Dependence of earthquake stress drop on critical slip‐weakening distance

Abstract

[1] Numerical simulations are conducted to investigate the dependence of the static stress drop of earthquakes on the critical slip-weakening distance. A fault model in a two-dimensional elastic medium is used, in which a locked zone (asperity) is assumed to exist between creeping zones. The presence of such a zone is commonly assumed for plate boundaries that have relatively low seismic coupling. Shear stress is concentrated at the edges of the locked zone and seismic rupture occurs when the strain energy release by rupture extension becomes sufficiently large to overcome the fracture energy. The static stress drop is calculated by taking the ratio of the average seismic slip to the length of seismic slip zone for the simulated earthquakes in the model, using various values for the normal stress applied to the fault and the characteristic slip distance of a rate-and state-dependent friction law. The simulation results indicate that the static stress drop is proportional to the square root of the product of the critical slip-weakening distance and the normal stress, when the seismic rupture starts near an edge of the locked zone. In contrast, when the seismic rupture starts near the center of the locked zone, the static stress drop increases linearly with normal stress and is independent of the critical slip-weakening distance. These simulation results may explain the relatively small depth dependence, as well as the large scatter, in observations of the static stress drop.

Effect of Seismogenic Depth and Background Stress on Physical Limits of Earthquake Rupture Across Fault Step Overs

“…The possibility of step over jumps can be affected by relations between seismogenic depth and the long‐term average stress at which a fault operates. In earthquake cycle models of faults loaded by deep creep (Kato, ), it is found that as W increases the average stress decreases. Fracture mechanics analysis of this problem leads to a relation that can be formulated as .…”

“…The fundamental results assuming homogeneous initial stress presented here can help understand the outcomes of such more complete models. For example, we expect initial shear stress to be mostly concentrated near the deep edge of the seismogenic zone due to creep on the deeper portion of the fault (see, e.g., Figure 1 of Kato, ). If this stress concentration is substantial, we should observe a tendency for ruptures on secondary faults to initiate in the deepest part of the seismogenic zone.…”

A shallow strong patch model for the 2011 great Tohoku-oki earthquake: A numerical simulation

“…Although some uncertainty is included in estimates of D c for earthquakes, D c of 1.5–2.0 m seems to be permissible [e.g., Zhang et al , 2003]. The recurrence interval T r of great earthquakes is controlled by fracture energy at the strong patch and the theoretical consideration suggests that T r is proportional to [ Kato , 2010]. We perform numerical simulations for various values of friction parameters to confirm that qualitatively similar results can be obtained for only higher σ n eff or only larger L at the shallow patch, though too large L leads to slow earthquakes or stable sliding [ Kato and Hirasawa , 1997].…”

Crack Models of Repeating Earthquakes Predict Observed Moment‐Recurrence Scaling

“…We point out that the definition of earthquake used here (based on a velocity threshold) probably does not accurately reflect the way seismic ruptures are recorded, making it difficult to directly translate our results into observable variations in source properties. In fact, a similar study by Kato (2012b) found constant stress drops for ruptures nucleating at the center, the discrepancy most likely explained by the use of a lower velocity threshold (0.01 m/s), which resulted in part of…”