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.
|Hawke's Bay sits above the subduction zone, where the Pacific Plate is moving under the Australian Plate
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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. These earthquakes can cause ground shaking, liquefaction, surface rupture and other ground damage, regional subsidence or uplift along with tsunami and landslides.
There are numerous active faults in the Hawke's Bay region both onshore and offshore. Many of these are surface faults where a rupture that initiated at depth has broken through to the surface and left a visible fault trace. Others are buried or 'blind' faults that slip at depth but do not rupture to the ground surface, so these are harder to recognise. The attached Active Fault Map shows generalised traces of active surface faults in the Hawke's Bay region prepared by GNS & NIWA scientists. Active faults are those faults that have moved within the last 125,000 years. While no surface traces of active faults have been mapped in the Napier and Hastings city areas, this is thought to be because material from historic floods and development have covered them over. Scientists believe both cities have 'buried’ or ‘blind’ fault sources including the large fault source that caused the Hawke’s Bay earthquake of 1931, known as the Awanui fault (which has an estimated recurrence interval of 5,000-10,000 years), but scientists are currently unable to map them. The subduction interface between the Australian and Pacific plates is the largest offshore fault in the region.
You can learn more about these in the HB Engineering Lifelines Report "Facing the Risks". which in Chapter 2 shows regional maps of ground shaking intensity, active faults and liquefaction susceptibility. Attached are liquefaction susceptibility maps for Hawke's Bay and Napier/Hastings completed by GNS Science in 1996. The scenarios GNS used to develop an understanding of liquefaction potential were earthquakes between M7.25-M8.1 with estimated mean return time (years) of between 500-900 years.
Previous Impacts in the Hawkes Bay
|Some land came up and some went down in 1931. Blue shows areas that dropped and red areas of uplift (Map courtesy of GNS Science)
In the past most moderate to large earthquakes in Hawke's Bay 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.
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 (this initiation point differs from some earlier reports and has been determined following further research by GNS Science). 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 2010 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.
Hawkes Bay Earthquake Stories & Pictures
|This new home in Eskdale was destroyed in the 1931 earthquake (Photo courtesy of Ruth Kay)
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 and the Hastings Library website.
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.
|Cleaning up after the Hastings 5.9 earthquake on 25 August 2008 (Photo courtesy of HB Today)
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. The 5.9 Hastings earthquake on the 25 August 2008 struck at 11.25 pm was only 10km deep and was felt from Bay of Plenty to Wellington. These continuing earthquakes are warnings to be ready for the next big one. The table below shows the expected return periods for levels of Modified Mercalli shaking that might be expected in the future.
1931 Earthquake Survivor Stories
|Click to enlarge
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. Remember to have a plan for getting back together in case family members are separated from one another during an earthquake, such as during the day when adults are at work and children at school.
- Pick safe places in each room of your home and your office or school. A safe place could be under a piece of furniture, such as a sturdy table or desk or against an interior wall away from windows, bookcases, or tall furniture that could fall on you.
The shorter the distance to your safe place, the less likely it is that you will be injured by flying debris during the shaking.
- Keep a torch and sturdy shoes by each person's bed.
- Practice drop, cover and hold on at least twice a year.
- Secure heavy objects both inside and outside your home. Visit www.eq-iq.org.nz or www.eqc.govt.nz/fixfasten to find out how to ‘quake safe’ your home.
- Seek qualified advice to make sure your home and critical buildings are securely anchored to their foundations.
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 when shaking starts, move no more than a few steps to a safe place and drop, cover and hold. Most people injured in earthquakes move more than three metres during the shaking. 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.
- If you have physical disability or mobility impairment limited mobility, the ground-shaking will make it difficult or impossible for you to move any distance - see brochure.
- If you cannot safely get under a table, move near an inside wall of the building away from windows and tall items that can fall on you.
- Cover your head and neck as best you can.
- Lock your wheels if you are in a wheelchair.
- In bed, pull the sheets and blankets over you and use your pillow to protect your head and neck
- If you are in bed, stay there, hold on, and protect your head with a pillow. You are less likely to be injured if you stay in bed. Broken glass on the floor can injure you.
- Stay away from windows. Windows can shatter with such force that you can be injured by flying glass even if you are several metres away.
- If you are outside, find a clear spot and drop to the ground away from buildings, trees, streetlights 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 in a vehicle, pull over to a clear location, stop and stay there with your seltbelt fastened until the shaking stops. If safety permits avoid stopping near or under buildings, trees, overpasses, and utility wires. Stopping in a clear location will reduce your risk, and a hard-topped vehicle will help protect you from flying or falling objects.
- If you are in a coastal area, move immediately to higher ground when shaking stops, or if the areas is flat move as far inland as possible in case tsunami follows the earthquake.
After an earthquake
- Expect to feel aftershocks, some of which may be very strong.
- Check yourself and then help those around you if you can.
- Look quickly for damage in and around the building and get everyone out if it appears unsafe as aftershocks following earthquakes can cause further famage to unstable buidings. Use the stairs, not an elevator.
- 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.
- Look for and extinguish any small fires. Fire is the most common hazard following earthquakes.
- Inspect utilities
- Check for gas leaks. If you smell gas or hear a blowing or hissing noise, open a window and get everyone out quickly. Turn off the gas, using 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 damage to the electrical system. If you see sparks or broken or frayed wires, or if you smell buring insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box, call an electrician first for advice.
- Check for damage to sewage/effluent and water lines. 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 radio in your vehicle.
- 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 There are useful Ministry of Health factsheets developed for the Christchurch Earthquake on coping with stress and anxiety. They assist in:
- understanding common emotional reactions to the earthquake
- learning positive ways of coping
- identifying when to get extra help that will enable people to cope better.
There are also factsheets for emergency response workers, health staff and volunteers.
How safe are Hawke’s Bay buildings in an earthquake?
Since the Canterbury earthquakes people have been asking how safe are Hawke’s Bay buildings in an earthquake? The following comments are useful:
The Institute of Professional Engineers advises it will be some time before conclusions about quake damage can be drawn on the basis of engineering analysis.
- New Zealand is divided in the Earthquake Section of the NZ Loadings Code, for building design, into earthquake risk zones. Christchurch is 0.6 (lowest risk zone) and Hawke’s Bay is 1.2 (Highest risk zone). This means that buildings in Hawke’s Bay are designed to withstand double the earthquake load that Christchurch buildings are designed for. This is a reflection of earthquake risk derived from historic earthquakes, and clearly may need to be reviewed following this one.
- Since mid 1970’s new buildings have been required to be designed to remain standing for people’s safety following earthquakes. This does not mean necessarily that they will be fully functional following an earthquake, but they should not collapse.
- In general it is understood that modern buildings in Christchurch have performed as required by the code. The Hotel that is being propped up did not collapse, but it is understood that possibly some unusual design features resulted in the building behaving differently.
- The Christchurch earthquake was 6.3 on the Richter scale (ie measurement of energy released by the earthquake). In the last 160 years there has been 20 earthquakes affecting Hawke’s Bay with magnitudes greater than 6. (Note that the difference between a 6 and a 7 earthquake is a factor of 30, and the difference between a 6 and an 8 earthquake is 900 times the energy).
- The 1931 Hawke’s Bay earthquake here was 7.8, so there was about 400 times more energy released in the 1931 earthquake than for the Christchurch one.
- Be aware that often loose furniture and bookcases may fall or move during an earthquake. By taking the advice from the Earthquake Commission to ‘Fix, Fasten and Forget’ you may save a life in an earthquake at your office or at home.
- Also learn how to respond correctly in an earthquake, for more advice see our earthquake information.
According to the Department of Building and Housing the Building Code is based on the kind of seismic event expected to occur every 500 years or so. The Christchurch earthquake may have been as much as three times this.
The New Zealand Building Code is in line with International best practice. It is continually revised and improved, however it is not retrospective, therefore, on the whole newer buildings in Christchurch performed much better than older buildings.
The Institute of Professional Engineers New Zealand have prepared a useful fact sheet, "Why Buildings Respond Differently to Earthquakes".
Misleading Advice 'Triangle of Life'
|Survivor's Camp at Nelson Park, Napier after Hawke's Bay Earthquake 1931
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 HB we can have some level of confidence in our buildings (see information above), so our advice under 'What to do' above is still the best for residents in Hawke's Bay.
If you want to know more about why the 'Triangle of Life' is not the best advice we suggest you visit the following websites:
|Correct action during an earthquake if indoors. Do not run out of a building during earthquake shaking as this was one of the causes of injury and death in 1931.