End of Cruise

We just pulled into Valparaiso an hour ago, ending our study of the earthquake rupture zone.  Make sure to check back for updates and progress we make on processing and analyzing the data that was collected. Thanks for following along!

SIOSEARCH Science Party:

Investigación en SIOSEARCH

El propósito de la expedición SIOSEARCH ha consistido en generar una nueva batimetría de detalle en la “zona de ruptura” del terremoto y compararla con la batimetría anterior, para intentar visualizar los efectos que pudo haber generado el terremoto en el fondo marino (movimiento de fallas, deslizamientos de terreno).

En qué consiste la batimetría?

La batimetría representa la morfología o relieve del fondo marino, es el equivalente submarino de la altimetría. Consiste en determinar la profundidad midiendo el tiempo que le toma a una onda acústica, enviada desde el barco, viajar a través del agua hacia el fondo marino y luego volver al barco.

Obteniendo el tiempo de propagación de la onda y conociendo la velocidad del sonido en el agua, se determina la profundidad a la cual se encuentra el fondo marino.

Cuando consideramos una onda de ecosonda, el tiempo se divide por dos ya que la onda debe viajar al fondo marino y volver.

Se habla de batimetría monohaz cuando se emite un solo haz acústico y se obtiene la profundidad en un punto, de este modo, a medida que el barco avanza, se obtiene un perfil del fondo marino.

En el caso de la batimetría multihaz se utilizan varios haces de sonido, que forman una franja transversal a la navegación del barco (ver figura) generando una imagen del fondo marino en el área bajo el barco, a medida que éste se desplaza, se va completando el mapa batimétrico.

a)    Batimetría multihaz. b) batimetría monohaz.

XBT como apoyo a la batimetría:

El registro batimétrico debe ser corregido regularmente utilizando sensores de temperatura. Los XBT (eXpendable BathyThermographer) permiten obtener un perfil de temperatura del océano (en este caso, hasta los ~1000 m). Cada XBT consiste en una sonda en cuyo interior se encuentra un termistor conectado a un hilo de cobre.

Los perfiles de temperatura vs profundidad registrados por los XBT, permiten calibrar la velocidad del sonido en el agua y a su vez corregir el registro batimétrico determinado por el ecosonda.

El XBT se lanza al mar desde la borda del barco mediante un dispositivo disparador diseñado para ello (ver foto). A medida que la sonda se hunde, los cambios en la temperatura del agua de mar van siendo registrados por el termistor y simultáneamente enviados al buque a través de hilo de cobre, luego los datos son graficados en una pantalla (mira los links).

Sensores de Presión:

Una herramienta muy interesante utilizada en esta investigación han sido los “sensores de presión” una técnica que permite medir la deformación vertical en el fondo del mar (Phillips et al., 2008).

Este instrumento permite medir elevaciones o subsidencias del fondo, mediante medidas instantáneas de la presión hidrostática en un punto, convirtiendo las presiones en profundidad. Estos cambios van siendo registrados durante el período de tiempo hasta que se recuperan desde el fondo del mar.

Estos sensores se depositan en el fondo marino y meses después se recuperan para obtener el registro, por tanto, un paso fundamental al iniciar el crucero, fue discutir y definir su mejor ubicación a lo largo de la zona de ruptura.

Links XBT:

http://www.aoml.noaa.gov/goos/uot/xbt-what-is.php

http://en.wikipedia.org/wiki/Expendable_bathythermograph

Referencias:

Phillips, K., Chadwell, D., Hildebrand, J. 2008. Vertical deformations measurements on the submerged south flank of Kilauea volcano, Hawaii reveal seafloor motion associated with volcanic collapse. Journal of Gephysical Research,  vol.113. 15p.

The Hunt for Underwater Landslides

Post by Ashlee Henig

The oceanographic research vessel of the University of Concepción, moved inland more than 1km by tsunami waves. Credit: Ruben Escribano.

The last day and a half have been spent searching the Chilean margin in shallow water depth for signs of landslides that may have contributed to the formation of the tsunamis that hit the Chilean coast in the hours after the M8.8 earthquake.  The tsunami waves caused most of the devastation on the coast of Chile between the cities of Concepción and Constitución.  The photo below, courtesy of Ruben Escribano and the INSPIRE cruise webpage, shows the University of Concepción’s research vessel Kay Kay II washed more than 1km inland after the tsunamis.

As mentioned in the “about” page, large movements of water triggered by geologic movements are the main cause of tsunami waves.  The most common of these geologic movements is the landslide.  Here is an image showing a variety of landslide types, most occurring on land, and some underwater.

Different types of landslides source: Geological Survey of Canada

Landslides can happen for many reasons, both natural and anthropogenic.  Natural causes include earthquakes that can shake debris loose and destabilize steep slopes, heavy rain, addition of mass to the top of a slope (e.g. by sediment accumulation), or removal of material from the base of a slope (by undercutting by waves, a river cutting into its banks, etc).  Humans contribute to mast wasting through overbuilding infrastructure and adding excessive stresses on the underlying land, mining, building dams and excessive irrigation and drainage systems, and through deforestation.

It is challenging to find underwater landslides because we have a lot of ground to cover out here on the Chile margin.  It helps us that we have an idea of where to look, and we know exactly what we’re looking for.  Submarine landslides have a very distinct shape that we can often see well with our shipboard mapping equipment (see previous blog).  A clear sign of an underwater landslide is a head scarp, or a steep, curved cutout in the side of a cliff, from where the material was removed.  Downhill of the head scarp we often find a pile of jumbled, blocky material forming a feature called the “toe” of the landslide. This is where the material removed from the cliff ends up.  Depending on the energy of the slide, the material in the landslide can travel 10s to 100s of kilometers downslope, and the blocks can be quite large, sometimes bigger than houses!  This is the material that pushes the water in its path, causing a potential tsunami.

Image of underwater landslide showing head scarp and toe. Source: Scripps Institution of Oceanography

It is worth noting that not every underwater landslide will cause a tsunami.  In fact, most don’t.  But in the case of the Chilean M8.8 earthquake, there was enough shaking that we have reason to believe that enough material may have broken off of the margin to cause the observed tsunami waves.

Gear Deployment and Data Collection

Post by Jared Kluesner

This past day we deployed some of the pressure sensors. The video below shows how we deploy equipment off the back of the ship using something called an A-frame. For the deployment of larger instruments, usually there are people on what we call "tag-lines" which help stabilize the equipment once it is lifted off the deck. This is extremely important because the ship is constantly pitching and rolling, which causes the instrument to swing. Tag-lines minimize this and provide more of a controlled equipment launch. As you can see, the seas where calm this past day so only one tag-line was needed.

Below is a short video displaying the collection of sonar data. The system updates after about 10 seconds. This is the speed at which the bathymetry data is processed and displayed in real-time in the lab. The video shows the sonar imaging a submarine canyon, which transports sediment from land to the deep trench axis. Many of these underwater canyons meander, similarly to rivers on land.

We have finished mapping the deeper part of the survey area and are now concentrating on shallower targets. Make sure to check the Ship Tracker to see where we are currently mapping!

Life at Sea

Ever wonder what it’s like to live out at sea on a research vessel? Ashlee here, and I’ve been out at sea on the Melville for 25 days straight so far. You might think I’d be going a little stir-crazy by now, but really I’m doing ok. I wanted to give you all a little virtual tour around the ship so you can see what life is like out here.

Most often everyone shares a room with another scientist. We sleep in bunk beds and try to arrange shifts so that only one person is in the room at any one time. There isn’t a lot of headspace in bed and often I bump an elbow or knee into the ceiling. Climbing on the ladder to the top bunk can be challenging when the seas are really moving but generally it’s fun, like bunking up at summer camp. Probably the hardest part is showering in rough seas and trying to wash your feet without falling over (you know how hard it is to do that on solid ground!). Lucky for us, the seas have been relatively calm, but let’s sea what happens now that I’ve made that comment….

A popular question is always “How’s the food?” Trust me, that’s the first thing I always wonder when I’m about to board a ship for the first time. I always bring snacks and goodies with me because I’m terrified that the food won’t be edible, and I usually never eat what I brought. The food on the ship is amazing! Nothing like the old school cafeteria with blobs of unrecognizable mush. We have fresh salad with every meal and a box of fresh fruit out at all times. The cooks have all sorts of tricks to keep food fresh and they feed us well. In 25 days, I haven’t had the same meal once. There are all sorts of snacks for in between mealtimes too so there’s no chance of starving on this ship!

But what about getting bored? On this cruise I have been so busy with science that there is no time to get bored. However, many of the ship’s crewmembers live onboard for several months out of the year and they make this their home keeping plenty of books and games in the library, and a whole collection of DVDs to borrow. There are also several exercise machines around for the particularly restless.

Deck operations are a whole other part of ship life.  Tomorrow we deploy our first instruments so I’ll leave it till then to explain…

Day 2!

For the past day and a half we have been mapping the seafloor next to where the cruise before collected data as they steamed into Valparaiso. Matching the "footprint" of the sonar is important, if you are off you will have gaps or overlap in the coverage. This is a delicate process that is based on how deep the seafloor is and what angle the sound waves are sent down from the bottom of the ship. This image provided by the U.S. Navy shows the cone shape footprint the sonar creates.

Multibeam Sonar

If the seafloor depth is very shallow then the sonar footprint is very small. Looking at the figure to the left you can see how the cone shaped footprint gets smaller the closer it is to the ship. In deep water the footprint is very large, so we can map a much larger area.

Below is a video that I took before we boarded the ship. We took a water taxi to the ship, which was anchored out in the bay. The video is a bit shaky, but gives a good view of the ship! The ship next the R/V Melville is a fueling barge.

SIOSEARCH en acción:

En estos días hemos estado mapeando el fondo del mar cerca de donde el crucero  INSPIRE recolecto datos antes. Es muy importante hacer calzar los datos de la huella del sonar, si estos no calzan habrá un "gap" (zona sin información) o un traslape de datos. Este es un proceso delicado que dependerá de qué tan profundo es el fondo del mar y en qué ángulo se envían desde el barco las ondas acústicas hacia abajo. En la imagen proporcionada por el US NAVY, se muestra la forma de cono que genera el sonar en la columna de agua, hasta tocar el fondo.

Si la profundidad del fondo del mar es muy somera, la huella del sonar abarcará un área menor, en cambio, aguas profundas, la huella es más grande y podemos mapear un área mayor. Mira la figura de arriba.

First day in Chile!

Click on image for full resolution. Background image provided by google maps.

Hello everyone and thanks for following along as we explore and map the region where the 8.8 magnitude earthquake and rupture occurred a few weeks ago. As we made our descent into Santiago this morning (after a 10 hour flight!) we could see the mighty Andes Mountains peaking through the cloud cover. Gazing out the plane window, I was reminded of the processes that created (and is still creating) these massive landforms, however I will get into that in the next few days.

Driving from Santiago to Valparaiso, we couldn’t help but notice that the lowland terrain and plant life looked very similar to southern California where Scripps Institution of Oceanography is located. Looking at a map, Valparaiso is at about 33 degrees south (latitude). San Diego is located at about 32.5 degrees north (latitude). I would like to ask local high school students and people following along why is this (please post ideas)?

Broken window

Fresh crack

As we arrived at our hotel today we noticed fresh cracks in the plaster/walls and broken glass panes. Hopefully there won’t be anymore large aftershocks!

Hello world!

Welcome to the SIO SEARCH blog! Check back regularly from mid to late March for updates from our science team.