Accelerating deformation seismicity patterns before the March 3, 2021 Thessaly strong earthquake. First results

A widely felt strong shallow earthquake with Mw 6.3 magnitude occurred in Thessaly (Central Greece) on March 3, 2021. This recent strong event attracted our interest to apply and evaluate the capabilities of the Accelerating Deformation method. Based on the recently proposed generalized Benioff strain idea which could be justified by the terms of Non-Extensive Statistical Physics (NESP), the common critical exponent was calculated in order to define the critical stage before a strong event. The present analysis comprised a complex spatiotemporal iterative procedure to examine the possible seismicity patterns at a broad region and identify the best one associated with the preparation process before the strong event. The starting time of the accelerating period, the size and location of the critical area are unknown parameters to be determined. Furthermore, although, the time of failure is already known, in the present research it was not set as a fixed value in the algorithm to define the other unknown parameters but instead different catalogue ending dates have been tried out to be with an objective way. The broad region to be investigated was divided with a square mesh and the search of events around a point has been carried on with different size circular and elliptical shapes. Among the obtained results, the solution which exhibits the most dominant scaling law behavior as well as the one which exhibits the smallest spatial area and yet the more dominant scaling law behavior are presented.

Analysis of Swarm Satellite Magnetic Field Data Before the 2016 Ecuador (Mw = 7.8) Earthquake Based on Non-negative Matrix Factorization

In this paper, based on non-negative matrix factorization (NMF), we analyzed the ionosphere magnetic field data of the Swarm Alpha satellite before the 2016 (Mw = 7. 8) Ecuador earthquake (April 16, 0.35°N, 79.93°W), including the whole data collected under quiet and disturbed geomagnetic conditions. The data from each track were decomposed into basis features and their corresponding weights. We found that the energy and entropy of one of the weight components were more concentrated inside the earthquake-sensitive area, which meant that this weight component was more likely to reflect the activity inside the earthquake-sensitive area. We focused on this weight component and used five times the root mean square (RMS) to extract the anomalies. We found that for this weight component, the cumulative number of tracks, which had anomalies inside the earthquake-sensitive area, showed accelerated growth before the Ecuador earthquake and recovered to linear growth after the earthquake. To verify that the accelerated cumulative anomaly was possibly associated with the earthquake, we excluded the influence of the geomagnetic activity and plasma bubble. Through the random earthquake study and low-seismicity period study, we found that the accelerated cumulative anomaly was not obtained by chance. Moreover, we observed that the cumulative Benioff strain S, which reflected the lithosphere activity, had acceleration behavior similar to the accelerated cumulative anomaly of the ionosphere magnetic field, which suggested that the anomaly that we obtained was possibly associated with the Ecuador earthquake and could be described by one of the Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) models.

Unified Scaling Law for Earthquakes: space-time dependent assessment in Kamchatka region

<p>The observed variability of seismic dynamics of the Kamchatka Region is characterized in terms of several moving averages, including (i) seismic rate, (ii) the Benioff strain release, (iii) inter-event time, τ, and (iv) the USLE control parameter, η (where USLE stands for Unified Scaling Law for Earthquakes, i.e. a generalization of the Gutenberg-Richter relationship accounting for naturally fractal distribution of earthquake loci, which states that the distribution of inter-event times τ depends only on the value of variable η).</p><p>The variability of seismic dynamics have been evaluated and compared at each of four out of ten separate seismic focal zones of the Kamchatka region and the adjacent areas defined by Levina et al. (2013), i.e., (1) seismic focal zone of the Kuril and South Kamchatka, (2) the northern part of the Kamchatka seismic focal zone, (3) commander segment of the Aleutian arc; and (4) the continental region of Kamchatka. In particular, we considered all magnitude 3.5 or larger earthquakes in 1996-2019 available from open data catalog of the Kamchatka Branch of GS RAS, Earthquakes Catalogue for Kamchatka and the Commander Islands (1962–present) http://sdis.emsd.ru/info/earthquakes/catalogue.ph).</p>

A Complexity View into the Physics of the Accelerating Seismic Release Hypothesis: Theoretical Principles

Observational indications support the hypothesis that many large earthquakes are preceded by accelerating-decelerating seismic release rates which are described by a power law time to failure relation. In the present work, a unified theoretical framework is discussed based on the ideas of non-extensive statistical physics along with fundamental principles of physics such as the energy conservation in a faulted crustal volume undergoing stress loading. We define a generalized Benioff strain function Ω ξ ( t ) = ∑ i = 1 n ( t ) E i ξ ( t ) , where Ei is the earthquake energy, 0 ≤ ξ ≤ 1 . and a time-to-failure power-law of Ω ξ ( t ) derived for a fault system that obeys a hierarchical distribution law extracted from Tsallis entropy. In the time-to-failure power-law followed by Ω ξ ( t ) the existence of a common exponent mξ which is a function of the non-extensive entropic parameter q is demonstrated. An analytic expression that connects mξ with the Tsallis entropic parameter q and the b value of Gutenberg—Richter law is derived. In addition the range of q and b values that could drive the system into an accelerating stage and to failure is discussed, along with precursory variations of mξ resulting from the precursory b-value anomaly. Finally our calculations based on Tsallis entropy and the energy conservation give a new view on the empirical laws derived in the literature, the associated average generalized Benioff strain rate during accelerating period with the background rate and connecting model parameters with the expected magnitude of the main shock.

MODELLING THE ENERGY RELEASE PROCESS OF AFTERSHOCKS

A stochastic model for the study of Benioff strain release during aftershock sequences is suggested. The stochastic model is elaborated after a compound Poisson process and is applied on data of the M7.1 Ocober 18, 1989 Loma Prieta aftershock sequence in northern California, USA. The temporal evolution of the number of events is first modelled by the Restricted Epidemic Type Aftershock Sequence (RETAS) model and then the identified best fit model is incorporated in the energy release analysis. The suggested model is based on the assumptions that there is no relation between the magnitude and the occurrence time of an event first and second, that there is no relation between the magnitude of a certain event and magnitudes of previous events. The obtained results from the examination of the energy release reveal that the suggested model makes a good fit of the aftershock Benioff strain release and enables a more detailed study by identifying possible deviations between data and model. The real cumulative energy release values surpass the expected model ones, which proves that aftershocks, stronger than forecasted by the model, are clustered at the beginning of the Loma Prieta sequence.

CORRELATIONS OF THE MEAN TIME AND MEAN MAGNITUDE OF ACCELERATING PRESHOCKS WITH THE ORIGIN TIME AND MAGNITUDE OF MAINSHOCK

Forty-five preshock sequences preceding corresponding strong (M≥6.4) mainshocks which occurred recently (since 1980) in a variety of seismotectonic regimes (W. Mediterranean, Aegean, Anatolia, California, Japan, Central Asia, South America) have been examined to identify new predictive properties. It has been observed that the mean origin time, , and the mean magnitude, of the accelerating preshocks of each sequence are correlated with the origin time, tc, and the magnitude, M, of the mainshock, respectively. The following relations have been derived: where sa (in Joule ½ /yr.104 Km2 ) is the Benioff strain rate in each preshock (critical) region and σ is the corresponding standard deviation. The possibility for using these relations as constraints in attempts for intermediate term earthquake prediction is discussed.

Combining earthquakes and GPS data to estimate the probability of future earthquakes with magnitude <i>M</i>_w ≥ 6.0

According to Wyss et al. (2000) result indicates that future main earthquakes can be expected along zones characterized by low b values. In this study we combine Benioff strain with global positioning system (GPS) data to estimate the probability of future Mw ≥ 6.0 earthquakes for a grid covering Taiwan. An approach similar to the maximum likelihood method was used to estimate Gutenberg–Richter parameters a and b. The two parameters were then used to estimate the probability of simulating future earthquakes of Mw ≥ 6.0 for each of the 391 grids (grid interval = 0.1°) covering Taiwan. The method shows a high probability of earthquakes in western Taiwan along a zone that extends from Taichung southward to Nantou, Chiayi, Tainan and Kaohsiung. In eastern Taiwan, there also exists a high probability zone from Ilan southward to Hualian and Taitung. These zones are characterized by high earthquake entropy, high maximum shear strain rates, and paths of low b values. A relation between entropy and maximum shear strain rate is also obtained. It indicates that the maximum shear strain rate is about 4.0 times the entropy. The results of this study should be of interest to city planners, especially those concerned with earthquake preparedness. And providing the earthquake insurers to draw up the basic premium.