Images courtesy of Google Earth 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. Images courtesy of Google Earth 5 KM

Shaking caused 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).

Tectonic setting (Big Picture) 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.

Aftershock mechanisms 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 west-southwest 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.

Historical Seismicity 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.

Seismic waves recorded in the UK Magnitude 7.8, SOUTH ISLAND OF NEW ZEALAND Sunday, 13th November at 11:02:57 UTC Seismic waves recorded in the UK M7.8, 13th November 2016 Velocity (counts/s) Surface -waves P-wave Image Credit: Bakersfield College, US. Source: http://www.vox.com/2015/5/13/8595157/inge-lehmann 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

Find out more…. 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

@seismologyUoL leonrios@liverpool.ac.uk