Physics-based Earthquake Simulator Research Articles

Stress, occurrence rates, and b-value on the Nankai megathrust system inferred from earthquake simulation

Summary We aim to improve our comprehension of the seismic process and to identify possible long-term predictability tools of strong earthquakes through the simulation performed by a new-generation simulator code based on a well-elaborated model of the earthquake sources. We applied our previously tested physics-based earthquake simulator to the Nankai megathrust fault system, characterised by a 13 centuries historical record of strong earthquakes. Our results show these significant seismicity patterns characterizing the seismic cycles: the average stress increases almost linearly, while its standard deviation decreases more and more rapidly as the next major earthquake approaches; the co-seismic stress drop and the simultaneous increase of the standard deviation mark the beginning of the new seismic cycle; and the b-value tends to increase some decades before major earthquakes and exhibits correlation with the occurrence rate. Our results encourage further investigations about the application of simulators in support of other methodologies of earthquake forecasting.

Deterministic seismic hazard analysis from physics-based earthquake simulations in the Eastern Betics (SE Iberia)

The low frequency of large destructive earthquakes in the Eastern Betics (SE Iberian Peninsula), not recorded in the instrumental seismic catalog, complicate the estimation of the maximum ground motion that could be reached. Knowing the characteristics and behavior of these large seismic ruptures is crucial for the study of seismic hazard. In this work, we have used a physics-based earthquake simulator to generate a 100 kyr catalog of seismic ruptures associated with seismogenic faults bordering the quaternary Guadalentin and Bajo Segura basins. From these ruptures, we have selected maximum earthquake scenarios, and those associated with certain probabilities of exceeding a severe magnitude from the synthetic catalog. The estimation of maximum peak accelerations (PGA) by means of ground motion prediction equations include a possible site amplification that we have calculated from a detailed geotechnical classification of soils. According to the simulations, the modeled faults have the capacity to generate maximum earthquakes with magnitudes ranging MW 6.7–7.4. Densely populated urban areas located along the Guadalentin valley, such as Lorca, could be subject to site-dependent PGA values close to 0.6 g on the Alhama de Murcia fault trace. Similar ground motion would affect the coastline of SE Alicante province when evaluating the maximum simulated event in the Bajo Segura offshore fault. But already from magnitudes around MW ∼ 6, PGA estimations exceed critical values of 0.5 g at the south side of the Bajo Segura basin and the city of Murcia, highly dependent of ground-motion amplification induced by thick deposits of very soft and saturated soils. Our scenarios reflect that other factors such as fault geometry, kinematics and the capability observed in the simulations to generate multi-fault ruptures also affect the spatial distribution of maximum ground motion in this region. We expect that this evaluation could contribute as an improvement guideline for future strong motion prediction studies prior to the settlement of new urban infrastructures in the Eastern Betics.

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.

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.

Physics-Based Simulation of Sequences with Foreshocks, Aftershocks and Multiple Main Shocks in Italy

We applied a new version of physics-based earthquake simulator upon a seismogenic model of the Italian seismicity derived from the latest version of the Database of Individual Seismogenic Sources (DISS). We elaborated appropriately for their use within the simulator all fault systems identified in the study area. We obtained synthetic catalogs spanning hundreds of thousands of years. The resulting synthetic seismic catalogs exhibit typical magnitude, space and time features that are comparable to those obtained by real observations. A typical aspect of the observed seismicity is the occurrence of earthquake sequences characterized by multiple main shocks of similar magnitude. Special attention was devoted to verifying whether the simulated catalogs include this notable aspect, by the use of an especially developed computer code. We found that the phenomenon of Coulomb stress transfer from causative to receiving source patches during an earthquake rupture has a critical role in the behavior of seismicity patterns in the simulated catalogs. We applied the simulator to the seismicity of the northern and central Apennines and compared the resulting synthetic catalog with the observed seismicity for the period 1650–2020. The result of this comparison supports the hypothesis that the occurrence of sequences containing multiple mainshocks is not just a casual circumstance.

Modelling earthquake rates and associated uncertainties in the Marmara Region, Turkey

Abstract. Modelling the seismic potential of active faults and the associated epistemic uncertainty is a fundamental step of probabilistic seismic hazard assessment (PSHA). We use SHERIFS (Seismic Hazard and Earthquake Rate In Fault Systems), an open-source code allowing us to build hazard models including earthquake ruptures involving several faults, to model the seismicity rates on the North Anatolian Fault (NAF) system in the Marmara Region. Through an iterative approach, SHERIFS converts the slip rate on the faults into earthquake rates that follow a magnitude frequency distribution (MFD) defined at the fault system level, allowing us to model complex multi-fault ruptures and off-fault seismicity while exploring the underlying epistemic uncertainties. In a logic tree, we explore uncertainties concerning the locking state of the NAF in the Sea of Marmara, the maximum possible rupture in the system, the shape of the MFD and the ratio of off-fault seismicity. The branches of the logic tree are weighted according to the match between the modelled earthquake rate and the earthquake rates calculated from the local data, earthquake catalogue and palaeoseismicity. In addition, we use the result of the physics-based earthquake simulator RSQSim to inform the logic tree and increase the weight on the hypotheses that are compatible with the result of the simulator. Using both the local data and the simulator to weight the logic tree branches, we are able to reduce the uncertainties affecting the earthquake rates in the Marmara Region. The weighted logic tree of models built in this study will be used in a following article to calculate the probability of collapse of a building in Istanbul.

Physics-based simulation of sequences with multiple main shocks in Central Italy

SUMMARYThe application of a physics-based earthquake simulator to Central Italy allowed the compilation of a synthetic seismic catalogue spanning 100 000 yr, containing more than 300 000 M ≥ 4.0 simulated earthquakes, without the limitations that real catalogues suffer in terms of completeness, homogeneity and time duration. The seismogenic model upon which we applied the simulator code was derived from version 3.2.1 of the Database of Individual Seismogenic Sources (DISS; http://diss.rm.ingv.it/diss/), selecting, and modifying where appropriate, all the fault systems that are recognized in the portion of Central Italy considered in this study, with a total of 54 faults. Besides tectonic stress loading and static stress transfer as in the previous versions, the physical model on which the latest version of our simulation algorithm is based also includes the Rate and State constitutive law that helps to reproduce Omori's law. One further improvement in our code was also the introduction of trapezoidal-shaped faults that perform better than known faults. The resulting synthetic seismic catalogue exhibits typical magnitude, space and time features which are comparable to those in real observations. These features include the total seismic moment rate, the earthquake magnitude distribution, and the short- and medium-term earthquake clustering. A typical aspect of the observed seismicity in Central Italy, as well as across the whole Italian landmass and elsewhere, is the occurrence of earthquake sequences characterized by multiple main shocks of similar magnitude. These sequences are different from the usual earthquake clusters and aftershock sequences, since they have at least two main shocks of similar magnitude. Therefore, special attention was devoted to verifying whether the simulated catalogue includes this notable aspect. For this purpose, we developed a computer code especially for this work to count the number of multiple events contained in a seismic catalogue under a quantitative definition. We found that the last version of the simulator code produces a slightly larger number of multiple events than the previous versions, but not as large as in the real catalogue. A possible reason for this drawback is the lack of components such as pore-pressure changes due to fluid-diffusion in the adopted physical model.

The short-term seismicity of the Central Ionian Islands (Greece) studied by means of a clustering model

SUMMARYEarthquake clustering in the area of Central Ionian Islands (Greece) is statistically modelled by means of the Epidemic Type Aftershock Sequence (ETAS) branching model, which is the most popular among the short-term earthquake clustering models. It is based upon the assumption that an earthquake is not fully related to any other one in particular, but rather to both all previous events, and the background seismicity. The close temporal proximity of the strong ($M \ge 6.0$) events in the study area offers the opportunity to retrospectively test the validity of the ETAS model through the 2014 Kefalonia doublet (Mw 6.1 and Mw 6.0) and the 2015 Lefkada aftershock sequences. The application of a physics-based earthquake simulator to the local fault system produced a simulated catalogue with time, space and magnitude behaviour in line with the observed seismicity. This catalogue is then used for the detection of short-term interactions between both strong and smaller events and the comparison between the two cases. The results show that the suggested clustering model provides reliable forecasts of the aftershock activity. Combining the ETAS model and the simulator code, though, needs to be more deeply examined since the preliminary results show some discrepancy between the estimated model parameters.

A physics-based earthquake simulator replicates seismic hazard statistics across California.

Seismic hazard models are important for society, feeding into building codes and hazard mitigation efforts. These models, however, rest on many uncertain assumptions and are difficult to test observationally because of the long recurrence times of large earthquakes. Physics-based earthquake simulators offer a potentially helpful tool, but they face a vast range of fundamental scientific uncertainties. We compare a physics-based earthquake simulator against the latest seismic hazard model for California. Using only uniform parameters in the simulator, we find strikingly good agreement of the long-term shaking hazard compared with the California model. This ability to replicate statistically based seismic hazard estimates by a physics-based model cross-validates standard methods and provides a new alternative approach needing fewer inputs and assumptions for estimating hazard.

Seismic hazard in southern Calabria (Italy) based on the analysis of a synthetic earthquake catalog

The application of a newly developed physics-based earthquake simulator to the active faults inferred by aeromagnetism in southern Calabria has produced a synthetic catalog lasting 100 ky including more than 18,000 earthquakes of magnitude ≥ 4.0. This catalog exhibits temporal, spatial and magnitude features, which resemble those of the observed seismicity. As an example of the potential use of synthetic catalogs, a map of the peak ground acceleration (PGA) for a given exceedance probability on the territory under investigation has been produced by means of a simple attenuation law applied to all the events reported in the synthetic catalog. This map was compared with the existing hazard map that is presently used in the national seismic building regulations. The comparison supports a strong similarity of our results with the values given in the present Italian seismic building code, despite the latter being based on a different methodology. The same similarity cannot be recognized for the comparison of our present study with the results obtained from a previous study based on our same methodology but with a different geological model.

What Can We Learn from a Simple Physics-Based Earthquake Simulator?

Physics-based earthquake simulators are becoming a popular tool to investigate on the earthquake occurrence process. So far, the development of earthquake simulators is commonly led by the approach “the more physics, the better”. However, this approach may hamper the comprehension of the outcomes of the simulator; in fact, within complex models, it may be difficult to understand which physical parameters are the most relevant to the features of the seismic catalog at which we are interested. For this reason, here, we take an opposite approach and analyze the behavior of a purposely simple earthquake simulator applied to a set of California faults. The idea is that a simple simulator may be more informative than a complex one for some specific scientific objectives, because it is more understandable. Our earthquake simulator has three main components: the first one is a realistic tectonic setting, i.e., a fault data set of California; the second is the application of quantitative laws for earthquake generation on each single fault, and the last is the fault interaction modeling through the Coulomb Failure Function. The analysis of this simple simulator shows that: (1) the short-term clustering can be reproduced by a set of faults with an almost periodic behavior, which interact according to a Coulomb failure function model; (2) a long-term behavior showing supercycles of the seismic activity exists only in a markedly deterministic framework, and quickly disappears introducing a small degree of stochasticity on the recurrence of earthquakes on a fault; (3) faults that are strongly coupled in terms of Coulomb failure function model are synchronized in time only in a marked deterministic framework, and as before, such a synchronization disappears introducing a small degree of stochasticity on the recurrence of earthquakes on a fault. Overall, the results show that even in a simple and perfectly known earthquake occurrence world, introducing a small degree of stochasticity may blur most of the deterministic time features, such as long-term trend and synchronization among nearby coupled faults.

The seismicity of the Central Apennines (Italy) studied by means of a physics-based earthquake simulator

The seismicity of the Central Apennines (Italy) studied by means of a physics-based earthquake simulator

SIMULATIONS OF SEISMIC ACTIVITY IN THE CORINTH GULF, GREECE, FAULT SYSTEM

The characteristic earthquake hypothesis is not strongly supported by observational data because of the relatively short duration of historical and even paleoseismological records. For instance, for the Corinth Gulf Fault System (CGFS), historical information on strong earthquakes exist for at least two thousand years, but they can be considered complete for M > 6.0 only for the latest 300 years, and therefore only few characteristic earthquakes are reported for individual fault segments. The use of a physics-based earthquake simulator has allowed the production of catalogues lasting 100,000 years and containing more than 500,000 events of magnitudes > 4.0. Our simulation algorithm is based on several physical elements, such as an average slip rate due to tectonic loading for every single segment in the investigated fault system, the process of rupture growth and termination, and interaction between earthquake sources, including small magnitude events. The application of our simulation algorithm to the CGFS provided realistic features in time, space and magnitude behaviour of the seismicity. These features include longterm periodicity of strong earthquakes, short-term clustering of both strong and smaller events, and a realistic earthquake magnitude distribution departing from the Gutenberg-Richter distribution in the moderate and higher magnitude range.

Erratum to: A physics-based earthquake simulator and its application to seismic hazard assessment in Calabria (Southern Italy) region

Erratum to: A physics-based earthquake simulator and its application to seismic hazard assessment in Calabria (Southern Italy) region

Precursory seismicity in regions of low strain rate: insights from a physics-based earthquake simulator

Precursory seismicity in regions of low strain rate: insights from a physics-based earthquake simulator

A physics-based earthquake simulator and its application to seismic hazard assessment in Calabria (Southern Italy) region

The use of a newly developed earthquake simulator has allowed the production of catalogs lasting 100 kyr and containing more than 100,000 events of magnitudes ≥4.5. The model of the fault system upon which we applied the simulator code was obtained from the DISS 3.2.0 database, selecting all the faults that are recognized on the Calabria region, for a total of 22 fault segments. The application of our simulation algorithm provides typical features in time, space and magnitude behavior of the seismicity, which can be compared with those of the real observations. The results of the physics-based simulator algorithm were compared with those obtained by an alternative method using a slip-rate balanced technique. Finally, as an example of a possible use of synthetic catalogs, an attenuation law has been applied to all the events reported in the synthetic catalog for the production of maps showing the exceedance probability of given values of PGA on the territory under investigation.

Using a physics-based earthquake simulator to evaluate seismic hazard in NW Iran

Using a physics-based earthquake simulator to evaluate seismic hazard in NW Iran