Wave Interaction of Reverse‐Fault Rupture With Free Surface: Numerical Analysis of the Dynamic Effects and Fault Opening Induced by Symmetry Breaking

• Published in: Journal of geophysical research. Solid earth 2019-02, Vol.124 (2), p.1743-1758
• Main Authors: Scala, A., Festa, G., Vilotte, J.‐P., Lorito, S., Romano, F.
• Format: Article
• Language: English
• Subjects: Acceleration; Asymmetry; Broken symmetry; Deformation; Dependence; Dipping; Dynamics; Earthquakes; Fault lines; free surface fault interaction; Free surfaces; Geological faults; Geophysics; Ground motion; Hanging walls; Inertia; Numerical analysis; numerical simulations; Radiation; Rupture; Rupturing; Sciences of the Universe; Seismic activity; seismic source dynamics; Slip; Static deformation; Subduction; Subduction (geology); Symmetry; Thrust; Thrust faults; Traction; Wave interaction
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2018JB016512

Several great earthquakes occur on thrust faults along both subduction and continental collision zones. These events often feature a large shallow slip patch, an asymmetric pattern for the ground motion, and the static deformation between the hanging wall and footwall of the fault. From a mechanical point of view, this asymmetry can be partially explained taking into account the interaction between the fault and the seismic radiation emitted during rupture propagation and stored in the hanging wall in the vicinity of the free surface. We numerically investigate the rupture dynamics along a thrust dipping fault impacting onto the free surface at a dip angle of δ = 20°, in a 2‐D elastic model. We show how the wave interaction of the rupture with the free surface leads to a breaking of the reflection symmetry. Compared to a rupture propagating in an infinite medium, this interaction enhances the slip rate in the updip direction as an effect of the coupling between slip and normal traction around the crack front. The breaking of symmetry leads to sizeable acceleration of the rupture toward asymptotic speed with inertia acquisition, and dependence of the rupture dynamics on the level of friction along the interface might produce an interface opening over a finite length in the vicinity of the surface. We finally explore how the wave interaction drives amplification and asymmetry of the shallow slip and the vertical displacement at the surface. The described effects should be considered in various numerical approaches and in interpretation of geophysical observations. Key Points Symmetry breaking from free surface/rupture interaction may enhance slip, ground motion, and tsunamigenic potential of shallow ruptures Rupture dynamics deviates from classical linear elastic fracture mechanics: inertial effects in the energy balance and shallow opening The effects of the interaction are strongly sensitive to the friction level; the higher the friction, the more important the interaction