Greetings.
The USGS Earthquake Science Center has a new nodal seismometer facility.
I’ll describe a little bit about what we have and what’s available
if anyone wants to use it.
Nodes, for anyone who’s not familiar with them, are a new generation of
seismometers that were really originally developed for the oil industry.
They’re small, portable, wireless, and they have an onboard GPS
and solid state storage. They have an internal rechargeable battery.
They can record ground motion, timing, and location all in the same package.
They can record for days, weeks, or even months in some situations.
They can record both below the ground surface or above the ground surface.
The ESC nodal seismometers are more research-oriented seismometers than
the oil industry type, which are a typical vertical component.
The ESC seismometers are three- component. We have 500 of them.
We have four 16-slot portable charging systems and comparable
harvesting systems. We have multiple field deployment tools –
which I’ll explain later, several laptop servers,
gigabytes of portable storage, and auxiliary equipment.
The ESC nodal seismometers, again, are three-component seismometers
with the internal battery that lasts about 30 to 40 days per charge.
Now, that battery is changeable, as you can see here on the right.
The sensor, recorder, and GPS is the top part of the unit, and the
bottom part is the battery with the spike on it for securing it to the ground.
Now, because it has internal GPS timing and location, you can –
it is recorded automatically, even if it’s buried up to a meter deep.
Now, they also have quite a wide recording range for frequencies,
from seconds up to about 1,000 hertz, and I’ll show
some slides on that in the next couple slides.
You can select a choice of gains from zero to 36 dB in 6-dB increments.
You can change the sampling rate from 0.25 milliseconds to 4 milliseconds.
It can be deployed in one to two minutes once you’re on site,
so they’re really fast for deployment. And they’re IP67 water- and dust-proof.
So, if you bury them in a marsh, still you can be assured
you’re going to get good data.
Now, as I mentioned, the frequency range is quite wide, and to examine that,
we did a study with UC-Berkeley, which was led by Taka’aki Taira.
And what we did was we put a node outside the UC-Berkeley vault,
one inside the vault with two broadband seismometers.
And here is the – here are the recordings from a magnitude 6.7 teleseismic event.
And the data are filtered from about 20 seconds to about 2 hertz.
And, as you can see, the data are very comparable,
particularly the in-vault node and the STS-1. It looks very similar.
But overall, all of the recordings look similar in that recording range.
And this is for the body waves. If you look at the S waves, again, this –
going down to about 33 seconds in frequency, you can see, again,
we have very comparable recordings for both the nodes and the broadbands.
So this shows us that we can get very good low-frequency data,
which is generally what you want for earthquake recordings.
But the nodes also go very high on the frequency scale,
up to about 1,000 hertz, which the broadbands do not do.
Broadbands typically top out at about 25 to 50 hertz.
So it makes the nodes a very flexible instrument.
Now, that makes them ideal for aftershock recordings,
short-term earthquake monitoring, noise studies, reflection and refraction
site characterization, guided wave recordings –
a whole series of the type of recordings that you might want to do.
And they are very simple to deploy. Basically, you need two things.
You need a node, and you need a simple magnet.
And that will start it – will record it. However, if you’re deploying
a lot of instruments, it’s good to have something called a field
deployment tool. And that’s the thing that looks like a calculator here.
It will – if you don’t have that field deployment tool, a compass
is probably another thing that you need when you go out.
Now, they’re very simple to turn on, and I’ll show just an example of this.
With that magnet – you put that magnet in a strategic location.
It’s turning on. You’re done. It’s going to record.
Now, if you’re deploying a lot of these things, as I mentioned,
you probably want to use this field deployment tool.
It uses RFID technology to identify the node.
It records wirelessly the lat, the lon, the serial numbers of the battery
and of the node, the line number, etc. – most of the information you need
in order to process the data in order to keep track.
So you don’t need pencil and paper to decipher what instrument went where.
So, it’s as simple as pushing a button,
like you show here, and all that data are recorded from the instrument itself.
Once you have that information when you deploy, when you come back to
pick up, it’s also a very simple process. You can be 1,000 miles away and
simply put in that you want to go to that site, and it will tell you the
directions you need to go in order to get there.
So locating the instrument is very difficult after it’s been out for
a month or two or three, and there’s been rain or wind,
and it’s very hard to locate the instrument. This FDT will help you
do that very easily. We also have chargers and harvesters.
They look like a small rolling suitcase. They’re portable.
They can plug into any 110 outlet. The chargers will charge batteries
in about four to six hours for a completely drained battery.
And the harvesters will download 16 nodes at 20 megabytes
per second per node. So they’re very efficient and very fast.
So, because we have four harvesters and four chargers, that means that
there can actually be four separate site investigations going on in different
locations by different PIs at the same time with a subset of the nodes.
This is what they look like – the harvester is on the left –
when you open it up. The charger is on the right.
So having these inside of a hotel room, you can do quick downloading and
recharging, get your instruments back out in the field very quickly.
The nodes are available to ESC scientists and collaborators to use.
Whereby, they can use just a few nodes, or they can use
all the nodes at the same time. And, again, we have about 500 of them.
The availability can be seen at this website shown here on the right bottom.
Now, one of the problems with portable seismometers in the past
has been that they’re notoriously unreliable.
Sometimes we have as much as 20% failure rate on the old seismometers.
But these nodes are incredibly durable, as you can see from this –
this is a video by SmartSolo.
[banging sounds]
Now, this is the tumble test. So, when they are thrown in
and tumbled around, 200 rotations, you’ll see, when they come out,
if they’re blinking green, that means they’re recording as they should be.
They’re also – this drop test, where you see the same thing.
If it blinks green, you’ve still got a good, functioning instrument.
[silence]
And, in this case, it blinks green.
There are also optional external batteries.
Like I said, the typical node will record for about a month to –
about 30 days to 40 days in the field, just on the internal battery.
But if you want to record for, say, three or four months, you can buy
these external batteries that are attached – they can buried
with the node, or they can be set on the ground surface.
very convenient for a little bit longer-term recording.
I’m going to show an example of a passive and an active study
that we’ve done using the nodes. Here is from Ridgecrest,
where deployed 461 nodes occupying 575 sites.
We got them out the day after the major earthquake – the 7.1,
and they recorded for about two months.
We have 12 linear fault-crossing arrays and 2 two-dimensional arrays –
one across the Garlock, one across the major seismicity, which you can
see here. Here’s the major seismicity shown in white.
We recorded about 14 terabytes of data during that time, and again,
we recorded – at least the network reported
30,000 earthquakes shown here. And we were able to record that.
Here is an example of a single station and a linear array.
And for the three components of those from the Ridgecrest nodal data.
We also conducted some studies whereby we conducted
guided wave studies.
On the right shown here is our linear array across the fault trace.
These yellow dots show where geologists mapped the faults.
And the red lines show those as well.
And, when we project those locations onto a plot of PGV versus
the station locations, we see we get these
prominent peaks where the two faults were met.
We also get a small peak in between, suggesting that there’s another fault
in the shallow subsurface that didn’t make it to the surface.
So we found, from many studies, that this is a very convenient way
to precisely map exactly where the faults are located.
Another study that was done using the nodal data was by White et al.
And here, using the nodal data – remember I said the network
located 30,000 earthquakes. Well, we were able to re-locate
approximately 95,000 earthquakes in this area, and much more precisely.
And, from that, we were able to develop a 3D tomography model
for the – both P and S for the region. Just an example to look, here is
a slice at 12 kilometers’ depth comparing the new model with the
SCEC Community Velocity Model, and you see there’s much more
resolution on the new model using the nodal data.
We’ve also conducted a number of active-source surveys,
mainly for site characterization and guided wave studies,
but also some noise studies using the nodes.
So, in summary, ESC has a new nodal seismometer facility.
We have about 500 three-component nodes and auxiliary equipment.
The nodes are available to ESC scientists and their collaborators.
And the node schedule is available at the website shown here.
If you want to use any of the nodes, you should contact someone from
the Nodal Committee, and those people are shown here below.
Thank you very much.
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