Dynamic Fault Interaction during a Fluid-Injection-Induced Earthquake: The 2017 Mw 5.5 Pohang Event

Abstract

The 15 November 2017 Mw 5.5 Pohang, South Korea, earthquake has been linked to hydraulic stimulation and fluid injections, making it the largest induced seismic event associated with an enhanced geothermal system. To understand its source dynamics and fault interactions, we conduct the first 3D high-resolution spontaneous dynamic rupture simulations of an induced earthquake. We account for topography, off-fault plastic deformation under depth-dependent bulk cohesion, rapid velocity weakening friction, and 1D subsurface structure. A guided fault reconstruction approach that clusters spatiotemporal aftershock locations (including their uncertainties) is used to identify a main and a secondary fault plane that intersect under a shallow angle of 15°. Based on simple Mohr–Coulomb failure analysis and 180 dynamic rupture experiments in which we vary local stress loading conditions, fluid pressure, and relative fault strength, we identify a preferred two-fault-plane scenario that well reproduces observations. We find that the regional far-field tectonic stress regime promotes pure strike-slip faulting, whereas local stress conditions constrained by borehole logging generate the observed thrust-faulting component. Our preferred model is characterized by overpressurized pore fluids, nonoptimally oriented but dynamically weak faults and a close-to-critical local stress state. In our model, earthquake rupture “jumps” to the secondary fault by dynamic triggering, generating a measurable non-double-couple component. Our simulations suggest that complex dynamic fault interaction may occur during fluid-injection-induced earthquakes and that local stress perturbations dominate over regional stress conditions. Therefore, our findings have important implications for seismic hazard in active georeservoir.

Constraining families of dynamic models using geological, geodetic and strong ground motion data: the Mw 6.5, October 30th, 2016, Norcia earthquake, Italy

“…We find that locally over-stressing the fault (i.e., assuming the initial stress just above yield stress as, e.g. Palgunadi et al, 2020) tends to create artificially large fault slip in the hypocentral area and unrealistic strong pulses in the synthetic seismograms. Instead, we gradually reduce the yield strength in a circular area centered at the hypocenter expanding at time-decreasing speed (Harris et al, 2018) which allows a smooth transition to fully spontaneous dynamic rupture propagation.…”

“…SeisSol reaches scalable performance up to several thousand nodes on modern supercomputers (Heinecke et al, 2014;Upho↵ et al, 2017) and has been applied in large-scale, data-integrated earthquake models, including crustal events (Wollherr et al, 2019;Ulrich et al, 2019), intraplate (Palgunadi et al, 2020) and megathrust earthquakes (Upho↵ et al, 2017). SeisSol uses unstructured tetrahedral meshes enabling geometrically complex models, such as branching and intersecting faults .…”

3D Linked Subduction, Dynamic Rupture, Tsunami, and Inundation Modeling: Dynamic Effects of Supershear and Tsunami Earthquakes, Hypocenter Location, and Shallow Fault Slip

“…Physics-based 3D earthquake modeling captures how faults yield, slide and interact (e.g., Ulrich et al, 2019a;Palgunadi et al, 2020) and can provide mechanically viable tsunami-source descriptions (Ryan et al, 2015;Ma and Nie, 2019;Ulrich et al, 2019bUlrich et al, , 2020. We use SeisSol (de la Puente et al, 2009;Pelties et al, 2012Pelties et al, , 2014 to solve simultaneously for frictional failure across prescribed fault surfaces and high-order accurate seismic wave propagation in space and time (illustrated in Figure 1, right).…”

An Efficient ADER-DG Local Time Stepping Scheme for 3D HPC Simulation of Seismic Waves in Poroelastic Media

“…In the second step, the predicted solution is corrected using numerical fluxes across element boundaries. The scheme is explicit in time, which is attractive from a computational perspective, since no global system of equations has to be assembled and solved [27] ADER-DG has been successfully used for a broad range of problems, for example, shallow water equations, relativistic magnetohydrodynamics or the Euler equations [58] In particular, ADER-DG is the basis of many seismological applications [13,19,16,24,25,58,59,17]…”

“…It makes use of unstructured tetrahedral meshes to easily incorporate topography and complex material discontinuities. SeisSol also allows modelling nonlinear rupture dynamics of earthquake sources [22,23,24,25]. SeisSol is optimised for the latest CPU [16,17] and GPU [26] based supercomputers.…”