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A piece of Active faults in New Zealand - 2: Three recent earthquakes in South Island

Part of the PATA (Paleoseismology Active Tectonics Archeoseismology) Days fieldtrip was dedicated to the Alpine Fault (see this post). Here I present few words and many pictures dealing with the recent earthquakes that have shaken the South Island, with a special focus on the M7.8 Kaikoura earthquake surface rupture of november 2016. Even one year after, most of the surface breaks and deformation features were still visible.

Before the conference, we spend one day in the northern rupture segments (Kekerengu and Papatea Faults). After the conference, we could admire during one day the southern ruptures (South Leader Fault) in the epicentral area. Then, we had a quick overview of the environmental impact of a large "intraplate" (Australian plate) earthquake (M7.5+) that hit the Murchinson region in 1929. And this wonderful trip in the antepode country finished in Christchurch where we could still see the scars of the 2010-2011 earthquake sequence.

Many thanks to our guides and to the organizing committee!

The Wall of Waiau, one of the most scenic spot along the 2016 Kaikoura earthquake surface rupture
The 1929 M7.5+ Murchinson earthquakeOn 1929/06/19, this large earthquake triggered many landslides in the mountainous Tasman region, as well as extensive liquefaction. This earthquake caused few damage to buildings and most of the death toll is due to landlsides (14 out of 17).
The associated surface rupture that could be recognized is short (8 km in the north-south direction) but it is quite nice close to the Buller Gorge gold mine, where we made a stop.
There, a reverse component of about 5 m (eastern block is uplifted) is observed.

The 1929 earthquake scarp in 1929 (photo: A. Turnbull Library, Wellington) vertically displaces the alluvial terraces. You cannot miss it, a bit less than a century after !
The 2016 M7.8 Kaikoura earthquake  Some words about the M7.8 Kaikoura earthquakeIn few words: this earthquake was responsible for 2 deaths and 57 injuries, as well as major damages to buildings in Wellington, which harbor traffic has been halted for months. One major consequence of the earthquake was the closure of the "Highway 1" that was fixed more than 1 year after.

Considering the Environmental Effects, this large inland event caused extensive surface faulting and related coastal uplift and landslides or rockfalls (with serious effects on the coastal road): this part of the post will focus on several of those effects. In addition, shaking generated offshore turbidites and a 5-7 m-high very local tsunami hit the coast. Inland liquefaction was also reported.

From a seismological point of view, this earthquake is complex (with at least 2 major phases of moment release), ruptured 21 fault segments, potentially including a deep thrust that could correspond to the southern part of the Hikurangi subduction interface, according to some authors. There are many papers available that provide an extensive overview of this event (e.g. Holden et al., 2017; Hollingsworth et al., 2017; Duputel et al., 2017; Hamling et al., 2017; Wang et al., 2018).

A "composite" earthquake with reverse and + lateral components, with long and "patchy" moment release. It was felt all over New Zealand.
I just remind here the major trends of this "unusual" surface rupture. The earthquake initiated in the "Contractional North Canterbury Faults" domain (Stirling et al., 2012) and propagated to the north into the "Strike-Slip Marlborough Fault System" domain, rupturing at least 21 crustal faults over a distance of ~150 km.
The source time function (SCARDEC) reveals that the earthquake lasted 2 minutes with two moment peaks: the first and smaller one initiated to the south on the strike-slip to reverse faults (e.g. The Humps, Hundalee, Leader Faults) and the largest one to the north on the major faults (e.g. Bridget, Jordan, Kekerengu Faults).

The surface faulting at the overall scale was summarized in a paper by M. Stirling and collaborators (2017). The geometrical arrangement of faults is really striking and surprising, even counter-intuitive because perpendicular faults ruptured all together up to the surface.
A special issue in Bulletin of Seismological Society of America will be released in 2018, with several papers on the surface ruptures: stay tuned!

This map of the 2016 Kaikoura EQ surface rupture is from Stirling et al. (2017) Here is a Google Earth view of the region, depicting the whole set of New Zealand active faults (red lines, data available at, the rough location of the 2016 surface rupture stretched over ~150 km, and the location of the 4 sites described below.

The South Leaders Fault (site 4)We are here not far from nucleation point of the M7.8 earthquake. Young and loose/poorly consolidated sediments are the outcropping bedrock. Besides surface faulting, the earthquake triggered many landslides.
The first place to visit is the "Wall of Waiau" with an oblique fault-related scarp, which is rapidly degrading.

This is a view of the North-South section of the South Leader Fault, illustrating the vertical and horizontal components of displacement. The scarp is rapidly degrading due to the bedrock lithology. The LiDAR derived displacement map was provided in the Fieldtrip guidebook (Upton et al., 2017).
  Progressing to the NE, the fault strike changes from Ñ-S to E-W, and there is a unique place with earthquake-related landslide and surface fault.  A close-up view of the EW section of the fault scarp, at the toe of the northern slope. Differential LiDAR (before/after) illustrates the vertical displacement during the earthquake (red: up; blue: down). In the background, the coseismic landslide scar.
Before/After pictures of the South Leader fault (red arrows)-related giant coseismic landslide that created two dams ("before" picture is from Upton et al., 2017) The Papatea fault (site 5) The Middle Hill station is the right place to observe the huge offset (up to 8 meters vertically) that was created during the 2016 earthquake along the N-S striking Papatea fault. This fault segment was not mapped as active before the event.
A general view of the distributed and large wavelength scarp
Within the bosque, open cracks, shear planes and evidences of offset are numerous
No, this is not a terrace riser ! The alluvial plain of the Clarence River was dramatically uplifted by 8 meters The Kekerengu Fault (site 6) There, the NE-SW striking fault experienced the maximum of surface displacement (mainly horizontal), and this is particularly outstanding at the Bluff Station where a cottage was offset by 10 meters from its foundations. Several hundred meters to the SW, the conference attendees are underlining the offset fence for better understanding.
A picture in november 2016 of the damaged cottage and a reconstruction (in Upton et al., 2017) of the before/after geomery  
Those orange jackets are perfect to depict the offset piercing line ! Those sand volcanoes are due to fluidization of saturated sediments under seismic waves Along the shoreline, the uplift along the Kekerengu fault is illustrated by the white fringe of weathered subtidal algae (Ward Beach). Those data of coastal vertical displacements were used to constrain the fault source geometry and slip distribution: see Clark et al., 2017. The whole coastal fringe at Ward beach was uplifted by 2.5 meters: the best illustration is that white fringe of dead algae stuck on the rocks of the wave-cut platform The recovering city of Christchurch I would like to finish this post with an illustration of earthquake damages in a populated area. Cities are vulnerable places, especially when they are located above the hypocenter and even for M~6 "moderate" earthquakes. Christchurch paid a heavy price during the February 2011 earthquake (185 fatalities), such as other places did in the recent past, such as L'Aquila (2009) and Amatrice (2016) in Italy. 
Around 6 months after the surface rupturing M7 Darfield earthquake in the Canterbury countryside ("only" ~100 injuries despite locally extreme shaking), a very strong aftershock nucleated beneath the city producing extensive damage, building collapses and huge liquefaction.
In 2017, during the last days in New Zealand after the PATA Days Conference, we could still observe the legacy of this "natural" phenomenon. Here are few examples.

This remnants are from a building that has probably been damaged (but did not collapse) during the earthquake; it has been demolished between 12/6/2012 and 19/10/2012 (Armagh Street X Gloucester Arcade)

The Cathedral has been first damaged during the M7 Darfield earthquake (september 2010) and partially collapsed during the february M6.3 event (picture on left from Wikipedia)
The Clarendon Restaurant and Bar, 250 m west of the Cathedral along the river bank, is abandoned since the quake

This bar/restaurant remained like it has been left during the 2011 earthquake
Welcome to the "Re:START container mall brand" (Cashel Street, along the river bank and close to the Remembrance bridge), a temporary solution that became an internationally famous icon and symbol of post-quake Christchurch innovation... Waiting for the construction of the "true" mall
An instant of contemplation with Austin (@TTremblingEarth), Klaus Reicherter (@ActiveFaults) and Gordon Seitz, at the Canterbury Earthquake National Memorial (Oxford Street X Montreal Street, along the river bank) Several new buildings exhibit those reinforcement crosses: are they really efficient features or comforting items?

Upton P., Langridge R. M., Stahl T., Van Dissen R. J., Howarth J., Berryman K., Clark K. J., Kelly K., Hammond K., 2017. 8th International PATA Days, Blenheim, New Zealand. Three-day post-conference fieldtrip; Northern South Island, Alpine Fault and Ruptures of the 2016 Kaikoura Earthquake, 17-19th November 2017. Lower Hutt (NZ): GNS Science. 64 pages. | Impressum