Weak and Shallow Secondary Frictional Faults Revealed by Large Earthquakes in Haiti

Abstract Geological, geodetic, and seismological observations show that large earthquakes damage the crust surrounding the main rupture and, sometimes, activate nearby, smaller, secondary faults. However, the long‐term tectonic role of such secondary faults and their behavior in response to earthquakes or tectonic loading are unclear. We describe secondary faults activated by the Mw 7.2, 2021 Haiti earthquake within the Enriquillo Plantain Garden Fault zone and show that they continued to slip for weeks after the main event, some of them slipping against the long‐term tectonic stress. We model this time‐dependent behavior as frictional slip in response to shear stress changes imparted by the earthquake. These faults, widely distributed in the hanging wall of the main rupture, are therefore very weak and capable of slipping under small stress changes. Therefore, they should also diffuse some of the tectonic loading between large earthquakes, reducing the amount of stress that accumulates at shallow crustal depths.