New Zealand and we have to keep them up and running, weather, computers and animals can all cause issues.

Lack of a view
First stop was up Mt Climie which on a fine day allows you to look over the Hutt Valley over Wellington the the South Island. Yesterday, however, it was very cloudy and windy so not much of a view!

Mt Climie is a repeater site for all of our Wairarapa stations a major comms hub for all of our Wellington stations and an important backup link, so when something isn't working we have to get up there right away and get it fixed! It didn't take Sam long to get it back up and running though.

Lucky the equipment is in a nice cosy concrete tank.
Sam fixing the radio



Todd and i looked helpful

Next stop was Moutere Hill in Levin, this is one of our cGPS sites, its on top of a hill in a farmers paddock. The boys put in a new lightning arrestor, this protects our equipment against surges and lightning, this one had gotten wet so was shorting - not very helpful, they think it was due to condensation in the cabinet.

View towards Levin
Todd and Sam hard at work
Locals on the way out.

Tuesday, December 17, 2013

GeoNet HQ : bells, whistles and flashing lights?

Now in exciting disaster movies when they show the experts and scientists, their offices look really exciting with flashing lights and all sorts of moving gadgets.

A few years ago i posted a wee video tour of our offices, we have had a few inquiries recently on what its like here at GeoNet HQ, so i thought i would make a brand new video.

So you can have a behind the scenes look at our offices,  unfortunately its not quite as exciting as the movies, unless there is a big event and then its all go!

So here it is:

video