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Emergency management for Tairāwhiti district

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Te Araroa and Kermadec earthquakes

Council’s scientist Dr Murry Cave provides the following understanding of the Te Araroa and Kermadec earthquakes and why we’re getting so many aftershocks.

There have been over 400 quakes since Friday’s 7.1, with the biggest a 6.1 magnitude on Saturday at 1.16pm.

Around 44 quakes have recorded around 4-5 but the rest have been between 1 and 3. Most of the aftershocks have been east of Te Araroa.

The location of that first big quake was originally thought to be 100km east-north-east of East Cape but has now been revised and relocated slightly further east, some 114 km off East Cape.

The quake did not occur on the Hikurangi margin but was around 24km west and is known as an intra plate earthquake.

There’s still some discussion about the sense of movement of the Te Araroa earthquake but the USGS have indicated that it’s largely strike slip where the movement is horizontal.  

This is consistent with its location, west of the Hikurangi Margin. As it did generate a small tsunami there’s likely to have been some degree of normal (vertical) movement as well as horizontal displacement.

A 6.1 earthquake associated with the Te Araroa quake was located further east, close to the main Hikurangi Margin Fault, but at this stage is still considered to be an intra plate earthquake.

It was just a few hours later, at 6.41am, that an earthquake of 7.4 hit 966km north of East Cape in the Kermadecs, followed by a larger 8.1 closer to this at 8.28am. As was the case with the Te Araroa earthquake, the initial locations were provisional and have since been amended.

Both of the Kermadec quakes were thrust faults with the 8.1 quake occurring on or very close to the plate margin, which is the northern extension of the Hikurangi Margin. Both quakes are indicative of a subduction type movement where rocks on the Pacific Plate slide underneath the rocks of East Cape.  

Both the Te Araroa 7.1 and the Kermadec 8.1 quakes generated small tsunami.

The Te Araroa earthquake showed as a 1m +/- oscillation on the Te Araroa tide gauge while the Kermadec quake produced a smaller 30cm-50cm oscillation at the gauge. These were expressed largely as very active shore waves surging back and forth.

At Tokomaru Bay a bore was videoed by Claudia Maaka and while this looked dramatic it did not result in waves above the normal high tide mark at the shore.

At Hicks Bay, some deeper water seaweeds were deposited at the high tide mark.

The 2 tsunami occurring in rapid succession is very unusual and the Tokomaru bore was probably more obvious as a result of the wave being pushed up as it became confined in the bay. This did not occur at Te Araroa as it is more open to the ocean.

Unusual wave surges were still occurring at Te Araroa at midday Saturday, highlighting that the effect of tsunami can last for more than 24 hours after the event.

The position of these quakes offshore of East Cape makes accurate determination of their size and precise location difficult due to the distance from the on shore seismograph network.

The magnitudes of the Kermadec quakes has been determined by USGS and GeoNet advises that it’s best to use the USGS(external link) magnitudes as the GeoNet system under reported their magnitudes.

GNS scientists will work on analysis of these events in the coming week and data will be updated.

We’ll update you as soon as this information comes to hand.  


Useful links

Rain and river levels - check environmental monitoring
For local road conditions - check our road updates
For state highway updates - go to NZTA's website(external link)
For latest weather forecast - go to the Metservice website(external link)

Tsunami inundation maps released

Dec 2019 - Council released a new Tsunami Inundation Assessment Report and maps showing inundation zones for our region.

Council as the Civil Defence Emergency Management Group approved publishing the report following confirmation that the information met the required national standard for tsunami modelling. 

The report and maps are based on new research into modelling of a local tsunami generated from a magnitude 8.9 earthquake centered in the Hikurangi Subduction Zone off the East Coast.

Chief Executive, Nedine Thatcher-Swann says a final review was requested to give assurance that the zones that could be affected by a local tsunami meet national guidelines.

Here's the report and inundation maps
Questions and answers about the inundation zones.

Evacuation routes will be added to the maps as soon as we have them. 

Being prepared for a disaster

It's important that you're prepared for a disaster. Get ready now so that you're better prepared to cope on your own for up to 3 days or more.

As a minimum, everyone needs: 

♦ enough food in your home to last 2-3 days.
♦ know where to get water, if your usual supply is not available.  
♦ alternative lighting - a torch with spare batteries or a wind up one, gas lantern or light-sticks. 
♦ a battery operated or wind up radio and spare batteries - don't forget your car radio as a last resort. 
♦ a first-aid kit, make sure you have essential medications. 
♦ blankets, survival blankets or warm waterproof clothing. 
♦ alternative cooking methods - BBQ or gas cooker. 
♦ to store important family documents where you can get them easily
♦ an emergency plan - where to meet family and how to contact one another if separated.

Useful links

Rain and river levels - check environmental monitoring 
For local road conditions - check our road updates 
For state highway updates - go to NZTA's website(external link) 
For latest weather forecast - go to the Metservice website(external link) 

We will broadcast over these stations during an emergency: 945 kHz AM - Talkback ZB  |  585 kHz AM - Radio Ngati Porou  |  90.9 FM - ZGFM  |  98.1 FM - Radio Ngati Porou  |  98.9 FM - More FM (Urban Gisborne)  |  90.1 FM - More FM (rural areas)  |  94.9 FM - Radio Live  |  95.7 FM - Turanga FM  |  88.5 FM - Uawa

Review of our CDEM function

An internal review of Tairawhiti Civil Defence and Emergency Management was carried out in December 2018. Here's a summary of the 40 recommendations presented to the CDEM Meeting 9 May 2019(external link)