Mentawai Gap—Tsunami Earthquake Risk Assessment (MEGA-TERA) Cruise Log
The Mentawai Gap — Tsunami Earthquake Risk Assessment (MEGA-TERA) project is a scientific expedition that aims to investigate the cause of tsunamis in the seismically active zone west of Siberut Island, near Sumatra.
Known as the Mentawai Gap, this is the only area of the Sumatra-Andaman subdution zone that has yet to release built-up tension, which could cause another potentially devastating tsunami not unlike the 2004 Indian Ocean tsunami. One of the scientific objectives of this expedition is to assess the tsunami hazard posed by this fault zone, and subsequently, help communities living in the affected areas to better prepare for such geohazards.
Co-led by Professor Paul Tapponnier, visiting Professor Satish Singh from Institut de Globe du Physique du Paris, and Dr. Nugroho Hananto from the Indonesian Institute of Sciences, this marine geophysics expedition involves state-of-the-art technologies such as high-resolution seismic instruments. Schmidt Ocean Institute’s research vessel Falkor is fitted with these high-tech scientific systems.
Schmidt Ocean Institute supports oceanographic research and technology development at sea by providing scientists with access to the research vessel Falkor through an open-call for research proposals every December. The MEGA-TERA expedition was a successful project that has gone through non-conflicted expert review.
Read more updates on the expedition via the MEGA-TERA cruise log below, or at Schmidt Ocean Institute's cruise log here.
June 20, Saturday
MEGATERA Final Video
As the MEGATERA expedition comes to a close, explore behind-the-scenes footage, watching the scientists and crew in action, and sharing their excitement in new discoveries.
Video by Mónika Naranjo González
June 24, Wednesday
Ten scientists, 24 hours a day, 7 days a week, over 32 days - A lot of time, knowledge and effort have been invested on our MEGATERA expedition, which has now come to an end. 17,597 square km of high-resolution bathymetry have been acquired, along with 2,665 km of seismic reflection profiling.
The Wharton Basin, the 2007 and 2010 earthquake epicenters, and the locked Mentawai patch were all part of this extensive geophysical experiment. It will take a few years for all of this data to be processed and implemented into hazard mitigation plans, but some very promising results are already showing.
The team found many active faults at the Wharton Basin with different orientations, suggesting that the whole area is deforming on different scales. This area was the site of the largest intra-plate earthquake ever known, and the strongest aftershock. It was such a powerful event that before it, scientists did not even believe such an earthquake was possible. The Wharton Basin is under enormous stress due to the continental collision taking place up north, and of course the Sumatra-Andaman subduction zone to the east. The deformation it presents will certainly be a source of discussion and learning in the scientific community.
West of Siberut Island lies the Mentawai Gap, a locked patch of the Sumatra-Andaman subduction zone that has not released its stored energy for over 200 years. This leads the experts to believe that a powerful earthquake will eventually originate here. Seismic images acquired during the expedition showed active faults near the Sunda Megatrench, both on the subducting and the overriding plate. A detailed analysis of this data will allow the scientists to better constrain the nature of a tsunami produced by an earthquake in this region.
Sharing the information
On the 22nd of June, 2015 R/V Falkor arrived in Padang, Sumatra, marking the end of an intense expedition. Padang was also the place for an outreach event in which the information and lessons learned so far were shared with students, media and local authorities. Different groups visited the research vessel throughout the day, and were invited to look at some of the images produced, as well as ask questions to the scientific party.
In the Padang area alone, more than half-a-million people reside less than five meters above sea level. There are over seven million people living along the central and southern coasts of Sumatra and the Mentawai islands. The findings produced by the MEGATERA expedition and subsequent application on tsunami mitigation plans will certainly translate into better quality of life for these communities.
The better the information that Sumatran communities and authorities have, the better mitigation plans there will be. TodayR/V Falkor sails through the Indian Ocean again, approaching its next destination. But the data produced will remain in Sumatra forever, providing deeper insight on the secrets of the ocean’s floor and empowering communities and authorities to better prepare.
Written by Monika Naranjo Gonzalez
June 20, Saturday
A Scotsman Onboard (or the Relevance of the 80's to MEGATERA)
Most people of my generation will think of something slightly different than a research vessel upon hearing the name “Falkor.”
Falkor is the luck dragon from the German fantasy novel The Never Ending Story - Research Vessel Falkor is named after this character. If you have the chance to visit the ship, you will notice several passages of the book inscribed on its walls. There are many references to this story throughout the ship. I have to confess I have never read the book - but I have seen the awesome 80's movie version (which despite its name does have an ending). You should also check out the incredibly cheesy and catchy song of the same name.
Anyway, I digress - in a previous blog I described a typical work shift at night. Today I thought I would share some of the other recreational things that may occur onboard of R/V Falkor.
As I am working on the nights watch it is a bit difficult to say when my day starts. I guess it would be around 5pm, when I usually get out of bed. I swiftly head up to the monkey deck to get a bit of fresh air and sunshine and occasionally chill out on the hammock and take in the sunset. That is right, my sunrise is the sunset.
After that it is down to the mess hall for dinner... actually, it is technically breakfast. The chefs cook up some delicious food, although it can be slightly strange having a full course meal with your morning (evening) coffee.
After dinner (or is it breakfast?) I try to relax a bit visiting the staff lounge (I am very proud to announce that I am currently undefeated in both FIFA and Tekken… just thought you should know).
I will often get to the gym before starting my shift. A bit of advice for anyone, trying to run of a treadmill on a moving ship can prove to be difficult! But you can get used to it with time, just try to avoid doing so when R/V Falkor has reached the end of the imaginary line through which it scans the seafloor, because at that point it will begin turning and changing course… and so will you.
Every so often I will get together with somebody of the crew to do something a little different, such as a movie on the big screen, karaoke or even relaxing in a homemade pool on the fore deck. You might think I am joking, but last night we saw the stars on our own private pool. Let me tell you, the night sky, coming from someone who has been living in Singapore for a couple of years, is a rare thing to be able to admire. The milky way floated on top of us clearly while we listened to the bow break through the small waves. Perfection.
My watch begins at midnight and goes on until 8 in the morning. During my watch I have to mind all of the computer screens and regularly log the information they provide. I also spend a good bit of my time processing the bathymetry data that we have acquired while cruising over the imaginary lines I talked about before. Occasionally, I will write pieces for our online blog.
Time passes by quicker than you would imagine. Around 6am the sun starts to rise and I try to steal a few minutes to check it out. Science is amazing, and if you can have a good time with the people that are next to you while conducting experiments, life can be very nice indeed.
Written by Stephen Carson
June 19, Friday
The Women of MEGATERA
Being at sea is a way of life that most people do not get to experience. It is a unique way of life, and it is wonderful. By being on a ship in the middle of the ocean, you are very likely to see something you haven't experienced before.
That was certainly what drove Joyce Young to her line of work. 15 years ago she left her native Scotland, and since then she has not lived in the same place for more than a year. “It’s nice to have a job that travels with you,” she says. Her passion for the underwater environment took her from diving resorts to superyachts. But something was missing: she felt she was not giving back to the sea. Only a month ago she started working as a Stewardess onboard of a Research Vessel for the first time, feeling that through R/V Falkor her adventures at sea will have a new purpose: creating knowledge that could ultimately benefit the ocean.
Passion seems to be a constant amongst seafarers: passion for the ocean and the experiences that take place when sailing around the globe. Take Verena Neher, Purser on the MEGATERA expedition. After taking care of all administration and interior management affairs, she finally turns off her computer and steps ashore in order to go and explore the new city she has arrived in. She never has any time to plan ahead, so when she is walking around, she allows each new place to surprise her. After a few blocks, she is always amazed at the fact that she is somewhere completely new, free to make up her own mind about it and not having to take anyone’s word for it. “The horizon does not end at the borders of your country,” she declares with a smile.
It is clear that if curiosity does not guide your steps, you will probably never be tempted to sail. Thirst for knowledge made Hélène Carton’s path cross with R/V Falkor. Hélène is a geophysicist participating on the MEGATERA expedition. She is no stranger to the waters of the Indian Ocean, but she keeps coming back for more. “I think all subduction zones have the potential to surprise me,” she explains. “Here there was a belief that the plate that is sliding down was doing so peacefully. What we call aseismic slip. But it turns out that is not the case. So we have to come back and reexamine - question our beliefs on how subduction zones function”.
Curiosity also led Colleen Peters (Lead Marine Technician onboard) to study marine sciences and continue exploring possibilities to define the job that would fulfill her the most. “I like to understand how things work. Troubleshooting is a big part of my job—if something breaks you have to figure out why it broke and how to fix it.” That is why, when she heard of the newly-formed Schmidt Ocean Institute, she did not hesitate to get involved. “I like to be part of things that are new and developing, it’s much more interesting to figure things out than to do what has already been done,” she declares.
It is challenging working on a ship: constant motion, high humidity, high heat, often in the rain. It takes determination. The kind of determination that would make a 16 year old start studying to become a sailor in spite of being the only girl of her family, also the youngest, all the while her family calling calling her dream crazy. “I knew I wanted something different” says Sandra Faryna, Deckhand onboard R/V Falkor. “I wanted no boundaries, I wanted to travel, I wanted something special, I wanted to be someplace like the ocean.” Eleven years ago, she started studying to do just that. “If I did not enjoy it, I would not be here. It’s as simple as that. I like being a Deckhand,” she says, filled with a seafarer’s determination.
Days turn to weeks, months, even years. Friends are the family you choose and that is certainly true onboard of R/V Falkor. This brings comfort to Shiella Bonita, Stewardess. She knows that saying goodbye to her son back in the Philippines in order to embark on a new expedition is never easy, but being greeted by people she has become very close with makes it much better. “I’m also very afraid of rough weather,” she confesses “but I love meeting new people and traveling to different places. If the waves are high or the work is difficult, everybody here helps each other”.
The sea may be calm. But the sense of an ongoing adventure when sailing through it never disappears. Frédérique Leclerc does not miss a sunset, or a sunrise. Sitting on R/V Falkor’s forecastle, she takes it all in. She refuses to take nature for granted. As a little girl, during a school fieldtrip to Massif Central in her native France, Frédérique realized what her passion was. Years later she became a tectonics expert. Her journey has led her from Martinique to Singapore, to R/V Falkor’s current expedition, off Sumatra, a mythical part of the world for young scientists. She laughs while she confesses that, in her line of work, just hearing the word “subduction” summons excitement; “subduction plates are linked to big earthquakes and active volcanoes, and we have a love for them.”
The key common thread amongst R/V Falkor’s women is an intense curiosity to understand the world around them, and a passionate desire to explore beyond the confines of shore-based normality. While it isn´t an easy life for them, the rewards and the knowledge that they are making a contribution to our understanding of the oceans outweigh the hardships. Not one of them would give it up without a fight.
Written by Monika Naranjo Gonzalez
June 18, Thursday
Prior to R/V Falkor’s departure from Singapore towards the Wharton Basin and the Mentawai islands, much was discussed about what could be found under the waters of the Indian Ocean. But Dr. Satish Singh was more interested in the unknown, and less intrigued by what they knew could be found. “That is how science is done, and how discoveries are made,” he said.
Sure enough, as data traveled from the depths of the ocean to the screens on the Science Control Room, surprises started to emerge. This is the most seismically active region on our planet, and still the scientific team did not expect to find the kind of mass wasting that they have witnessed.
In order to understand what mass wasting is, you may think of landslides. Geological structures are continuously fighting against gravity. But no matter how strong the mountain is, gravitational pull is constant, so when something changes the mountain’s ability to resist it, some material will precipitate to lower heights.
Mass wasting is a natural process that occurs in both mountains and seamounts - that is, it happens on underwater mountains as well.
The role of earthquakes
Mass wasting can be accelerated by external factors, such as earthquakes.
The violent shaking during an earthquake has the potential to break off sections of mountains or hills, causing them to slide down the slope. What remains is a geological structure with some evident erosion on its sides and debris at the bottom of it. The mountain will no longer rest at its angle of repose, it will be much steeper and vulnerable.
So if the scientists onboard of R/V Falkor already expected to find seamounts under these waters, and they knew that this area is under constant seismic pressure, what was the surprise?
The amount of mass wasting is astonishing. “We need time to process the data and understand if these are old geological structures,” said Dr. Singh, “but they look fresh to me. What this could mean is that these mountains are deteriorating at a higher pace than the natural erosion process.”
Combined bathymetry and seismic reflection data will not be enough to determine the age of these seamounts. But the observations open the door for interesting scientific discussions. In the future, measuring the pressure on the slope’s sediments and taking samples from the seafloor will help determine the precise age of the structures.
If the scientists find that the structures are old, then they might conclude that earthquakes are not to blame for the amount of mass wasting observed. But the images in the Science Control Room’s screens depicting seamounts that present “normal” erosion shapes sitting next to steep inclinations that look as if they had been cut with a knife seem to suggest that a lot of these landslides are the product of strong shaking all the way to the subduction front itself.
“This is beautiful,” says Dr. Singh. “Even if we cannot conclude anything just yet, these are very interesting observations.”
Written by Monika Naranjo Gonzalez
June 17, Wednesday
A Lighthearted Metamorphosis
“You are in my way, Pollywog!” said the Shellback menacingly. The Pollywog working at the Science Control Room had no option but to acknowledge its lower rank and move away. Science is still taking place onboard of R/V Falkor, but something else has been lurking inside the vessel. Suspicious smiles, concealed fishing nets, murmurs and costumes had all paraded briefly at some point or another during the past few days. And today, the Line Crossing Ceremony finally took place.
As R/V Falkor sailed from Singapore towards the Wharton Basin, it cruised through the Equatorial line, thus activating an unstoppable machine: the commemoration of a sailor’s first crossing. This tradition is thought to have been born to boost morale among seamen, but it could also be a test to ensure that new shipmates are capable of enduring the ocean’s rough conditions.
King Neptune himself honored R/V Falkor with his presence, conducting a thorough investigation dictating proper challenges that each Pollywog – sailors who have not crossed the Equator – should overcome in order to be deemed worthy of becoming a trusty and honorable Shellback.
The clock strikes 4
It was business as usual: The multibeam echosounder was gathering high definition bathymetric data while the seismic source sent waves to the seafloor. But then R/V Falkor’s speakers announced Neptune’s arrival, and he wasn’t alone. His wife Thetis was with him. Everyone was expected at the foredeck at once and every single one of the 20 Pollywogs went through the ceremony to receive a proper Shellback name.
Shellbacks at last!
Pollywogs no more, the newly initiated Shellbacks marveled at the greatness of being an honorable member and a celebration was in order. Now all onboard R/V Falkor can take comfort on the fact that every single one of them is qualified to sail the seven seas under the approving gaze of King Neptune himself.
Written by Monika Naranjo Gonzalez… A.K.A. Shellback Flying Fish
June 16, Tuesday
Tsunami Warning Systems
In a previous blog, we talked about the recent hollywood blockbuster San Andreas, and went on to describe the events that would likely occur if a large tsunami-generating earthquake took place in the Mentawai gap. Unlike the movies, in reality we do not have a big action star to save the day.
We are on our own when it comes to disaster mitigation, so the best way to prepare is improving our understanding of underwater earthquakes and their relationship with tsunamis. Applying that knowledge to the development of early warning systems is part of the strategy.
Tsunami early warning system
The 2004 Indian Ocean earthquake and tsunami took the world by surprise. In the aftermath, the international community came together to design an effective early warning system for this region: GITEWS (German Indonesian Tsunami Early Warning System) was born. Designed and installed during the course of several years, it was handed over to the Indonesian government to run and maintain from 2010 onwards.
How does it work? How can we know if a tsunami is approaching the coast? Over 300 sensors have been installed across Indonesia including seismometers, GPS stations, tide gauge stations and buoys. A warning center located in Jakarta runs non-stop, receiving data from all sensors. In the event of an earthquake, the early warning station receives multiple signals via satellite.
The data would then enable the staff at the station to determine:
- The location and strength of the quake,
- The rupture that caused the seismic vibrations and if there has been vertical movement in the sea floor, large enough to cause a tsunami,
- Tsunami detection through tide gauges and buoys with GPS signals that are able to detect changes in sea level.
The system is designed in such a way that the data can be received, processed and applied on a decision in under 5 minutes post-earthquake. The experts are then capable of choosing wether to issue a tsunami warning, and if so, which are the most critical places to warn.
R/V Falkor‘s contribution
Bathymetry has a huge effect on the propagation and height of tsunami waves. Computer programs are used to model flooding scenarios, and accurate bathymetry is key to producing reliable forecasts. The large amounts of high resolution bathymetric data being collecting onboard of R/V Falkor will certainly improve the results of such inundation maps.
Knowledge, information and education
It has been calculated that in the event of a tsunami generating eearthquake in the Mentawai gap, the first wave would reach the islands in 5-10 minutes and mainland Sumatra in 20-30 minutes. Even with an effective warning system in place, the window for reaction is very narrow. This is one of the reasons why education and outreach can be a vital component in tsunami defense.
As the MEGATERA expedition nears its completion, the experts onboard prepare to process the data and are confident that its application will add true value to the quality of life of coastal communities in Sumatra.
Written by Stephen Carson
June 15, Monday
When Corals Tell Stories
R/V Falkor is sailing above the Sumatra trench, filled with structures ready to trigger earthquakes and tsunamis. A key question to develop hazard mitigation strategies is to discover how often those structures break. Some of the clues to answer that question come from unexpected sources.
A group - led by Dr. Kerry Sieh and including scientists from EOS, LIPI and Caltech - has been searching more than 15 years for answers. Looking for the trace of past-earthquakes, they try to determine how strong and how frequently earthquakes can take place along this plate boundary, but there are no written records that could report earthquake occurrence.
Along the Sumatra subduction zone, and particularly in the Mentawai archipelago, the team is looking for a special marker of earthquakes: corals!
Not just any coral
Indeed, some corals, called micro-atolls, have the particularity to grow all the way up to the sea surface, their upper flat top constituting a marker of the sea level at the time of growth.
This marker is very useful to track sea level variation through time: if the coast subsides, the relative sea level will rise and the micro-atoll will grow upward, in a cup-shape. If the coast is uplifted, the relative sea level will drop, the exposed part of the coral will die and the immerged one will continue to grow at a lower level, so the micro-atoll will have a hat-shape.
How are corals and earthquakes linked? The Sunda and Indian plates are continuously converging, but the two plates can get locked at the plate boundary. When the accumulated stress is strong enough, an earthquake has to take place in order to release it. As the two plates slide against each other, the upper-plate is free to come back at its initial position and is consequently suddenly uplifted. This alternation of subsidence and uplift stages is known as the seismic cycle.
The Mentawai islands offer us unique characteristics to facilitate the reconstruction of earthquake history here. They sit above the locked part of the subduction zone and are located between the tropics, which enables them to grow coral micro-atolls. By studying the shape of the corals, we can infer what has been going on in the past.
By studying micro-atolls along the coasts of the Mentawai islands, Dr Kerry Sieh, Dr Belle Philibosian and colleagues were able to discover the trace of earthquakes as far back as 465 BC!
They showed that at the Mentawai islands, the subduction breaks every 200 years in multiple big events of a magnitude between 7 to 8, like the 1797 and 1833 historic events of the last cycle. In 2007, a sequence of earthquakes in the Mentawai announced a new cycle, but enough stress to produce a Mw 8.8 earthquake is still to be released.
The Big One is yet to come
A peculiar micro-atoll, found on Pagai Island is suspected to be proof of a previous tsunami earthquake and its study indicates that the 2010 Pagai tsunami earthquake, even if it generated considerable destruction, is unfortunately not the big one and stronger earthquakes are to be expected in the coming years.
As corals do their part to reveal earthquake and tsunami history, R/V Falkor continues to acquire high-definition data to locate and study possible tsunami generating sources and their strength, which will help better estimate tsunami hazard along the Mentawai and Sumatra coasts.
Written by Frédérique Leclerc
June 14, Sunday
MEGA-TERA Cruise, Week 4 video
See where (and how) the team on R/V FALKOR has been gathering seismic data on the #MEGATERA cruise.
June 14, Sunday
This past month the movie San Andreas, starring Dwayne "The Rock" Johnson was released in cinemas worldwide. The movie speculates on the catastrophic events that could take place if the San Andreas fault in California was to rupture. Although undeniably entertaining, the science in the movie has its faults.....sorry. For example, a strike slip fault on the continental crust is not going to cause a large tsunami, like the one pictured.
In light of this recent film, we have put together our own what if scenario regarding a future earthquake and tsunami in the Mentawai islands. This scenario is based on a report conducted by EOS and LIPI (Link Here), so it is a lot more accurate than San Andreas....although unfortunately it does not star The Rock!
In 2009, a Mw earthquake struck near the Mentawai islands, causing intense shaking, damage and loss of life in the islands as well as the mainland coastal city of Padang. Although a tsunami warning was issued, the earthquake did not cause a tsunami. The earthquake ocurred at depth, on a fault 85km below the sea bed, leading to little uplift on the sea floor and therefore, no tsunami.
Imagine a scenario in which a shallower and higher magnitude earthquake occurs in the same area as the 2009 earthquake, causing a tsunami. What can we expect to happen?
How high would the tsunami be?
The first wave would likely reach the Mentawai Islands 5-10 minutes after the earthquake. This would be followed by the first wave reaching the west coast of Sumatra around 20 to 30 minutes after the earthquake (times calculated by knowing the average speed of tsunami waves and distances to locations).
How high would the tsunami be? How far would it reach?
The height of a tsunami and the distance that it would reach inland can vary greatly along a coastline. This is because offshore bathymetry and onshore topography can also vary greatly, offering different obstacles to the incoming mass of water. Exposed, low lying areas tend to be the places where inundation is greatest and it is common for water to advance several kms. Bathymetry can greatly affect wave heights, areas with steeper continental slopes are more likely to produce larger waves. It is likely that wave heights would range from 5-15 or more meters in the Mentawai Islands to 5-11 or more meters in Padang.
Would the first wave be the biggest?
Probably, but maybe not. The earthquake would cause multiple waves covering a time span of at least 3 hours. During this time there would be a few large waves (as well as several smaller ones), so the first might not always be the biggest.
Would the sea water recede before the first wave arrives?
Contrary to popular belief, the sea does not always recede before a tsunami wave arrives. This phenomenon known as "drawdown" only occurs when the trough of the wave arrives at a coastline first. If sea water does recede then the first wave would be expected in minutes, so it would not provide much warning and therefore should not be used as an early warning sign.
How likely is this scenario?
Padang has past experience with tsunamis: both the 1794 and 1833 earthquakes caused tsunamis which struck the city. The 1794 tsunami was so powerful that a 150-200 tonne sailing ship was swept 1km onshore.
Sieh et al, 2008 proposed that the 2007 earthquake in the Mentawai patch was just the first in a series of larger earthquakes in the area. This areas previous recent history with past earthquakes and tsunamis suggests that its just a matter of time until a scenario like this occurs.
In order to better prepare ourselves for a scenario like this we must conduct further research into the geology and geophysics of the area. The detailed seismic and bathymetry data we aquire on this expedition provides an excellent opportunity to learn more about the geological history of the region. By acquring further knowledge about past events, we can better prepare ourselves for disasters in the future.
Written by Stephen Carson
June 11, Thursday
Streaming Exploration with Sound
R/V Falkor slows down to 2 knots. At this speed, the gentle swell that has accompanied the expedition from the start cradles the ship. At the aft of the vessel, everyone involved in the deployment of the seismic reflection gear is wearing safety gear, while at the bridge the officers monitor the procedure and keep a steady course.
First things first
A 1200 meter streamer, filled with 96 hydrophone clusters – called channels - rests on a winch. The streamer loads in first, and the whole deployment will take about an hour. “It’s a pretty straightforward process” says Anthony Deebank, from the SALT –Sea and Land Technology – team.
The tail buoy is attached to the streamer - its primary function is to drag the heavy equipment as it is released into the water. Once the streamer is up and running, the GPS system installed on the buoy will provide information on the streamer’s position, which will be later used when the data collected is being processed.
Every 300 meters orange wings slide away, hooked to the streamer. “Those are the birds,” explains Deebank, while attaching weights onto the equipment at designated positions. “They help to stabilize the streamer.” The combination of the birds and the weights will help keep the streamer at roughly 4.5 meters of depth.
Think of everything
The scientists request that the streamer floats at a specific depth. The depth will determine in which segments of the frequencies recorded they will be likely to find “ghosts,” or holes in the data.
Water salinity and temperature play a role. If the water is cold, the equipment will tend to float more. Likewise, the greater the salinity, the greater the buoyancy. By using a series of charts, the SALT team determines just how much weight must be attached to the gear.
Nothing is left to chance, and now that the whole length of the streamer is being trawled by R/V Falkor, it is time to deploy the main attraction.
An air-gun will create sound waves that travel to the bottom of the ocean and return to the surface after bouncing on different layers of the subfloor.
Deploying the seismic source takes an extra half-an-hour. Now R/V Falkor increases its speed to 4 knots, and keeps it constant. The air-gun creates waves every 25 meters, and once those waves are picked up by the hydrophones on the streamer, images begin to appear on the screens of the Visual Matrix.
The seismic reflection equipment will remain afloat, working day and night with only a few brief respites, whenever the constant vibration demands some swiftly served maintenance.
Written by Monika Naranjo Gonzalez
June 10, Wednesday
“We knew they were going to be there. But we didn’t know how many we could find, their actual length or exactly where they would be located. We just didn’t know how beautiful they would be!” says Dr. Hélène Carton. For two days, R/V Falkor has traced past earthquakes in the depths of the Indian Ocean west of Sumatra. The trail is not subtle.
The scientific team designed the imaginary lines that guide the way based on previous surveys conducted in the area, so when normal faults began to emerge, it was not their presence what surprised them, but the quality of the data that appeared on their computer screens.
“You have to understand what a challenge this is. To see these scarps at such depths!” Dr. Carton continues, “Particularly with this level of resolution. Yes, some dramatic scarps had been found before at subduction zones, but at depths of about 2000 meters. We are working here at about 6km and the information we are getting is extremely detailed.”
It would be a logical guess that the faults are named “normal” because the experts onboard expected to find them in this area. But the fact that the team refers to them as “normal faults” has nothing to do with how predictable their presence may (or may not) be.
There are different kinds of faults. The direction in which the blocks of seafloor move along the fault is the reason the faults are termed “normal.” In this case, fault is not a vertical line; it instead is a diagonal break, creating two parts: the plates are pulling apart, and the block with an overlapping layer is moving downwards. The two walls on the flat are named the “hanging wall” which is located above the fault plane and the “footwall,” which is under the fault.
So why are they here? As the Indo-Australian plate moves under the Eurasian plate, it bends. Not far from the trench itself, the bending reaches a tipping point in which some fractures are formed, just as if you took a chopstick and started to bend it. At some point, where the curve is most pronounced – called the outer-rise by scientists - the chopstick will break.
Which is convenient enough, because as Dr. Carton puts it, the underlying plate is preparing to be swallowed by the overlaying plate, being chopped into smaller pieces.
“Earthquakes are just like people,” says Dr. Shengji Wei, a seismologist from the Earth Observatory of Singapore, “They have their own personality, and intra-plate earthquakes tend to be the meanest”.
When the bending reaches a tipping point and the ocean floor fractures, it causes an earthquake. But as Dr. Wei points out, intra-plates ruptures lack the lubricant that sediments between moving plates can provide. Here, at the interior of the plate, the floor simply cracks, creating violent shakings.
“Even if the magnitude of these kinds of earthquakes tends to be smaller,” explains Dr. Wei, referring to the difference between the 2010 7.8 intra-plate earthquake and the 2004 9.3 megathrust earthquake, “Their rupture happens very fast and hence the seismic waves can be much stronger.”
Considering that the vibrations would be powerful, and that the amount of movement on the seafloor could be substantial, the possibility of big tsunamis is present, just like in 2010.
So as the sun sets again, the team has decided to extend some of the lines over the normal faults, following the fresh trace of angry earthquakes.
Written by Monika Naranjo Gonzalez
June 9, Tuesday
As night falls, lighting flashes over R/V Falkor and for an instant, it seems to be day again. The Indian Ocean has been very pleasant so far, but as we are in the tropics, rain and thunder are no surprise.
During World Ocean’s Day, we have reached the western coast of Sumatra and sailed overnight to get to our first survey location over the Mentawai gap.
Rain pours down all night long. But as the sun rises, clouds scatter and the ship’s outer decks begin to dry. Just in time, as R/V Falkor has reached its destination and it is time to get busy again.
New game plan
The lines are agreed upon and drawn by the scientific team. Over the daily morning meeting at the bridge, the final details are confirmed. Our targets over the next two weeks will be 26 imaginary lines, running parallel to the Sunda Megathrust – the place where the Indo-Australian and the Eurasian plate converge. The lines will guide R/V Falkor’s way, as we collect detailed seismic reflection profiles along their paths.
Early in the morning all the teams are ready. The crew assists the scientific team in the deployment of the seismic source and the streamer while in close communication with officials at the bridge. In the Science Control Room, the different screens show maneuvers and provide data on the status of the equipment. Soon after, the data gathering resumes.
Seismic reflection profiling provides accurate images of the subfloor structure - for a very thin segment of the ocean floor - down to a depth of around 2Km. This information is key to detect geological features such as active faults or past seismic event’s signatures.
At the same time, R/V Falkor´s multibeam echosounder is scanning the ocean bottom with a much wider scope, offering a high-resolution view of the existing underwater relief. Bathymetry and seismic reflection go hand-in-hand to deliver breakthrough information on the locked patch of the subduction zone.
The seas west of Sumatra guard many secrets. To unravel them is a puzzle, but one that the experts onboard enjoy. The challenge keeps Dr. Hananto, co-leader of the MEGATERA expedition, motivated: “We have to push ourselves; if we’re not open-minded then we can get stuck. We won’t be able to get anywhere. We have to look at all the details available to us and create something deeper than what we already know.”
Dr. Singh agrees: “Discoveries are made when you go where no one has gone before!” he declares. “Yes, it is not easy to get here, it takes a lot of effort, but in the end it will be worth it of course.”
Written by Mónika Naranjo González
June 8, Monday
Follow the tide
“I wouldn’t really say that any day at sea is particularly normal,” says Colleen Peters, Lead Marine Technician onboard of R/V Falkor´s MEGATERA expedition, as she talks about the changing nature of oceanic expeditions. “Despite our best efforts, anything can happen and we have to be prepared.”
When it comes to working at sea, plans must be carefully drawn but adjustments are to be expected. “One discovery or event can change the whole experiment. There has been times I have had to redesign a whole experiment at sea, and made a major discovery,” declares Dr. Satish Singh. This point has been particularly true for MEGATERA, as the expedition has followed the tide.
At the center of the action
The Wharton Basin is a tectonic area closely intertwined with the subduction zone next to Sumatra, the expedition’s original objective. What happens at the subduction zone might impact this zone, and vice versa. The 2004 great Indian Ocean earthquake activated faults on the Wharton Basin, for instance.
“The Wharton Basin is the most active intra-plate deformation zone on Earth,” said Dr. Singh, co-leader of the MEGATERA expedition, at the daily scientific meeting. He went on to explain how little is known about its recent seismic behavior: a magnitude 8.6 strike-slip earthquake, thought to be impossible in intra-plate zones, followed by a magnitude 8.2 aftershock.
And there, at the epicenter of that massive aftershock - just outside of Indonesia’s EEZ - is where R/V Falkor conducted a series of bathymetric and seismic reflection surveys over the last two weeks.
Solve the puzzle
Working on the Wharton Basin was not just an educated guess. Dr. Singh has already developed an independent proposal to carry out marine studies in this area, “It was on obvious target for us but we were still very surprised by the discoveries we’ve made,” points out Dr. Singh.
Pull-apart basins at fracture zones, active faults, underwater volcanoes, even a meandering canyon, have all appeared on the screens of the Visual Matrix. “The data we’ve collected so far will allow us to solve the maze-type structure of the 2012 great earthquake ruptures, and provide insight about the deformation in the Wharton Basin,” declares Dr. Singh. It seems the deformation in the Wharton Basin is more widespread than previously recognized, possibly allowing to address a first order generic problem in earth science.
On our way
“It has been like two expeditions in one,” explains Frédérique Leclerc, a tectonic scientist onboard. “Another advantage is that we have become very familiar with the quality of the results yielded by the multibeam echosounder, which is great, so we know that we can be even more ambitious on our Mentawai exploration”.
R/V Falkor is now sailing parallel to Sumatra’s west coast, on its way to the Mentawai gap. This particular area of the subduction zone has not released its stored energy in over 200 years. Scientists suspect an earthquake with a magnitude higher than 8 could originate here.
Well inside Indonesia’s EEZ and with all of the necessary permits at hand, the second half of the MEGATERA expedition has been delineated with greater detail, thanks to the clues provided by the depths of the Wharton Basin.
Written by Mónika Naranjo González
June 7, Sunday
A Day Onboard
As the MEGATERA criuse proceeds, the workflow and roles of crew has become second nature. The video above gives an inside look at how daily operations function onboard R/V FALKOR.
June 6, Saturday
Those in charge of keeping the night watch must first take an oath.
Not really. But they like to joke about it, because the night watch can get pretty exciting and we seem to have many Game of Thrones fans here on board R/V Falkor.
Night gathers, and now my watch begins…
The main job of the scientists on the watch is to log the bathymetric and seismic data collected every day of the MEGATERA expedition - and there is a lot of data! In addition too logging data, they also note any interesting geological features that they come across, such as faults and channels.
The science control room on board the R/V Falkor houses all of the data experts have collected. The new readings can be viewed on a series of monitors displaying bathymetry, navigation, seismic information, and many other relevant indicators.
It can initially be quite an intimidating sight: there is a lot of information on display and it can seem overwhelming. However, the team soon finds a rhythm working with the equipment and software, feeling at ease with the workflow. Before they start collecting data, they mark out lines (paths) for the ship to follow. The lines R/V Falkorfollows can change at a moments notice, depending on what kind of features they come across. This is why it is so important to always have an alert eye on watch as the course could be changed at any time.
I am the watcher on the walls…
Another job of the scientists on watch is to prepare for the unexpected.
Say, a rogue fishing boat that comes very close to crashing into our streamers. This actually happened 2 nights ago.
The adventure started when the scientific team received a call from R/V Falkor’s bridge informing them about an unresponsive boat that was heading our way. The crew tried to make contact with the boat in both English and Indonesian, to no avail. It was pitch black, 3 am. The only things barely distinguishable were the location lights on our ship and on the buoys at the end of the streamer.
This was quite a surprise, since we were in the middle of nowhere and had not seen another boat for days. Fearing the worst, the crew decided to alter the course to avoid a collision with our streamers, which stretch back 1200m. The night watchers anxiously followed the navigation displayed onscreen as the boat got closer and closer. A huge sigh of relief filled the Science Control Room when it finally missed our streamers.
For this night and all nights to come
The watch can be a pretty challenging job, as it requires constant attention. The night watch, from midnight till 8am can be especially tough, although the team does play some music to keep us going.
But then you come across a feature like a fault, channel or seamount. To discover and see something that no one else has ever seen is a truly exciting experience. It is these sights that keep us motivated and drive us on to make further discoveries. Then the watch - and the oath - are completely worth it.
Written by Stephen Carson
June 5, Friday
“The quality of the data is great,” announces Dr. Singh at the daily morning meeting on R/V Falkor’s bridge. For days, the ship has been navigating slowly, at just over 4 knots, while meticulously obtaining detailed imagery of an enigmatic portion of the Wharton Basin’s floor. This exercise translates into more than 530 Km of seismic reflection profiles and over 5250 Km2 of high-resolution bathymetry.
Bathymetric data acquired in real time gives the scientific team invaluable insight on where to focus their efforts. At first, the success was moderate: faults appeared where the experts expected them to be, therefore taking them closer to proving their theories. But now those clues have guided them further, in unexpected directions, and active features such as faults or gas chimneys have been identified.
“You think you can see it clearly, but as you come closer it’s either not there or it’s something different,” Dr. Singh says, referring the mysterious quality of this area. No one has been able to decipher, let alone prove, why the lithosphere of the Wharton Basin would rupture the way it did in a complex magnitude 8.6 strike-slip earthquake. The theories presented to explain the 2012 earthquake have all been like a mirage – possible from afar, but disappearing when carefully examined.
“Seismological studies have shown that the magnitude 8.6 earthquake rupture was complex, possibly involving multiple segments of a near-orthogonal conjugate network of faults,” points out Dr. Hélène Carton. This means the Wharton Basin’s floor may have ruptured in several perpendicular directions. The problem, she declares, is that there is no field evidence of such orthogonal faults, and experts are not even sure that faults can really spread like that.
A Basin Within the Basin
No one saw it coming. No one thought that the 2004 Indian Ocean earthquake would cause such devastation. Likewise, no one believed that a magnitude 8.6 strike-slip earthquake could originate in the interior of a plate. A magnitude 8.2 aftershock was also unprecedented.
And yet there it is, a small basin on the ocean floor: A clear signature of strike-slip deformation. Pull-apart basins are formed when blocks of lithosphere rub against each other and drift apart. This particular basin sits along a re-activated fracture zone that might have ruptured during the 2012 great earthquake.
Our planet’s crust shows the stretch marks left by its cooling, traces left for us to explore on its skin. More that 4km below the sea surface, this record is 70 meters deep, 2km wide and stretches for 5.4km. It is beautiful and promising: another great clue for intense detectives to follow.
Written by Mónika Naranjo González
June 4, Thursday
Most tectonic action goes on plate boundaries, its interior is not supposed to do much, but somebody forgot to tell the Indo-Australian plate. And so, on April 11th 2012 it did what nobody thought was possible: it produced the largest strike-slip earthquake in our planet’s history. A massive magnitude 8.6 followed by an equally baffling 8.2 aftershock. According to Dr. Satish Singh, we simply don’t understand what happened here, the Indo-Australian plate does not behave as a single, coherent plate.
What, where, why
Strike-slip earthquakes are different from those that occur at subduction zones. Their movement is mostly horizontal, like two blocks rubbing together. They do not lead to vertical displacement of water, which means that they are not associated with big tsunamis.
To the northeast of the Indian Ocean lies a marine area known as the Wharton Basin. This piece of our planet’s crust is under unimaginable stress: to the north, the Indian sub-continent is colliding with Eurasia at a rate of 37 to 44mm per year. This is how the great Himalayas were formed. To the east, there’s the monumental Sunda Megathrust where the Indo-Australia plate itself moves under the Eurasian plate. This combination might very well be why the Wharton Basin is one of the most actively deforming ocean basins in the world.
But why come here? Well, it seems that things may be connected. The MEGATERA expedition is working on the Wharton Basin trying to understand the deformation of the plate’s interior and identify the faults orientation and direction of motion that produced the 8.2 aftershock.
According to Hélène Carton’s research, the Sumatra-Andaman earthquake of 2004 activated dominantly strike-slip features on the plate. An increase in seismicity has been observed in the northern half of the Wharton Basin