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Plateau 'pop-up' in the great 1897 Assam earthquake
1CIRES & Geological Sciences, University of Colorado, Boulder, Colorado 80309-0399, USA. bilham@stripe.colorado.edu
Nature
|April 12, 2001
Summary
The 1897 Assam earthquake was caused by a steep reverse fault rupture beneath the Shillong plateau, not a Himalayan fault. This event caused significant uplift and high ground accelerations, impacting regional seismic risk.
Area of Science:
- Geophysics
- Seismology
- Tectonics
Background:
- The 1897 Assam earthquake caused widespread destruction in northeastern India.
- Previous theories attributed the earthquake to a north-dipping Himalayan thrust fault.
Purpose of the Study:
- To investigate the causative fault mechanism of the 1897 Assam earthquake.
- To analyze the deformation and seismic implications of the Shillong plateau uplift.
Main Methods:
- Analysis of geological evidence for fault rupture and uplift.
- Modeling of earthquake rupture dynamics and seismic wave propagation.
Main Results:
- The northern Shillong plateau experienced a violent uplift of at least 11 m.
- A buried, steeply dipping reverse fault, approximately 110 km long, was identified as the cause.
- The earthquake generated accelerations exceeding 1g vertically and surface velocities over 3 m/s.
Conclusions:
- The Assam earthquake resulted from the rupture of a fault bounding a crustal 'pop-up' structure.
- This event significantly altered local stress fields, reducing seismic risk in Bhutan but increasing it in northern Bangladesh.
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