Quake science undergoes change
Accurate details of earthquakes in pre-GeoNet days could take a week, as former seismologist
explains.
Cantabrians have my vote for the world’s best citizen seismologists. Within seconds of a minor rattle that would send Wellingtonians into the streets and Aucklanders into rehab, Cantabrians calmly report ‘‘magnitude 3.5, about 10km away’’. Seconds later the GeoNet app pings to confirm.
Earthquake-reporting apps like GeoNet are now commonplace worldwide and they are also being supplemented by clever technology that can help first responders know where to prioritise their efforts.
The geolocation of tweets (that can start within 20 seconds of an earthquake) help refine where the earthquake is being felt most strongly. Very fast computers, such as in the Japan Earthquake Early Warning, can also locate earthquakes rapidly. They then transmit information to shut down critical facilities and provide warnings of tens of seconds, enough for people to take cover.
All of this has happened in the past 15 years, since GeoNet was first set up as a partnership between GNS Science and the Earthquake Commission (EQC).
Before then, seismologists like me only knew an earthquake had occurred when the ‘‘drum’’ needles started shaking and the telephone for the seismological observatory became jammed with calls.
For those first 15 minutes or so the task was to find out from callers where and how the earthquake had been felt. The duty seismologists’ job was to calculate the location and magnitude, often based on telephoned readings from seismometers located around the country. This took at least 15 to 30 minutes; a very long time when every minute counts.
And that was during normal working hours.
At night or at weekends, the duty seismologist was alerted by a pager which signalled time to get into the office. One of the most experienced seismologists didn’t drive so when he was on duty that meant a rapid bike ride into the observatory. Earthquake reporting in those days was not ‘‘real-time’’ work.
Once the initial location and likely magnitude of an earthquake was calculated, then the task of refining the location meant waiting for recordings to be sent in from distant stations.
Many of those seismometers were located in rural areas, so if an earthquake occurred outside the regular servicing schedule then helpful landowners had to be coaxed into service. They had to change the drum paper or data tapes and then post them urgently to Wellington.
There they would be analysed and accurate locations and magnitudes finalised – these would usually be accurate to within about 10km at best and this process would take at least a week. By this time only research seismologists were interested.
So what happened? It wasn’t just the advent of new technology in the form of digital-data recording and transmission, or even faster earthquake-location algorithms.
The GeoNet partnership meant that the network of 30 seismometers was dramatically extended to more than 600 in the early 2000s. A dedicated unit was also set up at GNS Science to get more precise and faster earthquake locations. Their efforts over the past 15 years has meant we now have initial automated locations within seconds – a far cry from pre-GeoNet days.
The finalised locations have also dramatically improved. Earthquakes and their complex aftershock sequences can now be located with almost pinpoint accuracy and sometimes well within about 1km.
For research seismologists that is gold. It’s helping them to build up a very rich picture of where, when and how big our earthquakes are – and where they are not (yet). This increasingly detailed understanding of New Zealand’s seismic risk is what helps EQC negotiate reinsurance premiums that accurately reflect our national exposure to earthquake damage. No more paying more than we need.
Seismologists hate the ‘p’ word, but my prediction is that in 15 years or less GeoNet will not just be notifying us about earthquakes that have already happened. My pick is that our phones will be the seismometers of the future.
GeoNet will be citizen sourcing and providing real-time warnings in microseconds – faster than a seismologist can get on a bike.
Dr Helen Anderson QSO is a former research seismologist who worked in GNS Science last century. She was chief executive of the Ministry of Research, Science and Technology for six years and is now a director of various companies. She is passionate about helping New Zealanders understand their unique shaky isles.
A: Dr Helen Rutter, senior hydrogeologist, Aqualinc Research Limited says:
The potential for groundwater contamination is complex and determined by – how much contaminant there is, the rate it’s being leached downwards, how long the contaminants will take to get to the water table, where they enter the system, the aquifer vulnerability, how fast the water is moving and the water system’s removal capacity.
From the land surface, pathogens will be transported through the soils and sediments by recharge.
In many systems, this is relatively slow flow, and pathogens may die off or be reduced in concentration before they can migrate to any significant depth.
However, this is a function of the type of soil and sediments and rate of recharge.
For example, if there is a pathway or crack for rapid flow of water then they can quickly be transported to depth.
These rapid pathways might be formed through natural conditions, such as old root channels, pathways or cracks, or through artificially created pathways such as old wells that do not have a protected well head or are open.
There are also some sources of contaminants that bypass the soils and shallow sub-surface, such as septic tanks or faulty sewers, which, if they leak, have a more rapid pathway to access groundwater.
Connections between groundwater and surface waters can be very direct in some cases.
An example would be a shallow well located on a riverbank: the water taken from the well would be almost entirely river water.
Deeper wells and those located further away from surface waters would be likely to have a less direct connection with the surface water and more of the water is from land surface recharge.
In some cases, we can monitor a stream when pumping groundwater from a well, and observe a change in flow in the stream.
This implies a close connection between surface water and groundwater.
Source: Science Media Centre