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Earthquakes
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| Hastings Street, Napier 1931 - Frustrated by the lack of water, a fireman can only watch as Napier burns (Photo courtesy of Hawke's Bay Cultural Trust) |
Hawke’s Bay is one of the most seismically active regions of New Zealand and in the 160 years since substantial written records began, several large and damaging earthquakes have occurred. Most notably the earthquake of 1931 changed the landscape, the cities and has remained a prominent feature in Hawke’s Bay’s living memory. Hawke’s Bay experiences many smaller earthquakes each year, but another large earthquake can occur at any time.
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New Zealand lies along the boundary between the Australian and Pacific plates. In the North Island, the two plates meet in a collisional boundary at a subduction zone, where the Pacific plate is plunging beneath the Australian Plate.
The plates don’t move past each other easily and stress builds up on and near the boundary zone where they meet. When faults rupture suddenly to relieve built up stress, they produce earthquakes. Some faults are deep beneath the earth’s surface and some are visible as surface fault lines. The magnitude of an earthquake depends on the size and nature of the fault that ruptures and the amount of slip that occurs. Since the plates are constantly moving, earthquakes occur all the time, but most of these are too small to be felt by people. Sometimes, however, a large fault rupture occurs and produces a big earthquake. Large earthquakes can be very damaging to life and property and constitute a major hazard to people who live in earthquake prone areas.
Hawke's Bay’s Tectonic Setting
Hawke’s Bay is located on the Australian Plate, about 150 km west of the Hikurangi Trough, which marks the subduction boundary between the Pacific and Australian Plates. At this latitude, the two plates are converging obliquely at about 42 mm/yr. The interface between the two plates is a large fault that dips about 6° to the west near the Hikurangi Trough and steepens to about 25° below Hawke’s Bay.
Hawke’s Bay’s location above the subduction interface means that it is within a zone of high deformation, and as a consequence has many earthquakes.^Top^
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| A massive slip which swept across the roadway and beach below Bluff Hill, Napier 1931. |
Previous Impacts in the Hawkes Bay
More than 160 years of written records in New Zealand show that Hawke’s Bay is one of the most seismically active regions of New Zealand.
Most moderate to large earthquakes have been on shallow (<45 km deep) faults, but a few, such as the June 1921 Hawke’s Bay earthquake, were caused by rupture at greater depths. The largest historical earthquakes affecting Hawke’s Bay are listed in Table A. 1843 Western Hawke's Bay Because of considerable ground cracking and settlement of the river banks near Wanganui on the west coast, the large earthquake on 8 July 1843 had been thought to be centred close to that city. However, it has now been found that there were possibly coastal landslides south of Cape Kidnappers and ground cracking near Napier, suggesting the earthquake may have been centred closer to Hawke’s Bay than
previously thought, possibly along its western boundary. Investigation is continuing, although there are few
written records of this very early period of Hawke’s Bay’s history. 1863 Waipukurau A Magnitude 7.5 earthquake occurred on 23 February 1863. It is the second largest earthquake to occur in Hawke's Bay since 1843 with its epicentre near Waipawa and Waipukurau. Personal accounts from witnesses reveal the occurrence of numerous landslides, liquefaction, and surface faulting. Many chimneys were damaged in Napier. 1904 Cape Turnagain On 9 August 1904 a Magnitude M7-7.2 earthquake, centred inland from Cape Turnagain, damaged chimneys, buildings and roads from north of Napier to Masterton. Liquefaction, sand boils, landslides, and surface fractures were reported. There may also have been a small tsunami at Mohaka, possiblly caused by landslides at Cape Kidnappers. It is uncertain whether this earthquake occurred on the plate interface or in the subducted plate. 1931 Hawke's Bay On 3 February 1931, one of the three largest historical earthquakes ever recorded in New Zealand struck Hawke's Bay. The magnitude M7.8 earthquake was produced by rupture on a northeast-trending buried fault, probably the Napier-Hawke Bay Fault. The focus (initiation point) of the earthquake was about 20 km north and a little east of Napier and some 30km deep. There was only a minor surface rupture along a 15 km stretch of the fault, but the blind faulting produced an uplifted area of 1500 km2 with a maximum of 2.7 m of uplift . In Hastings, about 1 m of ground subsidence occurred. The Ahuriri Lagoon was raised 1-2 m and partially drained. Near Napier the coastline was raised and some boats moored in the harbour were left sitting on harbour floor. A tsunami was also experienced along parts of the Hawke Bay coast. The ‘Hawke’s Bay earthquake’ was the most devastating in New Zealand history. 256 people lost their lives, either from collapsing buildings or in the widespread fires that followed the earthquake. Many buildings at that time were constructed of unreinforced masonry or had poorly supported concrete facades that collapsed in the shaking. The fires that destroyed downtown Napier were left to burn as the water supply in town failed. All the bridges into town collapsed and the main roads into Hawke’s Bay suffered severe damage. The economic damage from the earthquake equates to about $300 million in 2006 values. The 1931 earthquake prompted a number of changes in New Zealand’s approach to earthquake hazard management. New construction regulations were developed so that structures would be built to minimise damage from earthquake shaking. Although construction regulations were not implemented until 1942, the government began to develop a system of earthquake insurance and compensation (which we know of today as the Earthquake Commission (EQC)), and civil defence strategies were enacted to ensure that public safety and relief would be taken care of in future earthquakes. ^Top^ Hawkes Bay Earthquake Stories
People who lived through the earthquake had some dramatic stories to tell and some are told below. You can also find more information on the 1931 Earthquake by visiting the Art Deco Website www.artdeconapier.com
1932 Wairoa
A magnitude M6.9 earthquake, centred near Wairoa, occurred on 15 September 1932. It may have been caused by a new rupture along the northeast extension of the Napier-Hawke Bay Fault that ruptured in the 1931 Hawke's Bay earthquake. However, the fault did not rupture to the surface. The shaking damaged buildings in Gisborne and Wairoa and caused the collapse of the Wairoa River bridge. The earthquake triggered a number of landslides near and northeast of Wairoa.
Other earthquakes
Other large earthquakes affecting Hawke's Bay have been documented since the middle of the nineteenth century. Some of the largest include the magnitude M7.0 Central Hawke's Bay earthquake of June 1921, a M7.3 earthquake on 13 February 1931 which was an aftershock of the Hawke's Bay earthquake, and the M7.6 Pahiatua earthquake on 5 March 1934. In addition, large earthquakes centred outside the region have casued strong shaking and damage to structures. In 1855 an M8.2 earthquake in Wairarapa caused moderately strong intensities of shaking in Hawke's Bay although its epicentre was more than 200 km south of Napier, and a Magnitude M7 deep earthquake in November 1914 centred in the Bay of Plenty was also widely felt in Hawke's Bay.
Numerous earthquakes in recent years have shaken Hawke's Bay, like the three significant earthquakes recorded in 2001. A Magnitude 5.8 quake with an epicentre close to Hastings on 15 October was widely felt, then a magnitude 5.0 quake on 24 October located 30 km northwest of Taupo was felt along the east coast of the North Island. On 8 December a magnitude 5.0 event located 30 km southwest of Gisborne produced a strong shake in many part of the region. These continuing earthquakes are warnings to be ready for the next big one.^Top^
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1931 Earthquake Survivor Stories
The following quotes are from 'The Shock of '31' By Geoff Conly, AH & AW Reed Ltd
Mr P.W Barlow, chief surveyor with the Napier branch of the Lands and Survey Department, had just completed drafts of letters to be typed when the room began to shake. He pushed his large swivel chair out from his desk, lay on the floor, put his legs under the desk and his head under the chair. He felt the culmination of the earthquake as a violent shake, 'similar to the shaking a fox terrier given when killing a rat' he said. Then came the big crash. Bricks were raining into the room and the dust was so thick he could not see his hand 25 centimetres away from his face.
Wilson Wright was 5 years old and never thought the sound of school bells would be replaced by the sound of an earthquake. At home, music from a gramophone echoed through his parents' house - his mother was busy with the household chores.
'The room shook, the chimney fell, and she ran outside as the second shock came,' said Mr Wright. His father, manager
of the freezing works at Pakipaki, escaped injury but found himself in an unlucky position when the quake struck.
'He stepped out on to the veranda roof over the railway siding, just as it collapsed. He described it was like coming down in a lift,
except he was chased by falling bricks. Afterwards he had the grim task of organising search parties to collect the dead bodies.'
Mavis Rowe was 16 when the earthquake struck and she was working at a Shamrock Street home.
'It was a hazy, muggy sort of day. Two of us must have been up the front of the house … and there was just this awful noise. For a minute you'd think a truck had run into the house,' she said. 'It was so noisy with the house creaking and groaning and the chimneys coming down. You couldn't in your wildest dream imagine what those quakes were like. There was stuff falling all the time. I grabbed Auntie'.
They found they couldn't get out of the back of the house, so they hurried back down the long hall toward the front door. But the quake had jammed the door shut. 'I was all prepared to get a shoe and break a window in the bedroom and push Auntie out. But another big jolt started and the door flew open. I pushed her down the hall and she never flew down those steps so fast in all her life!'
Outside, a wooden fence was swaying down and touching a lemon tree before swaying back up again. 'I thought, the ground will open up and swallow us, but there's nothing we can do about it' she says. Across the road, a woman was calling 'my crystal, all my crystal'. Mavis said 'I thought: what does she want crystal for? It's the end of the world, she won't need that'.
^Top^ What to do?
Most people in Hawke’s Bay will survive a large earthquake with little loss, but some people will be severely affected. Actions you take now can significantly help reduce damage to your home and business and help you survive.Before an earthquake - Develop a Household Emergency Plan and prepare an Emergency Survival Kit so that you can cope with being on your own for three days or more.
- Identify safe places in your home, school or workplace. A safe place is:
- under a strong table; remember to hold onto the legs
- next to an interior wall somewhere close to you.
A safe place should be no more than a few steps or two metres away to avoid injury from flying debris – so in your home identify a place in each room. - Secure heavy items of furniture to the floor or wall. Visit www.eq-iq.org.nz/ to find out how to ‘quake safe’ your home.
- Seek qualified advice to make sure your house is secured to its foundations. Also check that any renovations comply with the New Zealand Building Code.
During an earthquake Injuries and deaths during earthquakes are caused by falling objects and collapsing structures. Knowing how to protect yourself when the shaking starts may save your life - If you are inside a building, move to a safe place. Drop to the floor and duck under a strong table or desk. Cover your head and face to protect them from broken glass and falling objects. Hold onto the table or desk and be prepared to move with it. Hold your position until the shaking stops. This is called the ‘DROP, COVER and HOLD’ procedure.
- DO NOT run outside during the shaking or use the stairways or elevators. Many people are killed just outside buildings by falling bricks and other debris.
- If you are outside, get into the open, away from buildings, street lights and power lines. The greatest danger exists directly outside buildings, at exits, and alongside exterior walls. It is reported many earthquake fatalities occur when people run outside of buildings only to be killed by falling debris from collapsing walls. Ground movement during an earthquake is seldom the direct cause of death or injury. Most earthquake-related casualties result from collapsing walls, flying glass, and falling objects.
- If you are driving, pull over and stop. If safety permits avoid stopping near or under buildings, trees, overpasses, and utility wires. Stay in your car and wait for the shaking to stop.
- If you are at the beach or near the coast, move to higher ground as soon as the shaking stops in case tsunami follows the quake.
After an earthquake - Expect to feel aftershocks, some of which may be very strong.
- Help those around you if you can.
- If you are in a damaged building, after shaking stops, try to get outside and find a safe, open place.
- If you are trapped under debris, do not light a match, move about or kick up dust. Cover your mouth with a handkerchief or clothing. Tap on a pipe or wall so rescuers can locate you. Shout only as a last resort. Shouting can cause you to inhale dangerous amounts of dust.
- Extinguish any fires and wood burners or open fires immediately.
- Inspect utilities
- Check for gas leaks. If you smell gas, open windows and quickly leave the building. Turn off the gas at the outside main valve if you can safely and call the gas company from a neighbor's home. If you turn off the gas for any reason, it must be turned back on by a professional.
- Look for electrical system damage. If you see sparks or broken or evidence of electrical system damage, turn off the electricity at the main fuse box if it is safe to do so. If you have to step in water to get to the fuse box, call an electrician first for advice.
- Check for sewage and water lines damage. If you suspect sewage lines are damaged, avoid using the toilets and call a plumber. If water pipes are damaged, contact the Council and avoid using water from the tap.
- Listen to the radio for information and advice. If power is off, and you don’t have a battery operted radio, you could use a vehicle radio.
- If your property is damaged, take notes and photographs for insurance purposes.
For more information of earthquakes and earthquake preparedness go to:
www.geonet.org.nz or www.eqc.govt.nz ^Top^
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| Survivor's Camp at Nelson Park, Napier after Hawke's Bay Earthquake 1931 |
Misleading Advice 'Triangle of Life'
There is a widely circulated email by a self-professed rescue expert suggesting earthquake advice contradictory to what Civil Defence and the NZ Earthquake Engineering Society recommends, commonly known as the 'Triangle of Life'. Although the email source has been discredited in the US, where it originated, the email continues to resurface which is concerning as confusion about what to do can result in people getting seriously injured or killed in an earthquake.
In New Zealand we are fortunate to have sound building codes and earthquake resilient structures and can have some level of confidence in our buildings, so our advice under 'What to do' above is correct for residents in Hawke's Bay.
If you want to know more about why the 'Triangle of Life' is not the best advice for New Zealanders, we suggest you visit the following websites:^Top^
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