Download poster about Tsunami here.

What are tsunami?
Tsunami are a series of waves caused
by a displacement of water
Tsunami:
• Are long-period waves – up to 100 kilometres
• Travel quickly in the open ocean – up to 700 kilometres per hour
The difference between wind and water waves
• Slow down and increase in height as they approach land
• Behave like a rapidly rising/falling tide.
The difference between wind and water waves is shown to the right:
What causes tsunami?
Tsunami are mainly caused by earthquakes, landslides and volcanic
activity under the ocean.
Landslides
Earthquakes
Landslides, earthquakes and wind and waves diagrams courtesy Willem de Lange, University of Waikato.
Explosion
Impact
Types of tsunami
Image courtesy GNS Science
There are three main types of tsunami:
• Local source: travel time between the source, such as an earthquake in the
Southern Tonga-Kermadec Trench, and impact is one hour or less.
• Regional source: travel time between the source, such as Samoa or Tonga, and
impact is between one and three hours.
• Distant source: travel time between the source – such as South America or
Japan - and impact is greater than three hours.
Where do most of Whitianga’s tsunami come from?
Tsunami source areas in the Pacific
Most tsunami that impact Whitianga are distant source or local source –
from regions “0” and “2” in the diagram (top right).
What are we most concerned about?
We are most concerned about local tsunami events generated from large earthquakes along the Tonga-Kermadec Trench
subduction zone – the tectonic plate boundary between the Pacific and Australian plates.
How subduction zones along plate boundaries produce large tsunami.
Above images sourced from Natural Disasters Association (www.n-d-a.org)
How do we know that
Whitianga is vulnerable to tsunami?
New Zealand is impacted by numerous
tsunami every century
The most recent was the Japanese tsunami on 11 March 2011.
• The wave height of the recent Japan tsunami was 1.6 metres at
Whitianga – the highest recorded level on the mainland.
• Large distant tsunami events in the past century include the
SE Asian tsunami in 2004, and the Chilean tsunami in 1960.
Year
1562
1575
1586
1604
1730
1746
1835
1868
1877
1960
Earthquake
magnitude
unknown
“
“
“
“
8.6
unknown
Source
South-central Chile
Central Chile
Off Lima, Peru
Arica, Northern Chile
Valparaiso, Chile
Callao, Lima, Peru
Conception, Southern Chile
Arica, Northern Chile/ Southern
Peru
9.1
Inquique, Northern Chile
9.0
Southern Chile
9.5
Maximum run-up in
source region (m)
16
25+
26
16
16
24
14
18
21
25
Maximum run-up
in NZ (m)
Unknown
“
“
“
“
“
“
10 (Chathams); 4
(Mainland)
3.5
5
Large South American earthquakes since 1562 and
their impacts
• Large South American earthquakes have produced tsunami that
have impacted Whitianga over the past 500 years.
• Ancient (paleo) tsunami deposits along the north-east coast of the
North Island show evidence of a very large tsunami around the year 1450.
Ancient (paleo) tsunami evidence
The diagram mid-right shows the estimated maximum height of
Ancient
(paleo)
tsunami
evidence
in
the
North
Island
ancient tsunami deposits of various ages along the north-east coast of New
Image from Goff et al, 2010
Zealand. These deposits tend to support other research indicating that the
Tonga-Kermadec Trench is capable of producing a large tsunami from a maximum 9.4 magnitude earthquake event.
Background image: Whitianga, fishing from shell sand beach (courtesy Waikato Regional Council)
Distant source tsunami
• Distant tsunami take three or more hours from the time of the event until
they reach New Zealand.
• Because of their distant location, there
is usually enough time for official
warnings and co-ordinated evacuations
of coastal communities.
1960 Chile tsunami maximum amplitude plot
Travel times from the 1960 Chilean tsunami
• The 1960 Chilean tsunami took 12½
hours to arrive at Whitianga. This event arrived as a series of waves that
inundated Whitianga over a period of about six hours.
Maximum elevations of
various distant tsunami events
There are two primary factors that determine the impact of tsunami generated
by earthquakes – the size of the event and the direction of the fault.
1. New Zealand is particularly vulnerable to earthquakes generated
in Southern Peru, due to the orientation of the plate boundary.
2. The primary energy from the 1960 Chilean tsunami event was
directed towards the north-western Pacific region. Hawaii and Japan
suffered substantial loss of life and damage from this event, with
tsunami run-ups being almost eleven metres and more than six
metres respectively.
Map images courtesy NOAA / Pacific Marine Environmental Laboratory / Center for Tsunami Research
Tsunami from Southern Peru earthquake, 15
August 2007, magnitude 8.0
Tsunami from Japan earthquake, 11 March 2011,
magnitude 9.0
Local source tsunami
There are numerous local sources for tsunami to the
north-east of Whitianga.
Local earthquake
faults
Earthquake from
Tonga-Kermadec
subduction zone
Volcanoes
Landslides
• Earthquake: local faults in the Bay of Plenty, and large earthquakes from the plate
boundary in the Tonga-Kermadec Trench
• Volcanic: Mayor Island, and eruptions from undersea volcanoes on the Kermadec
Ridge to the north-east of New Zealand
• Landslide: failure of large undersea canyons off East Cape, and landslide hazards
from White Island.
Local tsunami sources
Local source tsunami
The single biggest risk is from a large earthquake along the plate boundary in the
Tonga-Kermadec Trench. The Tonga-Kermadec Trench may produce:
• an earthquake of magnitude 9.4 about once every 600-800 years, which could
produce tsunami run-ups of 15-20 metres along the north-east coast of the North
Island
• an earthquake of magnitude 9.0 about once every 400 years, which could lead to
run-ups of 6.5 metres in Whitianga
• Whitianga is particularly at risk from fault segments “2” and “3”, as waves from these
segments are directed straight into Mercury Bay
• recent scientific work suggests that the plates may be locked in places along the
Tonga-Kermadec Trench.
Tonga-Kermadec events and segments
Image courtesy GNS Science
Scientific modelling
and tsunami
1960 Chilean inundation
Scientific modelling facts
• The model used is 3DD Suite Computational Marine and Freshwater Laboratory
developed by Dr. Kerry Black.
• The model deals well with some of the major challenges of tsunami modelling such as
non-linear flow, wetting and drying on land and fast moving flows on dry surfaces.
• The model has demonstrated the ability to accurately replicate tsunami impacts on a
real-world scale such as the SE Asian tsunami event of 2004, and the impacts of the
1960 Chilean tsunami on Whitianga (in line with eyewitness reports).
• The model relies heavily on the use of detailed data on seafloor elevations
(bathymetry) and detailed data on land elevations in the town (LIDAR).
Tonga-Kermadec
Trench inundation
• The modelling assumes a magnitude 9.0 earthquake along segments 2 and 3 of
the Tonga-Kermadec Trench with a 450 kilometre rupture length, 100 kilometre
horizontal displacement and 15 metre vertical displacement
• The modelling was done by Dr. Gegar Presetya at the University of Waikato as part of
a PhD thesis.
Whitianga inundation maps produced
by the modelling
Tsunami zones
Two types of zones have been identified,
each with a slightly different purpose:
1, Hazard Zones: based on the modelling results from the Chilean and TongaKermadec Trench, the hazard zones show the areas of maximum probable impacts
to Whitianga. The zones are determined by the combination of inundation depths
and flow speeds:
•
High Hazard Zone (red): inundation depth of between 1.5 metres and three metres,
and flow speeds of between nine and 29 kilometres per hour
•
Medium Hazard Zone (yellow): inundation depth of between 0.5 metres and 1.5
metres, and flow speeds of between 1.8 and nine kilometres per hour
•
Low Hazard Zone (blue): inundation depth of less than 0.5 metres,
and flow speeds of less than 1.8 kilometres per hour.
Whitianga tsunami hazard zones
The hazard zones are primarily used to assist with land-use
planning due to the high degree of accuracy, although they are
also used to inform evacuation planning.
2, Evacuation zone: this zone identifies all land above 20 metres
in elevation, and has been developed by Councils and emergency
services to provide an indication of safe areas in the event of a
worst-case scenario (magnitude 9.4 event on the Tonga-Kermadec
Trench). It is anticipated that the inundation in a worst case
scenario would be significantly higher than the area covered by
the hazard zones.
Whitianga tsunami evacuation zone
The Japanese tsunami, 11 March 2011
Facts and figures
• The earthquake was a magnitude 9.0 “megathrust” event, with the epicentre
located 72 kilometres east of the Oshika Peninsula of Tohoku at a depth of
32 kilometres.
• The earthquake is the most powerful to have hit Japan, and one of the five
largest earthquakes recorded in the world since records began in 1900.
• The tsunami waves produced by the event ran up to 38 metres above sea level
in some areas, and travelled more than 10 kilometres inland in others.
• At May 2011, 15,000 deaths and 5,300 injuries had been confirmed, with
almost 11,000 people still missing.
Maps (above) courtesy New Scientist
• The tsunami waves damaged the Fukushima nuclear power plant, left
4.4 million homes without electricity and 1.5 million homes without
water, causing massive displacement of people. Insured losses alone
are estimated at $15 - $35 billion (US).
• The earthquake shifted the island of Honshu 2.4 metres to the east.
Images below courtesy National Geographic News
Slip map images sourced from http://supersites.earthobservations.org/sendai.php