Search for Direct Stress Correlation Signatures of the Critical Earthquake Model (original) (raw)
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Agu Fall Meeting Abstracts, 2003
We propose a new test of the critical earthquake model based on the hypothesis that precursory earthquakes are "actors" that create fluctuations in the stress field which exhibit an increasing correlation length as the critical large event becomes imminent. Our approach constitutes an attempt to build a more physically-based cumulative function in the spirit of but improving on the cumulative Benioff strain used in previous works documenting the phenomenon of accelerated seismicity. Using a space and time dependent visco-elastic Green function in a two-layer model of the Earth lithosphere, we compute the spatiotemporal stress fluctuations induced by every earthquake precursor and estimate, through an appropriate wavelet transform, the contribution of each event to the correlation properties of the stress field around the location of the main shock at different scales. Our physically-based definition of the cumulative stress function adding up the contribution of stress loads by all earthquakes preceding a main shock seems to be unable to reproduce an acceleration of the cumulative stress nor an increase of the stress correlation length similar to those observed previously for the cumulative Benioff strain. Either earthquakes are "witnesses" of large scale tectonic organization and/or the triggering Green function requires much more than just visco-elastic stress transfers.
Geophysical Journal International, 2004
We propose a new test of the critical earthquake model based on the hypothesis that precursory earthquakes are ‘actors’ that create fluctuations in the stress field which exhibit an increasing correlation length as the critical large event becomes imminent. Our approach constitutes an attempt to build a more physically based time-dependent indicator (cumulative scalar stress function), in the spirit of, but improving on, the cumulative Benioff strain used in previous works documenting the phenomenon of accelerating seismicity. Using a simplified scalar space and time-dependent viscoelastic Green's function in a two-layer model of the Earth's lithosphere, we compute spatiotemporal pseudo-stress fluctuations induced by a series of events before four of the largest recent shocks in southern California. Through an appropriate spatial wavelet transform, we then estimate the contribution of each event in the series to the correlation properties of the simplified pseudo-stress field around the location of the mainshock at different scales. This allows us to define a cumulative scalar pseudo-stress function which reveals neither an acceleration of stress storage at the epicentre of the mainshock nor an increase of the spatial stress–stress correlation length similar to those observed previously for the cumulative Benioff strain. The earthquakes we studied are thus either simple ‘witnesses’ of a large-scale tectonic organization, or are simply unrelated, and/or the Green's function describing interactions between earthquakes has a significantly longer range than predicted for standard viscoelastic media used here.
Investigating Time Dependent Stress Changes Globally Following Large Earthquakes (M≥7)
International Journal of Environment and Geoinformatics, 2021
Triggered earthquakes can cause disproportionate damages depend on their magnitudes. In fact, there is a causal link between the spatial distribution of those events and the stress changes induced by the mainshock. Co-seismic stress loading is one of the key factors in determination of triggering mechanism. However, the time lags ranging hours to years and the stress diffusion over wider areas cannot be evaluated with the co-seismic process alone. In some cases, the stress interactions for long periods and larger areas can be attributed to post-seismic viscoelastic relaxations. In this study, M≥7 earthquakes from the Global Centroid Moment Tensor (GMCT) catalogue are modelled as dislocations to calculate shear stress changes on following earthquake nodal planes near enough to be triggered. The catalogue scanned for all other events (4.5<M<7) that occurred within ±2° from the centroid rupture planes. According to Omori law, which is one of the most reliable time predictable dia...
Journal of Geophysical Research: Solid Earth, 2003
1] It has been recently suggested that moderate and large earthquakes can be triggered by similarly sized events at very long range. Here we study the main characteristics of earthquake triggering by determining its correlation length, time dependence, and directionality. The problem is examined at a global level, by using the Harvard centroid moment tensor catalogue. Our results show that the correlation lengths depend only weakly on the magnitude thresholds involved. No significant systematic triggering is observed for distances greater than the lithospheric thickness (100-150 km), and the correlation length magnitude is similar to the seismogenic thickness (10-20 km). The mean triggering distance and correlation length both increase with time very slowly compared with what would be expected from a normal diffusion process. This is consistent with a clock advance on the failure time based on the constitutive rules for subcritical crack growth following a transient change in the loading stress. The power law scaling disappears after a few months. A functional form for the probability of triggering as a function of time and distance is proposed on the basis of the properties of near critical point systems. The model fits the data well and could be used to calculate conditional probabilities for time-dependent seismic hazard due to earthquake triggering. An apparent directionality effect that was observed in the data set can be attributed to an artefact of poor depth determination. These results do not preclude individual long-range triggering with a potential directionality effect, but they do rule out a statistical correlation at distances much greater than the thickness of the lithosphere.
Precursory stress changes before large earthquakes; on a new physical law for earthquakes
Journal of Structural Geology, 2020
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Stress transfer and seismicity changes before large earthquakes
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 2001
PXTE1677 by:ELE p. 1 C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 0 (2001) 1-9 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés S1251-8050(01)01677-9/FLA
Accelerating seismicity and stress accumulation before large earthquakes
Geophysical Research Letters, 2001
The stress field that existed before a large earthquake can be calculated based on the known source parameters of the event. This stress field can be used to define a region that shows greater seismic moment rate changes prior to the event than arbitrarily shaped regions, allowing us to link two previously unrelated subjects: Coulomb stress interactions and accelerating seismicity before large earthquakes. As an example, we have examined all M≥6.5 earthquakes in California since 1950. While we illustrate the model using seismicity in California, the technique i s general and can be applied to any tectonically active region. We show that where sufficient knowledge of the regional tectonics exists, this method can be used to augment current techniques for seismic hazard estimation.
The evolution of regional seismicity between large earthquakes
Journal of Geophysical Research, 2003
1] We describe a simple model that links static stress (Coulomb) modeling to the regional seismicity around a major fault. Unlike conventional Coulomb stress techniques, which calculate stress changes, we model the evolution of the stress field relative to the failure stress. Background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress. The inhomogeneous field is chosen such that when these patches fail, the resulting earthquake size distribution follows a Gutenburg-Richter law. Immediately following a large event, the model produces regions of increased seismicity (aftershocks) where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced (stress shadows). The high stress levels in the aftershock regions decrease due to loading following the main event. Combined with the stress shadow from the main event, this results in a broad seismically quiet region of lowered stress around the epicenter. Pre-event seismicity appears as the original stress shadows finally fill as a result of loading. The increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches. As a result of this effect, the seismic moment release in the region around the future epicenter increases as the event approaches. Synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in California and Washington.
2020
Coseismic stress changes have been the primary physical principle used to explain after-shocks and triggered earthquakes. However, this method does not adequately forecast earthquake rates and diverse rupture populations when subjected to formal testing. We show that earthquake forecasts can be impaired by assumptions made in physics-based models such as the existence of hypothetical optimal faults and regional scale invariability of the stress field. We compare calculations made under these assumptions along with different realizations of a new conceptual triggering model that features a complete assay of all possible ruptures. In this concept, there always exists a set of theoretical planes that has positive failure stress conditions under a combination of background and coseismic static stress change. In the Earth, all of these theoretical planes may not exist, and if they do, they may not be ready to fail. Thus, the actual aftershock plane may not correspond to the plane with the maximum stress change value. This is consistent with observations that mainshocks commonly activate faults with exotic orientations and rakes. Our testing ground is the M 7.2, 2010 El Mayor-Cucapah earthquake sequence that activated multiple diverse fault populations across the United States-Mexico border in California and Baja California. We carry out a retrospective test involving 748 M ≥ 3:0 triggered earthquakes that occurred during a 3 yr period after the mainshock. We find that a probabilistic expression of possible aftershock planes constrained by premainshock rupture patterns is strongly favored (89% of aftershocks consistent with static stress triggering) versus an optimal fault implementation (35% consistent). Results show that coseismic stress change magnitudes do not necessarily control earthquake triggering, instead we find that the summed background stress and coseismic stress change promotes diverse ruptures. Our model can thus explain earthquake triggering in regions where optimal plane mapping shows coseismic stress reduction. KEY POINTS • Aftershock triggering potential is related more to the total stress rather than to the stress change. • The hypothetical optimal planes seldom predict the observed focal mechanism planes. • The total stress method significantly improves forecasts of future focal planes.
Global Observational Properties of the Critical Earthquake Model
The preshock (critical) regions of 20 mainshocks with magnitudes between 6.4 and 8.3, which occurred recently (since 1980) in a variety of seismotectonic regimes (Greece, Anatolia, Himalayas, Japan, California), were identified and investigated. All these strong earthquakes were preceded by accelerating time-to-mainshock seismic crustal deformation (Benioff strain). The time variation of the cumulative Benioff strain follows a power law with a power value (m ס 0.3) in very good agreement with theoretical considerations. We observed that the dimension of the critical region increased with increasing mainshock magnitude and with decreasing long-term seismicity rate of the region. An increase of the duration of this critical (preshock) phenomenon with decreasing long-term seismicity rate was also observed. This spatial and temporal scaling expresses characteristics of the critical earthquake model, which are of importance for earthquake prediction research. We also showed that the critical region of an oncoming mainshock coincides with the preparing region of this shock, where other precursory phenomena can be observed.