A recent swarm of earthquakes in Northland prompted an article in the New Zealand Herald that features our Whangarei Girls High School station WGHS1, and station manager Nick Major. What a great article, and congratulations to Nick and the girls in Whangarei to keep an ear out for earthquakes up North!
In recent months we have added many new schools to our network, including Maungatapu Primary School. Under direction of Chris Dixon, this school is very active in the sciences. Through the Ru network, it is able to also connect its Maori language immersion programme, for example; have a look at their “Ru Whenua” posters!
All their hard work has attracted the attention of local media, resulting in this great article about their recordings of a local swarm of earthquakes. Well done, Edward, Jackson, Jamie, and all the others at Maungatapu School!
At the moment, each Ru seismic station is sending a screenshot of its recordings to the University of Auckland. There are several ways to see this screenshot. For example here, and if you click on your station on our network map. If your screenshot is not up-to-date (and remember, seismologists’ clock is in UTC, not local time!), it is worth checking a few things:
Is the computer associated with your station working? If you see signal being recording on the screen, the answer is “yes.”
Is the signal you see on your screen “live?” In other words, is the latest part of the wiggles current? If not, make sure you hit the “now” button in jamaseis. Do you see new wiggles being recorded?
Next, open a browser on the computer of your station. Can you surf the web? If not, make sure you have a working ethernet connection. Because wireless connections are prone to timing out, we recommend wired connections. A reboot may prompt you to (re)make the connection to the internet, or you may need an IT person to help you.
If you have power (1), you are “live” (2) and you have an internet connection (3), but your screenshot is still out of date, please contact the Ru team at the university of Auckland.
The “textbook” method to estimate the epicentre of an earthquake is based on the arrival time difference between the primary and secondary seismic wave. From this time difference, we can estimated the distance from the station to the earthquake; in other words, from a single station, we know the earthquake happened anywhere on a circle centered on the station, where the radius is the estimated epicentral distance. The intersection of at least three station’s circles provides an estimate of the epicentre.
But how do we get the radius for each circle? In the figure below, you can see the seismograms from several of the Ru seismic stations for an earthquake near Rotorua, plotted as a function of their distance to Rotorua. The red and blue curves are predicted arrival times for the primary and secondary wave, based on a spherically symmetric earth. We made this figure for a publication in the European Journal of Physics, but the jupyter notebook that generates these figures is available here.
Shortly after midnight, last night, a severe earthquake struck the South Island. The full extent of the damage is not clear yet, and of course the members of the Ru network think about those affected by this event.
The seismic networks computed the thrust motion on the fault in a matter of minutes, and in this case the motion on the fault warranted a tsunami warning.
The New Zealand Herald features an article with the first reactions from geonet scientists. The mention of the Hope Fault is interesting. This fault is the southern-most fault of the Marlborough Faults (as far as we know!), which extend from the Alpine Fault. However, both Geonet and the USGS indicate a more southern placement of the epicentre. Besides, the Hope Fault is a strike-slip fault, whereas this event was a thrust fault! We at Ru wouldn’t be surprised if this event was slip (or slips, plural) on a combination of faults. In any case, there will much to learn from this event in the coming time. A discussion about the complexity of the tectonics in this area has already been posted on the USGS website.
Meanwhile, you can expect hundreds of aftershocks to fill your station helicorder screens in the coming days and weeks. If you get this message on Monday November 14th (local New Zealand time), you can see much of the action on our network page, similar to the image at the top of this post from Birkenhead Primary School.
The Ru workshop took place on the 27th-29th January 2016. It was great to bring a group of people together with such passion and enthusiasm for teaching, to share ideas and contribute towards the seismometers in schools program.
Day 1 took place at the University of Auckland’s City Campus. The morning revolved around the Auckland Lablet; Physics experimentation on an Android tablet. There were demonstrations to showcase Lablet being used record and analyse several physics experiments and some very useful ideas came out of the discussion.
In the afternoon, the group were able to get their hands on the TC-1 Seismometer and built four from scratch. This showed just how simple it can be to construct the TC-1 and it was a great success when all four completed devices recorded data without a hitch.
There were several excellent talks over the rest of the afternoon. It was particularly interesting to hear (and see) how Jonathan had utilized an Arduino (a key component of the TC-1), to run a weather station.
Day 2 was spent on Waiheke Island. There were some great presentations by Dan Hikuroa, Caroline Little, Katrina Jacobs, Glenn Vallender, Michelle Salmon and Martin Smith. The day was nicely rounded off with some fantastic refreshments.
The highlight of Day 3 was undoubtedly the field trip to Rangitoto Island. The weather was excellent and although it was quite a hike up to the top, it was universally enjoyed. It was great to have Dan along as a guide to share his knowledge of the geology of the island and it was particularly interesting to explore the lava tubes.
Overall the workshop had a great turnout. We hope everyone enjoyed the three days and gained some ideas and insights that will be helpful in their schools.
On November 16 2014, at 22:33:17 (UTC), an earthquake with magnitude 6.5 occurred some 155 km east of Te Araroa:
The stations of the Ru network recorded the resulting seismic waves, displayed in the figure below. The so-called “seismogram” for each station shows the propagation of the vibrations caused by the quake:
The horizontal position of each seismogram represents the distance from the epicentre to each station. The vertical time scale starts at the origin time of the earthquake.
For example, it takes roughly 180 seconds for the first seismic wave to get to station kkvc1 in Kaikoria Valley, some 1200 km from the epicentre. This means the average speed of this primary (or P-)wave is 6.7 km/s! Over this relatively short distances, you can almost draw a straight line through the onsets of energy on each seismogram, showing that the wave speed varies only by per cents in the subsurface under our network.
Also, notice how the seismograms change from station to station. For the close ones, the waves are bunched up in a relatively short time span, whereas for those stations with a greater epicentral distance, the “wave train” is longer. It turns out that in addition to the primary wave, there are other, slower, waves in this wave train. These include secondary (or S-)waves, and surface waves.
Finally, we should mention that the amplitudes of each seismogram are equalised to show the arrival times the clearest. In reality, the vibrations recorded closer the epicentre are much larger than those farther away.