The Seismic Experiment that Mapped the Depths
Far from the familiar tectonic boundaries where plates collide and diverge, the Mongolian Plateau presents a profound geological mystery. Despite being located thousands of kilometers from the nearest active plate boundary, this region experiences intense crustal deformation, widespread volcanism, and frequent earthquakes 1 .
For decades, scientists have debated what forces drive this activity in what's known as a "slowly deforming continental region" – where tectonic movements are subtle but still capable of generating major earthquakes 3 .
In 2012, an international team of seismologists embarked on an ambitious mission to solve this puzzle. The Central Mongolia Seismic Experiment would become one of the most comprehensive temporary seismic array deployments in the region, generating a wealth of data that continues to reshape our understanding of intracontinental dynamics 2 .
Region of intense crustal deformation
Uplifted region with active volcanoes
Thick lithosphere deflecting upwelling
Click on the points to learn about key geological features
Unlike permanent seismic stations that are often spaced hundreds of kilometers apart, temporary broadband seismic arrays provide dense coverage over specific regions of interest. These arrays can detect ground motions from earthquakes worldwide, and the resulting seismic waves – when recorded by multiple closely-spaced sensors – allow scientists to create detailed 3D images of the Earth's interior, much like a CT scan reveals hidden structures within the human body.
The Central Mongolia Seismic Experiment deployed 112 broadband stations across an impressive 900 × 600 km area stretching from Lake Khövsgöl in the north to the Altai Mountains in the south 2 . These stations were deployed as three separate subarrays over two mobilizations, each recording data for 21 months to capture sufficient seismic events for analysis 2 .
2010-2011
Site selection and logistical preparation for the deployment
2012
Installation of first set of seismic stations across central Mongolia
2012-2013
Continuous recording of seismic activity for 21 months
2014-Present
Processing data and publishing findings on Mongolia's subsurface structure
Researchers discovered two continuous slow anomalies extending from the deep upper mantle (800 km depth) to near the surface 6 . These "slow" zones indicate warmer, potentially rising mantle material.
The experiment documented complex deformation patterns across Mongolia. The Altai Mountains experience NE-SW shortening, while the Hangay Dome region and eastern Mongolia display W-E or NW-SE shear deformation 1 .
| Parameter | Specification | Significance |
|---|---|---|
| Station Count | 112 broadband stations | Provided unprecedented data density |
| Coverage Area | ~900 × 600 km | From Lake Khövsgöl to Altai Mountains |
| Deployment Period | 21 months per subarray | Sufficient to record numerous seismic events |
| Station Configuration | Three separate subarrays | Allowed focused regional analysis |
| Primary Applications | Local, regional, and teleseismic earthquake recording | Enabled multiple research approaches |
How the Experiment Worked
Conducting an experiment of this scale required sophisticated equipment and methodologies. Here are the key components that made the research possible:
| Tool/Technique | Function | Application in Mongolia |
|---|---|---|
| Broadband Seismometers | Detect and record ground motion across various frequencies | Captured everything from local tremors to distant quakes |
| Receiver Function Analysis | Uses converted seismic waves to image velocity discontinuities | Mapped Moho depth and crustal interfaces |
| Surface Wave Tomography | Analyzes surface wave dispersion to create 3D velocity models | Revealed S-wave velocity structures in crust and upper mantle |
| Teleseismic Tomography | Uses distant earthquakes to image deep mantle structures | Identified potential mantle plumes up to 800 km depth |
| Seismic Anisotropy Analysis | Measures direction-dependent wave speeds | Mapped patterns of mantle flow and deformation |
The deployment process followed a systematic approach:
This comprehensive approach allowed scientists to image everything from sedimentary layers near the surface to potential mantle plumes hundreds of kilometers deep.
| Discovery Area | Key Finding | Scientific Implication |
|---|---|---|
| Crustal Structure | Significant east-west differences in thickness | Explains varied tectonic responses across region |
| Mantle Dynamics | Two deep slow anomalies suggesting upwelling | Challenges existing plate tectonic models |
| Hangay Dome Anomaly | Thickened crust (45-55 km) but thinned lithosphere (60-80 km) | Supports combination of uplift mechanisms |
| Deformation Patterns | Combination of shortening and shear deformation | Result of multiple superimposed mechanisms |
| Earthquake Cycles | 25,000-year return time for large earthquakes | Redefines seismic hazard assessment in SDCRs |
The Central Mongolia Seismic Experiment demonstrates how temporary broadband arrays can revolutionize our understanding of continental dynamics. The findings have fundamentally altered how scientists view intraplate tectonics, revealing that even regions far from plate boundaries can experience significant deformation driven by deep Earth processes.
The research has crucial implications for earthquake hazard assessment in slowly deforming regions, suggesting that systematic appraisal of potential seismogenic structures is essential for accurate risk evaluation 3 . Rather than being randomly distributed, seismic risk in these areas concentrates on specific structures – it just takes much longer for sufficient strain to accumulate.
Future studies will build on this foundation, integrating seismic findings with other geophysical techniques such as gravity and magnetic data analysis 4 to further refine our models of Mongolia's unique tectonic setting. As more data emerges from this and similar experiments worldwide, we move closer to solving the enduring mystery of how continental interiors deform and evolve over geological time.
The legacy of the Central Mongolia Seismic Experiment extends far beyond its specific findings – it stands as a powerful example of how international scientific collaboration and temporary instrument deployments can illuminate hidden aspects of our planet's dynamic behavior.