Is Seismicity Operating at a Critical Point?

Nandan, Shyam; Ram, Sumit Kumar; Ouillon, Guy; Sornette, Didier

doi:10.1103/physrevlett.126.128501

Cited by 26 publications

(25 citation statements)

References 51 publications

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“…Speaking of duration, there is evidence 28 that the crust is in a critical state only under certain conditions often associated with imminent and widespread seismicity. The development of a critical state is what is believed to underlie the intense long-range spatial correlations and the surprising capacity of faults to react to tiny stress sources such as tides.…”

Section: Discussionmentioning

confidence: 99%

Correlation between seismic activity and tidal stress perturbations highlights growing instability within the brittle crust

Zaccagnino

Telesca

Doglioni

2022

Sci Rep

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Faults become more and more responsive to stress perturbations as instability mounts. We utilize this property in order to identify the different phases of the seismic cycle. Our analysis provides new insights about the features of impending mainshocks, which are proposed to emerge from a large-scale crustal-weakening preparation process whose duration depends on their seismic moments, according to the power-law T $$\propto$$ ∝ M$$_{0}^{1/3}$$ 0 1 / 3 for M$$_{0}$$ 0 $$\le$$ ≤ 10$$^{19}$$ 19 N m. Moreover, further studies are performed about the impact of tidal stress perturbation on seismicity; in particular, the relationship between frequency-magnitude scaling and perturbations is discussed, showing that the sensitivity of earthquakes to solid Earth tides decreases as their magnitudes increase.

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Section: Discussionmentioning

confidence: 99%

Correlation between seismic activity and tidal stress perturbations highlights growing instability within the brittle crust

Zaccagnino

Telesca

Doglioni

2022

Sci Rep

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“…The newly gained insights from forecasting experiments guide us in the search of the next generation earthquake forecasting models. Besides other discussed topics such as anisotropy, temporally or spatially non‐stationary background rate (Hainzl et al., 2008; Hainzl et al., 2013; Nandan et al., 2020), the importance of accounting for short‐term incompleteness when simulating, as well as a magnitude‐dependent distribution of aftershock magnitudes are emphasized.…”

Section: Discussionmentioning

confidence: 99%

Embracing Data Incompleteness for Better Earthquake Forecasting

2021

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We propose two methods to calibrate the parameters of the epidemic‐type aftershock sequence (ETAS) model based on expectation maximization (EM) while accounting for temporal variation of catalog completeness. The first method allows for model calibration on long‐term earthquake catalogs with temporal variation of the completeness magnitude, mc. This calibration technique is beneficial for long‐term probabilistic seismic hazard assessment (PSHA), which is often based on a mixture of instrumental and historical catalogs. The second method generalizes the concept of mc, considering rate‐ and magnitude‐dependent detection probability, and allows for self‐consistent estimation of ETAS parameters and high‐frequency detection incompleteness. With this approach, we aim to address the potential biases in parameter calibration due to short‐term aftershock incompleteness, embracing incompleteness instead of avoiding it. Using synthetic tests, we show that both methods can accurately invert the parameters of simulated catalogs. We then use them to estimate ETAS parameters for California using the earthquake catalog since 1932. To explore how model calibration, inclusion of small events, and accounting for short‐term incompleteness affect earthquakes' predictability, we systematically compare variants of ETAS models based on the second approach in pseudo‐prospective forecasting experiments for California. Our proposed model significantly outperforms the ETAS null model, with decreasing information gain for increasing target magnitude threshold. We find that the ability to include small earthquakes for simulation of future scenarios is the primary driver of the improvement and that accounting for incompleteness is necessary. Our results have significant implications for our understanding of earthquake interaction mechanisms and the future of seismicity forecasting.

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“…Model 1 uses the conditional seismicity rate given by Equation 1 but extends the standard ETAS model with a space‐varying background intensity function (Nandan, Ram et al., 2021; Zhuang et al., 2002) given by Equation 6, with the guiding idea that the future background earthquakes occur mostly in regions where the intensity of past background earthquakes has been high.…”

Section: Methodsmentioning

confidence: 99%

“…We use ≈1.2 million reported earthquakes (with M ≥ 1) within 1975-2020 in the study region (co-ordinates of the spatial polygon in Table S1 of Supporting Information S1) surrounding California in the Advanced National Seismic System (ANSS) earthquake catalog. Nandan, Ram et al (2021) (see their Figure S2 and section Text S2 in Supporting Information S1) have shown using several proxies that the catalog within this region and time can be considered to be reasonably complete above M = 3. Thus, we set the magnitude of completeness M c = 3 in this study as well.…”

Section: Description Of the Data Setmentioning

confidence: 98%

Are Large Earthquakes Preferentially Triggered by Other Large Events?

Nandan

Ouillon²,

Sornette

2022

JGR Solid Earth

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The observational science of seismology developed with the classification of earthquakes as either foreshocks, mainshocks, or aftershocks. Foreshocks precede mainshocks, which themselves trigger aftershocks obeying the Omori law. Time-independent forecasting methods do not take advantage of these widely observed dynamics to issue statements about future seismicity. However, time-dependent forecasts use these features but rely on different fundamental hypotheses about their genetic origin. A first class of methods appear quite agnostic on this topics (such as the M8 algorithm of Keilis-Borok and Kossobokov (1990); the Region-Time-Length algorithm of Sobolev and Tyupkin (1997); the Relative Intensity of Holliday et al. (2005); and the Proportional Hazard Model of Faenza and Marzocchi ( 2010)). Some other approaches consider that small earthquakes are mainly passive markers of the stress field in space and time, so their influence on future seismicity is negligible. This is the underlying concept of many earthquake precursor models such as the characteristic earthquake (D.

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Is Seismicity Operating at a Critical Point?

Cited by 26 publications

References 51 publications

Correlation between seismic activity and tidal stress perturbations highlights growing instability within the brittle crust

Correlation between seismic activity and tidal stress perturbations highlights growing instability within the brittle crust

Embracing Data Incompleteness for Better Earthquake Forecasting

Are Large Earthquakes Preferentially Triggered by Other Large Events?

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