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<title>Expedition 362 Sumatra Seismogenic Zone – JOIDES Resolution</title>
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<link>https://joidesresolution.org</link>
<description>Science in Search of Earth's Secrets</description>
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<title>Expedition 362 Sumatra Seismogenic Zone – JOIDES Resolution</title>
<link>https://joidesresolution.org</link>
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<item>
<title>Incoming! Oblique Subduction at the Sunda Subduction Zone</title>
<link>https://joidesresolution.org/incoming-oblique-subduction-at-the-sunda-subduction-zone/?utm_source=rss&utm_medium=rss&utm_campaign=incoming-oblique-subduction-at-the-sunda-subduction-zone</link>
<comments>https://joidesresolution.org/incoming-oblique-subduction-at-the-sunda-subduction-zone/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Sun, 25 Sep 2016 20:05:30 +0000</pubDate>
<category><![CDATA[earthquakes_659]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[Plate-Tectonics]]></category>
<category><![CDATA[strike-slip fault]]></category>
<category><![CDATA[Subduction]]></category>
<category><![CDATA[subduction zone]]></category>
<category><![CDATA[subduction zones]]></category>
<category><![CDATA[tectonics]]></category>
<guid isPermaLink="false">https://joidesresolution.org//incoming-oblique-subduction-at-the-sunda-subduction-zone</guid>
<description><![CDATA[The Indian and Australian Plates plow northeast into the Sumatra subduction zone, part of the larger Sunda subduction zone, at a... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/incoming-oblique-subduction-at-the-sunda-subduction-zone/" title="Continue reading Incoming! Oblique Subduction at the Sunda Subduction Zone">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p class="p1">The Indian and Australian Plates plow northeast into the Sumatra subduction zone, part of the larger Sunda subduction zone, at a speed of 45 mm/yr. The angle between the direction these two plates move relative to each other is not always at a right angle (90°) to the subduction zone itself–here it is about 50°. Sliding under the Sunda Plate at an angle is not easy, so several large strike-slip fault systems help to accommodate some of this movement. If you thought learning vectors in high school was pointless—think again. This is a perfect vector component problem!</p>
<p>Before we get to big words about big faults, let’s review vectors. If you want to walk from one corner of an intersection to the corner diagonally across from you, you typically go along one side of the intersection, wait for the pedestrian light, and then walk the other side. You’ve walked two sides of a triangle to get to your destination. The third side of the triangle is the line that connects your start and end points:</p>
<p><img fetchpriority="high" decoding="async" class="alignnone size-full wp-image-23600" src="https://joidesresolution.org//wp-content/uploads/2016/09/roadCross.png" alt="" width="306" height="244" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/roadCross.png 306w, https://joidesresolution.org/wp-content/uploads/2016/09/roadCross-300x239.png 300w" sizes="(max-width: 306px) 100vw, 306px" /></p>
<p> </p>
<p class="p1">Each side of the triangle is a vector, and we can think of the two pedestrian crossings as components (purple lines/arrows) of the vector that connects your start and end points (orange line/arrow). A vector is a quantity that has a magnitude (in this case length, the distance across the intersection = 20m) and a direction (NW). Any vector can be broken down into component lengths and directions at right angles, like the two sides of the intersection that you just walked.</p>
<p class="p1">The motion of the Indian Plate coming into the North Sumatran subduction zone is also a vector. We can break it down into two components: one parallel to the subduction zone (yellow arrow on map below) and one perpendicular to the subduction zone (orange red arrow). Because the Indian/Australian plate comes in at an angle other than 90º to the subduction zone, we call it “oblique subduction”. (Plate motion vectors and fault locations adapted from Meltzner et al., 2012.)</p>
<p><img decoding="async" class="alignnone size-full wp-image-23602" src="https://joidesresolution.org//wp-content/uploads/2016/09/subductvectors.jpg" alt="" width="640" height="462" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/subductvectors.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/subductvectors-300x217.jpg 300w" sizes="(max-width: 640px) 100vw, 640px" /></p>
<p>The main subduction zone thrust fault takes up primarily the NE-directed motion of the Indian Plate, perpendicular to the subduction zone. That is, the orange red component of the plate motion vector is taken up by earthquakes on the subduction zone that allow the plates to move past each other. Here are two models that show the motion of the plates during the 2004 M 9.2 Great Sumatra-Andaman Islands Earthquake. During the earthquake the plate overlying the subduction zone actually rebounded towards the SW, over the down-going Indian Plate. Notice that the arrows (from GPS measurements of ground motion change before and after the earthquake) point almost directly across the subduction zone at 90º (models from Chlieh et al., 2007, and Rhie et al., 2007).</p>
<p><img decoding="async" class="alignnone size-full wp-image-23601" src="https://joidesresolution.org//wp-content/uploads/2016/09/RuptureGPS.jpg" alt="" width="640" height="599" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/RuptureGPS.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/RuptureGPS-300x281.jpg 300w" sizes="(max-width: 640px) 100vw, 640px" /></p>
<p class="p2">But there is still plate motion to account for in the system: the yellow component of the overall plate motion. Faults parallel to the subduction zone take up the slack – This is fairly common in subduction zones because plates rarely meet exactly head on. These long, subduction zone-parallel faults are strike-slip faults. They’re nearly vertical in the subsurface, and motion along them can be seen looking straight down, as if looking at a map. The San Andreas Fault is a well-known example of a strike-slip fault that lets the Pacific Plate move north along the North American Plate. In Sumatra, the primary fault taking up this motion is the Great Sumatran Fault which runs along the center of the island of Sumatra. In fact, the fault runs very close to the volcanic arc of the subduction zone. The southwestern side of the fault moves to the northwest, the same direction as the plate motion not accounted for by subduction. There are also other strike-slip faults offshore, also parallel to the subduction zone, which help to take up some of this plate motion. This figure shows different historic and recent earthquakes in the Sumatra region, including along the Great Sumatran Fault, parallel to the Sunda Trench (Fig. 10 in McCaffrey, 2009).</p>
<p> </p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23598" src="https://joidesresolution.org//wp-content/uploads/2016/09/McCaffrey_SumatraFig.jpg" alt="" width="640" height="276" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/McCaffrey_SumatraFig.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/McCaffrey_SumatraFig-300x129.jpg 300w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
<p> </p>
<p class="p2">The Great Sumatran Fault carries its own seismic hazard that adds to the risk posed by subduction zone earthquakes and tsunami. On top of the seismic hazard, the southwestern and southern coast of Sumatra and Java host many active volcanoes. The volcanoes are also part of the subduction zone system: they are fed by molten material from the mantle because of the ocean crust subducting below. (That’s another post for another time!)</p>
<p class="p2">Here’s a map of the seismic hazard of Indonesia and Malaysia that shows the maximum amount the ground is likely to move during earthquake shaking in the next 50 years. “How much” is expressed as peak ground acceleration, in percent of the normal acceleration caused by gravity. “Likely” is a 10% chance that the ground will move that much during the 50 year time period. (Map created by the USGS based on data from a variety of sources. See Further Reading for full map poster with citations.)</p>
<p> </p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23603" src="https://joidesresolution.org//wp-content/uploads/2016/09/SumSeismHazUSGS.jpg" alt="" width="640" height="565" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/SumSeismHazUSGS.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/SumSeismHazUSGS-300x265.jpg 300w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
<p> </p>
<p class="p1">This type of plate boundary geometry is not unique to the Sumatra region. In many plate boundaries where plates converge at an angle rather moving straight toward each other, we see that long strike-slip fault systems help to take up the overall plate motion. The Liquine-Ofqui Fault and Atacama Fault serve a similar purpose in the Andean subduction zone in Chile. The Median Tectonic Line is the largest strike-slip fault in Japan and accounts for the oblique motion at the Nankai subduction zone. Learning about processes at one site on Earth can help us understand what’s going on elsewhere in the world!</p>
<p class="p1"><strong>Sources and Further Reading</strong></p>
<p class="p1"><u>General information</u></p>
<p class="p1"><u>Journal articles</u></p>
<p class="p1">Baroux et al., 1998. Slip-partitioning and fore-arc deformation at the Sunda Trench, Indonesia. Terra Nova, 10 (3), 139-144.</p>
<p class="p1">Bellier and Sébrier, 1995. Is the slip rate variation on the Great Sumatran Fault accommodated by fore-arc stretching? Geophysical Research Letters, 22 (15), 1969-1972.</p>
<p class="p1">Berglar et al., 2010. Structural evolution and strike-slip tectonics off north-western Sumatra. Tectonophysics 480, 119-132.</p>
<p class="p1">Chlieh, M., Avouac, J.-P., Hjorleifsdottir, V., Song, T.-R.A., Ji, C., Sieh, K., Sladen, A., Hebert, H., Prawirodirdjo, L., Bock, Y., and Galetzka, J., 2007. Coseismic slip and afterslip of the great (Mw 9.15) Sumatra-Andaman earthquake of 2004. Bulletin of the Seismological Society of America, 97(1A):S152–S173. <a href="http://dx.doi.org/10.1785/0120050631">http://dx.doi.org/10.1785/0120050631<</a></p>
<p class="p1">Fitch, T.J., 1972. Plate convergence, transcurrent faults, and internal deformation adjacent to Southeast Asia and the Western Pacific. Journal of Geophysical Research 77 (23), 4432–4460. <a href="http://onlinelibrary.wiley.com/doi/10.1029/JB077i023p04432/epdf" class="broken_link">doi:10.1029/JB077i023p04432<</a></p>
<p class="p1">McCaffrey, R., 2009. The Tectonic Framework of the Sumatran Subduction Zone, Annual Reviews in Earth and Planetary Sciences, 37, 345-366.</p>
<p class="p1">Meltzner, A. J., K. Sieh, H.-W. Chiang, C.-C. Shen, B. W. Suwargadi, D. H. Natawidjaja, B. Philibosian, and R. W. Briggs, 2012. Persistent termini of 2004- and 2005-like ruptures of the Sunda megathrust, Journal of Geophysical Research, 117, B04405,</p>
<p class="p1">Rhie, J., Dreger, D., Bürgmann, R., and Romanowicz, B., 2007. Slip of the 2004 Sumatra-Andaman earthquake from <dfn title="Look up the definition of Joint.">joint</dfn> inversion of long-period global seismic waveforms and GPS static offsets. Bulletin of the Seismological Society of America, 97(1A):S115–S127. <a href="http://dx.doi.org/10.1785/0120050620">http://dx.doi.org/10.1785/0120050620<</a></p>
<p> </p>
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]]></content:encoded>
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</item>
<item>
<title>The Earthquake that Triggered Expedition 362</title>
<link>https://joidesresolution.org/the-earthquake-that-triggered-expedition-362/?utm_source=rss&utm_medium=rss&utm_campaign=the-earthquake-that-triggered-expedition-362</link>
<comments>https://joidesresolution.org/the-earthquake-that-triggered-expedition-362/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Wed, 21 Sep 2016 22:01:47 +0000</pubDate>
<category><![CDATA[earthquakes]]></category>
<category><![CDATA[earthquakes_659]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<category><![CDATA[tsunami]]></category>
<guid isPermaLink="false">https://joidesresolution.org//the-earthquake-that-triggered-expedition-362</guid>
<description><![CDATA[In 2004, a magnitude 9.2 earthquake struck the northern Sumatra region and triggered a tsunami that inundated the Indian Ocean... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/the-earthquake-that-triggered-expedition-362/" title="Continue reading The Earthquake that Triggered Expedition 362">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>In 2004, a magnitude 9.2 earthquake struck the northern Sumatra region and triggered a tsunami that inundated the Indian Ocean coast. The disaster was an important reminder to earth scientists that we must better understand the processes at work in subduction zones so that we can help mitigate future disasters. The earthquake was extremely powerful and surprising to geologists in that it was able to break through the plate boundary to relatively shallow depths (5-7 km) below the seafloor. This poster explains some of the details about the events of 26 December 2004, which spurred the scientists on board Expedition 362 to drill into the seafloor and study the rocks and sediments that host major earthquakes once they reach the subduction plate boundary.<br />
<!--break--></p>
<p> </p>
<p>For further reading, check out our pages about earthquakes and subduction zones, two of the main topics under study by <a href="https://joidesresolution.org//expedition/362/">Expedition 362: Sumatra Seismogenic Zone</a>.</p>
<p>This poster is printable on 11×17 in paper.</p>
<p> </p>
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</item>
<item>
<title>Daily Science Report Explained</title>
<link>https://joidesresolution.org/daily-science-report-explained/?utm_source=rss&utm_medium=rss&utm_campaign=daily-science-report-explained</link>
<comments>https://joidesresolution.org/daily-science-report-explained/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Tue, 13 Sep 2016 17:44:18 +0000</pubDate>
<category><![CDATA[carbonate sediments]]></category>
<category><![CDATA[carbonate sediments core description]]></category>
<category><![CDATA[core description]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[sediment cores]]></category>
<category><![CDATA[sedimentary rocks]]></category>
<category><![CDATA[Structural Geology]]></category>
<category><![CDATA[Sumatra Seismogenic Zone sediment cores sedimentary rocks Structural Geology veins]]></category>
<category><![CDATA[veins]]></category>
<guid isPermaLink="false">https://joidesresolution.org//daily-science-report-explained</guid>
<description><![CDATA[Each day, our Staff Scientist/Expedition Project Manager sends out an update to the ship and to our colleagues on shore.... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/daily-science-report-explained/" title="Continue reading Daily Science Report Explained">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>Each day, our Staff Scientist/Expedition Project Manager sends out an update to the ship and to our colleagues on shore. The daily report summarizes the scientific findings from the day before. Here’s an example of a daily report, explained with photos!<br />
<!--break--><br />
Click on the photo at left to make it bigger. </p>
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</item>
<item>
<title>A Successful Story at Site U1480</title>
<link>https://joidesresolution.org/a-successful-story-at-site-u1480/?utm_source=rss&utm_medium=rss&utm_campaign=a-successful-story-at-site-u1480</link>
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<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Fri, 09 Sep 2016 22:05:00 +0000</pubDate>
<category><![CDATA[drilling]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[operations]]></category>
<category><![CDATA[Sumatra Seismogenic Zone operations]]></category>
<guid isPermaLink="false">https://joidesresolution.org//a-successful-story-at-site-u1480</guid>
<description><![CDATA[We finished our first site with success! We’re now at our second site, so here’s a little summary of what... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/a-successful-story-at-site-u1480/" title="Continue reading A Successful Story at Site U1480">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>We finished our first site with success! We’re now at our second site, so here’s a little summary of what we did at Site U1480. We met our primary science goal at the site: core the entire sedimentary sequence from seafloor down to the oceanic crust that forms the basement that the sediments rest on. That’s almost 1.4 km (0.8 mi)!<br />
<!--break--></p>
<p>While the scientists are writing up their reports, we’ll summarize a few of the things that we’ve been thinking about. I’ll have a few more posts for you in the next few days. Stay tuned!</p>
<p>(Click on the image at left to see it bigger.)
</p>
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</item>
<item>
<title>Sampling Sampler</title>
<link>https://joidesresolution.org/sampling-sampler/?utm_source=rss&utm_medium=rss&utm_campaign=sampling-sampler</link>
<comments>https://joidesresolution.org/sampling-sampler/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Sat, 13 Aug 2016 22:43:51 +0000</pubDate>
<category><![CDATA[core]]></category>
<category><![CDATA[core core flow]]></category>
<category><![CDATA[core flow]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[sampling]]></category>
<category><![CDATA[Sumatra Seismogenic Zone sampling]]></category>
<guid isPermaLink="false">https://joidesresolution.org//sampling-sampler</guid>
<description><![CDATA[After the core comes on deck at the catwalk and whole-round samples are taken for fossils and chemistry, it comes... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/sampling-sampler/" title="Continue reading Sampling Sampler">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>After the core comes on deck at the catwalk and whole-round samples are taken for fossils and chemistry, it comes indoors for the rest of its life. Then measurements and sampling really get underway.<br />
<!--break--><br />
<!--break--><br />
<!--break--></p>
<p>
</p>
<p>The story of core from catwalk to description table is a post for another time. Today (Sunday morning on board) we’ve been taking samples from yesterday’s cores since no new core has come up for a few hours. Instead of coring, we’ve sent instruments down the borehole to measure the temperature and pressure under the ocean floor. Until we get those results, here’s how sampling works on this expedition. </p>
<p><!--break--></p>
<p><img loading="lazy" decoding="async" alt="Scientists get a first look at a core after it was cut in half. They're looking for patterns in the sediment that can tell us about how the sediments were deposited, where they came from, and how they'll behave when they get to the Sumatra subduction zone." src="/sites/default/files/u375/DSC_3034.jpg" style="border: 3px solid; margin: 5px; float: left;" height="186" width="328" /></p>
<p>First, the split core gets laid out on description tables. The archive<br />
half, which will stay undisturbed for future generations, goes to the<br />
sedimentologists who look at the colors, compositions, and patterns of<br />
the sediments. They take tiny samples on the ends of toothpicks and<br />
smear those over glass slides so they can look at the sediments more<br />
closely under microscopes. At the same time, structural geologists<br />
examine the working half, looking for signs of deformation, like cracks<br />
and faults and folds. On this expedition, they’ll also estimate how<br />
strong the sediments are. Strength is how much force a material<br />
can withstand before it yields and deforms. In this core, the<br />
sediments are compacted mud, made mostly of clay. As you know from playing with clay and making ceramics, clay is very weak. It doesn’t take much force to make it change its shape. If you read Brian’s recent blog post, you’ll know that we found tens of meters of sand in recent cores. Sand has completely different strength from compacted mud. It’s pretty easy to destroy a sand castle, but it takes much more work to squish an unfired clay statue. (Side note: play with some squishable things that you have at home. Try bread, tofu, cooked carrots–how these things behave are very different from each other because they have different strength! You’re doing experiments like real earth scientists, though we usually squish rocks with big machines that are much stronger than our hands.)
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<p><img loading="lazy" decoding="async" alt="The archive half of the core undergoes high-resolution scanning and several " non-intrusive"="" analyses.="" "="" src="/sites/default/files/u375/DSC_3037.jpg" style="border: 3px solid; margin: 5px; float: left;" height="249" width="372" /></p>
<p>The archive half goes for high-resolution scanning and several different<br />
measurements that help scientists identify the composition of the<br />
sediments and correlate observations and measurements from other<br />
instruments. Printed copies of the core scan are useful for taking notes and recording observations!
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<p>The whole sample plan is agreed upon by everyone in the Science Party and reviewed by the Co-Chief<br />
Scientists even before drilling begins. The scientists assigned to a sampling shift put flags where samples will<br />
be taken based on sampling requests from their colleagues. The flags are color-coded and labeled to show what kind of sample is to be taken (see teaser photo for this post). The first samples that come out of the working half are for Moisture and Density (MAD). Since the sediment is fairly soft, we can remove these and other samples using little plastic tubes. The holes left behind get plugged with foam shapes that match the tube size. How clever!
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<p><img loading="lazy" decoding="async" alt="Samples are taken from the working half of the core according to a pre-approved plan agreed upon by all the scientists." src="/sites/default/files/u375/DSC_3049.jpg" style="border: 3px solid; margin: 5px; float: left;" height="254" width="377" /></p>
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<p>Here Freya samples with a metal scoop to get a bigger sample than is possible with the little tubes. She’s looking for diatoms, tiny creatures that build their skeletons out of silica. They’ve been around on Earth for a long time, but their shapes have changed enough over time that if she finds some in a sample, she can tell approximately how old that sample is from the shape or kind of diatoms.
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<p>Abby keeps track of who requested what samples, even if those people are sleeping right now! When the night shift goes to bed, the day shift will take over and do the same thing. Stay tuned…
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<title>Core on Deck!</title>
<link>https://joidesresolution.org/core-on-deck-5/?utm_source=rss&utm_medium=rss&utm_campaign=core-on-deck-5</link>
<comments>https://joidesresolution.org/core-on-deck-5/#respond</comments>
<dc:creator><![CDATA[Elizabeth Christiansen]]></dc:creator>
<pubDate>Fri, 06 Jun 2014 04:08:03 +0000</pubDate>
<category><![CDATA[core]]></category>
<category><![CDATA[core flow]]></category>
<category><![CDATA[EXP352]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<guid isPermaLink="false">https://joidesresolution.org//core-on-deck-5/</guid>
<description><![CDATA[These are the words we’ve waited to hear. Shortly before 12:30 AM (00:30) Tokyo time, the call went out: “core... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/core-on-deck-5/" title="Continue reading Core on Deck!">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>These are the words we’ve waited to hear.</p>
<p>Shortly before 12:30 AM (00:30) Tokyo time, the call went out: “core on deck; core on deck”. Scientists flocked to the catwalk to watch the first official core of Expedition 352 rise to the surface. Technicians moved into place: carrying the core to the catwalk; depositing it in the rack; wiping it off; marking and cutting sections. The IODP technicians fall into their roles naturally, moving and working together to get the job done while scientists look on with interest and curiosity about what is inside the liner surrounding the core. While initial tests and observations are begun, the waiting also begins as it takes approximately two hours for the core sections to equilibrate before observations can continue. In that time, another core should arrive on deck and the process (excitement then waiting) continues.</p>
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