1,720,981 research outputs found
Time-Space Evolution of the Groningen Gas Field in Terms of b-Value: Insights and Implications for Seismic Hazard
Full text linkThe Groningen gas field, located in the northeast of The Netherlands, is the Europe's larg-est onshore gas field. It was discovered in 1959 and production started in 1963: Continuous production leads to reservoir compaction and subsidence, gradually loading preexisting fault and induced seismicity that started about 30 yr into the production. The seismic hazard and risk related to the induced seismicity is determined not only for the rate of activity, but it is also equally influenced by the relative size distribution of the seismicity-the b -value. I reanalyze the spatial and temporal evolution of the b -value in the field using an alternative approach to overcome magnitude in completeness heterogeneity, and link it to the evolution of fault loading and subsidence. Spatial var-iations of b -values are found to vary between 0.61 and 1.3, with the lowest observed values observed in the location of the 2012 M 3.6 Huizinge earthquake. In the last 10 yr, the mapped b -values are more homogeneous throughout the field. The spatial and temporal evolution of the b -value in the field in this study is shown to be quite com-plex, and systematically linked it to the evolution of fault loading, absolute compaction, and the rate of compaction-an important finding that offers new insights into hazard reduction and mitigation strategies of extraction relation-induced seismicity. Compaction rates below 2 mm/yr are not correlated to seismicity above M 2.0 in the history of the field, suggesting that low-volume production may be safer than that previously assumed
Contamination of frequency-magnitude slope (b-value) by quarry blasts: An example for italy
Full text linkArtifacts often affect seismic catalogs. Among them, the presence of man-made contaminations such as quarry blasts and explosions is a well-known problem. Using a contaminated dataset reduces the statistical significance of results and can lead to erroneous conclusions, thus the removal of such nonnatural events should be the first step for a data analyst. Blasts misclassified as natural earthquakes, indeed, may artificially alter the seismicity rates and then the b-value of the Gutenberg and Richter relationship, an essential ingredient of several forecasting models. At present, datasets collect useful information beyond the parameters to locate the earthquakes in space and time, allowing the users to discriminate between natural and nonnatural events. However, selecting them from webservices queries is neither easy nor clear, and part of such supplementary but fundamental information can be lost during downloading. As a consequence, most of statistical seismologists ignore the presence in seismic catalog of explosions and quarry blasts and assume that they were not located by seismic networks or in case they were eliminated. We here show the example of the Italian Seismological Instrumental and Parametric Database. What happens when artificial seismicity is mixed with natural one?
Asperity-based earthquake likelihood models for Italy
Full text linkThe Asperity Likelihood Model (ALM) hypothesizes that small-scale spatial variations in the b-value of the Gutenberg-Richter relationship have a central role in forecasting future seismicity. The physical basis of the ALM is the concept that the local b-value is inversely dependent on the applied shear stress. Thus low b-values (b < 0.7) characterize locked patches of faults, or asperities, from which future mainshocks are more likely to be generated, whereas high b-values (b > 1.1), which can be found, for example, in creeping sections of faults, suggest a lower probability of large events. To turn this hypothesis into a forecast model for Italy, we first determined the regional bvalue (b = 0.93 ±0.01) and compared it with the locally determined b-values at each node of the forecast grid, based on sampling radii ranging from 6 km to 20 km. We used the local b-values if their Akaike Information Criterion scores were lower than those of the regional b-values. We then explored two modifications to this model: in the ALM.IT, we declustered the input catalog for M ≥ 2 and smoothed the node-wise rates of the declustered catalog with a Gaussian filter. Completeness values for each node were determined using the probability-based magnitude of completeness method. In the second model, the hybrid ALM (HALM), as a «hybrid» between a grid-based and a zoning model, the Italian territory was divided into eight distinct regions that depended on the main tectonic regimes, and the local b-value variability was thus mapped using the regional b-values for each tectonic zone. © 2010 by the Istituto Nazionale di Geofisica e Vulcanologia
A preliminary geochemical study of two cores from Massaciuccoli eutrophic lake, northern Tuscany, and paleoclimatic implications
No full textAbstract - Elevated organic carbon concentration in present sediments commonly derives from human and industrial activities and reflects the eutrophic status of a system. Furthermore, amount and type of organic matter may be used to reconstruct marine, lacustrine and continental paleoenvironments and paleoclimates because they depend on production and preservation rates, direct consequences of environmental changes. In September 2003 five 50 cm long cores were sampled in Massaciuccoli Lake, northwestern Tuscany, and two of them were chosen to investigate the impact of organic pollution sources on the system. Total content of organic carbon (TOC) and nitrogen (TN) were examined to study the eutrophic status of the lake, while TOC/TN ratio was used to distinguish between terrestrial and aquatic origin of organic matter. Results evidenced the presence of high organic matter concentrations in sediments and, in particular, its terrestrial origin, thus confirming inputs from land reclamation to water and sediment. According to such results, it appears that immission of nutrients, with consequent algal blooms, have a smaller impact than immission of land-derived organic matter in sediments. Moreover, one core probably recorded a climatic cycle, three times reiterated in the stratigraphic sequence
Comment on "Two Foreshock Sequences Post Gulia and Wiemer (2019)" by Kelian Dascher-Cousineau, Thorne Lay, and Emily E. Brodsky
Full text linkISSN:0895-0695ISSN:1938-2057ISSN:1938-205
Testing the b-value variability in Italy and its influence on Italian PSHA
No full textThe supposed b-value spatial variability is the central topic of many scientific works dealing with forecast modeling applications or geological correlations. If used for seismicity rate determination, the b-value plays an important role in probabilistic seismic hazard assessment, but how much does it influence the results? In the logic tree approach used for the new probabilistic seismic hazard map of Italy, named MPS04, one of the sources of epistemic uncertainty considered was the procedure for computing seismicity rates. Two alternatives were adopted: 1) to compute the activity rates for each binned magnitude class and 2) to compute a Gutenberg-Richter distribution. In the logic tree branches, where the Gutenberg-Richter distribution was adopted, the corresponding b-value was evaluated for each seismogenic zone: it spans between 0.63 and 2.01. After analysing the b-value variability in the Italian region, this work evaluates the impact of setting the b-value equal to I on the results of seismic hazard assessment in terms of PGA and energy release compared to the choices adopted for MPS04
Detection of quarry and mine blast contamination in European regional catalogues
No full textThe presence of quarry and mine blasts in seismic catalogues is detected using
the Wiemer and Baer (Bull Seism Soc Am 90(2):525–530, 2000) algorithm. The procedure
is based on the observation that quarry blasts generally take place during daytime hours:
the areas with a high ratio of daytime and night-time events are likely to be regions with
quarry activity. In the first part of this work we have tested the method, using both a
synthetic and a regional catalogue; in the second part the procedure has been applied to
some of the European regional catalogues available on line. The comparison between the
results obtained and the location of known quarries and mines for the analysed catalogues
confirms the reliability of the methodology in identifying mining areas
The influence of b-value estimate in seismic hazard assessment
No full textIn any probabilistic seismic hazard assessment an important role is played by the seismicity rates. This is confirmed by the wide and
controversial discussions about the procedures for their determination: Gutenberg and Richter distribution vs independent rates in
every magnitude class ; size of binned magnitude class; the fitting algorithm to use (least squares or maximum likelihood); and so on.
In 2004 a new probabilistic seismic hazard map of Italy, named MPS04 (MPS04 Working Group, 2004), was released adopting a logic tree
approach for exploring the alternative epistemic choices (Fig. 1). For seismogenic zonation (ZS9, MPS04 Working Group, 2004) (Fig. 2)
and catalogue (CPTI04; CPTI04 Working Group, 2004) no alternative models were explored.UnpublishedGeneva, Switzerlandope
Testing the b-value variability in Italy and its influence on Italian PSHA
No full textThe supposed b-value spatial variability is the central topic of many scientific works dealing with forecasting modeling applications or geological correlations. If used for seismicity rates determination, the b-value plays an important role in probabilistic seismic hazard assessment, but how much does it influence PSHA? In the logic tree approach used for the new probabilistic seismic hazard map of Italy, named MPS04 (MPS Working Group, 2004), one of the sources of epistemic uncertainty considered was the procedure for computing seismicity rates. Two
alternatives were adopted: 1) compute the activity rates for each binned magnitude
class and 2) compute a Gutenberg-Richter (1944) distribution. In the logic tree
branches where Gutenberg-Richter distribution was adopted, the corresponding bvalue was evaluated for each seismogenic zone: it spans between 0.63 and 2.01. After analysing the b-value variability in the Italian region, this work evaluates the impact of setting the b-value equal to 1 on the results of seismic hazard assessment in terms of PGA and energy release compared to the choices adopted for MPS04 (MPS Working Group, 2004).Published59-764T. Sismicità dell'ItaliaN/A or not JCRope
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