Mapping finite-fault slip in 3D from spatial correlation between seismicity and point-source Coulomb stress change

The main fault slip and energy release of earthquakes occurs many kilometers below the 
Earth’s surface at seismogenic depth. Complete understanding of large earthquakes requires
mapping the orientation, extent and amount of this fault slip. Such finite-fault slip maps are
typically obtained from inversion of measured or inferred surface phenomena, such as fault
offsets, shaking intensity, and time-varying or differential ground motion from seismograms,
GNSS or InSAR. Here we introduce and illustrate a procedure for mapping finite-fault slip
directly from seismicity and aftershocks—phenomena occurring at seismogenic depth around
an earthquake rupture. For specified source and receiver faults, we construct 3D maps of
source-fault slip by correlation of point-source Coulomb failure stress change (ΔCFS) kernels
across the spatial distribution of seismicity around an earthquake. This procedure finds for
points in 3D space what fault slip best explains, through ΔCFS, the surrounding distribution of
seismicity. These seismicity-stress maps show potential, relative, finite-fault slip; they can also
be used directly for quasi data-driven aftershock forecasting, and as prior constraint for other
slip inversion methods.

We confirm that the seismicity-stress procedure recovers the location of a synthetic point-
source given random seismicity predicted by ΔCFS for the point-source. We next show slip
maps from this procedure for the Parkfield CA area that match well other estimates of co- and
post-seismic slip for the 2004 M6 Parkfield earthquake, and of nearby, long-term slip related to
fast creep. We further confirm agreement between co- and post-seismic slip obtained by this
procedure and by other methods for the 2021 M6 Antelope Valley CA normal-faulting
earthquake. Finally, we show for the 2018 M7.1 Anchorage AK intra-slab earthquake how the
seismicity-stress procedure, combined with multi-scale precise hypocenter relocation, can
resolve the enigma of which mainshock faulting plane ruptured (the shallow, east-dipping
plane), and clarify what structures in the slab were activated in the energetic aftershock
sequence.