10:45 〜 11:00
[SCG46-07] Micro-seismicity clustering, aftershock decay and b-values during laboratory fracture and stick-slip experiments
★Invited Papers
キーワード：b-value, aftershocks, seismicity clustering
Earthquakes rarely occur in isolation but rather as sequences of events, clustered in space and time. We study seismic event clustering in controlled laboratory experiments where fault zone properties and stress can directly be monitored. We employ recently-developed statistical methods (e.g., nearest-neighbor clustering, R-statistic, Bi-statistic) to resolve seismic event interactions in series of experiments on in-tact and faulted Westerly granite samples. The samples exhibit different heterogeneity and roughness which strongly impact seismicity clustering.
Our result show that heterogeneity in intact-samples promotes spatial clustering of seismic events albeit without temporal (Omori-type) correlations. Aftershock-like clustering is absent even during fracture nucleation and propagation close to peak stress. Aftershock-like triggering occurs during stable sliding on freshly formed fractures and in the presence of large-scale stress heterogeneity. The detected aftershocks in these cases can be described by standard seismological relationships such as a modified Omori-Utsu relation and its associated inter-event time distribution and productivity relation. Similarly, stick-slip on rough faults is associated with notable spatial-temporal seismicity clustering and Omori-decay mirroring natural seismicity statistics. Homogenous, planar surfaces, on the other hand, produce few aftershocks after unstable slip. Fault roughness also governs b-values and focal mechanisms variability. Rough faults lead to more heterogeneous focal mechanisms, spatially distributed seismicity and high b-values. The variability in focal mechanisms can be explained by heterogeneous, underlying stress fields which limit rupture size and promote high energy release within aftershock sequences. We conclude that roughness and heterogeneity strongly affect events sizes, clustering and seismic energy partitioning between fore, main and aftershocks.
Our result show that heterogeneity in intact-samples promotes spatial clustering of seismic events albeit without temporal (Omori-type) correlations. Aftershock-like clustering is absent even during fracture nucleation and propagation close to peak stress. Aftershock-like triggering occurs during stable sliding on freshly formed fractures and in the presence of large-scale stress heterogeneity. The detected aftershocks in these cases can be described by standard seismological relationships such as a modified Omori-Utsu relation and its associated inter-event time distribution and productivity relation. Similarly, stick-slip on rough faults is associated with notable spatial-temporal seismicity clustering and Omori-decay mirroring natural seismicity statistics. Homogenous, planar surfaces, on the other hand, produce few aftershocks after unstable slip. Fault roughness also governs b-values and focal mechanisms variability. Rough faults lead to more heterogeneous focal mechanisms, spatially distributed seismicity and high b-values. The variability in focal mechanisms can be explained by heterogeneous, underlying stress fields which limit rupture size and promote high energy release within aftershock sequences. We conclude that roughness and heterogeneity strongly affect events sizes, clustering and seismic energy partitioning between fore, main and aftershocks.