Regional stresses inferred from coseismic slip models of the 2008 Mw 7.9 Wenchuan, China, earthquake

The weight of the mountains: Constraints on tectonic stress, friction, and fluid pressure in the 2008 Wenchuan earthquake from estimates of topographic loading

“…It is somewhat discrepant with stress orientations estimated at ∼800 m depth adjacent to the Beichuan fault in the Wenchuan Earthquake Fault Scientific Drilling Project Hole‐1 (WFSD‐1) borehole of the Wenchuan Earthquake Fault Scientific Drilling Project several years after the 2008 earthquake [ Cui et al , ], which show σ H max to be more orthogonal to the fault trace, suggesting that much of the right‐lateral component of shear stress was released during the earthquake. Our results are also similar to the orientations of total stress obtained by Medina Luna and Hetland [], although they were unable to constrain the magnitudes of stresses.…”

“…Sections of faults that ruptured in the Wenchuan earthquake (which we simply refer to as the “Wenchuan earthquake faults”) with shallow to moderate dips largely ruptured as thrust, and sections with steeper dips largely ruptured as strike slip. Medina Luna and Hetland [] concluded that this relationship is consistent with a uniform orientation of principal stresses, where the variation of the dip of the fault leads to a change in the direction of maximum fault shear stress, which they assumed to be parallel to the coseismic slip rake.…”

“…Therefore, stress is often treated in a semiquantitative manner, with an emphasis on directions and relative magnitudes of the principal stresses, either locally or regionally [e.g., Angelier , ]. These estimates of stress are commonly derived from strain, for example, from studies of earthquake focal mechanisms [e.g., Michael , ] or of fault slip data [e.g., Reches , ; Medina Luna and Hetland , ].…”

“…Assumption (1) is the common “Wallace‐Bott” assumption (named after Wallace [] and Bott []), and note that it ignores dynamic stresses during the earthquake process and only consider that fault slip is collinear with the accumulated stress on the fault prior to rupture. While this assumption should be subject to further testing, it is standard in all studies that infer stress from earthquake data [e.g., McKenzie , ; Angelier , ; Michael , ; Reches , ; Luttrell et al , ; Medina Luna and Hetland , ]. If topographic stresses are significant and produce shear in the direction of fault slip, then for given values of static friction and pore fluid pressure, we can calculate the amount of tectonic stress that can be added to the ambient stress field before the faults should rupture; given limited acceptable ranges for friction and fluid pressure, we are essentially able to place maximum constraints on tectonic stress.…”

Spatial and Temporal Variations in the Moment Tensor Solutions of the 2008 Wenchuan Earthquake Aftershocks and Their Tectonic Implications

“…However, we should not neglect that the northeast segments of Wenchuan mainshock rupture are dominated by strike‐slip motions; also, the number of strike‐slip moment tensors generally increases from southwest to northeast and dominated the north end (S6 segment). Medina Luna and Hetland () inferred that the Wenchuan mainshock was consistent with a homogeneous compressive state of stress, with most compressive stress trending approximately east‐west, prior to the occurrence of the Wenchuan earthquake. However, such a homogeneous stress might not explain many of the strike‐slip‐oriented stress measurements (e.g., both premainshock and postmainshock, Du et al, ) and the ENE‐WSE compressive stress direction at the northeast segment of Longmen Shan fault zone (measured after the mainshock, Q. C. Chen et al, ).…”