Monday, November 21, 2016
Last Night on the R/V Tangaroa
We are in the throes of the last moments of our cruise. Our coring team started the day by describing our final core of the cruise, followed by a scrubbing of the shipping container we called our laboratory for the past two weeks. We packed up all the remaining samples and conducted a white glove test. All samples have been entered in to the proper databases for the officials from New Zealand that concern themselves with these matters. There is a very strict accountability for all samples collected while aboard the cruise and it is vitally important (perhaps litigiously) to have these databases and samples in perfect order.
We have been working diligently to prepare the cruise report and materials for a press release to be presented at NIWA tomorrow. Drs. Barnes and Howarth will be interviewed by the press following their presentations on the science. The cruise report summarizes the scope of this project, our preliminary findings, and potential future research prospects.
We initially set out to collect data in the hopes of developing an earthquake chronology for prehistoric subduction zone ruptures. To this end will require a number of collaborative efforts with a range of topics that will include sediment routing studies, provenance analyses, physical sedimentology studies, radiometric age analyses, and tephra studies (including chronology). While aboard the R/V Tangaroa, there was an earthquake with a magnitude of M 7.8 that triggered slip on multiple fault systems (at least 5 other faults have been documented to have ruptured to the surface). This earthquake series is interesting in many ways and I will write more on this later on my earthquake blog at earthjay.com. Needless to say, there was impetus to modify our science plans in response to this large earthquake. This was obvious to all on board. There was also interest from NIWA and GNS to respond
to the earthquake in some way.
For the earthquake response, we decided to collect additional cores to supplement cores that already existed and to supplement cores that we had planned to collect. We also decided to collect shallow seismic data and multibeam bathymetric data to search for submarine surface rupture of the fault(s) involved in this complex earthquake.
I will present some of our initial findings after our press release tomorrow. People with telepathic abilities may be able to tell what I will post about. People without telepathic abilities might also forecast what my post may include.
It has truly been a pleasure and an honor to be at sea with this fine science crew. I have learned lots from them and I hope this has been mutual. We have lots of work to do to in the next few years, but I look forward to this with enthusiasm. I include a photo of the science crew above, as well as a map showing the core sites for the 61 cores we collected. I will post the cruise report when it is completed.
For the map, I include several inset figures. In the upper left corner is a map showing the recent seismicity in this region as produced by Geonet and posted to Twitter. In the upper right corner is a map showing the general tectonic setting as presented by AGU on one of their blogs. In the lower right corner is a map prepared by GNS that shows (a) the InSAR based estimates of deformation, (b) the faults in the region, and (c) the areas that have been observed to have surface rupture. This GNS map was also posted to Twitter.
Saturday, November 19, 2016
Here is one of the last sunsets of our voyage. What a wonderful voyage this has been.
I have not had as much time to post educational material about the cruise. I will try to write up some posts after I get back to the states to document the methods that we used on the cruise.
Today was a particularly exciting day. My day started with Drs. Jamie Howarth and Phil Barnes (chief scientist). As we started the shift, we got to see a multi-core that had just come aboard the ship. We also got to see a multi-core that had been collected prior to our arrival. Later we saw more MCs.
MCs are particularly revealing because the multi-corer rig is lowered to the sea floor and the cores gently fall into the sediment. An arm then moves into place beneath the core ends and traps the sediment in the core. If all works right, there is a little bit of water above the sediment so that we can collect and observe the sediment water interface. If this happens, we know that we are being able to observe all the sediment that was deposited (and not eroded) in the recent past. I also include a photo of the multi-corer.
In one channel core, we observed a deposit that we interpreted to be a turbidite that was silty sand at the base and fined upwards into a sandy silt. This turbidite was on top of some olive gray very fine sandy silt (the ubiquitous facies of hemipelagic sediment in our cores). Several dm below the turbidite was a second thinner muddy turbidite that we had also seen in other cores at this shallow stratigraphic depth. To note was that there was no oxidized sediment under the sandy turbidite.
In another MC, we found some muddy sediment overlying an oxidized layer of sediment. This ox layer has been observed in other MCs that were further from the earthquake. These ox layers are typically at the surface, unless something rapidly buries them.
Both of these cores appear to have a really young turbidite, possibly deposited "yesterday."
We will continue to collect more cores in an attempt to narrow down some details about this deposit and to increase the number of observations of this deposit.
Needless to say, we have more to say, but we will keep that to ourselves until we have more data and have submitted a paper draft to a journal (in the coming month or so). Today was most exciting and the science crew is very enthused at what we are observing while here on the R/V Tangaroa. This, plus the great views of the sunset as seen in the above photo.
Friday, November 18, 2016
Earthquake Response Cores
We think that we just cored a turbidite that was deposited by a turbidity current triggered by the M 7.8 NZ earthquake. We will need to do some radiometric analyses (7Be, 234Th, 210Pb, 137Cs) to test this hypothesis. More later. Attached are some photos. One is a slab collected from a multi-core, up is to the right. There is a dark sandy turbidite that overlies a dark grey mud turbidite. We hypothesize that the dark sandy turbidite is "yesterdays" turbidite. This was collected in a channel setting. The other photo shows a multi core with an orange layer. We hypothesize that this is the surficial oxidized layer that has a muddy turbidite deposited above it. This is from a terrace site, which would have been an over-levee flow, with lower energy (why the ox layer is present; it was eroded in the channel site). The third photo shows the slice of sediment at the top of the ox layer.
There is lots of life here, now dead. Two weeks ago, these organisms were living. Now they are not.
While working on the bridge, compiling some core data so that we can prepare some material for the cruise report, I got to work more with Dr. Barnes to develop our strategy for investigating evidence from "yesterday's" earthquake. We will be collecting several Multi-Cores in the region of the earthquake. We will also be collecting some high resolution bathymetric data to look for surface rupture of the fault in the seafloor. GNS has teams preparing to further document the terrestrial evidence for fault rupture, but we will be working offshore. I have prepared a map that shows some of the core locations that we hope to visit in the next couple of days. We will be collecting longer Piston Cores at some of these sites also, to evaluate a longer stratigraphic record. The Multi-Cores are only 60 cm long.
Tuesday, November 15, 2016
Caught Up and Planning Ahead
Today we were quite successful and described enough cores that we did not need to work after dinner. This gave me a chance to make a map that shows our progress. Also, I include some figures that have been posted on twitter from various sources. As I mentioned before, we plan on collecting some cores in the region near the M 7.8 earthquake in an attempt to find a turbidite that may have been emplaced as a result of strong ground shaking from that earthquake.
Above is my map. The planned core sites are still included. In addition, I have plotted the core sites where we have already collected cores (the red dots). Basically, we have collected cores in all the very high and most of the high priority sites. We are just ahead of schedule. We are lucky to be in this position as there have not been any major obstacles or mechanical catastrophes that sometimes happen. We have not endured a storm too big. We have not had any equipment failures. So, we have basically collected the minimum cores to be able to complete this study. If the ship stops to function tomorrow, we would have plenty of data to build a story.
We do intend to collect more cores on the way back south. These will include additional long cores (up to 6 meters) in high and medium priority sites. We will even collect some cores at low priority sites (we are heading out to the Hikurangi Trough to collect some cores right now, the green dots in the northeastern region of our planned coring area outlined in dashed white). We will also be collecting numerous multi-core cores (these sample the sediment-water interface so that we can develop Holocene depositional models). Data from these cores will help us estimate a latest Holocene hemipelagic sedimentation rate.
We are planning on leaving plenty of time to collect some cores in the southwestern part of our planning region, just offshore of the area that just ruptured multiple faults in the Cook Strait region. It appears that the initial earthquake may have been a thrust event that then triggered slip on several strike-slip fault systems. The USGS has prepared a fault plane solution, but please ignore it. It is vastly oversimplified and does not reflect the geometry of the mapped faults in the region.
I include an inset map from GNS that shows where they have documented surface ruptures from this earthquake series. There are estimates of 8-10 meters of offset on one strike-slip fault and up to 2 meters of uplift along the coast, probably on a thrust fault.
I include an inset map from Tim Wright that uses InSAR (Interferometric Synthetic Aperture Radar) data to estimate ground deformation. The blue colors represent down or away motion and the red colors represent up or towards motion. It is not possible to distinguish between down from away or between up from towards. The deformation supports the interpretation that this earthquake series is quite complex because of the fault interactions. The GNS team will take some while before they can get their boots on the ground, but we are all very excited to see what they find! I wish that I could extend my stay here a month to help out! (I need to get back to my classes to help them complete the semester)
<H2>Long Day and Deserved Sunset</H2>
<li>Last night was a stormy night with relatively high seas, so we all awakened with a low battery. I had several strange dreams. In one of them, I had a rental car stolen. I kept forgetting to call it in to the police. Eventually, late in the day, I was at the store purchasing some wine. The person selling me the wine asked me for my birthdate. Then they covered up part of the label on the wine bottle and asked me my name (strange dream). I told her my name and she asked me if I had a car stolen. When I said yes, she handed me the phone and I spoke to the police. They asked me which cars I had ever owned, one by one. In another dream I visited a friend Lisa Fitchett (Kato) and she had torn off her entire roof to her house. It was about to rain and all of her belongings were still on the wall (it was her parent's house, somewhere on the side of a mountain). She did not seem to care
that they would all be ruined by the rain. </li>
<li>Needless to say, everyone seemed to be a little tired all day today. There was also a feeling that seemed aligned with the disaster that had just taken place back at home. People chatted about how their family and friends were coping with the earthquake. Tourists were being helicoptered out of the region. I have been hearing some of the details from the geologists responding to this event. They have been on helicopter rides making initial assessments… The estimate from offset roads and the like is that the main strike-slip fault (the Kekerengu fault) ruptured in this earthquake slipped 8-9 meters!!! There have been observations of offsets on at least two other strike-slip faults, as well as inferred offset on a thrust fault that links some of the strike-slip faults. The ruptures are very complex and we will learn a tremendous deal about how faults interact with each other during
earthquakes like this. This is a major offset and the teams will be hitting the ground as soon as the roads open up. The helicopters are too busy helping people to spare any for science (at least, that is what we presume given the time delay on getting their boots on the ground. We are making plans on what we might do to make observations from the ship in relation to this earthquake. We are talking about where to take cores to find a probable turbidite, as well as possibly conducting some high resolution bathymetric surveys to look for fault offsets in the sea floor! This is really exciting!!!</li>
<li>We have continued to collect cores in excellent locations. There have been many turbidites in our cores. Some are sandy and easily seen. These can be identified by color changes as well as textural changes (the background sediment, hemipelagic sediment, is basically mud or "very fine sandy silt;" while these turbidites are sandy or "very fine to very coarse sand"). However, with my experience in Cascadia, Sumatra, and the Lesser Antilles, we have been able to identify some muddy turbidites that are only visible with color changes. Basically, the background hemipelagic sediment is lighter in color (probably due to nano fossil content) and the muddy turbidites are darker in color. Also, the turbidites often have a sharp basal contact, while the hemipelagic sediment has a gradual basal contact. I will try to post some photos of these examples later. </li>
<li>We are collecting X-Ray data while on board the ship. When we compare the X-Ray data with our lithologic logs, there is an excellent match. We have been able to capture most of the turbidites (even the muddy ones). Eventually the cores will be CT-scanned for higher resolution X-Ray data. Also, the cores will have core geophysical data collected (magnetic susceptibility, density, etc.). These additional data sets will be key for further stratigraphic correlation analysis. </li>
<li>These cores that we have collected promise to be excellent candidates to develop an earthquake story for the subduction zone here. This will take several years to be sure… But, we have turbidites, within each core, they appear to have unique structures (important for correlation!). The biggest challenge I see is obtaining sufficient mass of planktonic foraminifera to be able to get radiocarbon ages. Time will tell (pun intended). </li>
<li>Attached to this post is a sunset from tonight, Monique on the left and Jamie on the right. We sure deserved this after all the long days that we have been putting in. Now, it is time to catch up on some rest for another long day tomorrow. I am so lucky to be on this ship. Also, I am so very excited to work with an excellent science and ship's crew. Everyone is top notch. </li>
<li>I also include some other photos from a post from a couple days ago. We are cutting a core in the van in one photo. The piston corer is being recovered onto the ship in another. Jenny is cleaning a cone in one. More photos to come!</li>
Monday, November 14, 2016
<li>We have been a really good team on this ship. Dr. Barnes has done a terrific job preparing for our coring cruise. The geospatial data that he has collected and gained access to over the years is, by far, the most comprehensive and detailed (and of highest resolution) of any submarine data that I have used to plan a coring cruise. He has conducted hydrodynamic modeling to estimate potential flow paths. He has mapped the seafloor geomorphology to determine regions of erosion vs. deposition. There are still a great many unknowns, but having this knowledge in the forefront of the planning process clearly gives one a heads up on being able to select good coring sites. Of course, I only have the ability to recognize this due to the training that I have had, initially from Dr. Chris Goldfinger on my maiden research cruise offshore Sumatra. I have supplemented this experience elsewhere,
along different margins. </li>
<li>We have been traversing the fold and thrust belt / continental slope northwards. As I mentioned before (here or elsewhere), we test the hypothesis that the triggering mechanisms for the turbidity currents that lead to the turbidites that we core are triggered by earthquakes. We use one or more of the following methods as part of this test: (a) confluence tests using turbidite counts above a temporal/stratigraphic datum or correlations and (b) isolated source area tests using correlations. We are coring in various channel systems that have isolated source areas. We are looking in piggyback slope basins, also with (hopefully) isolated source areas. </li>
<li>We hope to find along-margin segments of the Holocene (at least) sedimentary record that are somewhat unique from each other so that we might be able to compare how the earthquake record might vary along strike. In the northern Hikurangi Trough, the subducting plate as abundant seamounts that are affecting the plate interface. In the southern Hikurangi Trough, the downgoing plate is smoother with a thicker sedimentary section (up to 6 km, Barnes p.c.). Generally, we think that this would result in larger magnitude earthquakes in the south and smaller magnitude earthquakes in the north. However, this is still a debated topic in plate tectonics. There are some indications that these two parts of the subduction zone are tectonically different. Wallace et al. (2014) present a paper about tsunami potential and they show that regions of slow slip earthquakes are much further up-dip
(shallower on the subduction zone fault) in the north, than they are in the south (in the figure, the green contours are the slip contours for the slow slip earthquakes). Also, they show a figure that displays the coupling ratio (the proportion of the plate convergence that is accumulated as strain along the fault). I include this figure in this post (red is more highly coupled, blue is less coupled). </li>
<li>I am still navigating how to post to my blog with limited internet access. I am attaching an image to an email that I am using to post to my blog. I also include some html that links to the image that I posted online last week.</li>
<a href=" http://earthjay.com/cruises/2016_new_zealand/literature/wallace_etal_2014_earthquake_tsunami_potential_hikurangi_fig_03.PNG">
<img src=" http://earthjay.com/cruises/2016_new_zealand/literature/wallace_etal_2014_earthquake_tsunami_potential_hikurangi_fig_03.PNG">
<li>Below is the figure caption for the above image (Wallace et al., 2014).</li>
Interseismic coupling coefficients (see red to blue scale) from campaign GPS measurements (Wallace et al., 2012a) and cumulative slip in slow-slip events (SSEs) from 2002–2012 (green contours, labeled in mm; from Wallace et al., 2012b). Dashed green contours show slip in a deep central Hikurangi SSE in 2008 (Wallace and Eberhart-Phillips, 2013). Dashed black contours showing the depth to the subduction interface (in km below sea level) are from Ansell and Bannister (1996), and thus present an earlier version of the interface geometry compared to the more recent one shown in Figure 1 from Williams et al. (2014).
<li>The GPS inversion that Wallace and her colleagues use to infer plate coupling is but a snap shot of a moment in time. We do not know if this represents the long term behavior of the fault nor how it might relate to earthquake recurrence, magnitude, segmentation, etc. It seems reasonable, but coming up with a Holocene earthquake record will be a big contribution to answering this question. </li>
<li>This morning there was a large magnitude earthquake. There is talk here in New Zealand (GNS) that there may be as much as 10 meters of slip along one of the major thrust faults in this region. There have been observations of surface rupture on multiple different faults (some are strike-slip). This is a very interesting earthquake and is quite complicated. Unfortunately two people died, but we are lucky that this earthquake occurred in a relatively sparsely populated area. </li>
<li>Needless to say, we will be modifying our plans slightly to take advantage of being on a research vessel at this moment in time, with a coring crew ready to take cores near the earthquake region. We are currently getting information from GNS (the New Zealand geological survey) and NIWA (the organization that Dr. Barnes is with, who runs the R/V Tangaroa). This information will inform us as to the best way that we might decide where to go and what data to collect. We will be taking cores in the region of today's earthquake. We may also collect some additional bathymetry data. We had some core sites located in this region, but they were a lower priority due to the complications of the geomorphology and faulting in this region. However, given that we just had an earthquake of a size that could trigger submarine landslides (there is an estimate that there are over 100,000 subaerial
landslides), as long as we core in the correct place, we should be able to core a seismoturbidite triggered by this earthquake. </li>
Below is a list of the science crew aboard the R/V Tangaroa:
<li>Philip Barnes </li>
<li>Alan Orpin </li>
<li>Peter Gerring </li>
<li>John Mitchell </li>
<li>Will Quinn </li>
<li>Geoffroy Lamarche </li>
<li>Susi Woelz </li>
<li>Jamie Howarth </li>
<li>Jason Patton </li>
<li>Sam Davidson </li>
<li>Simon Banks </li>
<li>Jenni Hopkins </li>
<li>Monique Mckeown </li>
<li>Aratrika Ganguly </li>