Fault Rupture Research Articles

ANN-Based Assessment of Soft Surface Soil Layers’ Impact on Fault Rupture Propagation and Kinematic Distress of Gas Pipelines

Large-scale lifelines in seismic-prone regions very frequently cross areas that are characterized by active tectonic faulting, as complete avoidance might be techno-economically unfeasible. The resulting Permanent Ground Displacements (PGDs) constitute a major threat to such critical infrastructure. The current study numerically investigates the crucial impact of soil deposits, which usually cover the ruptured bedrock, on the ground displacement profile and the kinematic distress of natural gas pipelines. For this purpose, a decoupled numerical methodology, based on Finite Element Method (FEM), is adopted and a detailed parametric investigation is performed for various fault and soil properties. Moreover, the advanced capabilities of Artificial Neural Networks (ANNs) are utilized, aiming to facilitate the fast and reliable assessment of soil response and pipeline strains due to seismic faulting, replacing time-consuming FEM computations. An extensive sensitivity analysis is performed to select the optimal architecture and training algorithm of the employed ANNs for both the geotechnical and structural parts of the decoupled approach, with suitable input and target values related to bedrock offset, fault and soil properties, surface PGDs, and pipeline strains. The proposed ANN-based approach can be efficiently applied by practice engineers in seismic design and route optimization of natural gas pipelines.

SeisSol input files for "Dueling dynamics: competition between low-angle normal fault rupture, splay faulting, & off-fault damage"

SeisSol input files for "Dueling dynamics: competition between low-angle normal fault rupture, splay faulting, & off-fault damage"

Slow Fault Slip Signatures in Coseismic Ionospheric Disturbances

AbstractRise times of earthquake moment release influence the spectra of seismic waves. For example, slow fault movements in tsunami earthquakes excite larger tsunamis than expected from intensities of short‐period seismic waves. Here we compare amplitudes of two different atmospheric waves, long‐period internal gravity waves and short‐period acoustic waves, excited by coseismic vertical crustal movements. We observe them as coseismic ionospheric disturbances by measuring ionospheric electrons using global navigation satellite systems. Four regular megathrust earthquakes Mw 8.0–9.0 showed that the internal gravity waves become ten times stronger as the magnitude increases by one. We found that the 2010 Mentawai earthquake, a typical tsunami earthquake, excited internal gravity waves stronger than those expected by this empirical relationship. On the other hand, amplitudes of acoustic waves excited by tsunami earthquakes were normal. This suggests that slow fault ruptures excite long‐period atmospheric waves efficiently, leaving a slow earthquake signature in ionospheric disturbances.

Large‐scale ground motion simulation of the 2016 Kumamoto earthquake incorporating soil nonlinearity and topographic effects

AbstractA large‐scale physics‐based simulation is conducted to investigate ground motion distribution in the Mw 7.0 2016 Kumamoto earthquake, Japan. The model simulates the earthquake scenario from fault rupture to wave propagation, and localized site response with consideration of the combined effect of soil nonlinearity and topographic amplification. The simulation domain is 51 km × 43 km × 25 km, and the obtained ground motion time histories are compared satisfactorily with recordings from KiK‐net and K‐NET. Ground motion distribution considering nonlinear soil response and topographic amplification is presented. A 3D equivalent linear model is developed to mimic the soil nonlinearity, and it is demonstrated that neglecting soil nonlinearity could over‐predict peak ground acceleration (PGA) and underestimate peak ground velocity (PGV) near the fault. The topographic amplification factors (TAFs) of PGA and PGV are found between 0.5 and 2.0, with a correlation coefficient of 0.7 between them. Predictive equations are proposed to correlate TAFs of PGA and PGV with topographic features, which are represented by relative heights obtained at different length scales. Finally, major earthquake damages are summarized with reference to the obtained ground motion intensity map.

Resource-based seismic resilience optimization of the blocked urban road network in emergency response phase considering uncertainties

For disaster management organizations, determining the required resources for pre-positioning and optimal resources allocation schedules are important problems in the preparation planning stage for emergency restoring blocked urban road networks. This study bridges the gap between seismic simulation of network obstruction due to roadside collapsed buildings, resource allocation scheduling, and Bruneau's proposed resilience index to assessment the required resources and optimal restoration planning. There are uncertainties in different parts of network restoration planning such as uncertainty in earthquake magnitude, fault rupture location, seismic intensity, building collapse, debris width, debris volume, and restoration time. Uncertainty in a part affects the realization of the next dependent part, therefore integrated framework is needed for realistic restoration planning that has not been addressed in the literature. In this paper, uncertainties are modeled based on probabilistic models to estimate the expected value of path restoration time. Topology-Demand base network functionality index is proposed to evaluate network performance after the earthquake. To optimize resilience, an algorithm based on Simulated Annealing is designed which determines the maximum required resources and optimal task sequences. The proposed framework is showcased by a road network in Tehran metropolis. Equivalent functionality curves are introduced to compare the effects of resource number on network emergency resilience. The optimization results indicate the six resources restore the network within two defined target times. Also, the results reveal that the effect of resource number on reducing the completion time decreases with increasing resources.

Hundalee Fault, North Canterbury, New Zealand: late Quaternary activity and regional tectonics

ABSTRACT The Hundalee Fault forms part of the southeastern margin of the 2016 Kaikōura Earthquake rupture zone. Its late Quaternary activity and structural character may offer insights to fault interrelationships associated with the 2016 rupture. Mapping of the Hundalee Fault revealed several pre-existing fault scarps. Trenching of a scarp across a fluvial terrace together with radiocarbon dating shows the occurrence of at least two, probably three, surface ruptures since 3.5 ka. The scarp records about 2.5 m of reverse-sense vertical deformation, mostly folding, of which ∼0.6 m occurred in 2016, along with subordinate sinistral slip. Fluvial terrace ages inferred from geomorphological relationships, together with the trenching results, indicate a long-term vertical slip rate of 0.2–0.4 mm/yr since at least 30 ka. Geological data indicate a relatively recently surface emergence of the Hundalee Fault from beneath a fault propagation fold. The 2016 Hundalee Fault rupture is interpreted as a break-out from an extensive blind thrust fault, whose motion triggered predominantly contractional rupture of an array of steeper near-surface faults. The thrust is hypothesised as having provided linkage in the 2016 rupture between the predominantly strike-slip ruptures of The Humps Fault to the southwest and the Kekerengu Fault to the northeast.

A Deeper Look Into the 2021 Tyrnavos Earthquake Sequence (TES) Reveals Coseismic Breaching of an Unrecognized Large‐Scale Fault Relay Zone in Continental Greece

AbstractLarge magnitude (Mw ∼ ≥6) earthquakes in extensional settings are often associated with simultaneous rupture of multiple normal faults as a result of static and/or dynamic stress transfer. Here, we report details of the coseismic breaching of a previously unrecognized large‐scale fault relay zone in central Greece, through three successive normal fault earthquakes of moderate magnitude (Mw 5.7–6.3) that occurred over a period of ∼10 days in March 2021. Specifically, joint analysis of InSAR, GNSS and seismological data, coupled with detailed field and digital fault mapping, reveals that the Tyrnavos Earthquake Sequence (TES) was accommodated at the northern end of a ∼100 km wide transfer structure, by faults largely unbroken during the Holocene. By contrast, the southern section of this relay zone appears to have accrued significant slip during Holocene. InSAR‐derived displacements agree with the loci of eight subtle, previously undetected, faults that accommodated coseismic and/or syn‐seismic normal fault slip during the TES. Kinematic modeling coupled with fault mapping suggests that all involved faults are interconnected at depth, with their conjugate fault‐intersections acting largely as barriers to coseismic rupture propagation. We also find that the TES mainshocks were characterized by unusually high (>6 MPa) stress‐drop values that scale inversely with rupture length and earthquake magnitude. These findings, collectively suggest that the TES propagated north‐westward to rupture increasingly stronger asperities at fault intersections, transferring slip between the tips of a well‐established, but previously unrecognized, relay structure. Fault relay zones may be prone to high stress‐drop earthquakes and associated elevated seismic hazard.

Multiscale Modeling of Fault Rupture–Soil–Foundation Interaction

Multiscale Modeling of Fault Rupture–Soil–Foundation Interaction

Rupture process and aftershock focal mechanisms of the 2022 M6.8 Luding earthquake in Sichuan

According to the China Earthquake Networks Center, a strong earthquake of M6.8 occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China (102.08°E, 29.59°N), on September 5, 2022, with a focal depth of 16 km. Rapid determination of the source parameters of the earthquake sequence is vital for post-earthquake rescue, disaster assessment, and scientific research. Near-field seismic observations play a key role in the fast and reliable determination of earthquake source parameters. The numerous broadband seismic stations and strong-motion stations recently deployed by the National Earthquake Intensity Rapid Report and Early Warning project have provided valuable real-time near-field observation data. Using these near-field observations and conventional mid- and far-field seismic waveform records, we obtained the focal mechanism solutions of the mainshock and M ≥ 3.0 aftershocks through the waveform fitting method. We were further able to rapidly invert the rupture process of the mainshock. Based on the evaluation of the focal mechanism solution of the mainshock and the regional tectonic setting, we speculate that the Xianshuihe fault formed the seismogenic structure of the M6.8 strong earthquake. The aftershocks formed three spatially separated clusters with distinctly different focal mechanisms, reflecting the segmented nature of the Xianshuihe fault. As more high-frequency information has been applied in this study, the absolute location of the fault rupture is better constrained by the near-field strong-motion data. The rupture process of the mainshock correlates well with the spatial distribution of aftershocks, i.e., aftershock activities were relatively weak in the maximum slip area, and strong aftershock activities were distributed in the peripheral regions.

Seismic Performance Evaluation of a Multi Storey RC Structure Subjected to Strong Ground Motions

Abstract: A tremor or a movement of the ground occurs during an earthquake on Earth's surface. Earthquakes can also cause landslides and volcanic eruptions. Natural disasters or human activity can produce earthquakes, which are defined as seismic events generating seismic waves. Earthquakes most commonly occur when geological faults rupture, however they can also occur as a result of volcanic eruptions, landslides, mine explosions, and nuclear testing. The study of structural behavior towards different ground motions is therefore one of the main criteria to determine damage intensity. Structural Analysis of a residential building is carried out by using ETabs Software. Present study is intended to study the dynamic behavior of Multistorey Reinforced Concrete structure by considering, an existing G+13 storey residential building is modeled and its structural behaviour is studied using Time history method by considering different high intensity earthquakes. The behaviour of the building is studied mainly for its base shear, Storey displacement and maximum joint displacement.

Hydraulic Stimulation of Geothermal Reservoirs: Numerical Simulation of Induced Seismicity and Thermal Decline

Enhanced Geothermal Systems (EGS) can boost sustainable development by providing a green energy supply, although they usually require the hydraulic stimulation of the reservoir to increase fluid flow and energy efficiency due to the low rock permeability at the required depths. The injection of fluids for hydraulic stimulation implies several risks, for instance, induced seismicity. In this work, we perform numerical simulations to evaluate the seismic risk in terms of fault reactivation, earthquake magnitude, and rupture propagation. The computational model includes the fully coupled thermo-hydro-mechanical equations and simulates faults as frictional contacts governed by rate-and-state friction laws. We apply our methodology to the Basel EGS project as a continuation of our previous work, employing the same parameters and conditions. Our results demonstrate that permeability stimulation is not only related to induced seismicity but also can induce a thermal decline of the reservoir over the years and during the energy production. The proposed methodology can be a useful tool to simulate induced earthquakes and the long-term operation of EGS.

Study on the multi-criteria seismic mitigation optimization of a single pylon cable-stayed bridge across strike-slip fault rupture zones

Bridge structures across active faults suffer the serious threats from large surface deformation and velocity pulses. This study focuses on developing a multi-criteria optimizing method and investigating the damping effect of the optimized damper system on a cable-stayed bridge across a strike-slip fault. A simplified baseline corrected method is adopted to recover the static offsets in near-fault records and the improved record-decomposition incorporation method is modified to produce artificial across-fault ground motions. A single pylon cable-stayed bridge across a strike-slip fault is taken as the case bridge and the refined nonlinear numerical model is established in OpenSees. The conventional multi-criteria decision making (MCDM) theory is improved by introducing new function forms and a control parameter to assess the best fault-crossing angles of the case bridge. The improved MCDM method is integrated with the beetle antennae search algorithm to optimize the damper system of the case bridge. Finally, the influence of fault-crossing angles and earthquake parameters (permanent displacements and ratios of maximum to permanent displacement) on the damping effect of the optimized damper system are investigated. The results indicate that the cable-stayed bridge reaches optimal seismic performance when the fault-crossing angle is around 90° (75°-105°) as both the biaxial nonlinearity of the pylon and the risk of the girder unseating are reduced. The damper system is efficiently optimized by the proposed method, and the displacement and force demand of the case bridge are balanced. Both the fault-crossing angles and earthquake parameters are observed to have considerable influence on the damping effects. More specifically, the damping effect on most seismic responses is optimized when the fault-crossing angle approaches 90° (60°-120°). As the permanent displacement increases, the damping effect on the pier-girder relative displacement is significantly reduced and the damping effect on the pier moments is moderately decreased. Moreover, the damping effect is improved for all the seismic responses as the ratios of maximum to permanent displacements increase, with the exception of transverse displacement.

A phase‐field model for quasi‐dynamic nucleation, growth, and propagation of rate‐and‐state faults

AbstractDespite its critical role in the study of earthquake processes, numerical simulation of the entire stages of fault rupture remains a formidable task. The main challenges in simulating a fault rupture process include the complex evolution of fault geometry, frictional contact, and off‐fault damage over a wide range of spatial and temporal scales. Here, we develop a phase‐field model for quasi‐dynamic fault nucleation, growth, and propagation, which features two standout advantages: (i) it does not require any sophisticated algorithms to represent fault geometry and its evolution; and (ii) it allows for modeling fault nucleation, propagation, and off‐fault damage processes with a single formulation. Built on a recently developed phase‐field framework for shear fractures with frictional contact, the proposed formulation incorporates rate‐ and state‐dependent friction, radiation damping, and their impacts on fault mechanics and off‐fault damage. We show that the numerical results of the phase‐field model are consistent with those obtained from well‐verified approaches that model the fault as a surface of discontinuity, without suffering from the mesh convergence issue in the existing continuous approaches to fault rupture (e.g., the stress glut method). Further, through numerical examples of fault propagation in various settings, we demonstrate that the phase‐field approach may open new opportunities for investigating complex earthquake processes that have remained overly challenging for the existing numerical methods.

Numerical investigation of the roles of gravel fabric on composite strata deformation induced by thrust faulting

In historical earthquakes, fault ruptures have caused significant ground deformation and infrastructure damage. Because the occurrences of earthquakes are hard to predict, it is critical to assess the area influenced by fault propagation for disaster resistance. Based on trench excavations in active fault zones, earthquake faults propagated through the composite strata with gravel deposits are common. However, the stratigraphy change of the overburden strata and the non-spherical granular particles of the gravel deposit are rarely considered in most case studies. This study proposes a procedure that utilizes digital image analysis and discrete element modeling to estimate the composite strata deformation induced by thrust faulting. The procedure is demonstrated through a series of small-scale sandbox modeling and a case study of the Chushan excavation site in Taiwan. The gravel fabric, including gravel volumetric content, aspect ratio and initial long-axis orientation, are considered in the parametric study as well as the configuration of the strata composition. Simulations show that fault propagation restricts in the overburden because the faulting-induced kinematic energy is mostly dissipated by clast rotation, resulting in a lower fault extended distance and a wider tri-shear zone. The rotation of the gravels shows good agreement with the range of the tri-shear zone, indicating that the long-axis orientations of gravels can be an indicator to interpret the faulting history. Overall, it is feasible to construct a reasonable numerical model for assessing fault rupture-composite strata interaction (FR-CSI) once the outcrop photo data are available. The proposed procedure is useful for efficient and reliable scenario modeling regarding earthquake hazard mitigation.

On various mechanisms of shear wave generation from underground chemical explosions in hard rocks

SUMMARY Significant shear waves observed during underground explosions can make them look similar to natural earthquakes. In the near field, they can be caused by the source geometry and emplacement conditions, heterogeneous and anisotropic properties of the rock mass, relaxation of a non-uniform in situ stress around the source after the departure of the shock wave as well as by activation of nearby faults. The stress relaxation mechanism is important at depth when the difference in main principal stresses becomes significant. Another mechanism of shear motion generation is due to explosive gas flow from the source cavity into the cracks initiated by the shock wave and joints connected to the cavity. Also, the shock wave from the explosion can cause weakening of the rock either due to permanent damage or shock-induced liquefaction at saturated joints. Numerical modelling of underground chemical explosions in hard rock at various confinement stresses has been conducted to compare various mechanisms of shear wave generation and their seismic characteristics with that of a simple fault rupture process observed during an earthquake.

Mechanical Behavior of Soil Foundations Reinforced with Geosynthetics Exposed to Normal and Reverse Fault Ruptures

Surface fault ruptures damage structures which are located at the intersecting zones of active faults. It is essential to consider the undesirable effects of surface fault ruptures when designing structures. Geotechnical measures such as reinforced soil foundations effectively mitigate the hazards related to surface faults. The present work conducted a series of tests on foundations reinforced with geosynthetics, including geogrids, geocells and geogrid-geocell layers. These tests simulated the behavior of 1.5 m-wide strip footings located in 6-m thick alluvium that had been displaced 60 cm. A total of 12 disparate tests in terms of the number and type of reinforcement were conducted at a scale factor of 10. Image analysis of the results indicated desirable behavior for reinforced soil foundations in terms of reduced angular distortion, uniform settlement and deviation of the fault path. For normal fault rupture, the angular distortion of foundations reinforced by one geogrid layer, one geocell layer, one geogrid-geocell layer or two or three geo-grid layers decreased by 60%, 30%, 70%, 80% and 80%, respectively. These results also revealed that an increase in the number of geogrid layers to more than two layers caused an insignificant decrease in angular distortion. The decrease in angular distortions observed for soil foundations reinforced by one geogrid layer, one geocell layer and one geogrid-geocell layer were 7%, 16% and 40%, respectively, for reverse faulting. The performance of a reinforced soil foundation subjected to normal faulting was more acceptable than that for reverse faulting.

Source Model and Characteristics of the 27 July 2022 MW 7.0 Northwestern Luzon Earthquake, Philippines

The geometry and kinematics of the causative fault of the 27 July 2022 moment magnitude (Mw) 7.0 earthquake, which is one of the strongest to hit northern and central Luzon in the past 30 years, were estimated through inverse modeling of line-of-sight interferometric synthetic aperture radar deformation. We modeled rupture along multiple candidate faults based on fit with the pattern of line-of-sight deformation, consistency with focal mechanisms, and compatibility with the known kinematics of the mapped active faults in the region. Our preferred fault model, located west of and parallel to the Abra River Fault (ARF), exhibits localized reverse-slip (average 67° rake) at 15-35 km down-dip. Peak slip occurs at 13-16 km depth, with 95 cm of pure reverse-slip. The existence of a reverse-slip dominated ARF-parallel fault rupture is consistent with a complex shear partitioning model, wherein the NW-SE oblique plate convergence is accommodated not only by the sinistral strike-slip Philippine Fault Zone and the major subduction zones, but also by minor faults in intervening crustal blocks.

Research on the Ability of Geodetic Records to Explain the Slip Distribution of Wenchuan, China, Earthquake

We establish a reasonable 3D complex fault model. The Global Positioning System (GPS) data is adopted to reproduce the slip distribution of the 2008 Mw7.9 Wenchuan earthquake. Utilizing the nonnegative least square method, the slip distribution of the fault plane is recovered. The results are as follows: (1) The released seismic moment of Wenchuan earthquake is 0.959 × 10 21 N · m . The deep of the rupture is mainly within 15 km. (2) The rupture mainly occurred along the Beichuan fault, indicating that the Beichuan fault is the main rupture fault. On the southern section of the Beichuan fault, the rupture is concentrated from Yingxiu to Longmenshan and from Yuejiashan to Qingping areas, with mainly thrust slip. On the northern section of the Beichuan fault, the slip is concentrated near the surface of Beichuan and Nanba areas, with thrust and strike slip. On the Pengguan fault, the slip is mainly located near Hanwang with thrust and strike slip. (3) The GPS data are useful for defining the slip in the shallow part but are useless to determine the slip in the deep part. Meanwhile, the time information of the rupture cannot be reproduced.

High‐Resolution Fault‐Rupture Imaging by Combining a Backprojection Method With Binarized MUSIC Spectral Image Calculation

AbstractBackprojection (BP) methods are widely used for estimating the fault rupture processes; however, they are inherently susceptible to noise. Hence, noise suppression is an important research target. In this paper, we develop a fault rupture imaging method by combining beamforming‐based BP and MUltiple Signal Classification (MUSIC), which realizes artificial noise suppression at a high spatial resolution. The stations are grouped into arrays according to the SH wave radiation coefficients, and MUSIC analysis is performed on each array. The MUSIC spectral images of these arrays are binarized and then multiplied by the BP images. Spatial filtering is also applied to the images based on the possible range of the rupture velocity and rise time. When tested using synthetic test data, the proposed method worked as expected. We then applied this method to the 2016 Kumamoto earthquake by interpolating the travel times from the observed travel times of relocated hypocenters using a 3‐D velocity structure model. In the area of large slip and slip rate approximately 30–50 km from the hypocenter on the Futagawa fault, the spatiotemporal evolution of the fault ruptures and waveform inversion results were generally in harmony. The distributions of the low‐ and high‐frequency seismic radiations are complementary, as is understood in the context of fault rupture physics. This method can aid in understanding and modeling the details of seismic radiation sources, enabling the accurate prediction of strong ground motion even in near‐fault areas.

3D Coseismic Surface Displacements From Historical Aerial Photographs of the 1987 Edgecumbe Earthquake, New Zealand

AbstractEarthquake surface deformation provides key constraints on the geometry, kinematics, and displacements of fault rupture. However, deriving these characteristics from past earthquakes is complicated by insufficient knowledge of the pre‐event landscape and its post‐event modification. The 1987 Mw 6.5 Edgecumbe earthquake in the northern Taupō volcanic zone (TVZ) in New Zealand represents a moderate‐magnitude earthquake with distributed surface rupture that occurred before widespread high‐resolution topographic data were available. We use historical aerial photos to build pre‐ and post‐earthquake digital surface models (DSMs) using structure‐from‐motion techniques. We measured discrete and distributed deformation from differenced DSMs and compared the effectiveness of the technique to traditional field‐ and lidar‐based studies. We identified most fault traces recognized by 1987 field mapping, mapped newly identified traces, and made dense remote slip measurements with a vertical separation resolution of ∼0.3 m. Our maximum and average vertical separation measurements on the Edgecumbe fault trace (2.5 ± 0.3 and 1.2 m, respectively), are similar to field‐based values of 2.4 and 1.1 m, respectively. Importantly, this technique can discern between new and pre‐existing fault scarps better than field techniques or post‐earthquake lidar‐based measurements alone. Our surface displacement results are used to refine subsurface fault geometries and slip distributions at depth, which are further used to investigate potential magmatic‐tectonic stress interactions in the northern TVZ. Our results suggest the Edgecumbe fault dips more gently at depth than at the surface, hosted shallow slip in 1987, and may be advanced toward failure by interactions with nearby magma bodies.