From Eos: “Bhutan Earthquake Opens Doors to Geophysical Studies”
13 August 2018
György Hetényi
Rodolphe Cattin
Dowchu Drukpa
Taktsang, also known as the Tiger’s Nest, is a famous cliffside monastery in western Bhutan. Recent geophysical surveys have uncovered evidence of past earthquakes in this region that were much stronger than more recent events. Credit: iStock.com/KiltedArab
In 2015, a magnitude 7.8 earthquake shook the Gorkha District of Nepal, killing more than 9,000. The memory of this event is still vivid for the residents of this central Himalayan nation.
But farther east in the mountains, in Bhutan, many residents doubt the likelihood of a similar event happening to them. Bhutan had experienced several other earthquakes with a magnitude of about 6 during the past century. However, there was no clear evidence that Bhutan had ever seen an earthquake similar to the M7.8 Nepal event.
Findings from recent geophysical exploration suggest that this confidence may be overly optimistic. These results have shown that the eastern Himalayas region is extremely complex compared with the rest of the mountain belt.
The kingdom of Bhutan sets great store in its traditions and its principle of Gross National Happiness. Although its rugged terrain and remote location have allowed this kingdom to preserve its unique culture, these factors have also limited the development of international collaborations there, notably in the Earth sciences. This situation changed in 2009 after a damaging M6.1 earthquake that claimed 11 lives persuaded Bhutan to open its doors to exploration of the region’s geophysics.
Our team studied mountain-building processes in this region after the 2009 earthquake. After 7 years of multipronged field campaigns, we learned that Bhutan’s geodynamics are as unique as its culture. The region’s crustal structure, seismicity, and deformation pattern are all different from what scientists had speculated previously.
During our campaigns, we found evidence that at least one M8 earthquake had, in fact, occurred in Bhutan. This means that other earthquakes of this magnitude could occur in the region again [Hetényi et al., 2016b; Berthet et al., 2014; Le Roux-Mallouf et al., 2016].
A Different Plate?
Although the western and central Himalayan arc curves gently from Pakistan to Sikkim and has a low-lying foreland, the eastern third curves more sharply and has significant topographical relief south of the mountain belt, namely, the Shillong Plateau and neighboring hills (Figure 1). Previous studies proposed that these structures accommodate part of the India-Eurasia tectonic plate convergence. These earlier studies also proposed that the great 1897 Assam earthquake (M8.1) had relieved some of the strain between these converging tectonic plates, thereby lowering earthquake hazard in Bhutan.
Fig. 1. Topographic map of the 2,500-kilometer-long Himalayan arc and surrounding region, with formerly (yellow) and newly (pink) cataloged seismicity. The dextral fault zone (white arrows) between Sikkim and the Shillong Plateau marks the break of the India plate, east of which a zone of complex 3-D deformation begins. Red dates mark the three largest earthquakes mentioned in the text. Green lines mark the surface trace of the megathrust along which the India plate underthrusts the Himalayan orogen, as well as the thrust faults bounding the Shillong Plateau. Political boundaries are shown for reference. Abbreviations: Pl. = plateau; Pr. = Pradesh; Sik. = Sikkim.
We collected new gravity, geodetic, and seismology data, and we found that the lithosphere—the rigid top layer of Earth—beneath Bhutan and the Shillong Plateau is most likely not part of the Indian plate or, if it once was, that it is now detached from it. The demarcation between plates stretches in a NW–SE direction, without a surface trace, but it is evident in a middle to lower crustal zone of continuously active seismicity and dextral (right-lateral) motion [Diehl et al., 2017]. This fault zone most likely hosted an M7 earthquake in 1930.
Research team member Théo Berthet monitors data collection during a campaign to a less visited region in central Bhutan. The Black Mountains, which rise to 4,500–4,600 meters, are visible in the background. Credit: György Hetényi
Our GPS measurements confirm the relative motion of the newly defined microplate. These measurements also show that this microplate is rotating clockwise with respect to the Indian plate [Vernant et al., 2014]. The different behaviors of the two lithospheres are clearly expressed in their differences in flexural stiffness along the strike direction of the orogen (mountain belt). The flexural stiffness beneath Nepal is homogeneous [Berthet et al., 2013] but is comparatively weaker beneath Bhutan [Hammer et al., 2013].
A similar, but less well defined, deep seismicity zone, with distinct GPS vectors and flexural signatures, may mark another terrain boundary farther east along the Himalayas in Arunachal Pradesh [Hetényi et al., 2016a].
Not a Safe Haven
India’s 1897 Assam earthquake, which occurred farther south, is only a few human generations in the past and has not completely faded from memory. No event since then has reached magnitude 7 in Bhutan, and many of the local population believe that big earthquakes cannot happen there.
However, the return period of large Himalayan events is longer than oral history: Western Nepal, for example, has not experienced a significant event since 1505. It is true that over the past decades, the seismicity rate in Bhutan has been low, but we have found evidence of several great earthquakes in the past on the local megathrust.
Geomorphological analysis of uplifted river terraces in central Bhutan revealed two major events over the past millennium [Berthet et al., 2014]. A newly excavated paleoseismological trench has documented surface rupture during a medieval event and a 17th–18th century event [Le Roux-Mallouf et al., 2016]. Calculations based on newly translated historical eyewitness reports, macroseismic information, and reassessed damage reports have constrained a M8 ± 0.5 earthquake on 4 May 1714 [Hetényi et al., 2016b].
Thus, the seismic gap proved to be an information gap: The entire length of the Himalayas can generate earthquakes with a magnitude greater than 7.5, and it has done so in the past 500 years.
The landscape in eastern Bhutan, south of Trashigang, typically features incised valleys, steep slopes, and terraces. The hut in the center is shown in the inset for scale. The view here is to the east, and the hut is located at 27.2784°N, 91.4478°E. Credit: György Hetényi
Differences at Multiple Scales
The major change along the Himalayas occurs between their central western part (with a single convergence zone) and the eastern third (with distributed deformation including strike-slip motion), and the east–west extent of Bhutan exhibits even greater complexity. The crust appears to be smoothly descending in western Bhutan and is subhorizontal in the eastern part of the country [Singer et al., 2017a]. Our measurements of seismic wave speeds in the upper crust show important changes across the country, and they coincide well with the geological structure mapped at the surface [Singer et al., 2017b].
The most striking difference between western and eastern Bhutan is the crustal deformation pattern. In the west, the accommodation of present-day crustal shortening is very similar to the rest of the Himalayas: The plates in the megathrust region are fully locked [Vernant et al., 2014], and microseismicity (the occurrence of small events) is scattered across the crust [Diehl et al., 2017]. In the east, the locked segment of the megathrust is shorter, and it focuses most of the microseismic activity within a smaller region. Also, the fault appears to be creeping (sliding without producing significant seismicity) in both shallower and deeper segments [Marechal et al., 2016].
This variation of loading and background seismicity warrants further research along the entire Himalayan orogen because there is very little existing insight into variations of structures and processes at such short distance scales.
Gangkhar Puensum, a mountain in north central Bhutan, is clearly visible from the main road between Ura and Sengor, looking north-northwest. Gangkhar Puensum, at an altitude of 7,570 meters, is the highest unclimbed peak on Earth. For religious reasons, mountaineering above 6,000 meters is prohibited in Bhutan, so this record is very likely to remain. Credit: György Hetényi
Bhutan Is Moving Forward
Bhutan is an exotic place that has self-imposed isolation for a long time, but the country’s technology is now catching up at a rate that is higher than for the rest of the Himalayan regions. During our 2010 campaign, we used paper traveler’s checks, and we lacked individual cell phones. During our 2017 campaign, we had access to automated teller machines (ATMs) and 3G internet.
Likewise, our 7 years of field campaigns in this region have advanced our geophysical exploration and geodynamic understanding considerably. Still, there is a strong need to continue and build on the existing knowledge, which includes freely available seismological, gravity, and GPS data from our projects.
Focusing on three areas would help improve future development in Bhutan:
Broadening timescales. Acquiring long-term data needed to confirm or to adjust interpretations made on relatively short timescales is possible only with national observatories. We have launched seismology and GPS monitoring initiatives, and we hope for long-term funding and training of local manpower for all levels of operation.
Broadening investigations. Some fields of study have advanced dramatically, including work on glacial lake outburst floods and on landslides. Others, like seismic microzonation, have been limited so far and could benefit from more extensive efforts. There is also a strong need for up-to-date building codes that reflect the scientific knowledge coming from these investigations.
Increasing public awareness of natural hazards. The Bhutanese Ministry of Home and Cultural Affairs now has a full department devoted to disaster management that includes well-trained employees and comprehensive administration. However, education is the key to reaching the broadest population possible, which requires regular adaptation of school curricula and concise, practical information that local residents from any generation can understand.
We hope that recent efforts by our teams have promoted progress in the right direction. We also hope that large portions of the population will be sufficiently aware to deal with the next natural disaster. As our research shows, the next event may come sooner than previously thought.
The main Himalayan peaks in northwest Bhutan, on the border with southern Tibet, are, from left to right, Chomolhari, Jichu Drake, and Tserim Kang. Exact altitudes are debated, but Chomolhari is higher than 7,000 meters, and Tserim Kang towers above 6,500 meters. Credit: György Hetényi
Acknowledgments
The authors gratefully acknowledge all scientific, fieldwork, and logistical help provided by participants of the projects GANSSER and BHUTANEPAL, carried out in collaboration with the Department of Geology and Mines and the National Land Commission, Thimphu, Bhutan, and with support of Helvetas. Research highlighted in this article became possible thanks to the seed funding of the North-South Centre (ETH Zurich), followed by funding from the Swiss National Science Foundation (grants 200021_143467 and PP00P2_157627) and the French Agence Nationale de la Recherche (grant 13-BS06-0006-01).
References
Berthet, T., et al. (2013), Lateral uniformity of India plate strength over central and eastern Nepal, Geophys. J. Int., 195, 1,481–1,493, https://doi.org/10.1093/gji/ggt357.
Berthet, T., et al. (2014), Active tectonics of the eastern Himalaya: New constraints from the first tectonic geomorphology study in southern Bhutan, Geology, 42, 427–430, https://doi.org/10.1130/G35162.1.
Diehl, T., et al. (2017), Seismotectonics of Bhutan: Evidence for segmentation of the eastern Himalayas and link to foreland deformation, Earth Planet. Sci. Lett., 471, 54–64, https://doi.org/10.1016/j.epsl.2017.04.038.
Hammer, P., et al. (2013), Flexure of the India plate underneath the Bhutan Himalaya, Geophys. Res. Lett., 40, 4,225–4,230, https://doi.org/10.1002/grl.50793.
Hetényi, G., et al. (2016a), Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies, Sci. Rep., 6, 33866, https://doi.org/10.1038/srep33866.
Hetényi, G., et al. (2016b), Joint approach combining damage and paleoseismology observations constrains the 1714 A.D. Bhutan earthquake at magnitude 8±0.5, Geophys. Res. Lett., 43, 10,695–10,702, https://doi.org/10.1002/2016GL071033.
Le Roux-Mallouf, R., et al. (2016), First paleoseismic evidence for great surface-rupturing earthquakes in the Bhutan Himalayas, J. Geophys. Res. Solid Earth, 121, 7,271–7,283, https://doi.org/10.1002/2015JB012733.
Marechal, A., et al. (2016), Evidence of interseismic coupling variations along the Bhutan Himalayan arc from new GPS data, Geophys. Res. Lett., 43, 12,399–12,406, https://doi.org/10.1002/2016GL071163.
Singer, J., et al. (2017a), The underthrusting Indian crust and its role in collision dynamics of the eastern Himalaya in Bhutan: Insights from receiver function imaging, J. Geophys. Res. Solid Earth, 122, 1,152–1,178, https://doi.org/10.1002/2016JB013337.
Singer, J., et al. (2017b), Along-strike variations in the Himalayan orogenic wedge structure in Bhutan from ambient seismic noise tomography, Geochem. Geophys. Geosyst., 18, 1,483–1,498, https://doi.org/10.1002/2016GC006742.
Vernant, P., et al. (2014), Clockwise rotation of the Brahmaputra Valley relative to India: Tectonic convergence in the eastern Himalaya, Naga Hills, and Shillong Plateau, J. Geophys. Res. Solid Earth, 119, 6,558–6,571, https://doi.org/10.1002/2014JB011196.
Author Information
György Hetényi (email: gyorgy.hetenyi@unil.ch), Faculty of Geosciences and Environment, Institute of Earth Sciences, University of Lausanne, Switzerland; Rodolphe Cattin, Géosciences Montpellier, University of Montpellier, France; and Dowchu Drukpa, Department of Geology and Mines, Ministry of Economic Affairs, Thimphu, Bhutan
See the full article here .
Earthquake Network projectEarthquake Network is a research project which aims at developing and maintaining a crowdsourced smartphone-based earthquake warning system at a global level. Smartphones made available by the population are used to detect the earthquake waves using the on-board accelerometers. When an earthquake is detected, an earthquake warning is issued in order to alert the population not yet reached by the damaging waves of the earthquake.
The project started on January 1, 2013 with the release of the homonymous Android application Earthquake Network. The author of the research project and developer of the smartphone application is Francesco Finazzi of the University of Bergamo, Italy.
Get the app in the Google Play store.
Smartphone network spatial distribution (green and red dots) on December 4, 2015
Meet The Quake-Catcher Network
The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers. With your help, the Quake-Catcher Network can provide better understanding of earthquakes, give early warning to schools, emergency response systems, and others. The Quake-Catcher Network also provides educational software designed to help teach about earthquakes and earthquake hazards.
After almost eight years at Stanford, and a year at CalTech, the QCN project is moving to the University of Southern California Dept. of Earth Sciences. QCN will be sponsored by the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Center (SCEC).
The Quake-Catcher Network is a distributed computing network that links volunteer hosted computers into a real-time motion sensing network. QCN is one of many scientific computing projects that runs on the world-renowned distributed computing platform Berkeley Open Infrastructure for Network Computing (BOINC).
The volunteer computers monitor vibrational sensors called MEMS accelerometers, and digitally transmit “triggers” to QCN’s servers whenever strong new motions are observed. QCN’s servers sift through these signals, and determine which ones represent earthquakes, and which ones represent cultural noise (like doors slamming, or trucks driving by).
There are two categories of sensors used by QCN: 1) internal mobile device sensors, and 2) external USB sensors.
Mobile Devices: MEMS sensors are often included in laptops, games, cell phones, and other electronic devices for hardware protection, navigation, and game control. When these devices are still and connected to QCN, QCN software monitors the internal accelerometer for strong new shaking. Unfortunately, these devices are rarely secured to the floor, so they may bounce around when a large earthquake occurs. While this is less than ideal for characterizing the regional ground shaking, many such sensors can still provide useful information about earthquake locations and magnitudes.
USB Sensors: MEMS sensors can be mounted to the floor and connected to a desktop computer via a USB cable. These sensors have several advantages over mobile device sensors. 1) By mounting them to the floor, they measure more reliable shaking than mobile devices. 2) These sensors typically have lower noise and better resolution of 3D motion. 3) Desktops are often left on and do not move. 4) The USB sensor is physically removed from the game, phone, or laptop, so human interaction with the device doesn’t reduce the sensors’ performance. 5) USB sensors can be aligned to North, so we know what direction the horizontal “X” and “Y” axes correspond to.
If you are a science teacher at a K-12 school, please apply for a free USB sensor and accompanying QCN software. QCN has been able to purchase sensors to donate to schools in need. If you are interested in donating to the program or requesting a sensor, click here.
BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience.BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.
Earthquake safety is a responsibility shared by billions worldwide. The Quake-Catcher Network (QCN) provides software so that individuals can join together to improve earthquake monitoring, earthquake awareness, and the science of earthquakes. The Quake-Catcher Network (QCN) links existing networked laptops and desktops in hopes to form the worlds largest strong-motion seismic network.
Below, the QCN Quake Catcher Network map
ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States
The U. S. Geological Survey (USGS) along with a coalition of State and university partners is developing and testing an earthquake early warning (EEW) system called ShakeAlert for the west coast of the United States. Long term funding must be secured before the system can begin sending general public notifications, however, some limited pilot projects are active and more are being developed. The USGS has set the goal of beginning limited public notifications in 2018.
Watch a video describing how ShakeAlert works in English or Spanish.
The primary project partners include:
United States Geological Survey
California Governor’s Office of Emergency Services (CalOES)
California Geological Survey
California Institute of Technology
University of California Berkeley
University of Washington
University of Oregon
Gordon and Betty Moore Foundation
The Earthquake Threat
Earthquakes pose a national challenge because more than 143 million Americans live in areas of significant seismic risk across 39 states. Most of our Nation’s earthquake risk is concentrated on the West Coast of the United States. The Federal Emergency Management Agency (FEMA) has estimated the average annualized loss from earthquakes, nationwide, to be $5.3 billion, with 77 percent of that figure ($4.1 billion) coming from California, Washington, and Oregon, and 66 percent ($3.5 billion) from California alone. In the next 30 years, California has a 99.7 percent chance of a magnitude 6.7 or larger earthquake and the Pacific Northwest has a 10 percent chance of a magnitude 8 to 9 megathrust earthquake on the Cascadia subduction zone.
Part of the Solution
Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of the ShakeAlert system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm’s way. This can be done by detecting the first energy to radiate from an earthquake, the P-wave energy, which rarely causes damage. Using P-wave information, we first estimate the location and the magnitude of the earthquake. Then, the anticipated ground shaking across the region to be affected is estimated and a warning is provided to local populations. The method can provide warning before the S-wave arrives, bringing the strong shaking that usually causes most of the damage.
Studies of earthquake early warning methods in California have shown that the warning time would range from a few seconds to a few tens of seconds. ShakeAlert can give enough time to slow trains and taxiing planes, to prevent cars from entering bridges and tunnels, to move away from dangerous machines or chemicals in work environments and to take cover under a desk, or to automatically shut down and isolate industrial systems. Taking such actions before shaking starts can reduce damage and casualties during an earthquake. It can also prevent cascading failures in the aftermath of an event. For example, isolating utilities before shaking starts can reduce the number of fire initiations.
System Goal
The USGS will issue public warnings of potentially damaging earthquakes and provide warning parameter data to government agencies and private users on a region-by-region basis, as soon as the ShakeAlert system, its products, and its parametric data meet minimum quality and reliability standards in those geographic regions. The USGS has set the goal of beginning limited public notifications in 2018. Product availability will expand geographically via ANSS regional seismic networks, such that ShakeAlert products and warnings become available for all regions with dense seismic instrumentation.
Current Status
The West Coast ShakeAlert system is being developed by expanding and upgrading the infrastructure of regional seismic networks that are part of the Advanced National Seismic System (ANSS); the California Integrated Seismic Network (CISN) is made up of the Southern California Seismic Network, SCSN) and the Northern California Seismic System, NCSS and the Pacific Northwest Seismic Network (PNSN). This enables the USGS and ANSS to leverage their substantial investment in sensor networks, data telemetry systems, data processing centers, and software for earthquake monitoring activities residing in these network centers. The ShakeAlert system has been sending live alerts to “beta” users in California since January of 2012 and in the Pacific Northwest since February of 2015.
In February of 2016 the USGS, along with its partners, rolled-out the next-generation ShakeAlert early warning test system in California joined by Oregon and Washington in April 2017. This West Coast-wide “production prototype” has been designed for redundant, reliable operations. The system includes geographically distributed servers, and allows for automatic fail-over if connection is lost.
This next-generation system will not yet support public warnings but does allow selected early adopters to develop and deploy pilot implementations that take protective actions triggered by the ShakeAlert notifications in areas with sufficient sensor coverage.
Authorities
The USGS will develop and operate the ShakeAlert system, and issue public notifications under collaborative authorities with FEMA, as part of the National Earthquake Hazard Reduction Program, as enacted by the Earthquake Hazards Reduction Act of 1977, 42 U.S.C. §§ 7704 SEC. 2.
For More Information
Robert de Groot, ShakeAlert National Coordinator for Communication, Education, and Outreach
rdegroot@usgs.gov
626-583-7225
ShakeAlert Implementation Plan
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