Between 55 million and 40 million years ago, the northern edge of what is now India began to slam into the giant slab of Earth’s crust that today carries Nepal and Tibet. This ancient collision had a terrible after-effect this past Saturday: The deadly earthquake, centered in Nepal, which had an estimated death toll of nearly 4,000 people as of Monday evening.
India bulled its way under Nepal those many millions of years ago, shoving the northern land skyward. That move began to create the towering Himalaya, including Mt. Everest. The collision is still going on, as India moves several centimeters north each year, and this has created an unstable fissure in the planet’s crust, known as the Himalayan frontal thrust fault. This boundary zone, shown below, continues to release enormous earthquakes. Saturday’s magnitude 7.8 disaster appears to overlap a segment that released a 8.1 magnitude quake in 1934, according to Susan Hough, a seismologist with the U.S. Geological Survey in Pasadena, California. That quake killed an estimated 10,700 people.
Here are illustrations that show, first, how the initial collision occured, then how the thrust fault is continuing to fracture the crust in the area, and finally where the frontal thrust fault lies in relation to other cracks in this very quake-prone zone.