How is earthquake data measured, computed and published ?

Geonet, The New Zealand governmental office who publishes earthquake information, released a very good describing article how an earthquake is measured, monitored, computed etc. has a constant interest in explaining the background of earthquake numbers for his readers. We hope that this article will clarify a number of issues concerning earthquakes.

To make rapid locations of earthquakes GeoNet operates a country-wide network of seismic stations that transmit their data to the GeoNet Data Management Centre (DMC) where it is analysed by automated processes. If the automated processes detect an earthquake the Duty Response Team is notified and if the Duty Officer confirms that the earthquake is real and significant, the earthquake information is released.

The seismic stations operated by GeoNet consist of a seismometer and a seismograph. A seismometer is a sensitive instrument that generates a small electrical current in response to ground shaking. The electrical current is digitised by the seismograph and transmitted continuously to the DMC in real time. This digital recording of ground shaking is the raw data used to make earthquake locations. The seismic stations are supplemented by a network of strong-motion seismographs, which only transmit data whenever they detect a higher level of shaking, typically from earthquakes that will have been felt by the public.

The real-time seismic data is received by the DMC data reception computers located at Avalon (Lower Hutt) and Wairakei (near Taupo) and analysed automatically for possible earthquakes. The computer processes look for ground shaking that is distinct from the normal background activity (such as that caused by weather and oceans) and may be associated with an earthquake. These occurrences are called detections. If a detection is deemed significant, then the relevant portion of the data is parcelled up and sent to the DMC data analysis computers. They store all the detected earthquake data, grouping the detections from different stations into earthquake data sets. The detections are examined for P (primary) and S (secondary) wave arrivals from the earthquake, and the times of these arrivals are inverted against seismic velocity models for the earth to yield the best location for the event. The magnitude of the earthquake is determined at a station by measuring the maximum amplitude of the seismic signals, and relating them to the distance of the station from the event, together with the characteristics of the seismometer and seismograph. The magnitudes from all available stations are then averaged to give an overall value for the event.

It also provides locally recorded data from global earthquakes to the International Seismological Centre in the United Kingdom, and preliminary earthquake information to the National Earthquake Information Center, part of the United States Geological Survey responsible for locating major earthquakes worldwide. The waveform data and the located hypocentres are freely available to the worldwide community of researchers through the Resources section of this website.

Courtesy Geonet and GNS Science – Link to the original article of Geonet – GNS Science

Improved New Zealand tsunami monitoring system in place

The likely impact of tsunami on New Zealand’s coastline is now better understood following the completion of a major project to install sea level monitoring devices.

Sea level gauges have been installed at 17 sites around New Zealand and offshore islands. Pressure sensors at the gauges measure any significant change in the sea level, with data being transmitted in real time to GNS Science’s GeoNet data management centre.

GNS Science assesses the data and advises the Ministry of Civil Defence and Emergency Management (MCDEM) about the level of threat posed by tsunami. MCDEM is responsible for managing the response to any threat, which may include issuing public warnings.

The tsunami network project, led by Land Information New Zealand (LINZ), now forms an important component of a wider tsunami monitoring system for New Zealand and across the Pacific.

Graeme Blick, Chief Geodesist at LINZ, said the project was initiated following the devastating Boxing Day 2004 tsunami in the Indian Ocean, caused by a 9.3 magnitude earthquake off the coast of Sumatra. Waves up to 1 metre in height were recorded at sites around New Zealand 18 to 25 hours after the earthquake occurred, highlighting New Zealand’s vulnerability to tsunami.

Mr Blick said the installation took five years to complete, and was made more challenging by the rough and rugged environment in which the sea level gauges were installed, and the long process of obtaining approvals and consents. The last sensor was installed in July 2010.

Agencies involved included GNS Science, MCDEM, NIWA, MORST, Waikato University and consultancy firm URS, as well as Australian agencies involved in the development of a similar network there.

“The fact the network was completed on time and within budget is testament to the cooperative effort that went in to the project,” Mr Blick said.

GNS Science worked closely with LINZ, providing technical expertise throughout the installation phase. Dr Ken Gledhill, Geohazards Monitoring Manager for GNS Science, said the project was a great example of collaboration across the public and private sectors.

Over the past 150 years, New Zealand has experienced about 10 tsunami higher than 5 metres, which can put people and property at risk. Large earthquakes can have devastating effects, both on land and water, Dr Gledhill said, as the people of Christchurch can testify.

“Since installation of the network began in 2005, several large regional and distant earthquakes have generated tsunami,” he said. “The network has successfully detected these, including the 2009 Samoan and 2010 Chilean earthquakes and the resulting waves that hit our coastline.” (Source : GNS Science)

Picture “Sourced from LINZ. Crown Copyright reserved.”

Huge Tsunami preparedness exercise in New Zealand today

tsunami sign

Image by bookish in north park via Flickr

On the exception of Canterbury, because of the recent traumatic earthquake,  New Zealand’s will test it’s ability to respond to a massive tsunami on Wednesday.

More than 100 agencies nationwide will take part in the exercise.
New Zealand will test the new updated national tsunami advisory and warning plan.

The revised plan makes use of new scientific modeling from GNS Science that allows for distinct threat warnings to be issued for 43 coastal zones.

“It is a good example of how science can help response to an emergency,” he added.

Exercise Tangaroa, named for the god of the sea, rivers, lakes and all life within them, will begin with a simulated Pacific Tsunami Warning Center alert that a major tsunami may have been created by an earthquake off the coast of South America.

National warnings, clearly labeled as simulation messages, will be issued by the Ministry of Civil Defense and Emergency Management to the National Crisis Management Center and agencies throughout the country.

Participants include all 16 regional civil defense emergency management groups, most local authorities, central government departments, emergency services, scientific agencies, welfare organizations, utilities, the transport sector and some media.

Read more here

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