What caused the April 25, 2015 Nepal Earthquake?
Regional compression produces broadly distributed earthquakes north of the 2,900-km-long Himalayan plate boundary. However, the historical earthquake record indicates that the largest earthquakes, shown by their rupture areas, occur on the shallow portion of the megathrust boundary.
This animation discusses the evolution of the Himalaya in a broad tectonic context and focusses more closely on the 2015 Nepal earthquake.
It is worth it to watch video footage from a surveillance camera, in concert with a graph of GPS motion that occurs at 2min 55sec (created by UNAVCO).
The Kathmandu Basin is a broad valley in the foothills leading to the high Himalayas. This valley was formerly the site of a lake within which up to 600 meters of thickness of river delta and lake sediment accumulated. Compared to bedrock around and beneath the basin, seismic waves from the Gorkha earthquake caused these lake sediments to shake like Jello in a bowl.
An IRIS Teachable Moment PowerPoint presentation created for this earthquake can be downloaded from: www.iris.edu/hq/retm/event/3363.
For more-technical presentations and publications, please visit: ds.iris.edu/ds/nodes/dmc/specialevents/2015/04/25/nepal/.
[It is important to note that although this is a "megathrust" earthquake, it is above sea level thus does not produce tsunamis.]
- The Indian Plate collided with the Eurasian Plate ~50million years ago
- Regional compression produces broadly distributed earthquakes.
- The largest earthquakes occur on the shallow portion of the megathrust boundary
- The Gorkha earthquake of April 2015 displaced Kathmandu over 1.2 m south.
- Population growth near the plate boundary is at risk.