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1

Analysis of seismic magnitude‑frequency distribution in northern and central Chile

Sánchez Ewin

Acta Geophysica

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2023

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Vol. 71, no. 4

1619--1630

EN

A new model, recently presented by the corresponding author, was performed in order to obtain relevant information from the frequency-magnitude distribution of earthquakes observed in northern and central zones of Chile. The model, which can be seen as a generalized non-extensive distribution, was applied to 240 data sets (seismic magnitudes) recorded over 10 years throughout the Chilean territory, since January 01, 2011. The results allow us to know in both zones the behavior of the Gutenberg-Richter and non-extensivity parameters proposed by the model. Also, a specific parameter gives us some clues about the scaling between the released energy and the inter-plate fragments size considered in the non-extensive earthquake literature. The monthly relative variance, related to fluctuations which control the behavior of the energy distribution, shows a similar trend to the respective monthly seismic average magnitude, revealing a transition toward seismic stability after the 8.4 Mω strong earthquake occurred on September 16, 2015, in Chile. After this event, fit parameters suggest that the northern zone releases more energy in contrast to the central zone. For comparison purposes, a well-known non-extensive model widely used today was applied as well.

2

An updated version of the ETAS model based on multiple change points detection

Benali Amel, Zhuang Jiancang, Talbi Abdelhak

Acta Geophysica

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2022

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Vol. 70, no 5

2013--2031

EN

The stationary Epidemic-Type Aftershock Sequence (ETAS) model is applied to seismicity in Central Italy, in order to study the temporal changes of the corresponding earthquakes time series. However, the residual analysis reveals that some features of the observed seismicity cannot be captured by the stationary ETAS model in its standard formulation. In this case, a decision-tree algorithm is developed to deal with inference problems linked to the estimation of specific time points where stationarity may be potentially broken. Specifically, this algorithm considers the subdivision of the whole time period into two or more subintervals that join in specific time points called change points, where significant time variation in the ETAS parameters is observed. As a result, a three-stage ETAS model with two change points is selected as the best model describing seismicity of the Central Apennines region during the time period 2005–2017, compared to the standard ETAS model. The variation of the estimated ETAS parameters is statistically significant from one stage to another. In particular, the three-stage ETAS estimates of background seismicity rates are found to be increasing from one stage to another over time.

3

Temporal response of magnitude distribution to fluid injection rates in The Geysers geothermal field

Leptokaropoulos Konstantinos, Staszek Monika

Acta Geophysica

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2019

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Vol. 67, no. 1

327--339

EN

The influence of fluid injection rates on the magnitude distribution of the seismicity which occurred in the NW part of The Geysers geothermal site is studied here. A direct comparison between injection rate changes and b value response is attempted after appropriate selection of data subsets. Due to the relatively small sample (1121 events, corresponding to an average rate of ~ 0.45 events/day), we also aggregated seismic activity into two families corresponding to increasing and decreasing injection rates, respectively. The b values were calculated as a function of time lag related to the injection activity. In agreement with previous studies, we found a statistically significant direct relation between b values and injection rate changes, which occurred at a zero or very short time lag (from 0 to ~ 15 days). However, the b value changes are related to the slope (i.e., the second derivative of injection volume), instead of the absolute values of injection rates. The increasing injection rates correspond to b = 1.18 ± 0.06, whereas the decreasing injection rates correspond to b = 1.10 ± 0.05. The corresponding values estimated by the repeated medians technique are b = 1.97 ± 0.20 and b = 1.50 ± 0.13. Both differences are significant at 0.05 level.

4

Analysis of microseismicity associated with the 2017 seismic swarm near the Aegean coast of NW Turkey

Mesimeri M., Kourouklas C., Papadimitriou E., Karakostas V., Kementzetzidou D.

Acta Geophysica

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2018

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Vol. 66, no. 4

479--495

EN

A thorough spatiotemporal analysis of the intense seismic activity that took place near the Aegean coast of NW Turkey during January–March 2017 was conducted, aiming to identify its causative relation to the regional seismotectonic properties. In this respect, absolute and relative locations are paired and a catalog consisting of 2485 events was compiled. Relative locations are determined with high accuracy using the double-difference technique and differential times both from phase pick data and from cross-correlation measurements. The spatial distribution of the relocated events revealed a south-dipping causative fault along with secondary and smaller antithetic segments. Spatially, the seismicity started at the westernmost part and migrated with time to the easternmost part of the activated area. Temporally, two distinctive periods are observed, namely an early period lasting 1 month and a second period which includes the largest events in the sequence. The investigation of the interevent time distribution revealed a triggering mechanism, whereas the ETAS parameters show a strong external force (l[1), which might be attributed to the existence of the Tuzla geothermal field.

5

On the testing of seismicity models

Molchan G.

Acta Geophysica

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2012

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Vol. 60, no. 3

624-637

EN

Recently a likelihood-based methodology has been developed by the Collaboratory for the Study of Earthquake Predictability (CSEP) with a view to testing and ranking seismicity models. We analyze this approach from the standpoint of possible applications to hazard analysis. We arrive at the conclusion that model testing can be made more efficient by focusing on some integral characteristics of the seismicity distribution. This can be achieved either in the likelihood framework but with economical and physically reasonable coarsening of the phase space or by choosing a suitable measure of closeness between empirical and model seismicity rate in this space.

6

Efficient testing of earthquake forecasting models

Rhoades D.A., Schorlemmer D., Gerstenberger M.C., Christophersen A., Zechar J.D., Imoto M.

Acta Geophysica

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2011

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Vol. 59, no. 4

728-747

EN

Computationally efficient alternatives are proposed to the likelihood- based tests employed by the Collaboratory for the Study of Earthquake Predictability for assessing the performance of earthquake likelihood models in the earthquake forecast testing centers. For the conditional L-test, which tests the consistency of the earthquake catalogue with a model, an exact test using convolutions of distributions is available when the number of earthquakes in the test period is small, and the central limit theorem provides an approximate test when the number of earthquakes is large. Similar methods are available for the R-test, which compares the likelihoods of two competing models. However, the R-test, like the N-test and L-test, is fundamentally a test of consistency of data with a model. We propose an alternative test, based on the classical paired t-test, to more directly compare the likelihoods of two models. Although approximate and predicated on a normality assumption, this new T-test is not computer-intensive, is easier to interpret than the R-test, and becomes increasingly dependable as the number of earthquakes increases.

7

Badanie grupowania w przestrzeni parametrów tła sejsmicznego przed dużym trzęsieniem ziemi

Lasocki S.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

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2009

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T. 35, z. 2/1

515-522

EN

To asses correctly distances between events in a parameter space we replace the values of parameters with the values of their cumulative distributions. The cumulative distributions result from the kernel estimation. We apply this approach to analyze seismicity preceding MW6.5 Kozani-Grevena (Greece) earthquake from 13.05.1995. The analysis reveals premonitory clustering of seismicity in the time-distance subspace.