Magnitude production imbalances and the present seismogenicity state of the San Andreas Fault system
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Discussion on the Maximum Magnitude of Earthquake possibly Occurred in Shanxi Province in the Future
According to the magnitude-frequency formula,we educed the computing formula for estimating the recurrence period of earthquake with different magnitude and the maximum magnitude of earthquake possibly occurred in the coming future in this paper.Furthermore,the maximum earthquake magnitude in the future and the medium-long term seismic trend in Shaanxi province are preliminarily studied by using the ample historical earthquake data.
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Various approaches have been proposed to forecast the maximum expected earthquake magnitude that may be induced by fluid injection in a given area. Proposed forecast methods include a geometrical approach based on inferred dimensions of the stimulated volume; a formula that predicts maximum magnitude based on a putative linear relationship between maximum seismic moment and net injected volume; and a probabilistic approach based on seismic-activity rate. In this study, the probabilistic approach is extended to include a tapered Gutenberg-Richter distribution, which accounts for the effects of finite-fault dimensions. Each method makes specific assumptions that impact the applicability of the maximum-magnitude forecast, leading to divergent implications for monitoring and mitigation. Starting from basic concepts from earthquake seismology, we outline the theory and applications of these forecasting methods and test the maximum-magnitude forecasts using published examples of induced earthquakes. The majority of published examples are consistent with the putative volumetric limit, but a number of anomalous hydraulic-fracturing-induced events suggest that maximum magnitude is ultimately limited by geology (i.e., fault dimensions) rather than operational factors (e.g., net injected volume). Progress in understanding maximum magnitude may contribute to improved public communication and a stronger scientific foundation for traffic light criteria.
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By employing natural time analysis, we analyze the worldwide seismicity and study the existence of correlations between earthquake magnitudes. We find that global seismicity exhibits nontrivial magnitude correlations for earthquake magnitudes greater than ${M}_{w}6.5$.
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Abstract The maximum likelihood estimation of earthquake hazard parameters (maximum regional magnitude m max , activity rate λ, and the Gutenberg - Richter parameter b ) from incomplete data files is extended to the case of uncertain magnitude values. Two models of uncertainty are considered. In the first one, earthquake magnitude is specified by two values, the lower and the upper magnitude limit. It is assumed that such an interval contains the real, unknown magnitude. In the second model, uncertainty of earthquake magnitude is defined in the same way as it was proposed by Tinti and Mulargia (1985): the departure of the observed (apparent) magnitude from the true, unknown value is distributed normally. The proposed approach allows the combination of catalog parts of different quality, e.g., those where the assessment of magnitude is questionable and those with magnitudes determined very precisely. As an illustration, the proposed procedures are applied for the estimation of seismicity parameters in western Norway with adjacent sea areas.
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Abstract The magnitude-frequency relationships of earthquakes of magnitude M L 2.0 or higher in North China, Shandong and neighboring areas since 1970 are calculated, and the long-term and annual-scale seismic intensities are analyzed. The maximum intercept magnitude and the annual-scale seismic intensity are M L 7.5 and M L 5.5, respectively, in North China within a long time frame. The three-year-scale time scan predicts that the maximum intercept magnitude and the seismic intensity in 2022 will be M L 5.3 and M L 4.8. In contrast, the maximum intercept magnitude and the annual seismic intensity in Shandong and neighboring areas are M L 6.2 and M L 4.5, and the three-year scale time scan predicts the corresponding values in 2022 will be M L 4.8 and M L 4.2, respectively. The predicted maximum earthquake magnitude in Shandong in 2022 has a high probability (63%) of not exceeding M L 4.8. Furthermore, the theoretical annual average occurrences and recurrence interval for each earthquake magnitude in Shandong and neighboring areas are calculated, with an average of 30 earthquakes per year for magnitude 3.0, 3.1 earthquakes per year for magnitude 4.0, once every 3.1 years for magnitude 5.0, 29 years for magnitude 6.0, 282 years for magnitude 7.0, and 2713 years for magnitude 8.0. The maximum intercept magnitude in North China has gradually weakened in the past 50 years, yet this tendency is not obvious in Shandong. It is noteworthy whether this indicates seismic activities in North China have gradually entered a quiet period.
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Parameters of seismic hazard are estimated by the application of the maximum likelihood method. The technique is based on a procedure which utilizes data of different quality, e.g., the ones where the uncertainty in the assessment of the magnitudes is great and those where the magnitudes are computed with great precision. In other words, the data were extracted from both historical (incomplete) and recorded (complete) files. The historical part of the catalogue contains only the strongest events, whereas the complete part can be divided into several subcatalogues each one assumed to be complete above a specified threshold magnitude. Uncertainty in the determination of magnitudes has also been taken into account. The method allow us to estimate the seismic hazard parameters which are the maximum regional magnitude, Mmax , the activity rate, l, of the seismic events and the well known b-value, the slope of the magnitude-frequency relationship. The parameter b, which is interrelated to b (b = bloge), is also obtained. All these parameters are of physical significance. The mean Return Periods, RP, of earthquakes with a certain lower magnitude M ³ m are also determined. The method is applied in some regions of the circum-Pacific belt, which includes various tectonic features, and where catastrophic earthquakes are known from the historical era. The seismic hazard level is also calculated as a function of the form q(Mmax , RP7.5 ) and a relative hazard scale (defined as an index K) is defined for each seismic region. According to this, the investigated regions are classified into five groups of very low, low, intermediate, high and very high seismic hazard levels. This classification is useful for both theoretical and practical reasons and provides a picture of quantitative seismicity.
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Abstract Selections of events from seismicity catalogs on the basis of size are universally made on the basis of magnitude. Such a selection implicitly assumes that these magnitudes provide a temporally consistent measure of earthquake size or that systematic errors in magnitudes are constant. Several techniques can be used to test this assumption. Results of application of these techniques to local and teleseismic catalogs indicate that in many cases this assumption cannot be justified. Two different techniques for identifying changes in systematic errors in magnitude are described here and applied to recent seismicity data from Parkfield, California. One technique relies on comparisons of seismicity rates before and after a possible change in magnitudes. The other uses station magnitude corrections to redetermine magnitudes. Both of these techniques indicate that a systematic decrease in magnitudes by 0.18 to 0.19 units occurred at Parkfield during November 1984. This decrease was associated with the installation of six low-gain stations in the Parkfield region. It is clear that changes in stations distributions can have significant effects on magnitudes and that these changes must be accounted for in all seismicity studies which use magnitude as a selection criteria. The results of past studies which have not accounted for these changes must be reevaluated.
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