Thursday, July 25, 2013

Rapid Response - finale

Following on from Tuesdays post on what our rapid response team were up to (and what happens at GeoNet after a large quake) here  I have some more pics from the teams final day out installing temporary sites.  In total the team deployed 8 new sites in and around Kekerengu, Renwick, Cape Campbell, Wairau, Seddon and White Bluffs.

A strong motion sensor was added to the existing Cape Campbell site
Sam installing the strong motion sensor
Dan and Todd at Kekerengu
Lara setting up the weak motion site south of Renwick

Sam with his trusty spade

The team all finished after installing a strong motion site at the Seddon Fire Station

Tuesday, July 23, 2013

Cook Strait Quakes : Rapid response team - and what happens at GeoNet HQ after a big quake?

Dan packing a seismometer


Following the weekends quake activity we had a rapid response team travel down to Marlborough yesterday, they will install temporary instruments to improve the quality and quantity of data being recorded by our network of instruments.

Loading up the vehicles
After loading up two vehicles the team of four were on the ferry and over to the South Island.
The next morning the team then split up into two, With Dan and Todd traveling to Wairau Valley to install a strong motion site, and then onto Port Underwood to install a weak motion site. 

The other team of Sam and Lara were being tailed by the TV3 Campbell Live cameras for the morning while they installed a combination site (weak and strong motion instruments) south west of Seddon in the hills, and then they were off to White Bluff to install another.

Strong motion instruments record the larger damaging shaking from earthquakes, while the weak-motion sites are more sensitive and record the smaller shakes.

I have pics from the teams below and a map showing where the places they have traveled to are, i also have a more detailed blog on how we set up temporary sites here

First strong motion site installed in a Wairau Valley Garage

Port Underwood site 1/2 way through
Dan and Todd at Port Underwood
Map showing the site locations, Stars are the largest quakes
Planning where they are going
TV3 cameras filming
Seddon combo site all finished


What happens at GeoNet HQ after a big quake?

Fridays 5.7 showing on a screen

We have a lot of different people who all come together after a large quake, each work in different areas of science and at the end it all comes together so we can figure out what is going on under the earth.

To start off with we are usually standing around looking at the screens showing the quake details, for a change on Friday most of us in GeoNet felt this event.

We have a duty officer on duty 24/7, their main role is to check the location of the quakes (after our automated system SeisComP3 )  but
The media are around lots
during a larger event they become 'media stars' with of lots of phone calls from the media and in events like this weekends, the news crews often come into GeoNet to do TV interviews.  This happens right in the middle of GeoNet in our 'media room'. This is also where we have our meetings and our offices are located off (so sometimes we are sneaking around behind the camera trying not to make too much noise)
A meeting of scientists all working on the quakes


The scientists all working on the quake sequence (from GeoNet, GNS Science and other occasionally other agencies like NIWA) have also been meeting here twice a day to discuss who is working on what, and their findings. Each have their own specialty but in a large event they all come together so we can try and figure out what is happening and what possibly might happen in the future.

Communication team working on getting the info out
We also have a 'crisis communications' team, who all come from different parts of GNS Science and GeoNet, and together we make sure that the current science information is getting out to the public, and what other information we need to get out.

So next time there is a large earthquake, you read a news story or see a scientist on the news - you now know what is going on behind the scenes.

Sunday, July 21, 2013

A weekend of Earthquakes - what is going on???

I spoke with this weeks (lucky) duty officer Anna Kaiser who said :

At this stage we might call it an earthquake "doublet" with two quite closely spaced similar sized events in very similar locations. And there have been several aftershocks over M4 following this mornings earthquake  (where there was only one following Fridays).

Historically there have been several quakes over M5 in the general Cook Straight region in the last decade, and there was also an earthquake swarm in 2005. Back in 1977 there was an M6 in a similar location and depth.

The pic above shows a live shot of aftershocks being recorded by our instruments spread out over NZ.

What is an aftershock?

Aftershocks are earthquakes that follow the largest of an earthquake sequence. They are smaller than the mainshock, can continue over a period of weeks, months, or years, and In general, the larger the mainshock, the larger and more numerous the aftershocks, and the longer they will continue.
A section of the aftershocks following 5.8(yellow) on July 21

Aftershock Rules?

A common aftershock  'rule-of-thumb' applies to the magnitude, quite often ‘the largest aftershock will be one unit below the magnitude of the main shock'. So if you have a magnitude 8 earthquake, you would expect a magnitude 7 aftershock. So in this case with this mornings magnitude 5.8 earthquake, we would anticipate a magnitude 4.8 aftershock. and we got a 4.9!  

There are other rules involving a bit of math and the amount of aftershocks and their rate of decay, with the second day having half as many aftershocks as the first, and so on. But in general the magnitudes will get smaller and the amount of quakes less frequent over time, though this can vary., such as this weekend when you get another large quake.

Of course as this is the earth we are speaking of, it does not always play by the rules!

Why so many earthquakes?

In New Zealand, the Australian and Pacific plates push against each other along a curving boundary. At the southern end of the South Island, the Australian Plate dives down (subducts) below the Pacific Plate whilst in the North Island the opposite situation occurs with the Pacific Plate being pushed under by the Australian Plate. In between, through most of the South Island, the two plates grind past each other along the Alpine Fault. The Hikurangi Trough marks the collision boundary to the east of the North Island, and is where oceanic lithosphere (the Pacific Plate) descends into the Earth’s interior as a huge inclined slab.

Is this normal? 

Yes!  Because of where we live (see above) we get lots of earthquakes, some of them are large and scary. It does occasionally seem like we are getting more than normal, but its just how the earth works.

For example here is a map showing quakes over magnitude 5 from 1992 -> 2012, and you can see they tend to follow the line of the plate boundary.  

There is also the fact that we have the internet, smartphones etc. and are more aware of what is happening around us, where as before you might not know unless you felt an earthquake.

What does this mean? 

Unfortunately we don't have earthquake crystal balls just yet, so we can't say if this means 'the big one' is coming, or if this sequence will stop 'the big one' etc.  All we can do is be prepared - so check out the Get Ready Get Thru website  for what to do before, during and after an earthquake.  

You can also read more on a post i did here Lots of earthquakes - what does this mean?

Tuesday, July 9, 2013

Felt it : Placenames, typos and AWOL reports

We get lots of felt reports for our earthquakes, which is great, but we often have to go though and fix them when they turn up in odd places. (Which is fine but we get people emailing in, worried about the reports being in the wrong spots).

We had a few emails about this earthquake on the right, in this case the suburb was 'Golden Bay' which is at the top of the South Island close to the earthquake, but there is another 'Golden Bay' on Stewart Island, this felt report is obviously on the wrong island!

The problem comes when filling out the 'Felt It' report form. Now after an earthquake you can feel quite shaken up, but if we can limit the incorrect addresses we can stop reports going AWOL!

 This is the beginning of the form where you put your name and address, if you hover over the ? on the form it tells you why we want this information - and it's not Big brother or spy agencies! To see how and where an earthquake has traveled / damage etc. we need to know where you are.

The tricky bit seems to be putting in addresses , now we do have a few double-ups in place names here in wee New Zealand, some places added in 'North' to make it easier: 
Havelock  :  Havelock North
Palmerston  :  Palmerston North
Waimate  :  Waimate North

But others didn't:
Waikawa, Marlborough  :  Waikawa, Southland
Manaia, South Taranaki  :  Manaia, Coromandel 
 And that's just the towns, there are lots of doubled up suburbs! 

So here are a few things to help the system know where you are: 
* Put your address/suburb/town etc. in the the separate boxes, not all on one line. 
* Don't abbreviate Nth, Chch etc. it gets really confused with these! 
* Watch your spelling
Our form has dropdown menus too, so when you start to type you will get some options to choose from.

And we do always aim to make this process quicker and easier, exciting things to come later in the year!


The rest of the AWOL felt reports are from people who clicked on the wrong quake, or they thought they felt it and it was a truck going past or strong wind (or a dream..)