- Here I summarize the cruise and results from our cruise.
- While at Sea, there was an interesting series of earthquakes, beginning with an M 7.8 earthquake near Kaikoura.
- Here are a couple posts about the earthquake and our response. I include some of this content below on this page.
- We headed 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 collected 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
- Below is a map that shows the general region where we planned 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 collected cores in sedimentary basins along the slope and in channel and other depositional settings along turbidite channel systems in the trench. We used the 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 looked 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 is the plot from Wallace et al. (2009) that shows the seismicity from 1990-2007.
- Here is the map from Wallace et al. (2009) that shows the regional and local tectonics in the Hikurangi Trough.
Here are some of the inset maps on their own, with their original figure captions as blockquotes.
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.
Tectonic setting of the Hikurangi margin. Modified from Barnes et al. , 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. . 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. . 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 is a figure that shows our existing knowledge of the historic subduction zone earthquakes for this region (Wallace et al. (2014).
- Here is a figure that shows our existing knowledge of the prehistoric subduction zone earthquakes (Paleoseismology) for this region (Wallace et al. (2014).
Here are some figures that show the historic and prehistoric history of earthquakes in this region, with their original figure captions as blockquotes.
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.
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).
- More can be found here.
- I was at sea on the R/V Tangaroa collecting piston cores offshore along the Hikurangi subduction zone this month. While I was at sea, there was a large earthquake, probably along one of the upper plate faults in this region. I present a simple interpretive poster below. This earthquake series is in a complicated part of the Earth where a subduction plate boundary turns into a transform plate boundary. There was a tsunami warning for the nearby coasts, but not for a global tsunami.
Geonet is a website in New Zealand that is a collaboration between the Earthquake Commission and GNS Science. Here is the website at Geonet where one can find the most up to date observations and interpretations about this M 7.8 Kaikoura Earthquake series.
- Below is a map that I prepared that shows the earthquakes (magnitude M ≥ 2.5) for the month of November as green circles (diameter represents earthquake magnitude). I also plot earthquakes with magnitudes M ≥ 5.5 from the period of 1950-2016. These are from the USGS NEIC, so the regional network run in New Zealand may have a larger number of earthquakes. I present two maps, one with a 250 m resolution bathymetric grid as a base and one with a Google Earth satellite based map as a base. This is not an official GNS nor NIWZ figure, but they were major supporters of the TAN163 cruise that I participated on, so we can attribute the core data to these organizations.
- I placed the moment tensors for the larger earthquakes during this time period since the M 7.8 earthquake. The main earthquake is a compressional earthquake, probably on an upper plate fault. The M 7.8 earthquake triggered slip on other thrusts and some strike-slip faults in the region. Surface deformation measured using Interferometric Synthetic Aperture Radar (INSAR) is localized, supporting the upper plate rupture interpretation. Slip on the thrust during the 7.8 is estimated to be about 10 meters, which is also the maximum slip on some of the strike-slip fault systems. There have been some excellent photographs of the fault rupture (I will include these in a later post). Most of the large earthquakes are strike-slip, but there are some connecting faults that show thrust mechanisms. I also show the regions of different faults that have been observed to have surface ruptures.
- After the earthquake, we changed our plans to conduct some post-earthquake response analyses. We collected additional cores to search for sedimentary evidence of the M 7.8 earthquake. We also collected sub-bottom profile and bathymetric data to search for seafloor exposed fault rupture. The cores we collected for our general study are shown as red cross-dots. The cores we collected as the earthquake are plotted as yellow cross-dots.
- I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
- I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
- In the upper right corner is a map from NIWA (Phil Barnes). This map shows some of the major faults in this region. I placed the observed fault offsets on this map as orange lines. This map is on the NIWA website, but I will find the Barnes publication this came from and post that in a follow up web page.
- In the lower right corner is a map from Geological and Nuclear Sciences (GNS) in Māori: Te Pū Ao. This map shows the regional faults and where there have been observations of surface rupture. The coseismic (during the earthquake) Global Positioning System (GPS) observations. Earthquakes are also plotted.
- To the left of that is a figure from the Geospatial Information Authority of Japan (GSI). This is a summary figure showing modeled uplift as compared to InSAR analysis results. Note how localized the deformation is. I will present and discuss the analyses that went into this figure in a follow-up report.
- To the left of that is a generalized tectonic map of the region.
I include some inset figures. Here is some information about them. Below I include the original figures with the figure captions as blockquotes.
- More can be found here.
- Below are some presentation slides from our press conference.
- We arrived at port about 8 AM and the press conference was at 2 PM. No rest for the wicked. The fearless leaders of our R/V Tangaroa research cruise were Drs. Philip Barnes from NIWA and Jamie Howarth from GNS Science.
- Here is the digital press release as displayed blow: (pdf)
Here are the slides that we put together for our press conference.
Some Cruise Videos
- 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.