Earthquake ruptures modulated by waves in damaged fault zones

• Published in: Journal of geophysical research. Solid earth 2014-04, Vol.119 (4), p.3133-3154
• Main Authors: Huang, Yihe, Ampuero, Jean-Paul, Helmberger, Don V.
• Format: Article
• Language: English
• Subjects: Acceleration; Attenuation; Damage; damaged fault zone; Deformation; dynamic rupture simulation; Earthquake damage; Earthquakes; Fault lines; Fault zones; Faults; Geological faults; Geophysics; head wave; Kinematics; Modulus of elasticity; Oscillations; P-waves; Plastic deformation; Plastics; Plate tectonics; Properties; reflected wave; Reflected waves; Rock; Rocks; Rupture; Rupturing; Seismic activity; Seismic phenomena; Seismic velocities; Seismic wave velocities; Seismic waves; Seismology; Slip; Stress distribution; Wave velocity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2013JB010724

Faults are usually surrounded by damaged zones of lower elastic moduli and seismic wave velocities than their host rocks. If the interface between the damaged rocks and host rocks is sharp enough, earthquakes happening inside the fault zone generate reflected waves and head waves, which can interact with earthquake ruptures and modulate rupture properties such as rupture speed, slip rate, and rise time. We find through 2–D dynamic rupture simulations the following: (1) Reflected waves can induce multiple slip pulses. The rise time of the primary pulse is controlled by fault zone properties, rather than by frictional properties. (2) Head waves can cause oscillations of rupture speed and, in a certain range of fault zone widths, a permanent transition to supershear rupture with speeds that would be unstable in homogeneous media. (3) Large attenuation smears the slip rate function and delays the initial acceleration of rupture speed but does not affect significantly the rise time or the period of rupture speed oscillations. (4) Fault zones cause a rotation of the background stress field and can induce plastic deformations on both extensional and compressional sides of the fault. The plastic deformations are accumulated both inside and outside the fault zone, which indicates a correlation between fault zone development and repeating ruptures. Spatially periodic patterns of plastic deformations are formed due to oscillating rupture speed, which may leave a permanent signature in the geological record. Our results indicate that damaged fault zones with sharp boundaries promote multiple slip pulses and supershear ruptures. Trapped waves in fault zones modulate the kinematic properties of ruptures Relations between fault‐zone structure and rupture properties are characterized Fault zone waves enable rupture at speeds unstable in homogeneous media