(In this post, each paragraph is presented in English y en español)

Mankind has always tried to understand the natural world. However, our understanding of observations is limited by the tools used to observe these events. Natural disasters like earthquakes and volcanos, and their capacity for destruction, have marked the communities that have suffered their attacks and inspired them to find explanations. Thus, the Araucanians of South Chile created gods in the volcanoes or the underground Serpentine Trentren Vilu and Caicai Vilu as the causers of earthquakes.

La humanidad siempre ha tratado de entender el mundo natural. Sin embargo, nuestra comprensión de esta, estará limitada por las herramientas que podemos utilizar para observarla. Desastres naturales como terremotos y volcanes, y su capacidad de destrucción, han marcado las comunidades que han sufrido sus embates e inspirado a encontrar explicaciones. Así, los araucanos del sur de Chile crearon dioses en los volcanes o a las serpientes subterráneas Trentren Vilu y Caicai Vilu como causantes de terremotos.

This mixture of fascination and concern persists today and a variety of modern techniques are being used to study and anticipate certain events, especially in countries located along the Pacific Ring of Fire. Our study region is south-central Chile, where the Nazca plate subducts beneat the South American plate.

Esta mezcla de fascinación y preocupación todavía persiste y una variedad de técnicas modernas se están utilizando para estudiar y anticipar ciertos acontecimientos, especialmente en países situados a lo largo del Anillo de Fuego del Pacífico. La región de estudio del presente proyecto es el centro-sur de Chile, donde la placa de Nazca subducta debajo de la placa Sudamericana.

Several methods are used to study the subduction zone. Seismic reflection is the method of choice for this study aboard the R/V Marcus Langseth research vessel.

Varios métodos son utilizados para estudiar las zonas de subducción. La reflexión sísmica es el método elegido para este estudio, a bordo del buque de investigación R/V Marcus Langseth.

To image beneath the seafloor, the R/V Marcus Langseth uses the gear described in the previous post. The terabytes of raw data are processed using various geophysical methods to arrive at models that can be used to infer the structure and composition of the earth’s subsurface along the Nazca-South American subduction zone.

La forma en que el R/V Marcus Langseth es capaz obtener una imagen del fondo marino esta descrito en el post anterior. Los terabytes de datos brutos se procesan usando varios métodos geofísicos, para así llegar a modelos que se pueden utilizar para inferir la estructura y la composición de la subsuperficie de la tierra a lo largo de la zona de subducción Nazca-Sudamerica.

The data must be reorganized into Common Depth Point gathers, or CDP gathers, in which shot and receiver offset are spaced equally from the point of reflection. With the data organized thus, students onboard are able to generate preliminary velocity models and time migrated seismic sections, allowing initial interpretations to be made.

Los datos deben reorganizarse en la geometría de Punto Común Profundo, o CDP (por sus siglas en inglés), donde la posición del disparo y del receptor están ordenados por su punto de reflexión. Con los datos organizados de esta manera, los estudiantes a bordo pueden generar modelos de velocidad preliminares y secciones sísmicas migradas en el tiempo, para así realizar interpretaciones iniciales.

Figure 1. Simple ray diagram of a CDP gather (top). Illustration of normal moveout correction determined through velocity analysis of reordered seismic traces (bottom).

Figura 1. Diagrama simple de rayos ordenados por CDP (arriba). Ilustración de la corrección normal moveout (abajo) determinada mediante el análisis de velocidad de trazas sísmicas reordenadas.

Figure 2. Seismic section showing preliminary results of line MC03. The horizontal axis is the trace number and the vertical axis is two-way travel time on a vertical path through the ocean and earth in seconds.

Figura 2. Sección sísmica que muestra los resultados preliminares de la línea MC03. El eje horizontal es el número de traza y el eje vertical es el tiempo de ida y vuelta (two-way travel time), en un trayecto vertical a través del océano a la tierra en segundos.

The next step will be to apply additional processing techniques for removing reverberations and other unwanted artifacts in the data to see more clearly and deeper into the subduction zone. We will also use models of subsurface seismic velocities generated by Dr. Eduardo Contreras-Reyes, University of Chile, Santiago (and a member of the science party for this expedition) using other types of data to convert the vertical axis from time to depth beneath the seafloor. The techniques should allow us to image deeper and expand on the earlier work. In great scientific fashion, collaborative minds from multiple institutions here on the Langseth live and work together to solve problems that will help improve our understanding of the planet we co-inhabit.

El siguiente paso será aplicar técnicas de procesamiento adicionales para eliminar las reverberaciones y otros artefactos no deseados en los datos para ver más claramente y más profundamente en la zona de subducción. También utilizaremos modelos de velocidades sísmicas subsuperficiales generadas por el Dr. Eduardo Contreras Reyes, Universidad de Chile (miembro científico de esta expedición), utilizando otros tipos de datos se convertirá el eje vertical del tiempo en profundidad por debajo del fondo marino. Estas técnicas deberían permitirnos obtener imágenes profundas del subsuelo y así ampliar el trabajo anterior. De esta manera, los científicos provenientes de diversas instituciones unen sus mentes aquí en el Langseth, viven y trabajan juntos para resolver problemas que ayudarán a mejorar nuestra comprensión del planeta que habitamos.

(contributed by Sebastian Bahamondes and Edward Zhang)

(a personal view from Jorge Gaete, scientific observer from the Chilean Naval Hydrographic Office)

A simple title; yet so short to describe an interesting experience. January 8th 2017 marked the first milestone of this 44-day experience on the coast of this far-away country well known for its huge Earthquakes and Tsunamis. For R/V Marcus G. Langseth just another trip; for some of the scientists another research project on a life-long career; for many others…a complete mystery.

From the visit of Chile’s President and the United States Ambassador to the difficult maneuver to refuel the ship, everything was new and exciting. Starboard, port, bow, stern, upper deck…simple directions given by kind crew members to some of us to try to reach our cabins. Pretending to have understood those directions, like lab mice we kept making wrong turns before finding our new home within this amazing ship.
During the initial few days, our headaches and heavy stomachs kept us trying to discover what had convinced us to accept this journey…”What was I thinking…” was a common question every night. Whether it was the support of a fellow student, the encouragement of one of the main scientists, or the friendly and hilarious remark of one the crew in the middle of the late watch, somehow we started to feel more at home. Delicious meals, free ice cream and chats with new friends were just some of the arguments to start to enjoy this trip. The view of multiple species of petrels and albatrosses soaring effortlessly in the cold wind above a dark blue sea added an exciting feeling of adventure.

With contagious patience and passion, Robert, Dave, Alan, Todd, Tom, Tina, Josh, Gilles and Ambrose, the instrumentation experts, invited us to participate on the long streamer deployment, adding “birds” to countless yards of the yellow streamer, which would unveil the secrets of the lower layers of this active part of the Ring of Fire ring that surrounds the Pacific Ocean. A photo in full deck outfit (hardhat, steel-toed boots, and lifejacket) could even turn into an unexpected birthday gift, something to brag about on your Facebook or Instagram account. With precise and coordinated actions, the crew deployed the streamer and switched to the more dangerous air gun deployments. With secure and brief instructions, all four air-guns arrays went off the stern and marked the true beginning of the cruise.

After the initial shock of getting used to strict meals hours and 4 hour watches, our bodies and minds started to grasp the true beauty of this research, and soon the first week onboard came to an end. A permanent internet link with family and friends connect us to the mainland until the strong sound of the returning seismic waves as we try to sleep reminds us that this truly is a different world. Yet the fact of falling asleep shows that we are no longer strangers on uncharted land…or sea.
As the days pass by, we comfortably approach the end of the first half of the cruise and “Life onboard” turns into just “Life.” We begin to understand that, as many have said before, “It’s not the Destination that matters, but the Journey itself.”

Seabirds illuminated by the setting sun.

The two main components necessary for seismic reflection data collection are the air guns and the streamer. The air gun array on the ship contains compressed air (a total of 6600 in³) which is fired off at about 2000 psi. The airguns fire at a set distance interval (either 37.5 and 50 meters for this cruise), which can be adjusted for each line, if needed. The energy from the air guns then travels through the water column, and reflects off the seafloor, or continues through the boundary and reflects off a different layer in the subsurface. These reflections travel back through the layers they penetrated, and through the water column once again. This is where the streamer comes into play. The streamer uses groups of hydrophones in spatial intervals to detect the reflected energy. Hydrophones contain piezoelectric crystals, which detect changes in pressure. The groups of hydrophones detect the signal, then average it for the group, and send it back to the computers on board the ship. There are 1212 channels detecting pressure changes, and the streamer is 15 kilometers (about 9.3 miles) long.

The air gun arrays and streamer can be set to the desired depth (currently 9 and 10 meters, respectively). The air guns are kept afloat by buoys on the surface, and their depth is determined by ropes and metal chains that connect them to the buoys. The streamer is kept afloat with foam inside the tube, and with depth-controlling devices placed periodically on the streamer, called birds. The birds are used to adjust the depth of the streamer while it is in the water, and have wings that are controlled by the onboard computing system and can be directed to move the streamer up and down.  If a big ship is about the steam over the streamer, the birds can be directed to dive.

 

 

 

 

 

 

 

 

 

— Kelly Olsen and Brooklyn Gose

Pictured above are various members of the Scientific Party. All scientific efforts on board are made possible by this wonderful group of people. The technical crew, led by the Chief Science Officer Robert Steinhaus, is in charge of all seismic acquisition hardware and software, including deployment of seismic gear as well as handling the large amounts of data brought in from all instruments. The Chief and Co-Chief scientists are responsible for designing the project, creating a viable project proposal, applying for necessary grant funding, and successfully guiding the project into fruition. Data processors work day in and day out to process data as it is acquired, allowing the science party to view the preliminary images and discuss what we see as we continue with the project. Graduate students are brought on the cruise to learn about the types of data they work on through hands-on experience. Each are assigned a watchstander shift, during which they are in charge of logging navigational information and important mishaps that may occur during acquisition, along with observing and learning about the details of marine seismic acquisition by helping with deployment of instruments and monitoring of instrument software. Finally, Protected Species Observers (PSO’s) accompany the science party on the cruise in order to ensure the experiment does not negatively affect protected species such as pinnipeds, dolphins, sea turtles, and whales. These hardworking people provide the skills necessary to collect high-quality data which will help improve our understanding of earth systems. The collaboration of such minds ensures the efficiency and safety of the cruise, allowing science to take place and learning to continue!

— Compiled by Brooklyn Gose

“CEVICHE “es el nombre del proyecto, el cual representa un esfuerzo de colaboración entre científicos de la universidad de Texas en Austin, Universidad del estado de Oregón y la Universidad de Chile.

En estos momentos nos encontramos a bordo del R/V Marcus Langseth, barco de investigación americano, sustentado por la fundación nacional de ciencias y operado por el observatorio Lamont-Doherty, ambos en Estados Unidos.

Nuestro objetivo es realizar perfiles de la estructura del margen continental, en el segmento costa fuera de Chile central-sur, un recorrido de 1400 km, el cual incluye la región de Illapel (afectada por el terremoto del año 2015), terremoto del Maule (año 2010) y Valdivia ( año 1960). Este proyecto nos dará un mejor entendimiento de las características en los límites de las placas tectónicas, en las zonas de subducción, donde la acumulación de grandes cantidades de energía, y eventos de deslizamiento que se propagan por una gran área sin encontrar barreras, lo que produciría terremoto de mayores magnitudes. Nuestro objetivo general es identificar las características de las estructuras de la tierra, las cuales pueden ser comparadas con observaciones antes realizadas, durante y después de grande terremotos, para así poder tener una mejor imagen y entendimiento de los procesos físicos que llevan a que se produzcan estos terremotos de mayores magnitudes. Este estudio nos mostrará un conocimiento de modelos más preciso y detallado que nos podrá ayudar a anticipar terremotos de grandes magnitudes en las zonas de subducción en los márgenes de Chile, así como en otros lugares.

El día 9 de Enero, antes de dejar el puerto, tuvimos la suerte de ser anfitriones de distinguidos visitantes, en los que se incluía la presidenta de la república de Chile, Michelle Bachelet, el presidente de la fundación chilena de Ciencia y el embajador norteamericano en Chile. Tanto la tripulación como los científicos y los líderes técnicos del proyecto Ceviche discutieron los objetivos del crucero destacando los instrumentos que se utilizarían en este proyecto.

Para más información, se pueden dirigir a el siguiente enlace http://impresa.lasegunda.com/2017/01/13/V/fullpage#slider-8.

Luego de recargar combustibles a las afueras de la costa de Valparaíso, comenzamos nuestra travesía en la tarde del 11 de enero.

Los invitamos a volver a este blog, el cual se estará actualizando constantemente con más información de lo que vayamos aprendiendo.

This cruise represents a collaborative effort between scientists from the University of Texas at Austin, Oregon State University and the Universidad de Chile. We are currently on board the R/V Marcus Langseth, a US research ship supported by the National Science Foundation and the operated by the Lamont-Doherty Earth Observatory.

Our goal is to image the structure of the continental margin along a 1400-km long segment offshore south-central Chile that includes the source region of the 2015 Illapel , 2010 Maule and 1960 Valdivia earthquakes to better understand the characteristics of the plate boundary that allow subduction zone slip events to grow into giant subduction zone events. All earthquakes begin small; a great earthquake occurs when the plate boundary remains locked long enough to accumulate enough strain in the adjacent plates to lead to a large amount of slip and when that slip can propagate over a large area without encountering barriers. Our overarching objective is to identify features of Earth structure that can be compared to other geophysical observations made before, during and after large earthquakes in order to better understand the physical processes that lead up to a great earthquake. This knowledge should result in more accurate and detailed models for interpreting ongoing observations in an effort to better anticipate great earthquakes in the Chile subduction zone and elsewhere.

On January 9, prior to leaving port, we hosted tours of the ship for distinguished visitors, including President Michelle Bachelet of Chile, the President of the Chilean Science Foundation and the US Ambassador to Chile. The ship’s crew and the scientific and technical leaders of the CEVICHE science party discussed the objectives of the cruise as well as highlighting the tools to be used for this project. For a discussion of cruise objectives in Spanish, see http://impresa.lasegunda.com/2017/01/13/V/fullpage#slider-8. After refueling while at anchor off Valparaiso, we got underway on the evening of January 11.

We invite you to return to this blog as we add posts about life at sea, who we are, what we are learning.