Seismological evidence for a multifault network at the subduction interface

Area of Science:

• Earthquake seismology and subduction zone dynamics.

Background:

• Subduction zones produce Earth's largest earthquakes, but their detailed structure and influence on seismic/aseismic slip are poorly understood.
• Geological studies suggest deformation occurs on meter-thick faults within a 100m-1km thick seismogenic interface.
• Seismological studies often image the seismogenic interface as a wider band of seismicity, obscuring meter-scale fault activity and its role in the seismic cycle.

Purpose of the Study:

• To investigate the seismic activity of meter-thick faults at the plate interface in subduction zones.
• To understand how these meter-scale structures influence deformation and afterslip propagation.
• To improve the realism of earthquake rupture and hazard models for subduction zones.

Main Methods:

• Utilized a local three-dimensional velocity model for high-resolution imaging.
• Analyzed dense seismic observations from over 1,500 double-difference relocated earthquakes in Ecuador.
• Mapped seismicity to reveal fault geometry and its relationship with seismic and aseismic slip.

Main Results:

• Detected meter-thick faults exhibiting seismic activity within the subduction zone plate interface.
• Observed earthquakes occurring on single or multiple, simultaneously active, subparallel planes.
• Demonstrated that this geometrical complexity directly affects afterslip propagation, highlighting fault continuity's influence on slip.

Conclusions:

• Meter-thick faults are active and play a crucial role in controlling slip behavior at the seismogenic interface.
• The geometric complexity of faults significantly influences afterslip propagation dynamics.
• Findings necessitate more realistic earthquake rupture and hazard models for subduction zones, incorporating detailed fault structures.