title: Investigating the earthquake cycle of normal faults
Creators: name: Bie, Lidong
Publisher: name: University of Liverpool Repository
Year: 2015

description: Geodetic observations of crustal deformation through the earthquake cycle provide unique opportunities to gain essential knowledge of faulting mechanisms, lithospheric rheology, and fault interaction. Normal faults, an integral geologic unit responsible for crustal deformation, are specifically investigated in this thesis, via three case studies in two significantly different tectonic environments: the 2008 Mw 6.3 Damxung and Mw 7.1 Yutian earthquakes on the Tibetan Plateau, and the 2005 Mw 7.8 Tarapaca earthquake in the northern Chile subduction zone. To move toward realistic slip models, I consider crustal layering for the Damxung earthquake, and non-planar rupture for the Yutian earthquake. The Damxung study shows that assuming a homogeneous crust underestimates the depth of slip and overestimates the magnitude, in comparison to a crustal model with a weak sedimentary lid. A curved fault model composed of triangular dislocation elements (TDEs) for the Yutian earthquake recovers the geodetic observation better than rectangular fault segments. Normal faulting earthquakes are characterized by shallow slip deficit, which is partially compensated by patchy afterslip around, but no deeper than, the coseismic rupture. The complementary and partially-overlapping relationship between coseismic slip and afterslip implies complexity of frictional properties in both down-dip and along-strike directions. Postseismic deformation induced by viscoelastic relaxation (VER) following normal faulting earthquakes is fundamentally different in pattern from that produced by afterslip. This difference enables identification of afterslip as the major postseismic mechanism for the Damxung and Yutian earthquakes, and VER for the Tarapaca earthquake. In addition to understanding the faulting mechanism, I also place constraints on local rheological structure. In central Tibet, where the Damxung earthquake occurred, lack of noticeable VER-related signal allows a lower bound of 1 × 1018 Pa s for the viscosity of the lower crust/upper mantle. In northern Chile, geodetic observations following the Tarapaca earthquake indicate a weak layer with viscosity of 4 – 8 × 10^18 Pa s beneath a higher-viscosity lower crust and mantle lithosphere, and a strong continental forearc. Based on the co- and post-seismic models, I investigate fault interaction from a perspective of static stress change. Stress computation suggests that the 2014 Mw 6.9 strike-slip event close to the Altyn Tagh fault occurred on a fault that was positively stressed by the Yutian earthquake, and the Altyn Tagh fault to the east of the 2014 rupture is a potential locus for future failure. Although the Coulomb stress change on the 2014 Iquique earthquake rupture is negative due to the Tarapaca earthquake and its postseismic VER process, positive loading on the shallow-dipping nodal plane of its M 6.7 preshock suggests that the Tarapaca earthquake may have acted as an indirect trigger of the 2014 Iquique earthquake. Both studies reveal the role played by normal faults in interacting with other types of faults and have implications for seismic hazard assessment.