Getting ready for the cruise!

2016.11.09

Getting ready for the cruise!

• We will be heading to sea to search for submarine landslide deposits called turbidites. There are several ways that these landslides can be triggered. Earthquakes are the most common landslide trigger on land and probably also in the submarine environment.
• I have worked on turbidite Paleoseismology cruises offshore of Sumatra, Cascadia, and the Lesser Antilles. These are all places where there is an active subduction zone. I have documented these cruises on my research cruise blog humboldt-jay.blogspot.com. The research offshore of Sumatra was for my Ph.D. dissertation and is ongoing. The coring we conducted offshore of Cascadia was in support of Dr. Chris Goldfinger’s research on the spatiotemporal variation in earthquakes along the Cascadia subduction zone. Recently, we received the Kirk Bryan Award from the Geological Society of America for the USGS Professional Paper 1661-F. This past summer I participated on a French cruise aboard the NO Pourquoi Pas? The principal investigator for this Caribbean cruise was Nathalie Feuillet, from Institut de Physique du Globe de Paris (IPGP) in Paris.
• We will be collecting sediment cores aboard the R/V Tangora, a National Institute of Water and Atmospheric Research Ltd (NIWA) research ship. R/V stands for “research vessel.” Here is the website that has information about the R/V Tangora. : www.niwa.co.nz/services/vessels/niwa-vessels/rv-tangaroa

Background

• Below is a map that shows the general region where we plan on taking cores. The principal investigator for this cruise is Dr. Phillip Barnes, from NIWA. Dr. Barnes has done an incredible job planning for this cruise and I outline the general strategy below. As always, we will modify our plan as our experiences during the cruise inform us.
• We will be collecting cores in sedimentary basins along the slope and in channel and other depositional settings along turbidite channel systems in the trench. We will be using classic methods (well, this is a new science, so it is funny to call these classic methods) used by many who look for seismoturbidites. We will be looking for sites that have sources of sediment that are isolated from each other. We are especially interested if these sites extend for distances larger than the length of faults that might be additional sources of ground motions that might trigger submarine landslides. We will also be looking for sites that permit us to apply the confluence test, which also requires sites that have isolated source distances that are sufficiently large.

I include some inset maps that have some other background material.
• In the upper right corner is a map that shows the general plate tectonics of this region. This comes from Mike Norton via Creative Commons. The Pacific plate: Australia plate relative plate motions are shown in orange. Note how the plate motion is increasingly oblique as slip is transferred from the Kermadec-Hikurangi subduction zone systems in the north to the Alpine fault system (via Marlborough) in the south, then again to the subduction zone even further south.
• In the upper left corner shows seismicity as plotted by Wallace, et al. (2009). These are earthquakes from 1990 through December 2007. The figure on the right shows the deeper events with their depth represented by color.
• In the lower right corner is another figure from Wallace et al. (2009). This one shows more detailed fault mapping in the accretionary prism. These are offshore thrust faults that are additional sources of ground shaking for triggering turbidites. It will be important to be able to extend our correlations beyond any individual fault system to be able to link any given correlated turbidite to ground motions from the megathrust. There are also some strike-slip faults that may also confound our analysis, particularly in the southern Hikurangi margin. In this inset is a cross section showing that the accretionary prism is composed on imbricate thrust faults. These are the additional sources of ground shaking that are mapped in plan view on the map (labeled “Forearc domain” in the cross section).

Here are some of the inset maps on their own, with their original figure captions as blockquotes.

• Here is the plot from Wallace et al. (2009) that shows the seismicity from 1990-2007.


Selected seismicity between January 1990 and December 2007 (inclusive), from the GeoNet database (http://geonet.org.nz). Events shown are only those which were recorded by six or more stations, with nine or more observed phases, with unrestricted location depths, and RMS of arrival time residuals less than 1.0 s. Magnitude range of events shown is 0.29–6.99. (left) Events shallower than 33 km. (right) Events greater than 33-km depth.

• Here is the map from Wallace et al. (2009) that shows the regional and local tectonics in the Hikurangi Trough.
  

  Tectonic setting of the Hikurangi margin. Modified from Barnes et al. [2009], copyright 2009, Elsevier. (a) Detailed bathymetry (NIWA), topography, and active faulting (black lines) of the onshore and offshore subduction margin. Dashed contours indicate sediment thickness on lower plate from Lewis et al. [1998]. Bold white dashed line shows the back of the accretionary wedge and the front of a deforming buttress of Cretaceous and Paleogene rocks covered by Miocene to Recent slope basins [from Lewis et al., 1997; Barnes et al., 1998b, 2009]. A–A0 line denotes cross-section location in Figure 1d. Dashed black lines show locations of seismic reflection lines from Figure 4, labeled by line number. White arrow shows Pacific/Australia relative plate motion in the region from Beavan et al. [2002]. Onshore active faults from GNS Science active faults database (http://maps.gns.cri.nz/website/af/). TVZ, Taupo Volcanic Zone; NIDFB, North Island Dextral Fault Belt; LR, approximate location of Lachlan Ridge; KR, approximate location of Kidnappers Ridge. (b) Broader-scale New Zealand tectonic setting. (c) Regional tectonic framework. RI, Raoul Island; NZ, New Zealand; HT, Hikurangi Trough. (d) Interpretive cross section across the strike of the subduction margin. Cross-section location denoted by A–A0 line in Figure 1a.

Here are some figures that show the historic and prehistoric history of earthquakes in this region, with their original figure captions as blockquotes.

• Here is a figure that shows our existing knowledge of the historic subduction zone earthquakes for this region (Wallace et al. (2014).
  

  Tectonic setting of the Hikurangi subduction zone at the boundary between the Pacific and Australian Plates. Black contours show the depth to the subduction interface (Williams et al., 2014). Red dots = historical subduction thrust events (all MW < 7.2). Gray dots = continuous GPS sites (http://www.geonet.org.nz). Arrows show convergence rates at the trench in mm yr–1 (Wallace et al., 2012a). PB = 1947 Poverty Bay earthquake. TB = 1947 Tolaga Bay earthquake. WF = Wairarapa Fault, the site of the 1855 earthquake. BL = Big Lagoon. MP = Mahia Peninsula. Black lines onshore are active faults (http://www.data.gns.cri.nz/af). In the forearc, most of these faults are either right lateral strike-slip or reverse. The strike-slip faults help to accommodate the margin-parallel component of relative plate motion.

• Here is a figure that shows our existing knowledge of the prehistoric subduction zone earthquakes (Paleoseismology) for this region (Wallace et al. (2014).
  

  Map in upper panel shows locations of published Holocene records of coseismic vertical deformation along the Hikurangi Margin. Timeline in lower panel shows the approximate ages and types of impact found at different sites along the margin (note that this is an overview that does not show individual dates and their errors). We use black horizontal lines on the timeline to indicate times when vertical deformation occurs at multiple sites along the margin (summarized in the right panel of the timeline). These lines are also used on the map to indicate the approximate lateral extent of deformation and the strength of evidence for occurrence of a great subduction thrust earthquake. *Site 1: Clark et al. (2011) and Hayward et al. (2010). Site 2: McSaveney et al. (2006). Site 3: Berryman et al. (2011). Site 4: Hayward et al. (2006). Sites 5 and 6: Cochran et al. (2006). Site 7: Berryman (1993). Site 8: Wilson et al. (2006).

References

• Wallace et al., 2009. Characterizing the seismogenic zone of a major plate boundary subduction thrust: Hikurangi Margin, New Zealand, Geochem. Geophys. Geosyst., 10, Q10006, doi:10.1029/2009GC002610
• Wallace, L.M., U.A. Cochran, W.L. Power, and K.J. Clark. 2014. Earthquake and tsunami potential of the Hikurangi subduction thrust, New Zealand: Insights from paleoseismology, GPS, and tsunami modeling. Oceanography 27(2):104–117, http://dx.doi.org/10.5670/oceanog.2014.46.