A long-standing problem in paleoseismic studies is to distinguish
between aseismic and seismic slips along faults. We address this problem
by characterizing the magnetic fabrics of rock samples around mesoscale
normal faults of aseismic origin, and comparing them to those around
co-seismic normal faults. Detailed sampling profiles along traverses,
<0.2 m up to ~20 m from both sides of the
faults, indicate symmetric and unchangeable magnetic fabrics of
deformation origin that are coaxial with the regional strain field.
These results are essentially different from magnetic fabrics detected
around co-seismic normal faults, which show fault-related fabrics with
asymmetric and changeable orientations. The analysis demonstrates two
end-member cases of magnetic fabrics in association with aseismic and
seismic slips along faults. We suggest that magnetic fabric analysis
provides a powerful and efficient tool to characterize inelastic
deformation around faults, enabling to distinguish between seismic and
aseismic slip histories.