Earthquake Simulation Research Articles

Seismic performance of a full‐scale five‐story masonry‐infilled RC building subjected to substructured pseudodynamic tests

AbstractThis paper discusses the results of a series of hybrid earthquake tests on a full‐scale reinforced concrete (RC) building with masonry infills. The prototype was a five‐story structure representing the vulnerable part of a typical RC building in Southern Europe, with beams stronger than the columns and masonry infill walls weaker than the surrounding frame elements. The specimen was subjected to a sequence of unidirectional earthquake simulations of increasing intensity up to conditions of significant damage to the infills, using the pseudodynamic (PsD) testing method with substructuring. The input ground motion was a real earthquake recording, slightly modified in amplitude and frequency to match the elastic design code spectrum. The physical substructure of the hybrid model consisted of the first story of a two‐story mock‐up structure built in the European Laboratory for Structural Assessment (ELSA); the second story ensured realistic boundary conditions at the top of the first one. The characteristics of stories two to five were simulated by a numerical finite‐element model developed in OpenSEES and updated throughout the test sequence using data obtained from preceding tests. The experiments were terminated with the onset of a soft‐story mechanism at the first story of the physical substructure for an earthquake with a peak ground acceleration of 0.3 g. The paper summarizes the key characteristics of the specimen and the major observations from the hybrid tests, illustrating the evolution of structural/nonstructural damage and the cyclic hysteretic building response. The attainment of significant damage limit states is correlated with experimentally defined engineering demand parameters and ground‐motion intensity measures for the performance‐based seismic assessment of buildings. Data and observations from these experiments add substantially to our understanding of the effects of masonry infills on the seismic behavior of RC‐framed structures.

Seismogenic potential and tsunami threat of the strike-slip Carboneras fault in the western Mediterranean from physics-based earthquake simulations

Abstract. Strike-slip fault ruptures have a limited capacity to generate vertical deformation, and for this reason they are usually dismissed as potential destructive tsunami sources. At the western tip of the western Mediterranean, in the Alboran Sea, tectonics is characterized by the presence of large transcurrent fault systems and minor reverse and normal faults in a zone of diffuse deformation. The strike-slip Carboneras fault is one of the largest sources in the Alboran Sea and therefore with the greatest seismogenic capacity. It is also one of the active structures with higher slip rates in the eastern Betic fault zone and has been proposed as the source of the damaging 1522 (M 6.5; Int. VIII–IX) Almeria earthquake. The dimensions and location of the Carboneras fault imply a high seismic and tsunami threat. In this paper we present tsunami simulations from seismic sources generated with physics-based earthquake simulators. We have generated a 1 Myr synthetic seismic catalogue consistent on 773 893 events, with magnitudes ranging between Mw 3.3 and 7.6. From these events we have selected those sources producing a potential energy capable of generating a noticeable tsunami, those sources being earthquakes with magnitudes ranging from 6.71 to 7.62. The Carboneras fault has the capacity to generate locally damaging tsunamis; however, on a regional scale its tsunami threat is limited. The frequency–magnitude distribution of the generated seismic catalogue reflects the variability of magnitudes associated with the rupture of the entire fault, departing the upper limit from the classical Gutenberg–Richter potential relation. The inter-event time for the maximum earthquake magnitudes is usually between 2000 and 6000 years. The use of physics-based earthquake simulations for tsunamigenic sources allows an in-depth characterization of the scenarios, allowing a qualitative leap in their parametrization.

Kesiapsiagaan Bencana Perawat di Rumah Sakit Rujukan pada Area Rentan Bencana di Indonesia: Studi Deskriptif

Background. Indonesia based on its geographical, geological, hydrological and demographic conditions is prone to disasters. Pre-disaster preparedness in health services are very important phases in reducing the impact of a disaster. Nurses are health workers with the largest number in a hospital, and have an important role in a disaster.The purpose of this study was to explore nurses’ perception regarding disaster preparedness in referral hospitals in disaster-prone areas in Indonesia.
 Methods. This study was a cross-sectional study. The cluster random sampling technique was used in the recruitment of 217 respondents from 4 referral hospitals in Indonesia. Self-report questioner were utilized and it was modified from Disaster Preparedness Evaluation Tool (DPET) and Emergency Prepardeness information Questionairre (EPIQ). Univariate and bivariate analyses were applied to describe the data.
 Results. The mean age of the respondents was 37.6 ± 8.9 years and the average length of service was 14 years ± 9.6 years. Respondents were mostly female, had vocational education level, were married, worked in wards, worked as clinical nurse, had no disaster experience but worked in hospitals that had experienced disasters. The average of nurses’ perception of disaster preparedness is 2.68 ± 0.32. Respondents have attended 88.5% BHD training, 76.5% APAR, 60.8% fire simulation and 42.4% earthquake simulation. Disaster experiences and research locations influence the disaster preparedness of nurses in referral hospitals in Indonesia. There were no statistically significant differences in nurses’ preparedness for disasters on gender, education level, marital status, place of work, position.
 Conclusion. Nurses’ experience in dealing with disasters increases the perception of disaster preparedness among nurses. Therefore, regular training and simulations are required in the health services of disaster-prone areas in Indonesia.

Seismic risk assessment of a large metropolitan area by means of simulated earthquakes

The determination of seismic risk in urban settlements has received increasing attention in the scientific community during the last decades since it allows to identify the most vulnerable portions of urban areas and therefore to plan appropriate strategies for seismic risk reduction. In order to accurately evaluate the seismic risk of urban settlements it should be necessary to estimate in detail the seismic vulnerability of all the existing buildings in the considered area. This task could be very cumbersome due to both the great number of information needed to accurately characterize each building and the huge related computational effort. Several simplified methods for the assessment of the seismic vulnerability of existing buildings have been therefore presented in the literature. In order to estimate the occurrence of damage in buildings due to possible seismic phenomena, the published studies usually refer to response spectra evaluated according to seismic events expected in the territory with assumed probabilities. In the present paper seismic events are instead simulated using a modified Olami–Feder–Christensen (OFC) model, within the framework of self-organized criticality. The proposed methodology takes into account some geological parameters in the evaluation of the seismic intensities perceived by each single building, extending the approach presented in a previous study of some of the authors. Here, a large territory in the Sicilian oriental coast, the metropolitan area of Catania, which includes several urbanized zones with different features, has been considered as a new case study. Applications of the procedure are presented first with reference to seismic sequences of variable intensity, whose occurrence is rather frequent in seismic territories, showing that the damage can be progressively accumulated in the buildings and may lead to their collapse even when the intensities of each single event are moderate. Moreover, statistically significant simulations of single major seismic events, equivalent to a given sequence in terms of produced damages on buildings, are also performed. The latter match well with a novel a-priori risk index, introduced with the aim of characterizing the seismic risk of each single municipality in the considered metropolitan area. The proposed procedure can be applied to any large urbanized territory and, allowing to identify the most vulnerable areas, can represent a useful tool to prioritize the allocation of funds. This could be a novelty for risk policies in many countries in which public subsidies are currently assigned on a case-by-case basis, taking into account only hazard and vulnerability. The use of an a-priori risk index in the allocation process will allow to take into due account the relevant role of exposure.

Physics-based earthquake simulations of the Anninghe-Zemuhe-Daliangshan-Xiaojiang fault system in Southwestern China

Seismic hazard evaluation is important for urban construction and earthquake disaster prevention and mitigation. However, because of the long recurrence intervals of large earthquakes (hundreds to thousands of years), seismic hazard assessment based on relatively short-term (tens of years) observational seismic catalogs is difficult. Synthetic seismic catalogs provide a useful way to assess long-term seismic hazards. Based on the Coulomb failure criterion, we apply a quasi-static physics-based earthquake simulator (Virtual Quake) in a tectonically complicated region with several major strike-slip faults, namely, the Anninghe, Zemuhe, Daliangshan and Xiaojiang (AZDX) faults, in southwestern China. The slip rates of these major faults are constrained by GPS data, and friction is constrained by laboratory experiments. Considering the stress interactions among the fault system, a synthetic catalog over 20,000 years is simulated. The simulated catalog shows consistency with the observed seismicity in the spatial distribution of large earthquakes, b value and mean seismic rate. Based on the synthetic catalog, the mean recurrence intervals and probabilities of the recurrence interval for strong earthquakes (M ≥ 7) in each fault section are presented in detail. Moreover, qualitative analysis of seismic hazards is conducted for the AZDX fault region. Our results provide a helpful index to evaluate seismic hazards in such a complicated region. Plain language summaryEvaluating seismic hazards is important for building codes, risk prevention and mitigation. Because large earthquakes are rare, modern observed earthquake catalogs are too short to evaluate seismic hazards precisely. Thus, numerical simulations are used to obtain synthetic earthquake catalogs for seismic hazard evaluation. Here, we present a physics-based model of stress accumulation, transfer and release, and simulate an earthquake sequence in the Anninghe-Zemuhe-Daliangshan-Xiaojiang fault system, southwestern China. Thus, we obtain a synthetic catalog over 20,000 years. By comparing the spatial distributions of large earthquakes, b values, and mean seismic rates of the synthetic catalog and observed catalog, we find that the synthetic catalog is consistent with the observed catalog. Based on the synthetic seismic catalog, we summarize the mean strong seismic recurrence interval and the probability of the recurrence interval for each fault section. Qualitative analysis of seismic hazards is conducted for the AZDX fault region. Our results can help to evaluate long-term seismic hazards in a multiple-fault system.

Improving organisational resilience: the TURNkey project

Facilities managers have a key role to play in improving organisational resilience to disaster events. However, there is currently limited support available to help them understand and systematically manage related issues. At the strategic level, they need to understand the physical, operational, and organisational risks associated with individual and cascading events. At the operational level, they need to develop mitigation interventions to reduce and manage these risks. This paper discusses results from the TURNkey project, which developed a forecasting, early warning and consequence response platform to assist decision-makers prepare for, respond to and recover from a potential earthquake event. It looks at this disaster management platform through the lens of business, outlining the opportunities and challenges facilities managers face when using it to manage organisational resilience. First, the paper presents an overview of the TURNkey platform and describes a series of end-user use cases that were developed to identify the key business issues the platform needed to address. The paper then reports the results of a hypothetical case study undertaken as part of a regional earthquake simulation to show how the outputs from the TURNkey FWCR platform can be integrated into existing resilience plans. The paper concludes by highlighting outstanding integration issues and the role that facilities managers can play in helping resolve them. Although the paper draws on evidence from earthquake disasters, its findings and conclusions are generic, and applicable to any disaster event.

Characterizing the Final Stage of Simulated Earthquake Nucleation Governed by Rate‐And‐State Fault Friction

AbstractPrevious experiments and modeling on earthquake nucleation reveal accelerating slip and development of a final patch of fixed or expanding length, but whether the nucleation phase is spatially large enough to be detected in real‐Earth conditions with durations long enough to be helpful is unknown. This study performed a suit of simulations of the nucleation process based on the rate‐and‐state friction law on homogeneous faults started from a “locked” state. Our results reveal the development of a weakening‐zone core (WZcore, defined as a region bounded by two outwardly moving shoulders of stress distribution during the early phase, and later bounded by two inwardly shifting edges between the stress‐releasing region and stress‐increasing exterior) where stress releases continuously, which expands first to a dimension less than the half fault length then shrinks to a final length before re‐expanding. The slip rate within the WZcore is above several times of the driving rate, and the high‐rate region expands constantly up to the instability. The WZcore is similar to a strain‐releasing zone in our new experiment. Under the assumption that much higher seismicity rate can be observed within the WZcore due to higher slip rate and stress‐releasing state as augmented driving force for small asperities, these nucleation features, as well as the slip rate levels in our model, are consistent with step‐like increases in seismicity preceding large subduction earthquakes. On the time scale, duration of the WZcore is weeks before large subduction earthquakes under high driving rate, but years on low‐rate continental faults.

Spectral acceleration basin amplification factors for interface Cascadia Subduction Zone earthquakes in Canada’s 2020 national seismic hazard model

Canada’s 2020 national seismic hazard model (CSHM 2020) provides hazard estimates for interface Cascadia Subduction Zone (CSZ) earthquakes in southwestern Canada using four ground motion models (GMMs) with equal weights. Two out of the four GMMs were derived using data primarily from subduction earthquakes in Japan so their use in CSHM 2020 includes a “Japan-to-Cascadia” factor to account for local site conditions. Despite this regional factor, the GMMs do not explicitly consider the amplification effects from the Georgia sedimentary basin below Metro Vancouver. This study benchmarks ground motion shaking from a suite of 30 physics-based simulations of M9 CSZ earthquakes, which explicitly account for basin effects for periods exceeding 1 s, to corresponding estimates from interface GMMs in CSHM 2020. Using this comparison, this study proposes site-specific and period-dependent basin amplification factors for a range of sites located within the Georgia sedimentary basin. The average basin amplification factors at the deepest basin location reach values as high as 2.24 and 6.29 at a 2 s period with respect to basin-edge and outside-basin reference locations, respectively. We evaluate the proposed factors by comparing them against long-period amplifications observed in empirical strong motion recordings from the 2001 M6.8 Nisqually earthquake. A framework to incorporate the proposed basin amplification factors in the calculation of CSHM 2020 uniform hazard spectra (UHS) is also proposed. The modified UHS ordinates at the deepest basin location reach values that are 58% to 271% higher, at a 2 s period, than non-basin UHS estimates when amplification factors are calculated with respect to basin-edge and outside-basin reference locations, respectively.

Drop, Cover, and Hold On versus Fetal Position in the Triangle of Life to Survive in an Earthquake: A Delphi Study.

This study aims to determine and compare the effectiveness of Drop, Cover, and Hold On versus Fetal Position in the Triangle of Life regarding reducing casualties during earthquakes and establishing a consensus among medical search and rescue experts. In this study, the data collected from ten experienced medical search and rescue professionals were analyzed using a three-stage Delphi technique to compare Drop, Cover, and Hold On versus Fetal Position in the Triangle of Life. At the end of the first round of Delphi, all of the experts mentioned the following factors: age, position, and surface area of the injured person. A victim's time under rubble and the experience of search and rescue teams are two prominent factors related to search and rescue. After the earthquake simulation in the second round, mannequin damage rates were examined by opening rubble pavement and tunnels. Following the second round of ratings, a third round of questionnaires was administered. As part of this questionnaire, participants were asked to give a score from one to ten based on their level of agreement. Whether they agreed or disagreed with Fetal Position in the Triangle of Life and Drop, Cover, and Hold On using a ten-point Likert scale, and the agreement rates were measured and compared. Experts completed a comparison of the two positions in the third round. According to this expert consensus, the Fetal Position in the Triangle of Life has the following advantages over Drop, Cover, and Hold On: reduced surface area, less crush injuries, protection of a larger body part from injury, better protection from hypothermia, and better maintenance of basal metabolism.

MCQsim: A Multicycle Earthquake Simulator

ABSTRACT Multicycle earthquake rupture simulators generate long sequences of earthquakes along predefined fault geometries for statistical analysis of earthquake recurrence and related rupture characteristics. Based on the physical approximations of long-term crustal deformation and the short-term rupture process, they can provide a deeper understanding of the inner workings of the “earthquake machine” as well as inform seismic hazard assessment by filling the observational gap between instrumental seismology and paleoseismology. With MCQsim, we introduce a multi-cycle rupture simulator that (a) can work with complex, nonplanar fault geometries and heterogenous models of fault strength, (b) includes different approximations of long-term stress accumulation, (c) incorporates elastic signal propagation velocity, (d) distinguishes between stable, conditionally stable, and unstable portions of the fault, and (e) includes postseismic relaxation and afterslip. The generated earthquake catalogs allow the identification of parameters that dominate system behavior while also providing probabilities of future ruptures based on their preceding behavior. Here, we focus on the technical aspects of how MCQsim, which is based on elastostatic dislocation theory and the boundary element method, approximates both the seismic cycle and the earthquake’s rupture process. We provide exemplary simulation outputs for verification and validation purposes.

Shaking table test of a new special-shaped arch bridge

In this work, a shaking table test was conducted on a new special-shaped arch bridge consisting of an inclined arch and a curved beam called BIACB. In order to meet a landscape requirement, the design of BIACB is unique and complex. Therefore, different from conventional bridges, it exhibits a prominent space effect and unpredictable complex seismic responses. To check the seismic performance of the BIACB, a 1:40 scaled test model was designed and fabricated to achieve a shaking table test by using simulated earthquake. The seismic responses of the tested BIACB model under three typical seismic excitations (El-Centro wave, Taft wave and Artificial wave) were explored. It is found that: (1) The scaled test bridge model can well reflect the seismic response characteristics of the prototype bridge verified by the corresponding finite element analysis. (2) Obvious dynamic amplification phenomena in the transverse and vertical directions of the bridge were observed, showing that the vertical response of the curved beam is greater than the transverse one, while the transverse response of the leaning arch is much more apparent than the vertical one. Generally, the seismic responses of BIACB under transverse seismic excitation are more obvious than those under longitudinal seismic excitation. (3) Higher-order vibration mode of the BIACB has a substantial participation under the longitudinal seismic excitation. (4) The inclined arch significantly amplifies the impact of vertical seismic excitation on the BIACB. (5) The relative variation amplitudes of suspender force of short suspenders on the BIACB are greater than that of long suspenders under longitudinal seismic excitation. The research findings are of great potential to critically guide the seismic design of relevant bridges.

Seismic retrofit of reinforced concrete shear walls using fibre reinforced polymer composites

This study studies seismic retrofitting of RC shear walls with externally linked aluminium tube polymers (CFRP). Three stages complete the research study. This method examined two eight-story CFRP-repaired RC shear walls. Excited walls were tested. The wall design was considered in NBC and CSA-A23.3–04. Throughout. The École polytechnique de Montréal's shake table simulated earthquakes to assess wall seismic resistance. Vibrations make the sixth panel more demanding and nonlinear. Panel six finished the tale. The earth's surface and twelfth-level walls were repaired and retested on a shaking table with varying ground motion excitation levels. Ground motion stirred the walls toward the end. Phase 2 involved the erection of three RC shear barriers. My college Structures Laboratory evaluated cyclic lateral stimulation panels. Evaluate the panel's performance. Two FRP panels and the control wall were tested. These panels were evaluated to determine the optimal method. All three ceiling tiles have code-designed parts, including the sixth-story stiffener panel. All building shear walls exceed construction criteria; hence, all wall panels have these features. These walls can handle the eight-story shear stresses. Continuous axial load, synchronized cyclic moment, and shear force were tested on the top panel. The panel could withstand all three forces. FRP retrofitting improved the wall panels' flexural and shear strengths. FRP retrofitting failed. Third, a computational macromodel simulated gripping and recycling wall panels under cyclic pressures. This simulation determined the longer-lasting wall panel type. Control wall panels were tested to discover whether they outperformed retrofitted ones. The two existing RC shear walls and three RC wall panels' FRP-retrofit schemes performed well and enhanced flexural strength, proving the retrofit's key aims. The quadratic numerical macromodel recreated monotonic and cyclic responses in wall panels under cyclic stresses. Nonlinear effects were accounted for using the nonlinear model.

Open-source simulation of strongly-coupled fluid-structure interaction between non-conformal interfaces

Design code-based “life-safety” requirements for structural earthquake and tsunami design offer reasonable guidelines to construct buildings that will remain standing during a tsunami or seismic event. Much less consideration has been given to assessing structural resilience during sequential earthquake and tsunami multi-hazard events. Such events present a series of extreme loading scenarios, where damage sustained during the earthquake influences structural performance during the subsequent inundation. Similar difficulties exist with respect to damage sustained during tropical events, as wind and fluid loading may vary with structural response or accumulated damage. To help ensure critical structures meet a “life-safety” level of performance during such multi-hazard events, analysis software capable of simulating simultaneous structural and fluid dynamics must be developed. To address this gap in understanding of non-linear fluid-structure-interaction (FSI), an open-source tool (FOAMySees) was developed for simulation of tsunami and wave impact analysis of post-earthquake non-linear structural response of buildings. The tool is comprised of the Open-source Field Operation And Manipulation software package and OpenSeesPy, a Python 3 interpreter of OpenSees. The programs are coupled via preCICE, a coupling library for partitioned multi-physics simulation. FOAMySees has been written to work in a Linux OS environment with HPC clusters in mind. The FOAMySees program offers a partitioned conventional-serial-staggered coupling scheme, with optional implicit iteration techniques to ensure a strongly-coupled two-way FSI solution. While FOAMySees was developed specifically for tsunami-resilience analysis, it may be utilized for other FSI applications with ease. With this coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) program, tsunami and earthquake simulations may be run sequentially or simultaneously, allowing for the evaluation of non-linear structural response to multi-hazard excitation.

Characterizing the seismic response of a molten salt nuclear reactor

AbstractOne Generation IV nuclear reactor, which uses a fluoride salt as a coolant, graphite reflector blocks as a moderator, and circulating buoyant TRISO pebbles as fuel is at an advanced stage of development. To characterize the seismic behavior of components of this reactor, validate numerical models for analysis, and develop recommendations for design, a set of earthquake‐simulator experiments on a scaled model of the reactor vessel and its internals was executed on a six‐degree‐of‐freedom earthquake simulator. The model was seismically isolated at its base using two types of spherical sliding bearings. The scaled model involved representations of the prototype reactor vessel, core barrel, reflector blocks, coolant, and spherical fuel pebbles. The material and geometric properties of different test components were selected based on a dynamic similitude scaling analysis and an approximate length scale of 0.4. Four sets of three‐component earthquake motions were used as inputs for testing. Instrumentation on the test specimen recorded the dynamic responses of the outer vessel, core barrel, and reflector‐block assembly, the hydrodynamic responses (sloshing and hydrodynamic pressure) of the liquid coolant, pebble consolidation under earthquake shaking, and the behavior of the isolation systems. This paper describes the design of the experiments and presents key results from the tests. The dynamic responses of the outer vessel, core barrel, and the reflector blocks revealed that the components responded as a unit for the intense shaking used in the experiments. The sloshing response of the fluid in a thin annulus near the perimeter of the vessel was heavily damped. The change in the packing fraction of the pebble bed under repeated, intense 3D earthquake shaking was less than 3%. Seismically isolating the vessel substantially reduced demands on its internal components.

The 2022 Seismic Sequence in the Northern Adriatic Sea and Its Long-Term Simulation

We studied the long-term features of earthquakes caused by a fault system in the northern Adriatic sea that experienced a series of quakes beginning with two main shocks of magnitude 5.5 and 5.2 on 9 November 2022 at 06:07 and 06:08 UTC, respectively. This offshore fault system, identified through seismic reflection profiles, has a low slip rate of 0.2–0.5 mm/yr. As the historical record spanning a millennium does not extend beyond the inter-event time for the largest expected earthquakes (M≃6.5), we used an earthquake simulator to generate a 100,000-year catalogue with 121 events of Mw≥5.5. The simulation results showed a recurrence time (Tr) increasing from 800 yrs to 1700 yrs as the magnitude threshold increased from 5.5 to 6.5. However, the standard deviation σ of inter-event times remained at a stable value of 700 yrs regardless of the magnitude threshold. This means that the coefficient of variation (Cv=σ/Tr) decreased from 0.9 to 0.4 as the threshold magnitude increased from 5.5 to 6.5, making earthquakes more predictable over time for larger magnitudes. Our study supports the use of a renewal model for seismic hazard assessment in regions of moderate seismicity, especially when historical catalogues are not available.

Structural connection with predetermined discrete variable friction forces

This paper presents a simple and practical structural connection able to develop predetermined discrete variable friction forces at target design displacement levels. The innovative connection is termed Modified Friction Device (Modified FD). Modified FDs are used to transfer the seismic induced horizontal forces from the floors to the core wall seismic force-resisting system of a building. The schematics of the physical embodiment of the Modified FD are presented. The components and the assembly of the Modified FD are discussed. The mechanics of the Modified FD are explained. Results from static structural analyses of two types of finite element models of the Modified FD are presented. The first model is developed using solid finite elements and it is used to assess the expected kinematics and the expected force-displacement response of the Modified FD. The second model is developed using a truss finite element and it can be used to efficiently simulate the force-displacement response of the Modified FD in numerical earthquake simulations of structural systems. The force-displacement response of the Modified FD computed using a numerical earthquake simulation of an eighteen-story reinforced concrete core wall building model is presented. The seismic response of the building model with Modified FDs is compared with the seismic response of the building model with monolithic connections and the seismic response of the building model with friction devices with constant friction forces. The results presented in this paper show that it is possible to develop a simple and practical structural connection with predetermined discrete variable force-displacement response to limit the seismic induced horizontal forces transferred between the floors of the flexible gravity load resisting system and the core wall piers in high-performance earthquake resilient buildings.

Apparent Low‐Velocity Belt in the Shallow Anninghe Fault Zone in SW China and Its Implications for Seismotectonics and Earthquake Hazard Assessment

AbstractThe Anninghe fault forms the eastern boundary of the Sichuan‐Yunnan block in Southwest China and has been identified as an earthquake gap zone. This study intends to construct the upper crustal shear wave velocity (Vs) structure beneath the Anninghe fault to understand its seismotectonics and potential large earthquake hazards. We deployed a dense seismic array along the southern central Anninghe fault valley. From the 3‐month continuous records, we calculated vertical‐component cross‐correlation functions (CCFs). However, the surface wave signals in the CCFs are intensely interfered by near zero‐time‐lag noise. We proposed a mode separation method based on the high‐resolution linear Radon transform, which suppressed the interfered noise and greatly enhanced the surface wave signals for ambient noise tomography of the Vs structure. The fine upper crustal structure reveals a distinct narrow low‐velocity belt within a depth of 3 km beneath the Anninghe fault zone. At deeper depths (4.5–8 km), the narrow low‐velocity belt shifts to the east and correlates with the distribution of local earthquakes. Combining previous results with our new findings, we presented a seismotectonic model of the southern central Anninghe fault, which interprets the narrow low‐velocity belt as a water‐contained fracture zone that forms a seismogenic zone at deeper depths under transpression. In addition, we demonstrated through scenario earthquake simulations that fine structures play a significant role in the assessment of earthquake hazards along the Anninghe fault. As such, this study provides a typical window into seismotectonics and large earthquake hazards in the active southeastern Tibetan Plateau.

Rupture-induced dynamic pore pressure effect on rupture

The ordinary elasticity model is often used in dynamic rupture earthquake simulation without incorporating the poroelasticity effect in rocks. In consideration that rocks are porous and saturated, we carry out a two-dimensional simulation of spontaneous rupture in a poroelastic medium with a finite difference time domain scheme. In particular, the influence of the rupture-induced pore pressure on the rupture process is investigated. The fault plane is idealized as an impermeable layer of negligible thickness, and the rupture is assumed to be governed by the slip-weakening friction law. Results show that an impermeable fault plane leads to a rupture-induced pore pressure change, which promotes or hinders the rupture process by altering effective normal compressive stress (normal compressive stress minus pore pressure). It is remarkable that super-shear rupturing will occur when the porosity of the rock around the fault increases to some extent. The comparison with the permeable fault model suggests that the permeability of the fault and the porosity of rocks around the fault significantly influence the dynamic rupture process.

Hazard-informed optimization of seismic networks for earthquake early warning—the case of the Lower Rhine Embayment (western Germany)

Earthquake early warning (EEW) systems can serve as a viable solution to protect specific hazard‐prone targets (major cities or critical infrastructure) against harmful seismic events. Using the example of the Lower Rhine Embayment (western Germany), we present a novel approach for evaluating and optimizing seismic networks for EEW purposes. The network optimization is applied to simulated earthquake scenarios from a hazard-compatible stochastic catalog, which represents a realization of the seismicity in the target area over a given period of time. We propose a densification of the existing network in the area by pre-selecting a number of potential sites with an optimal station configuration using a microgenetic algorithm, minimizing an appropriate cost function associated with the network layout. We show that the new decentralized network significantly improves the warning time and the accuracy of the warnings for levels of shaking for threshold levels of at least 0.02 g. Although the accuracy of the alerts for other cities outside the target area varies depending on their location, we demonstrate that the updated network layout will also improve the warning times for neighboring cities.

The role of three-dimensional fault interactions in creating complex seismic sequences

A physics-based earthquake simulator should reproduce first-order empirical power-law behaviors of magnitudes and clustering. These laws have emerged spontaneously in either discrete or low-dimension continuum simulations without power-law or stochastic heterogeneity. We show that the same emergence can occur in 3-D continuum simulations with fault interactions and rate-and-state friction. Our model approximates a strike-slip fault system as three en echelon faults. Simulations show spatio-temporally clustered earthquake sequences exhibiting characteristic Gutenberg-Richter scaling as well as empirical inter-event time distribution. The Gutenberg-Richter scaling occurs only in partial ruptures that result from fault interactions. With fault interactions, partial ruptures emerge when seismogenic width W over characteristic nucleation length L∞ is larger than 16.24, but none occur without fault interaction. The mainshock recurrence times of individual faults remain quasi-periodic. The system mainshock recurrence time is a combination of short-term Omori-type decay and Brownian passage time. Higher W/L∞ increase short-term clustering probability to at most 30%. These results indicate that physics-based multi-cycle models adequately reflect observed statistical signatures and show practical potential for long-term hazard assessment and medium-term forecasting.