Scientists Report the Ground Beneath the Sierra Nevada is Moving

The latest scientific evidence points to surprising geologic changes occurring beneath California’s Sierra Nevada mountain range. Reports indicate that the outermost layer of the earth, our planet’s crust, is sinking into the layers beneath. Scientists refer to this as lithospheric foundering.

Lithospheric foundering, also known as delaminating, is thought to be responsible for the planet’s mountain ranges. As the outer layer of the earth moves downward, the pressure beneath pushes upward, filling the gap with the remaining less dense material. As the action continues, it can create mountain ranges. The same process can also produce volcanic activity.

What the Sierra Nevada Evidence Reveals

The Sierra Nevada’s lithospheric foundering means the area is still geologically alive, changing, and capable of yielding valuable insights. The range will undoubtedly appear different to future generations of Earth’s inhabitants with change lasting happening over a staggering number of human lifespans but only in a blink of an eye for geologic features.

The foundering is ongoing and moving northward through the mountain range. The most obvious result of a loss of crust is in the southern Sierra. Scientists believe foundering in that area ended millions of years ago. More recent evidence appears in the central part of the mountain range, which is home to far deeper seismic activity than scientists would expect.

The varying degrees of foundering in the Sierra Nevada area provide a geological panoramic portrait of the growth and change of continents. Research scientists and authors Vera Schulte-Pelkum and Deborah Kilb published their findings in a recent issue of Geophysical Research Letters.

Kilb, comparing decades of seismic activity records, noticed earthquakes were occurring much deeper beneath the Sierra Nevada than conventional wisdom says they should. Earthquakes can happen at tremendous depths, but Kilb, a project scientist working at San Diego’s Scripps Institution of Oceanography in San Diego, explained that, in California, they typically occur between 10 and 18 kilometers or 6 and 11 miles deep. Surprisingly, she was finding records of seismic activity that was between 20 and 40 kilometers (12.4 and 25 miles) deep.

How the Researchers Gathered Evidence

Kilb conferred with Professor Schulte-Pelkum at the University of Colorado Boulder. The two scientists used existing data to create a multi-dimensional representation of what was happening far below ground. The process is called receiver function analysis.

Scientific receiving stations in earthquake-prone areas record the seismic vibrations reaching their sensors. How the waves travel through the ground and interact with various materials gives away important data, revealing the subsurface structure it encounters. For example, receiver functions can tell researchers the composition of the earth's layers, such as the mantle and the crust.

Between the mantle and the crust is an area called the Moho. Its full name is the Mohorovicic Discontinuity. It gets its name from the researcher who discovered it in 1909 by analyzing the rise in the velocity of seismic signals as vibrations reached the area. The change indicated the presence of a region distinct from the mantle and the crust in terms of its material composition and density.

Achieving a better understanding of how to use existing data to gain new insight could prove useful when examining other earthquake areas. The research could also shed valuable light on how our planet gave birth to its continents.