Question from Leyn from Porirua. They are my thoughts do we know from previous events
if it's common for the entire structure to chain one single event or whether it tests about giant
sections that's a good question the Alpine Fault is a 600 kilometer long structure that runs across
the South Island. Now the fault itself is actually considered constituted of three segments and two
of them actually capable of generating very large earthquakes and I do so very regularly. Every 300
years and the last one was in 1717 ad. So if you can do the math quickly you can see that
we are overdue for a nap and for earthquakes in our generation or in our children's generations
lifetime. And this would be the two signals I'm sure they did in a previous month this would be
a magnitude eight plus earthquake. Now in terms of impact, it will mean very strong shaking in
the faults, this is a really unusual fault its very narrow and so a lot of the shaking may be
concentrated near the faults but it would still be some strong shaking at large distances on
the Alpine fault. It will not only be strong but it will also be very long. The fault will
take more than two minutes to break me now the beauty is that this fault is being very strongly
very well studied as a lot of our research going on around that better characterizing
the past earthquakes better characterizing the ground shaking from the earthquakes and
as also research for magnets looking into a better community engagements and civil defense
preparedness for future and bang focal point so I hope this answered your question in thank you
Melissa from why can I ask you how do you decide which town or city to use on your
best quite location so for example when a quake says it's 40 kilometers northwest of peripera who
when really it's closer to Laverne on the map so the way this works is that JUnit has a table of
locations and sort of a hierarchy of which ones to use so for example Piper who is on that table
in Levin is actually low above table calculate say why but when anything occurs sort of finds
which location on their table is the closest and then we'll report the earthquakes location
relative to them but there is a caveat that if it's something like Chatham Islands then it will
actually look for the city so a larger location to report relative to a lot of time we see if there's
an earthquake in the Kermadec are something like that it's proof far to the northeast of New
Zealand we'll say 4,000 kilometers northeast of [ __ ] town and anything where it's really closer
to another location but that locations either not in the table or it's not as large in Swami
where I'm originally from the candidates from Winnipeg probably one of the least likely places
in the entire world where you would ever have an earthquake okay so Jessica from Auckland asked
how do you get accurate readings of earthquake location size and depth so this is kind of the
main thing that about seismology is pointing out Worth quakes are the key thing is to find
out if you have a seismic station to find out how far the earthquake is from that particular
station and to do that we use p-waves and s-waves which are the two fastest traveling waves p-waves
being the fastest if you can work out what the difference in time is between them and if we
know how fast each of those waves travel we can figure out the distance but that only tells you
how far the earthquake is from the station not in what direction so if you use three stations
then there is only going to be a single point that it's going to be satisfying the different distance
requirements for each of those stations that will be the location of the earthquake in practice we
usually use at least ten stations to get the location to get the depth that kind of works
about the same way if you have a station directly over the earthquake because any can use the
difference between the P and the s arrival times knowing the earthquake can only be down or almost
straight down most of the time though you don't have a station over the earthquake and so you
have to use the computer model you kind of find the best step that fits magnitude comes down to
knowing or looking at the amplitude of the signal so how big the signal is and using the assumption
that if you earthquake of a given magnitude say magnitude five the amplitudes this far at a
station that's how to come this way you'd expect it to be smaller so this big at a station 200
kilometers away and by measuring the amplitudes knowing the distance plug that into a formula get
the magnitude of the earthquake so thank you Jessica and I hope that answers your question
so this question is from Louis and Napier and it's why can I hear the rumble of an earthquake
what makes the noise so this is a really good question Louis and to answer it I'll have to do go
on a brief foray into earthquake physics but I'll try to keep it light most of the seismic energy
released during an earthquake travels through the earth in two ways the P wave or pressure wave
and the S wave or shear wave and what you feel generally in an earthquake is when the S wave
arrives where you are however the P wave travels faster and so they can arrive several seconds
before the S wave depending on how close you are to the earthquake center and the P wave you
might not feel it but it could vibrate buildings a little bit and also the frequency content of the
P wave can cross over into the audible spectrum for humans hope that answers a question Louis so
I have my little like thermos I got pineapples on it it says stand tall be sweet on the inside
and wear a crown yeah it's good general philosophy okay this questions from Rachel and Christchurch
when there is an earthquake do some of the rocks of bedrock actually break or crumble a
good question yes during an earthquake the rocks to break as rocks are squeezed they store energy
and the amount of squeezing it when it exceeds the breaking strength of the rocks the rocks
might break and release that energy as heat and seismic waves and it's those seismic waves that
are the earthquake the likely place for a rock to break is where there's a weakness which can be
observed in the forms of cracks I'm really really small ones all the way to quite large ones and in
a really big earthquake the weakness is usually a fault plane and when that's at or near the surface
we can often see the broken or crumbling rocks deeper in the ground though the pressure all
around the rocks is really high so the rocks don't actually crumble and the damage occurs
in the form of cracks or micro fractures hope that answers your question this is a question from Jane
and Auckland and the question is the earthquake in Christchurch was recently said to be an aftershock
from nearly 10 years ago how can you tell the difference between an aftershock and the new
earthquake I think the place to start with that one is to understand what an aftershock is and
there's there's not really a clear definition of it and what we how we tend to think of aftershocks
is there enough to talk is just another earthquake but it's an earthquake that's occurring earlier in
time because it was influenced by this this big impact from from the initial main shock that kind
of shook up the earth and causes the earthquakes tap and happen earlier so we can think that
earthquakes that happen immediately after the main shock those those are for sure those are
going to be aftershocks and as you get further and further away from time they're less likely
to be aftershocks - meaning they're less likely to be influenced by that first event and the way we
can start to understand that as we look at the the numbers of events that were occurring prior to the
main shock and compare that whatever is occurring now and right now we're still getting more say
after earthquakes of magnitude 3 and greater in the Christchurch region and we're prior to tar
field so everything that's happening now is still influenced by by the main shock that our field
event so hopefully that helps you to understand why this is still considered and after self
I was at university doing physics and philosophy and I kind of realized that I wanted something
that had a bit more outdoorsy element to it this is a question from Stephen in Wellington in the
current lockdown we are are we noticing fainter smaller earthquakes than under normal conditions
so that's a pretty good question and you might have seen it picked up in some news outlets around
the world and the short answer is is yes so the lockdown has seen a reduction in human generated
seismic noise and this any reduction in noise will let our seismometers pick up Paynter signals which
might be generated by smaller earthquakes and this will have been especially noticeable in
places like Auckland Christchurch or Wellington where there's a much greater human noise source
but the longer answer is not really so in general there are other sources of noise in New Zealand
that are more important than human noise notably the wind and the ocean the other thing is when we
build our network and design our stations we try to minimize the sources of potential noise and we
know it one of the easier ones to get away from and then the third point is that well we might be
able to detect some of these very small signals on a few sites to be located an earthquake needs to
get picked up on multiple sites so those kind of small earthquakes might not be generating enough
seismic energy to travel far enough to be picked up by enough sites to be locatable and so I hope
that answers your question Stephen okay Christian thorn as I hear from bajas since the ninety seven
point eight back in 2016 has put more stress on the twenty cent actions owned by Wellington up
to the east coast of the North Island how can you tell the fault line has been stressed we
know we know the kaikoura earthquake has put more stresses on the Hickock subduction zone for two
reasons the first reason is that that he connected subduction zone is very close to the crack where
the petcock falls a fraction so by redoubling the force happening more pressure on the nearby folks
the second reason is that the ground shaking near the kaikoura earthquake was actually very strong
therefore the stress levels are very strong as well now how do we measure this well if we had
instruments we could actually measure it directly from instruments a big question he could not use
subduction zone he's actually buried on the ground twenty kilometres deep we actually have computer
models that tell us the level of stress that is made that is expected us at this particular
location and we can do so because a very we have a very detailed source model of the crack so we have
a source magari on the fourth model and we can extrapolate that model onto the faults that were
interested in so i hope that answers your question as I am thank you so this is poppy which is elect
interior and what she looks by doe so here she's really not she's quite a strong little creature
Emily from haumana asks is there any evidence of a correlation between seismic activity in lunar
phases so it's quite a good question there have been a few earthquakes where moans been super
mobile whatever so was natural to ask these kinds of things it's a difficult question to
answer because a lot of complexity here is there whether an earthquake will occur is mainly due
to tectonic forces so the Builder who stress from low to high plates moving but the moaning son who
can play a small element and met the moon and the Sun they both support the air and they're
pulling if it works to sort of release stress holding back a folds or promote stress on a
fault then that can cause an earthquake well they're really attached wasn't here's quake
the earthquake was going to happen anyway it's just making that earthquake occur a little bit
earlier than it would otherwise and they're totally in you know quite rare cases were
of vultures they are really well aligned for the particular way that the moon son
this questions from Carrie and Alexandra is it true that damage is less than an earthquake if
you live near the fault line where the epicenter is good question in general this is not true as
the closer you are to the earthquake epicenter the stronger ground shaking and damage can be
um there are a lot of factors that can influence the intensity of shaking from an earthquake this
can be dependent on the type of earthquake the type of soil geological structures underground
all of these things can influence seismic waves and create more or less shaking regardless of
where you are relative to the earthquake another way that we can mitigate damage
from earthquake shaking is through engineering design we study a lot of different aspects of
earthquakes in the earth so that we can provide the best estimates possible of ground shaking
so that when engineers design our buildings in infrastructure they can do so in the best way
possible I hope that answers your question and this is a question from Diana and Hawke's Bay
do a cluster of small earthquakes indicate a big earthquake is coming that's a really good question
one that's very relevant to lots of things going on around Sealand and I guess the place to start
with this one is that every earthquake that occurs influences the probability of future
earthquakes occurring in the region so in short yeah they do increase the probability of future
earthquakes but then we have to also look at that swarms or clusters happens for different
reasons this could be things such as volcanic activity which moves fluids around in the crust
of the earth or we have things called slow slip earthquakes which are quite large earthquakes
that happen on the subduction zone that take say one week or some months to occur we don't
feel those earthquakes but they do trigger lots of make other smaller earthquakes occur
in clusters and not all of these clusters are the same in terms of how they influence future
earthquake activities and that's something we're working on to try to better understand it so so
hopefully that that answers your question on the role of clusters and future earthquakes