(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.