Answering fundamental questions about geohazards to improve the livelihoods of communities in Southeast Asia and beyond
Focus on Nepal
Nepal is the home to stunning landscapes and the tallest mountain range in the world. It is also the site of the largest active continental thrust fault called the Main Frontal Thrust. This system of faults stretches 2,000 kilometres along the boundary where the Indian subcontinent is smashing into the Eurasian plate. This collision, which began about 50 million years ago, is still building the tallest mountains in the world and has produced many large, catastrophic earthquakes along the way.
One such quake was the April 2015 7.8-magnitude earthquake in Nepal, which claimed more than 9,000 lives and left hundreds of thousands of people homeless. While the complex nature and vastness of the fault make it difficult to quantify earthquake hazard for the tens of millions of people living nearby in Nepal and India, these factors are precisely why it is important to learn about this fault. Through intensive research, our scientists are acquiring more insight into these events and passing on this knowledge to help communities at-risk be more resilient to earthquakes.
Searching for the Trace of Great Earthquakes
The Main Frontal Thrust has produced some of the most catastrophic earthquakes in history, including the 8.4-magnitude 1934 Bihar-Nepal event that killed more than 15,000 people. Yet, no one had found where these quakes had ruptured the surface, leading many geologists to conclude that these faults were “blind”—that the earthquake's fault had not reached the surface of the earth.
Without surface evidence, it is difficult to answer important questions about how often earthquakes occur and how large they may be. That was what Principal Investigator Paul Tapponnier and his team set out to do: to find the undiscovered surface ruptures of four historic earthquakes and eventually decipher the history of 5,000 years of earthquakes along the Main Frontal Thrust in eastern Nepal. In recent years, the team demonstrated that great Himalayan earthquakes in past centuries were not “blind” as previously thought.
In 2016, Tapponnier and his team focused on refining their mapping along the thrust in eastern Nepal using techniques that included the first 100 kilometre-long airborne LiDAR survey along the front and 14C and cosmogenic sample dating in order to quantify the seismic uplifts of multiple alluvial terraces. They found seven large earthquakes dating back 4,500 years and, with this information, Tapponnier and his team were able to estimate an average recurrence interval of 600 to 800 years between these large earthquakes.
They also investigated the earthquake that killed the king in Kathmandu in 1334. That event broke a different fault segment than the 1255 AD earthquake. The team believes that the 1334 quake occurred in sequence, just west of the 1255 AD event, postdating it by only 89 years. This short lag time raises the question of whether another great earthquake similar to the 1934 event could occur fairly soon, perhaps in the next few decades. This makes it even more critical for Tapponnier and his team to search for the ruptures of other great historical earthquakes along the Himalayan Front in order to better prepare for the next one.
Below the Surface
Because of the challenges in locating and characterising surface faults along the Main Frontal Thrust, subsurface data is important to fill gaps in knowledge about Nepal’s active tectonics and geology. In 2014 and 2015, Principal Investigator Judith Hubbard used the EOS Vibroseis Minibuggy to image faults and related deformation underground. The truck works by shaking the ground, creating seismic waves that travel through the rocks. The waves reflect off stratigraphic layers and can be processed to produce detailed images of underground faults and folds. Thus far, Hubbard’s team has collected 135 kilometres of high-resolution profiles. This dataset is the first of its kind in the Himalayas. With this technology, Hubbard has successfully imaged various segments of the Main Frontal Thrust and produced a more precise model of the faults and folds at work, paving the way towards better hazard estimates.
Hubbard’s team also uses the record of rocks exposed at the surface to understand the geology underground. Following the April 2015 Nepal earthquake, she and her team re-evaluated the subsurface geology around the area of the earthquake, and they discovered something new: the plate boundary fault is made up of several fault segments that look almost like stairs, with flats separated by ramps. The 2015 earthquake rupture happened on one of the flats, and was stopped by ramps on all sides. The idea that the geometry of a fault can control the path and size of an earthquake is a significant step forward in understanding earthquake size and dynamics along the Himalayan front.
In the coming year, Hubbard is drilling boreholes along the Main Frontal Thrust. She will analyse them with a dating technique that measures the last time the rock was exposed to light. With this new knowledge, she’ll be able to better estimate slip rates along the faults, providing a clearer understanding of the deformation and earthquake risk for nearby communities.
“I’ve always liked mountains; it drove me to study geology,” Professor Paul Tapponnier says. Born and raised in the French Alps south of Geneva, Prof Tapponnier’s affinity with mountains brought him to study the highest peaks on the planet: the Himalayas and Tibet. It was fitting then, that he moved to Singapore in 2009 to lead the tectonics group at the Earth Observatory of Singapore, closer to the mountains that he had spent much of his life studying.
One of the most distinguished scientists of his generation in the field of tectonics, Prof Tapponnier’s innovative research led to a renaissance in neotectonics, the study of Earth’s crust’s animated history. He spent more than 30 years at Institut de Physique du Globe de Paris in France. There, he created the prestigious Laboratoire de “Tectonique Mécanique de la Lithosphère”, France’s top centre for tectonic research. He has received numerous scientific awards and top honours for his achievements, including membership of the American and French Academies of Sciences.
Much of our understanding of tectonics in Asia comes from Prof Tapponnier’s lead research since 1975. He pioneered the use of satellite images to study the geology of vast areas, setting a precedence for modern research methods. Prof Tapponnier combined geologic and geophysical data with satellite images to propose that large earthquakes and deformation in Eastern Asia could be explained by India’s collision with Asia. This model explained large-scale movements inside the entire Asian continent, including the uplift and growth of the Tibetan Plateau, the opening of the South China Sea, and rifting in Russia’s Lake Baikal.
Despite these findings, there was still a puzzle about Asia that the French geologist was bent on solving: while great earthquakes with magnitudes in excess of 8.0 had devastated the Indian-Eurasian collision front over the past century, the scientific community debated whether these earthquakes’ ruptures ever reached the surface. Thus far, no one had found any surface evidence of these major earthquakes. Without a sign of surface slip, it is nearly impossible to reconstruct earthquake history and assess the potential return times of future events. “You can’t do much when you haven’t found the surface breaks,” says Prof Tapponnier.
He thus set out for Nepal, determined to find out whether these great earthquakes had left traces at the surface or not. The search was guided by the spectacular uplift of terraces along riverbanks. After sending the charcoal samples that the team had painstakingly collected from many sites for radiocarbon dating, Prof Tapponnier and his team discovered a record of seven surface-rupturing earthquakes in the last 4,500 years. They included the devastating 1934 Bihar-Nepal and the 1255 AD earthquakes, its precursor, that destroyed much of Kathmandu. From the age data, Prof Tapponnier’s group also determined a recurrence interval of 700 ± 100 years for the most catastrophic events in the region, vastly improving seismic hazard understanding along the Himalayan Front.
Besides his trailblazing work in Nepal, Prof Tapponnier has been an active partner of other tectonic studies across Asia. Together with Professor Satish Singh, his former colleague from the Institut de Physique du Globe de Paris, now Visiting Professor at the Earth Observatory of Singapore, he co-led the Mentawai Gap—Tsunami Earthquake Risk Assessment (MEGA-TERA) project, an international research expedition that surveyed the Sunda Megathrust off the western coast of Sumatra, Indonesia. The expedition yielded new bathymetric maps and seismic sections, vastly improving the understanding of earthquake-related deformation along the Sunda Trench.
In addition, Prof Tapponnier’s work in China at the north edge of Tibet has added new estimates of the rate of slip along the Altyn-Tagh Fault, one of the largest strike-slip faults in the world. His research methodology is as innovative as ever, with one recent project creating a complex 3D computer model of India’s collision with Asia using the Discrete Element Modelling technique, and another measuring deep electrical conductivity to understand fault geometries below the surface.
Throughout his career, Prof Tapponnier has contributed tremendously to the understanding of large-scale continental tectonics and earthquakes. There is such a sparkle in his eyes whenever he talks about the Earth, one can’t help but feel that even at 70, nothing will slow him down.
Caroline Bouvet de Maisonneuve
Assistant Professor Caroline Bouvet de Maisonneuve was seven years old when she saw ash falling into her garden in Manila, Philippines, where she lived. She vividly remembers the June 15, 1991 eruption of Mount Pinatubo, one of the most violent of the 20th century. Pinatubo’s ash cloud rose 40 kilometres into the air, extending across the sky for hundreds of kilometres. Pyroclastic flow engulfed the villages at the foot of the volcano, depositing ejecta up to 200 metres deep.
Now a volcanologist at the Earth Observatory of Singapore, Asst. Prof Bouvet de Maisonneuve is studying volcanoes in the Philippines and across Southeast Asia. She began her schooling in Geneva, Switzerland, studying earth sciences. “I wanted to do something related to nature,” she explains. After a field trip to the Massif Central in the centre of France, where she had seen a mesmerising landscape of volcanic deposits that had been preserved for thousands of years, she decided to pursue volcanology. Lured by the prospect of returning to Asia and to do research at the Earth Observatory, Asst. Prof Bouvet de Maisonneuve moved halfway around the world to Singapore in 2012 after completing her PhD.
One of her research interests includes assessing hazards from volcanoes in Southeast Asia to better forecast future eruptions. On the Indonesian island of Sumatra alone, there are more than 30 active or potentially active volcanoes, but only a handful of them have been studied. “There are so many possibilities for volcano research in this region, because there are so many volcanoes that haven’t been intensely studied,” says Asst. Prof Bouvet de Maisonneuve.
And because of its proximity to Singapore, there is a possibility that ash produced by eruptions from Sumatra’s volcanoes might have reached Singapore in the past 2,000 years, although volcanologists have not yet found any evidence of this in geologic history. This prompted Asst. Prof Bouvet de Maisonneuve and her team to focus on Singapore’s volcanic hazard as they work to reconstruct eruption histories of Southeast Asia’s volcanoes. Her team analyses boreholes and road cuts across Singapore to look for ash layers from historic eruptions. Right now, they are focusing on unambiguously identifying the meter(s)-thick deposit from the Toba supervolcano in Indonesia that erupted violently 74,000 years ago. That was its most recent eruption, and one of the largest in recorded history.
Coming full circle, another of the volcanoes that Asst. Prof Bouvet de Maisonneuve is interested in researching is Mount Pinatubo, the very volcano that inspired her career. She says, “It was quite special for me, knowing that I had witnessed that eruption.” There was, however, something baffling about Mount Pinatubo’s eruption: it released nearly 20 million tonnes of toxic sulfur dioxide into the atmosphere and this sulfur gas cooled the planet by 0.5 degrees Celsius for the next three years.
But where exactly did the sulfur come from? Asst. Prof Bouvet de Maisonneuve is hoping to solve this puzzle by tracing the isotopic signature of sulfur in the volcano’s deposits. Preliminary results show that the sulfur mostly came from an injection of basalt into the magma chamber. Because sulfur dioxide has a negative impact on our atmosphere, it is important to understand how it is transferred, released, and whether large sulfur-producing eruptions like that of Mount Pinatubo are typical or not.
“If we understand why Pinatubo had ejected so much sulfur dioxide, it will help us understand how volcanoes may affect our planet’s climate,” says Asst. Prof Bouvet de Maisonneuve. In the long run, she hopes to solve some of the mysteries surrounding volcanoes, such as identifying the processes that lead to an explosive eruption and how to quickly assess hazards for communities living near active volcanoes.
In 2002, Associate Professor Nathalie Goodkin was working as an investment banker in the United States when Larson B, part of the Larson ice shelf in Antarctica, collapsed. The ice sheet, roughly four and a half times the size of Singapore, melted in the span of just 35 days. Right then and there, she decided to leave her promising career for climate science. “I realised there was so much we didn’t know about how the oceans impacted climate,” Assoc Prof Goodkin says of her decision to switch careers. “I wanted to see how these systems worked at a fundamental level.”
She enrolled in the Chemical Oceanography PhD joint programme at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution. After her receiving her doctorate, Assoc Prof Goodkin studied ocean chemistry in Bermuda before moving to Asia. Her main tool is the geochemistry of corals, which are similar to trees—they record climate signatures in seasonal bands. In 2012, Assoc Prof Goodkin joined the Earth Observatory of Singapore where she started the Marine Geochemistry research group and built a laboratory. Of her move to Singapore, Assoc Prof Goodkin says, “It was a once-in-a-lifetime opportunity to answer big, integrative questions across Southeast Asia.”
One of the big questions she wants to answer revolves around the Southeast Asian monsoons. The summer and winter monsoons are the major drivers of climate in Southeast Asia, where too much or too little rain can threaten agriculture and damage infrastructure. Understanding how the monsoons have varied in the past will be critical to forecasting regional climate. Assoc Prof Goodkin is investigating how changes to sea temperature, salinity, and circulation affect the Southeast Asian Monsoon. She and her team study stable isotopes in corals to reconstruct climate from the past 500 years and use circulation models to evaluate future changes in ocean patterns.
One project that stands out involves a massive coral dubbed “Tho Nhat,” Vietnamese for “The Big One.” Assoc Prof Goodkin and her team drilled a four-metre long core sample from the coral. By studying the sample, her team is able to gain insight into climate signatures recorded by the coral, such as ocean salinity, temperature, and circulation. Using annual radiocarbon measurements from the late 16th century to the mid-20th century, she could see how monsoons tracked with different global climate patterns such as the Arctic Oscillation and the El Niño Southern Oscillation. This is no easy feat, considering that getting approval to sample corals is a delicate job requiring diplomacy with local communities. “We spend a lot of time getting to know our collaborators and reassuring the community that we won’t impact the reef long-term and we will use the samples to their fullest,” she says. “We try to understand what questions the community has, then we try to answer those questions and generate critical information for that community.”
Another big project that Assoc Prof Goodkin is involved in examines how changes to the western Pacific impact the South China Sea. With funding from the Ministry of Education, she and her collaborators are working on building regional models to put the work of the last 5-years into a larger context.
Next year, Assoc Prof Goodkin will continue to investigate how corals record ocean-atmospheric exchanges, reconstruct past climate histories, and model data to gain insight to future oceanic changes. In the face of a warming climate, her work is critical to understanding how regional climate may change.
- Records of Early Holocene post glacial sea level rise from the Singapore Kallang Basin: stepped or continuous?
- Historical typhoons, storm surges and other extreme sea level events in the South China Sea and western Pacific
- EOS participation in “Hazards, Tipping Points, Adaptation and Collapse in the Indo-Pacific World” a project integrating history and science
- Sediment transport processes under tsunami waves—A case study of tsunami deposits in a coastal cave in Aceh, Sumatra
- Elevation, facies and timing of coral terraces in Sumba Island: a revisit
- Spatial and temporal variations in stable isotopic compositions of precipitation in Southeast Asia
- Summer school to help broaden the education and networks of Ph.D. students in the MarGe laboratory
- Continuous haze monitoring in Sumatra
Satish Singh and Paul Tapponnier
- Marine Investigation of the Rupture Anatomy of the 2012 Great Earthquake (MIRAGE)
- Mentawai Gap – Tsunami Earthquake Risk Assessment (MEGA-TERA)
- The Bengal-Assam syntaxis: Geometry and kinematics of active faulting
- Earthquake ruptures in China: Testing earthquake recurrence models
- Discrete element modelling of fault nucleation and propagation in collision zones
- A quantitative reappraisal of historical earthquakes in Indonesia using uniformly assessed macroseismic observations from the Dutch colonial period
- Seismic behaviour of sinistral strike-slip faults of the Shan Plateau
- Myanmar earthquake geology
- Neotectonics of the Sumatran Fault
- Probabilistic seismic hazard assessment for northern Southeast Asia: Transition to the Southeast Asia earthquake model
- Search for the impact crater of the Australasian tektites
- Singapore‐Wiscar Partnership (SWAP)
- Paleoseismology and paleogeodesy of the Sumatran Subduction Zone
- Constraining short- and long-term tectonic deformation above the Manila Trench, Western Luzon, Philippines, using uplifted corals and beach dunes
- Physics of the earthquake cycle: Full lithosphere dynamics
- Testing the potential of Wave Gliders for ocean exploration and seafloor geodesy in SE Asia
- Cluster Expansion – Computer resources for the Observatory
- Sumatran tectonic geodesy
- The SuMO (Sumatran Fault Monitoring) campaign GPS project
- Myanmar–India–Bangladesh–Bhutan (MIBB) tectonic geodesy
- A geodetic study of sinking cities and subsiding deltas in East and Southeast Asia
- Monitoring tropical peatland degradation and subsidence with InSAR
- Earthquake seismology of Myanmar
- Broadband earthquake seismology in SE Asia
Caroline Bouvet de la Maisonneuve
- Assessing the hazard from Sumatran volcanoes
- Magma degassing and controls on eruption styles
- Pattern recognition of crystal zoning as a means to quantify volcanic processes
- Time scales of volcanic unrest and dynamics of magma ascent
- Dynamics of dyke propagation
- Volcanic eruption: location and characterization using infrasound
- Laboratory volcanoes: Repose; unrest; eruption
- MUON tomography at Mayon volcano, Philippines – Toward a better understanding of open-vent systems
Hazards and Society
- Interaction of geohazards and settlements through the past millennium, Banda Aceh, Indonesia
- Aftermath of Aid
- Understanding climate change and its impacts: The influence of knowledge, trust, values, and social norms
- WEB GeoTouch 2.0
- Living with Disaster – Qualitative characterization of risk, metrics and typologies for resilient cities
- EOS Art Projects
- The Tsunami of New Dreams
- Merapi Interactive
- Earth Girl Volcano
- Knowledge Capsules