Download Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND Sunday, 13 th

Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Earthquake location & overview
A magnitude (Mw) 7.8 earthquake
has stuck the South Island of New
Zealand. It hit just 93.5 km NNE of
Christchurch at a relatively shallow
depth of 23 km. This event triggered
a number of different earthquakes
and
landslides.
The
biggest
aftershock measured 6.5 (Mw).
Shortly after the main shock, a
tsunami warning was issued to those
on the Northern coast with waves
hitting roughly two hours afterwards.
So far this event has claimed the lives
of two people. The extent of the
damage is still being assessed,
however the cost will be substantial.
5 KM
Images courtesy of Google Earth
Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Shaking caused
There was Moderate (V) to Severe (VIII) shaking in much of the north east of
the South Island and the south of the North Island (fig. A), while the
earthquake was felt throughout the most of the country.
A
B
Fig. B shows the response
of a simple oscillator to the
earthquake at a period of 1
second.
Many
buildings
are
susceptible to periods of
this kind and we can see
that the shaking at these
periods around Wellington
is low-moderate at up to
~20% g (~2 m/s/s).
Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Tectonic setting (Big Picture)
New Zealand is located on the
boundary between the Australian
and the Pacific plates，two of the
Earth‘s great tectonic plates. Most
of the southeastern part of the
South Island is on the Pacific Plate
while a smaller northern section
of the South Island lies on the
Australian Plate.
New Zealand tectonic sketch map (from GNS
Science)
The Hikurangi Trench is the collision boundary at east of the North Island, where oceanic
lithosphere (the Pacific Plate) descends beneath the North Island as a huge inclined slab. This
subduction also lead to the activities of volcanoes in New Zealand.
Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Tectonic setting (Detailed Look)
Aftershock
mechanisms
The Pacific plate moves to the westsouthwest with respect to the
Australia plate at a rate of ~ 40 mm/yr.
This boundary is complex, involving a
transition from subduction along the
Hikurangi Trench to the east of the
North Island, to transform faulting
through the South Island.
Main shock
mechanism
The rupture was close to the northeast end of the Alpine fault, where the Australian Pacific Plate boundary transitions from right lateral transform to a convergent boundary
along the Hikurangi Trench. The main shock occurred on this mega thrust, where the
pacific plate subducts beneath New Zealand. Two of the biggest aftershocks then occurred
within the overriding plate, and hence have a very different focal mechanism.
Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Historical Seismicity
Earthquakes are common in
New Zealand but only a few
are as devastating as this
event.
Some of the most notable
events are the Darfield /
Christchurch earthquakes – a
Mw 7.0 on 3rd September,
2010 and a Mw 6.1 on 21st
February, 2011 and. Both of
these event are linked and
were damaging. The 2011
event claimed 100’s of lives,
to which they are still
recovering today.
Mw 7.0 – Sept, 2010
Mw 6.1 – Feb, 2011
Image courtesy of the USGS.
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Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Seismic waves recorded in the UK
Image Credit: Bakersfield College,
US.
Source:
http://www.vox.com/2015/5/13/8595
157/inge-lehmann
Surface
-waves
P-wave
Velocity (counts/s)
M7.8, 13th November 2016
•
Above are the seismic waves emitted from the New Zealand
earthquake, measured at the UK (colour corresponds to site).
•
There are no obvious S-wave arrivals contained in the waveforms,
this is likely as the UK would be in the ‘S-wave shadow zone’ with
respect to the location of the event
Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND
Sunday, 13th November at 11:02:57 UTC
Find out more….
• BGS (British Geological Survey) – seismology and earthquakes – frequently asked questions
http://www.earthquakes.bgs.ac.uk/education/faqs/faq_index.html
• IRIS (Incorporated Research Institutions for Seismology) – learning about earthquakes
http://www.iris.edu/hq/programs/education_and_outreach/students
• UK School Seismology Project – classroom activities, videos and support documents
http://www.bgs.ac.uk/schoolseismology/home.html
• USGS (United States Geological Survey) – FAQs, glossary, posters, animations
http://earthquake.usgs.gov/learn/
• USGS summary of the earthquake
https://www.usgs.gov/news/magnitude-78-earthquake-new-zealand
• Geoscope Summary of the earthquake
http://geoscope.ipgp.fr/index.php/en/catalog/earthquake-description?seis=us1000778i
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@seismologyUoL
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