arXiv subjects

Shiqing Xu

Publications and source records attributed to Shiqing Xu.

4 recordsLinked to original sources

arXiv2024

Back-Propagating Rupture: Nature, Excitation, and Implications

Recent observations show that certain rupture phase can propagate backward relative to the earlier one during a single earthquake event. Such back-propagating rupture (BPR) was not well considered by the conventional earthquake source studies and remains a mystery to the seismological community. Here we present a comprehensive analysis of BPR, by combining theoretical considerations, numerical simulations, and observational evidences. First, we argue that BPR in terms of back-propagating stress wave is an intrinsic feature during dynamic ruptures; however, its signature can be easily masked by the destructive interference behind the primary rupture front. Then, we propose an idea that perturbation to an otherwise smooth rupture process may make some phases of BPR observable. We test and verify this idea by numerically simulating rupture propagation under a variety of perturbations, including a sudden change of stress, bulk or interfacial property and fault geometry along rupture propagation path. We further cross-validate the numerical results by available observations from laboratory and natural earthquakes, and confirm that rupture "reflection" at free surface, rupture coalescence and breakage of prominent asperity are very efficient for exciting observable BPR. Based on the simulated and observed results, we classify BPR into two general types: interface wave and high-order re-rupture, depending on the stress recovery and drop before and after the arrival of BPR, respectively. Our work clarifies the nature and excitation of BPR, and can help improve the understanding of earthquake physics, the inference of fault property distribution and evolution, and the assessment of earthquake hazard.

physics.geo-ph↗

arXiv2023

The sharp turn: backward rupture branching during the 2023 Mw 7.8 Turkey earthquake

Multiple lines of evidence indicate that the 2023 Mw 7.8 Turkey earthquake started on a splay fault, then branched bilaterally onto the nearby East Anatolian Fault (EAF). This rupture pattern includes one feature deemed implausible, called backward rupture branching: rupture propagating from the splay fault onto the SW EAF segment through a sharp corner (with an acute angle between the two faults). To understand this feature, we perform 2.5-D dynamic rupture simulations considering a large set of possible scenarios. We find that both subshear and supershear ruptures on the splay fault can trigger bilateral ruptures on the EAF, which themselves can be either subshear, supershear, or a mixture of the two. In most cases, rupture on the SW segment of the EAF starts after rupture onset on its NE segment: the SW rupture is triggered by the NE rupture. Only when the EAF has initial stresses very close to failure, its SW segment can be directly triggered by the initial splay-fault rupture, earlier than the activation of the NE segment. These results advance our understanding of the mechanisms of multi-segment rupture and the complexity of rupture processes, paving the way for a more accurate assessment of earthquake hazards.

physics.geo-ph↗

arXiv2023

An energy-based perspective on the correlation between stress drop and rupture speed

Stress drop $\Delta\tau$ and rupture speed $V_r$ are two important earthquake source parameters that control the characteristics of rupture process and the associated ground motion. However, how the two parameters correlate with one another is currently still under debate. Here I use an energy-based approach from fracture mechanics to understand the correlation between $\Delta\tau$ and $V_r$. This approach is built on the balance between fracture energy $G_c$ and dynamic energy release rate $G_d$ (which itself is a function of $\Delta\tau$ and $V_r$). By synthesizing various observations within a unified fracture-energy ($G_c$) framework, I show that near constant $G_c$ can yield a positive correlation between $\Delta\tau$ and $V_r$, whereas variable $G_c$ dependent on space, time or off-fault damage may cause a negative correlation between $\Delta\tau$ and $V_r$. These results reconcile the debate on the correlation between $\Delta\tau$ and $V_r$ and suggest a need to examine the condition of other factors (such as $G_c$). Additional factors may complicate the evaluation of the correlation between $\Delta\tau$ and $V_r$ when rupture process is inferred from far-field observations, accompanied by strong spatiotemporal variation, or followed by additional phases, which should be investigated by future studies.

physics.geo-ph↗

arXiv2017

Non-monotonicity of the frictional bimaterial effect

Sliding along frictional interfaces separating dissimilar elastic materials is qualitatively different from sliding along interfaces separating identical materials due to the existence of an elastodynamic coupling between interfacial slip and normal stress perturbations in the former case. This bimaterial coupling has important implications for the dynamics of frictional interfaces, including their stability and rupture propagation along them. We show that while this bimaterial coupling is a monotonically increasing function of the bimaterial contrast, when it is coupled to interfacial shear stress perturbations through a friction law, various physical quantities exhibit a non-monotonic dependence on the bimaterial contrast. In particular, we show that for a regularized Coulomb friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is a non-monotonic function of the bimaterial contrast, and provide analytic insight into the origin of this non-monotonicity. We further show that for velocity-strengthening rate-and-state friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is also a non-monotonic function of the bimaterial contrast. Results from simulations of dynamic rupture along a bimaterial interface with slip-weakening friction provide evidence that the theoretically predicted non-monotonicity persists in non-steady, transient frictional dynamics.

cond-mat.mtrl-sci↗