GeoNet, Open Data and Reward

On Wednesday 7 November 2012 GNS Science won the “Open Science” category at the New Zealand Open Source Awards 2012 (we also won the “Government” category for GeoNet Rapid, see Figure 1).

From Wikipedia:

“Open science is the umbrella term of the movement to make scientific research, data and dissemination accessible to all levels of an inquiring society, amateur or professional. It encompasses practices such as publishing open research, campaigning for open access, encouraging scientists to practice open notebook science, and generally making it easier to publish and communicate scientific knowledge.”

For GeoNet, Open Science is all about our Open Data policy, which was a founding principle of GeoNet and a very important factor in our success. This has allowed the rapid uptake of data and for third party websites to use GeoNet information in new and novel ways including websites with a regional focus (such as Canterbury Quake Live which started operation following the beginning of the Canterbury earthquake sequence in 2010).

Figure 1: The GNS Science (GeoNet) Open Source awards 2012. Left is the award for GeoNet  Rapid in the  "Open Source use in Government" category and on the right the "National eScience Infrastructure Open Science" award for the GeoNet Data Policy and Services.

Many New Zealander’s reading this will remember the “user pays” phase of our development starting in the late 1970s, accelerating through the1980s and 1990s, and continuing into the 2000s. During this period it was government policy that all data and information had an immediate intrinsic value and this must be paid by the “end user”. The result of this was the drastic drop in the use of many data sources, and the trend for policy and decision making to become “data free zones”. 

When GeoNet began operation in 2001, the concept of Open Data was very unusual in New Zealand. Therefore, the fact that it was included as a requirement in the contract between the Earthquake Commission (EQC) and GNS Science was revolutionary, and one of several ground-breaking features of the arrangements between the two organisations. EQC insisting on an Open Data policy is yet another demonstration of how visionary and forward thinking the management and Board of EQC were at the time (and continue to be) with their support of  GeoNet and its part in New Zealand's geological hazards mitigation strategy. What if the Canterbury earthquakes had occurred before the establishment of GeoNet when there was only one real-time seismic sensor in the whole of Canterbury?

There has been a huge change in the last decade, and now most institutions in New Zealand (and internationally) accept the value proposition that Open Data is important for the advancement of science and the overall goals of New Zealand society (and GeoNet now has over 600 sensor network sites). We live in a beautiful but geologically active land. In our naturally active environment, the GeoNet Open Data policy has quickly led to a better understanding of the perils we face and the mitigation measures required.

For example, following the destructive Christchurch Earthquake of 22 February 2011 the openly available GeoNet strong ground shaking data was crucial to the understanding of the levels of damage and what changes were needed in the building codes before reconstruction began.The observed level of damage was greater than expected from a moderate sized earthquake, but the data were available to demonstrate the very high energy (maximum shaking levels over twice the force of gravity) compared to the magnitude. Detailed earthquake source modelling was possible showing that the fault ruptured up to a shallow depth beneath the Christchurch central business district. GeoNet data are central to the publication of four Canterbury special issues of scientific journals, and features in numerous scientific papers and presentations at conferences, enriching our understanding of this important earthquake sequence.

So Open Data it is, and we are pleased that after 12 years the significance of the GeoNet Open Data policy is publically recognised - thanks to the New Zealand Open Source Awards!

GeoNet and Tsunami - Part One

One of GeoNet’s roles is as science advisers to the Ministry of Civil Defence & Emergency Management (MCDEM) on tsunami response. Currently this is mainly confined to regional and distant source tsunami caused by earthquakes. So how do we carry out our role?

There are three major aspects of the role – data and information, expert advice and warning systems and international engagement. I will outline each of these in turn – in this blog I will just concentrate on the tsunami (sea level) gauge network.

As a part of GeoNet we operated a tsunami gauge network of 17 sites around New Zealand and on offshore islands. These sites have twin pressure sensors in the ocean to record sea height change. The network is operated in partnership with Land Information New Zealand (LINZ) with the GeoNet Earthquake Commission (EQC) contribution supporting the data communications and processing. All the data is made available to the international data centres, particularly the Pacific Tsunami Warning Centre, (PTWC) in Hawaii, as well as being available from the GeoNet website.

A question we are often asked is: do these sites provide warning? And the answer (I am a scientist after all!) is yes and no. Yes, the gauges on offshore islands will provide an hour or two warning of a tsunami “surges” heading for mainland New Zealand, and ones on the mainland coast will provide some warning for other parts of New Zealand. But a gauge very close to you will be no help to you for warning. Tsunami warning is very international so we rely on information from other countries gauges, and other countries rely on our gauges – particularly our cousins across the ditch (for non-Australians or New Zealanders, that is the Tasman Sea) who may be threatened by a large earthquake at the bottom of New Zealand’s South Island.

Another really important use for these tsunami gauges is the calibration of tsunami forecast models. Since the Indian Ocean Tsunami on Boxing Day 2004 there has been huge progress with models that forecast the likely impacts from earthquake caused tsunami once accurate information earthquake is available. This is particularly true for ocean basin wide tsunami, where the tsunami waves may travel for many hours before being a threat on a distant shore. If the likely impacts can be forecast in advance then effective evacuation is possible without the economic losses of over evacuation or the issues caused if people are asked too often to evacuate but no tsunami occurs (the “cry wolf” affect).

Figure 1: Recordings of the Japanese Tsunami around the New Zealand Coast on the LINZ GeoNet Tsunami Gauge sites. Note the largest surges at Gisborne and the Chatham Islands are four to six hours after the first arrivals.

Recent Pacific Ocean basin wide tsunami have provide a rich data source for refining tsunami models. For example, the Japanese tsunami of 11 March 2011 was well recorded around the New Zealand coast (see Figure 1) with surge heights of around a metre in places. These measured values were very close to the forecast levels and increase our confidence that we can effectively warn New Zealand communities without closing the whole New Zealand coast. Figure 1 also demonstrates a really important observation – tsunami surges from distant tsunami just keep coming. In Gisborne and the Chatham Islands the largest surges occurred many hours after the first arrivals. If you cannot see the shark any more it may be safe to go back in the water (see Jaws if you don't understand the reference), but with tsunami take extra care for many hours after you see the first rise and fall of the sea.

In my next tsunami blog I will go into more detail about how we use the data and information and expert advice to advise on likely tsunami impacts.

Felt Intensity – What You Feel is What You Get!

How do we size an earthquake?

A few earthquakes over the last few months have got me thinking about how we talk about earthquake size. In the western world we are quite focused on magnitude, but that only gives a starting point. I have already bored you enough about earthquake magnitude in a few previous blogs (see What’s the Magnitude?; Deep Earthquakes and Magnitudes; and Deep Earthquakes and Magnitude – Again!) – but to recap, an earthquake magnitude is an estimate of the true size of an earthquake independent of the observer (or where the observer is). The magnitude is only the start of the story if you want to understand the likely impacts of an earthquake. Not all earthquakes are created equal; some are more energetic than others even if they have the same magnitude. Some direct shaking energy towards where people live, and where you are compared to the earthquake source is very important. All this leads to the idea of shaking intensity – a mapping of the levels of shaking caused by an earthquake rather than a single number like magnitude.

Modified Mercalli Shaking Intensity

  

If you want to characterise how you feel an earthquake, then felt intensity is what you are after. This is a measure of the shaking where you are, and is given (at least in New Zealand) by the Modified Mercalli (MM) scale which covers the range from not felt (MM 1: Imperceptible) to complete destruction (MM 12: Completely devastating). Obviously an earthquake’s impact and the level of damage it causes are related to the intensity. The MM value at a particular place depends on the distance from the earthquake, its size and depth, the kind of rocks between you and the source and material you or the building you are in rests on.

ShakeMap (or where did the map go?)

On the old GeoNet website we had a display on the front page based on the shaking at each recording station (Figure 1). Although this gave a good indication of the where maximum shaking levels were being recorded by our instruments (and I know some of you want it back!), it could be biased by instrument issues and was often misinterpreted. So it was good for a quick look, but not really very useful for characterising the potential damage in detail.

Figure 1: The "ShakeNZ" plot for the Christchurch  Earthquake  of 22 February 2011. This map shows the shaking  levels as squares around the sensor sites which change colour and get larger as the shaking level increases.

We are working towards having a ShakeMap (as developed by the United States Geological Survey, see the USGS Shakemap site) available for larger earthquakes which will indicate the distribution of shaking (see Figure 2 for an example). This map will be produced within a few minutes of an earthquake occurring and be based on data from the sensor sites and a knowledge of how the earthquake waves travel through the Earth (tailored for New Zealand conditions). The map will show MM intensity but we will also be able to provide information in forms that are suitable for use by engineers interested in the level of shaking experienced by buildings or other structures in the region. This can include shaking accelerations at different periods of oscillation – different size structures are more susceptible to different shaking oscillations caused by earthquakes.

Current planning should see ShakeMap on the new GeoNet website within the next few months.

Figure 2: An example ShakeMap for the Christchurch Earthquake of 22 February 2011. This is  an example of what the ShakeMap on the new GeoNet website may look like.

So what about shaking duration?

This is a hard one as the perceived duration will depend both on the size of the earthquake and where you are (a bit like intensity) but is also very dependent on the near surface structure under your feet. For example, if you live in a valley the shaking waves will “bounce around” in the valley and the shaking will go on for much longer than if you were on a hard rock site. We can estimate how long the fault takes to rupture (by studying the earthquake waves recorded on our instruments), but how long the Earth shakes depends on the size and distance, and how many ways the earthquake waves reach you (some waves “bounce” around in the Earth so the shaking goes on much longer than the fault break time). For these reasons we do not usually use duration as a measure of earthquake size.

To put this in terms of recent experience the fault-break of the Christchurch Earthquake (22 February 2011) was over in just a few seconds, but the shaking went on longer because of the near-surface structure under the city. But the total duration in areas of maximum damage was only around 10 - 15 seconds. Compare that to a possible Alpine Fault earthquake much further away from Christchurch where the shaking intensity would be much less in the city (in fact even much less than the Darfield Earthquake of 4 September 2010) but the shaking would go on for minutes. Duration is not a good indication of likely earthquake impacts. 

GeoNet – Past, Present and Future

GeoNet needs your input …. But first some background:

Why do we need GeoNet?

New Zealanders live on the edge - astride the Pacific-Australia plate boundary, a part of the Pacific “Ring of Fire”. The level of earthquake hazard in New Zealand is similar to that of California and most communities have some exposure to this hazard. Additionally there is a significant volcanic hazard, both from the cone and caldera volcanoes of the central North Island and the volcanic field underlying its largest city, Auckland. Throughout New Zealand, landslides may be triggered by extreme weather or earthquakes, and the coastal areas are prone to tsunami, both from distant and local sources.

The case for GeoNet

In 2000 at the invitation of the New Zealand Earthquake Commission (EQC), GNS Science proposed the establishment of GeoNet, a geological hazards monitoring system. GeoNet would facilitate the detection, data gathering and rapid response to New Zealand earthquakes, volcanic activity, landslides, tsunami and the slow deformation that precedes or follows large earthquakes. This followed more than five years of equipment trials, capability reviews and widening concern about national geophysical infrastructure, the purpose and renewal of which had been largely overlooked during a major restructuring of the Government science sector in the early 1990s.

EQC launched GeoNet in 2001 through its research and education programme. In partnership with Land Information New Zealand (LINZ) and the Department of Conservation, EQC’s long-term support and direction of GeoNet has facilitated the creation of world-class capabilities.  GeoNet now has sensor networks throughout New Zealand (over 550 sites), distributed data collection, processing and distribution capabilities and a programme of continual improvement. In 2009, EQC renewed its commitment to GeoNet for a further decade, with the strategic focus shifting from delivery of minimum geographic coverage, to more sophisticated management of data and information to meet evolving user needs.

The GeoNet Review

Every four years an international strategic review of GeoNet is conducted to ensure its performance and map future directions and the next one will take place in late October this year. Earlier reviews took place in 2004 and 2008.

Since the 2008 review, the earthquakes in Canterbury have provided an extreme test of all GeoNet systems.  It is therefore timely to consider how GeoNet might be enhanced or extended to maximise the value of investment in the system.  This contemplates wider use of the collected information beyond the core geological hazards area.  For example, the current networks could be adapted to support country-wide, high-accuracy real-time positioning applications for many different sectors.

GeoNet Needs Your Input ….

If you regularly use GeoNet data and information for your work or analysis, or have used GeoNet data in a major project, we want to hear about it.  For example, we are aware that many people have used GeoNet strong-motion data in the analysis of the impacts of the Canterbury earthquakes and in published research papers, but the source of the data has not always been attributed, so it is hard for us to identify all related work without your help.

We are particularly keen to hear how GeoNet might be significantly improved in future. Please submit brief (maximum one page) summaries on either or both of these topics as soon as possible, not later than  21 September to geonet-review@gns.cri.nz.Your experience and ideas will inform the planning and direction for the next few years, so please help make a difference. 

Deep Earthquakes and Magnitude – Again!

The recent large earthquake in the Taranaki Bight was an excellent example of the kind of event I discussed in a previous blog – deep and widely felt. It was felt strongly in places far away from where it occurred, and demonstrates the usual confusion between felt intensity, local magnitude and more modern measures of earthquake size.

The Local (Richter) magnitude 7.0 earthquake occurred at 10:36 pm on Tuesday 4 July (New Zealand Standard Time) about  60 km south of Opunake (out to sea) at a depth of about 230 km. The main details of the earthquake and its relationship to other events are covered by a newsstory on the GeoNet website. This earthquake was very widely felt in New Zealand - from almost the top of the North Island to the bottom of the South Island. But if you look at the distribution of felt reports (see Figure 1) it was most strongly felt along and up the subducted plate from the epicentre. As I explained in a previous blog this is because the energy from the earthquake travels up the plate rather than directly to the Earth's surface. It is also interesting how many people in the Canterbury region reported feeling the earthquake quite strongly. This is again because the tectonic plate "guides" the earthquake energy down the East Coast of New Zealand - it is not unusual to have deep earthquakes under the North Island felt in Christchurch but not directly above where they occur!

Figure 1: The pattern of the more than 6000 felt reports received on www.geonet.org.nz (the new GeoNet Rapid Beta site recorded a similar number) for the deep M7.0 earthquake of 3 July 2012

This earthquake again demonstrates how this "guiding" of earthquake energy causes our New Zealand Local Magnitude (used by the current GeoNet website) to overestimate the magnitude compared to international estimates. The earthquake "feels" larger to most New Zealanders than it actually is! For example, the United States Geological Survey (USGS) recorded this as a M6.2 earthquake, the GeoNet Rapid (Beta) site estimated the magnitude at M6.5, while our own estimate for the Moment Magnitude was M6.3. Who is right? The last three numbers quoted (6.2, 6.5, 6.3) are all basically estimates of Moment Magnitude which is based on the actual source characteristics of the earthquake. In an ideal world all these would give that same value, but this range of values is reasonably normal. The Local Magnitude is known to be about 0.5 magnitude units high for deep earthquakes (because of the effect described above), so all these values are about what we would expect. If we were currently using GeoNet Rapid as the official site (we will be from early September) the earthquake would have been reported as a M6.5.

This large overestimation of magnitude does not occur for shallower earthquakes, although estimates of magnitude from different systems will show some variation. For example, a recent earthquake west of Christchurch (Friday, July 6 2012 at 3:29 pm NZST) was assigned a magnitude of M4.8 by both our current GeoNet systems and the USGS and M4.9 by GeoNet Rapid (Beta). However, another deep earthquake on Saturday, July 7 2012 at 12:50 pm NZST again shows the deep earthquake effect, with GeoNet Rapid (Beta) giving it a magnitude of M5.2 compared to M5.7 for our current system.

This event also demonstrates the speed of GeoNet Rapid. The first location appeared in 1 minute 27 seconds (although at that stage the magnitude estimate was less than M6), and the magnitude "stabilised" at M6.5 in less than 2 minutes 30 seconds. Knowing the depth and location for a large offshore earthquake that quickly is very useful - it immediately tells us that no tsunami will be generated (the earthquake is too far below the sea bed). In fact many people will have had access to the location before the shaking was over!

GeoNet and the Art of Earthquake Location Part 2

In my previous blog I discussing the principles of earthquake location, but we also have some reasonably difficult practical issues. The most important of these is how to identify the arrival of the earthquake waves when there are many sources of ground shaking. These include the background actions of the oceans on the shores, weather noise (such as wind, rain, thunder, etc.) and humans and other animals (see Figure 1). In fact it is what we call “cultural noise” which causes us the most difficulty. This is the noise us humans make going about our everyday lives (vehicles, factories, and just people walking around). This is obviously worse in cities where there are many of us causing ground noise. To avoid this many of our recording sites are as far away from people as possible! Another GeoNet blog (see GeoNet – Shaken not stirred) gives a very good example of seismic noise made by a large group of people. For all these reasons considerable skill is required to “pick” the first arriving earthquake waves which may be buried in ground shaking noise. Moving this to an automated process is difficult, but good progress has been made.  Machines now do the job more consistently than humans, but can still more easily be fooled by noise.

Figure 1: The GeoNet seismograph station near Denniston on the west coast of the South Island. The image shows two earthquakes near the centre, but also a lot of "cultural" noise. This site is prone to disturbance by nearby mining operations, which show as small, similarly-sized blobs during usual working hours.

An additional practical problem is making sure the correct earthquake arrivals are associated with the correct earthquake. In New Zealand where more than 20,000 earthquakes are located each year there are often earthquakes happening at the same time in different parts of the country. If the automatic processing mixes the arrivals from one earthquake with another event the calculated location will be inaccurate. To avoid this the computer is actually making 100s of estimates every second seeing if a “picked” phase arrival will fit any earthquake location. In this process an earthquake location needs to have a good level of accuracy before it is accepted. But some bad events do get through when there is a large amount of ground noise or signals from distant earthquakes are mixed with nearby events.

Our new earthquake analysis system, GeoNetRapid (currently in Beta) is based on the SeisComP3 system developed by GFZ in Potsdam, Germany which is made freely available and has a large and active user community (for details see my colleague’s blog). This system automatically identifies earthquake wave arrival times (phases), associates the phase into earthquake events and then provides a location and depth with error estimates (and magnitude estimates). Additionally, within GeoNet Rapid we are using many decades of earthquake and tectonic research in New Zealand in the form of a three dimensional model of how earthquake wave speeds vary around New Zealand. This allows for the more accurate estimation of the true location and depth of earthquakes. But even with all this new technology the machines will sometimes get it wrong. For larger felt earthquakes recorded on many stations this is now rare and will continue to improve as we refine GeoNet Rapid. For more details on how to use GeoNet Rapid see GeoNet Rapid - Why is it different?

Links
How do seismologists locate an earthquake?
Foo Fighters rocked Auckland!
GeoNet Rapid (the Beta website)
The SeisComP3 earthquake Analysis System (the heart of GeoNet Rapid)
GeoNet Rapid - Being Faster
GeoNet Rapid - Why is it different?

GeoNet and the Art of Earthquake Location - Part 1

Using the recordings of earthquake waves at GeoNet stations and some simple mathematics we can easily calculate an earthquake’s location. Yeah Right! (non-New Zealanders should check here and Figure 1 to understand the above statements). Earthquakes are complicated ruptures of the rock within the Earth. We imagine them as simple fault breaks deep underground, usually showing as nice straight lines where they reach the Earth’s surface. This simple picture is far from what actually happens - most earthquakes do not break the Earth’s surface, and larger earthquakes usually rupture more than one fault. This is why asking “what fault was that earthquake on?” is usually the wrong question unless you are talking about a large earthquake. For example, only the Darfield (September 2010) earthquake in the Canterbury earthquake sequence caused an identifiable surface rupture. Using various kinds of land surveying (very accurate GPS and satellite radar mapping) and many recordings from ground shaking sensors we can build up a picture of the faults which ruptured in the major earthquakes in the sequence. What we have found is that each earthquake is actually made up of several fault breaks within the Earth.

Figure 1: Yeah right! Tui beer is promoted through a humorous advertising campaign which uses stereotypes, heavy irony and the phrase Yeah Right. This phrase has become a part of New Zealand culture.

Let’s look at the earthquake location process in a bit of detail, including an “Earthquakes 101”. When we talk about the location and depth of an earthquake we are actually referring to the place where the fault rupture starts and begins sending out earthquake waves. A very big earthquake can break a fault (or faults) 100s of kilometres long, but its location will be given as the point where it starts. Technically we refer to the point on the Earth’s surface above where the rupture starts (referred to as the focus or hypocentre) as the epicentre (or just the location). The earthquake’s focus will be some depth below the Earth’s surface directly below the epicentre (Figure 2).

Figure 2: Earthquake location terms. Image from “Earthquakes and Plates”

The location process involves measuring the arrival time of the earthquake waves (referred to as phase arrivals or just phases) at our ground shaking sensors. There are two main types of earthquake waves, imaginatively called primary (P; see Figure 3) and secondary (S; see Figure 4) waves. P-waves are like sound waves which travel through the Earth and are much faster than S-waves, which could also be referred to as shaking waves as they cause a side to side motion. It is the S-waves that cause most earthquake damage. In the upper 10 km of the Earth’s crust P-waves travel at about 4.5 to 6.5 km per second and S-waves at 3 to 4 km per second. There are other kinds of earthquake waves which are a combination of the main wave types. The difference in arrival time between these two wave types indicates the distance from the earthquake to the recording station (a bit like counting the seconds between the lightning flash and the sound of thunder gives an estimate of how far you are from a storm).

Figure 3: A representation of how P-waves, which are compressional waves (like sound waves) travel through the Earth. Copyright 2004-10.  L. Braile.  Permission granted for reproduction and use of animations for non-commercial uses.

Figure 4: A representation of how S-waves, which are transverse waves travel through the Earth. Copyright 2004-10.  L. Braile.  Permission granted for reproduction and use of animations for non-commercial uses.

Calculating the location, depth and size of an earthquake would be much easier if the earth beneath our feet was uniform and composed of just one kind of rock. But the rocks are layered, made of a variety of rock types, are full of fractures and far from uniform. In fact because of the alignment of some rock crystals and cracks earthquake waves may travel at different speeds in different directions! So that simple mathematics I mentioned above (tongue in cheek) gets complicated very quickly. Usually we ignore all these complications and just assume the speed of earthquake waves only varies with depth within the Earth. This works reasonably well if the wave speeds only change a small amount from place to place, but New Zealand’s location on a tectonic plate boundary means that using the simple approach can introduce large errors. The earthquake location process uses the phase arrival times to calculate the position of the earthquake source in relation to all the stations which recorded the earthquake waves using the travel times and distances involved (the simple mathematics I talked of above, see here for a more detailed description). In general the more stations recording an earthquake the better the estimation of location and depth will be.  But also the most accurate locations are calculated when the recording stations surround the earthquake, and the poorest locations are when the earthquake occurs outside the sensor network (such as offshore). The long thin nature of New Zealand means recording stations often do not surround an earthquake’s location.

In my next blog I will talk about how we identify the P and S waves that are crucial to getting an earthquake location.