Date Published: April 25, 2019
Publisher: Public Library of Science
Author(s): Bo Shao, Guiting Hou, Shuan-Hong Zhang.
The interaction of active faults as a factor affecting the mechanisms of large earthquakes has been observed in many places. Most aftershock and clustering earthquake sequences do not recur on the main seismogenic fault but are controlled by fault interactions with adjacent seismic structures. Four groups of conceptual models were generated in this study to determine how the geometry of the seismogenic faults controls the distributions of stress fields and earthquakes. The influences of the fault length ratio, center distance, overlap ratio, echelon distance and fault opening angle were considered in a 2D viscoelastic model. The results indicate that the interaction in the slipping zone is larger when collinear interacting faults are more closely positioned, with one fault lengthening. For noncollinear faults, the interaction is stronger as the inner tips pass each other, which impedes their growth after some degree of overlap. Additionally, fault interaction at the slipping zone becomes stronger as the opening angle approaches 180°. We further generated a 3D viscoelastic model of fault interactions in Central North China Block and applied the finite element method to analyze the relationship between distributions of earthquakes and fault geometry. The calculated results reveal well-matched higher stress and maximum shear strain concentrations in the southern part of the Fen-wei Graben Zone than in other zones in Central North China Block, which can be explained by the longer faults, shorter center distances, shorter overlap lengths and larger opening angles. The stress distributions and fault interactions should be considered in long-term seismic hazard assessment in these zones.
Interactions between active faults have been observed in many places, and stress-change calculations for such interactions can reveal information about the dynamics and evolution of earthquakes, e.g., in California[1–4]. The motivation behind this study is to shed light on the dynamics of seismic initiation and migration by analyzing the interaction between different faults with various geometries and kinematics.
Factors affecting the mechanisms of large earthquakes in the CNCB mainly include the coupling of the velocity anomaly body and active faults[45–47], the constraints on the boundaries of different active blocks[48, 49] and the anisotropy of the lithosphere. The current seismic hazard assessment relies on the characteristic earthquake recurrence model, i.e., the detailed locations of the active faults[51, 52]. However, most of the aftershock and clustering earthquake sequences do not recur on the main seismogenic fault but are controlled by the fault interactions of the adjacent seismic structures . Additionally, the mechanism of newly formed active faults is the result of interactions, such as the formation of the San Andreas Fault at the Mendocino triple junction .
The conceptual models considered the influences of the fault length ratio, center distance, overlap coincidence ratio and opening angle, and the following primary conclusions are drawn: