A new science paper reveals unusual surface deformation during the 2019 Ridgecrest earthquake that hit near the San Andreas Fault, California.
Through their analyses, the scientists discovered hundreds of previously unmapped fractures surrounding the 2019 Ridgecrest earthquake sequence.
While most deformation associated with an earthquake is in the same direction as the fault rupture, the geoscientists found areas of deformation that moved in the opposite direction.
Their model analysis showed that these regions moved in this direction because of inelastic deformation, which helped to accommodate the overall fault rupture for the sequence.
In other words, these retrograde fractures did not actually slip in the wrong direction, but the low strength material in the damaged fault zone, which has now seen three major earthquakes, deformed in response to the stress change from the new earthquakes.
Meanwhile, further work is needed to determine the age of these young faults, and whether they slip deep into Earth’s crust or only near the surface.