A Structural Interpretation of the Aftershock "Cloud" of the 1992 Mw 7.3 Landers Earthquake

Abstract

We analyze the spatial relationship of relocated aftershocks to the principal rupture planes of the M w 7.3 1992 Landers mainshock from a structural point of view. We find that the aftershocks constitute primarily a several-kilometer-wide damage zone centered on the mainshock rupture planes. The intensity of damage decreases away from the principal faults. Less than half of the aftershocks occurred within 1 km of the mainshock planes, and perhaps only 5% of the aftershocks are candidates for rerupture of the mainshock faults. Moreover, it seems that aftershocks along the Landers rupture have b-values that correlate well with the complexity of the mainshock rupture. Low b-values occur along segments that are simple, whereas higher b-values correlate with sections that are more complex. Thus, structural complexity appears to correlate with a greater relative abundance of small earthquakes. These observations imply that aftershock populations reflect fault populations in the medium surrounding the principal faults rather than the behavior of the mainshock planes themselves.

New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone: Observations from a dense seismic array

“…Barka et al (2002) also measured a~5 m surface displacement following the 1999 İzmit earthquake. Therefore relatively high b-values for the stepover area east of the junction should be expected due to structural heterogeneity (King, 1986;Liu et al, 2003;Wiemer and Katsumata, 1999). The aftershock studies (Aktar et al, 2004;Karabulut et al, 2002;Özalaybey et al, 2002) indicate a cluster of earthquakes in the fault junction, emphasizing a stress accumulation following the İzmit earthquake.…”

Landers 1992 “Reloaded”: Integrative Dynamic Earthquake Rupture Modeling

“…Mapped surface traces and distributed off‐fault deformation indicate that structural complexity is enhanced close to the hypocenter (Liu et al, ; Milliner et al, ). The rapid rupture initiation could potentially be delayed by considering fault structures more complex than the curved, yet purely strike‐slip fault geometry used in our simulation.…”

Three-dimensional models of elastostatic deformation in heterogeneous media, with applications to the Eastern California Shear Zone

“…Such damage zones may result from distributed inelastic deformation associated with the propagation and coalescence of cracks and joints during fault growth (Segall & Pollard 1980;Vermilye & Scholz 1998;Manighetti et al 2001), relaxation of stresses at geometric irregularities (Liu et al 2003;Dieterich & Smith 2007) or dynamic loading at the propagating rupture front (Rice et al 2005;Fialko 2007). Field observations suggest that the thickness of the cataclasite zones correlates with the cumulative fault slip (Scholz 1987).…”