Thursday, September 24, 2015

Whats up with those deep quakes?

As many of you know New Zealand is right in the middle of the boundary of the Australian and Pacific tectonic plates and this is the cause of all of our earthquakes and volcanoes!

In the North Island the Pacific plate is going down underneath the Australian plate (this is called subduction) and this is why we get those deep earthquakes in the middle of the North Island.

This mornings M5.1 quake was 167km deep and we received over 3000 felt reports from people who felt it. Due to its depth the quake was not damaging, and most of the reports were of light/weak intensity.  (you can read more on intensity here).

Felt reports from the M5.1 event.
The energy released by deep NZ earthquakes travel more efficiently up the denser subducting Pacific plate, rather than the overlying Australian plate and as a result these earthquakes are often felt very strongly to the south-east of where they occurred. So you will often see more felt reports away from the quake than directly above it.

This is shown well on the M5.1 quake today, the image to the left shows the felt reports we received.  As you can see most of the reports are away from the quake (highlighted by a rad star).

Deep quakes (100km+) in NZ over the past year

What about the rest of NZ?

In the bottom of the South Island the opposite is happening with the Australian plate subducting under the Pacific plate, so we also get deep events here.

And in the middle, for most of the South Island, the two plates are colliding and grinding past each other (why we have the cool Alps)

You can see exactly how the plates are moving under NZ, on a cool diagram here.

Here is a handy video by GNS Science, which explains how the tectonic plate boundary creates faults and earthquakes in NZ.

Friday, September 4, 2015

The M7.1 Darfield Earthquake Anniversary

I'm sure most of New Zealand remembers either waking up to the shaking at 4:35am, or to the news of the earthquake 5 years ago. It was a day that changed many peoples lives from damaged homes and buildings, to some months later where friends and loved ones lives were tragically lost in the M6.3 Christchurch quake.

Although far in distance from Christchurch,  life at GeoNet also changed on that day, from all the science to be done, to the thousands of aftershocks that needed to be located.  This ultimately led to our big change to an automated earthquake location system SeisComP3 and our big website update (you can read more on that here).

Some stats from the Darfield quake

You can read more about the earthquakes and the science behind them, on the Canterbury Quakes page  including, news stories and the numbers of aftershocks the region has had. 

Tuesday, April 7, 2015

That Earthquake Felt Bigger

... is something we often hear at the office.

Now while an earthquakes magnitude is the true size of that particular quake and the energy it released at the source, it does not describe how that energy was directed,  and how the quake was felt on the surface.

So you can have two magnitude 5 quakes in different towns, with very different results:
~ one causes no damage and not all people felt it,  while the other caused damage in most houses,was felt my most people, and many were shaken and scared.
So why the difference? Read on to see

This is where Intensity comes in

You can see each quakes intensity on our website - its based on a number scale but we have added in words and colours to make it easier/quicker to see. You can see in the table below, the scale ranges from MM1 - unnoticeable (which may be felt by some people)  to Severe - which covers damaging up to worse case scenario MM12.

The two Christchurch quakes this Easter Weekend, both M3.8, were both MM5/Moderate - which if you read below in the table, were not small quakes!

So next time you look at an earthquake, check out its intensity - it will give you a better idea of the effects the quake had on people/buildings etc. on the surface.  If you look at your regions quakes you will see two intensities given, so how the earthquake was felt at its location, and how the earthquake was felt at your location. The Auckland page is a good example of this, as they don't frequently get quakes in the Auckland region, so you can see the quakes listed are all of a larger intensity, but only felt 'weak' in Auckland.

Full page here

So those two Magnitude 5 quakes...
~ The first had an intensity of MM4/ light  and the second was MM6/Strong
So you cannot take a quake at its magnitude/face value, you really need to know the MMI level to truly know how the people on the surface felt it.

Some Intensity examples of our quakes: 

The 2014 Eketahuna quake was MM8

The 2013 Lake Grassmere quake was MM9  and the Cook Strait quake was MM8

Both the 2010 Darfield earthquake, and the 2011 Christchurch earthquake were MM9

The 1855 Wairarapa, and 1931 Hawkes Bay earthquakes both had an intensity of MM10!

Check out the boss' blog with more on felt intensity.

Tuesday, March 31, 2015

A Tardis Trip Down Memory Lane ...

The Beginning - Red and Green

The website that we all know and love, first appeared on the internet on May 20 2002.  


As you can see it was pretty basic, with just the latest quakes and volcano cameras and volcanic alert levels.
Recent Quakes

It was nice and bright (and festive) and featured our lovely red and yellow stars for the earthquakes locations.

In April 2004 we added in 'Felt it' to the quakes, so you could tell us how and where you felt an earthquake.

Fun Fact: To date, the most felt reports we have ever received for an earthquake was 13,900+ for a M3.9 Auckland Quake

April 2007 - 5 shades of Gray  

In 2007 we had a big update, as well as a fresh new look we added in a lot more information on our volcanoes, quakes, landslide and tsunami. We also added in information on our network, data and maps and our latest news.





 2010 - Canterbury

Now when the Sept 4 Darfield earthquake occurred, the website looked pretty similar, though it had the cool 'Shake Map' which lit up when an earthquake occurred. (why did this go?)

It was this time that GeoNet became a household name, if you check out the 'Google Trends' graph below you will see we were flying under the radar for a bit!  Luckily we had an awesome team of geeks and our website stood up to this heavy traffic! 




Fun fact: we had more web traffic in the week following the Sept 4 quake than the whole previous year!

  Back in 2010 we had our duty officers locating the earthquakes and this took up to 20min so it was around this time we were getting the "Hurry up GeoNet, how big was it" comments! 

 And due to the large amount of aftershocks we were locating, we were limiting the quakes posted on the website, to the larger, more widely felt events. So then we had lots of “I felt it, why isn’t it on the website” comments!   So we knew we needed to fix this!


The Fix 

Comparing the two systems EQ posting time

So instead of a person logging on to their computer after they were alerted of an event, SeisComP3 automatically went to work as soon as the data started coming in! 


And in 2012 we launched the 'GeoNet Rapid' Beta website and then in September it went live. This was the biggest change to the website yet, and it took people a while to get used to the new way but the speed was definitely appreciated.  You can read more on how it works here

And this brings us to the website we have now, it may not be obvious but we are always working behind the scenes on to keep it awesome, and continue to make it better!

Monday, December 22, 2014

2014 - So this was our year ...

Another year almost over!  I thought i would keep it simple and just show you how our year was (its interactive so you can hover over the graphs and see the numbers)

I hope you all have a fantastic holiday break, though many of you, like us, will be working throughout!  And we look forward to another great year in 2015!
And yeah, i am aware that by posting this, the jinx factor is now pretty high .......

Friday, November 14, 2014

Climbing a volcano : the Tongariro Alpine Crossing

On November the 8th I did the Tongariro Alpine Crossing with my partner and two friends, it was a beautiful day and the mountains looked amazing with a fresh topping of snow!

Tongariro is actually a complex of multiple volcanic cones that was constructed over a period of 275,000 years, the active vents include Te Māri, Emerald Lakes, North Crater and Red Crater. Erosion during the last Ice Age has worn away what was once a large mountain into the amazing hiking destination that it is today. The crossing is 19.4km long and is often called one of the worlds best day walks, the down side of this 'best' status is that the walk is very popular and hundreds of people complete it daily.

The beginning!
We started out at 8:30am with the shuttle dropping us off at Mangatepopo car park, the first hour or so is a nice, mostly flat walk where you can enjoy the scenery.

South Crater
After lulling us into a false sense of security the trail took us to the second stage, the aptly named 'Devils Staircase'.  This is where you climb over 300m up across old lava flows, from eruptions in 1870, and other volcanic deposits (pyroclastic flows in 1975).

This was my least favorite part of the walk, and why there are no photos, however the view from this was impressive and we could even see Mt Taranaki in the distance.  The snow started to come into play on this section, with lots of portions of the track very slippery and covered in snow, I was very grateful for my hiking pole!

We then had a nice flat stroll in the snow across South Crater (which is actually a basin not an actual crater) toward our next climb up to Red Crater, this section had lots of snow and even a chain to clamber up!

On the edge of Red Crater looking towards Ngauruhoe 
The view from Red Crater rim is amazing, although there was lots of snow you could still see where it gets its name from. The red colour is caused by the oxidation of iron in the rock. 

It was then onto (my second least favorite part) the steep scree path down to the Emerald Lakes.

The Emerald Lakes

The Emerald Lakes are actually explosion craters filled with water, they get their neat colouring from minerals that have leached from the thermal area around them.

Beautiful Blue Lake

After walking across central crater (another faker, it's not a true volcanic crater) the next stop was Blue lake, it is an old lava vent and also gets its colour from the minerals that have dissolved into it.

Central Crater

In 2012 we had 2 eruptions in Tongariro, the first activity there since 1897. The volcano is still in a state of unrest and you can see steam and gas plumes from the Te Maari craters most days. 

Looking down to Lake Rotoaira and Lake Taupo in the distance

Te Maari steaming away

The track runs parallel to the craters so you get a great view of the activity on your way down, as well as amazing views across to Lake Taupo.

An impact crater from the Te Maari eruption in 2012

Flying rocks from the 2012 eruption damaged tracks and the Ketetahi hut. You can also see a few impact craters caused by these flying rocks on the way down, they show just how destructive these rocks can be.

The end of the crossing was a long gradual descent, with lots of steps, to the Ketetahi carpark and our awaiting shuttle!

It was an amazing 7.5 hours and I definitely recommend adding it to your 'cool things to do in NZ' list.

My Crossing Recommendations:
*Proper hiking boots. The trail can be rough and in our case, snowy!
*Layer your clothing, merino is good for warm and cool temperatures
*Hiking pole(s) are good, especially if you are as uncoordinated as myself.
*Sunscreen (don't forget your hands, i did learn that the hard way!)
*Pack for the changeable weather, don't get caught out!
*Take plenty of food and water.
*Knees - the 1200m decent is mostly steps, if you have knee issues think twice or take strapping/braces etc! The long hike out is very painful with a sore knee.
*And remember you are walking on an active volcano, pay close attention to the information warning signs

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 
Te Ara - The Encyclopedia of New Zealand