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  • 1
    Publication Date: 2016-07-26
    Description: Confidence in scientific models accumulates by continuously validating the model’s predictions by observations. We compared the seismic-hazard forecasts of the four published versions of the U.S. Geological Survey National Seismic Hazard Maps with observed ground motions. A large dataset is necessary for a statistically meaningful comparison, and so our comparison was based on an aggregated approach such that the observations and the forecast in a region (California, and the central and eastern United States [CEUS]) were combined and compared as a whole. We used instrumental records in California and macroseismic intensity in the CEUS since 2000 as the observation, which was largely prospective to the hazard maps. We verified that the observed seismic hazard based on macroseismic intensity was consistent with that based on instrumental records, making model evaluation in the CEUS, for which instrumental records were almost nonexistent, viable. The observed hazard was found to be generally consistent with the forecasted one for peak ground acceleration (PGA) in California and for both PGA and spectral acceleration at 1 s (SA1) in the CEUS. Forecasted hazard for SA1 for California appeared to be conservative. Recent versions of the hazard map were in better agreement with observations in California. Small earthquakes, as expected, were found to have insignificant impact on SA1. Induced earthquakes in the CEUS have increased the observed seismic hazard but did not invalidate the hazard model as a whole. We examined the resolving power of the test by computing its statistical power.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2016-04-07
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 3
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    Seismological Society of America (SSA)
    Publication Date: 2016-01-08
    Description: The data compilation of "Did You Feel It?" (DYFI) and other similar Internet-based macroseismic intensity databases relies on the voluntary responses from Internet users. A region of no responses could mean no perceivable ground shakings or no volunteers submitting responses. We examined the earthquake and socioeconomic conditions that affected the number of DYFI responses received for a region. A resulting statistical model described the expected number of DYFI responses received for an earthquake. We also showed that residents in California and the central and eastern United States followed similar behavior in responding to DYFI, despite the vast difference in seismicity for the two regions. This study allows for a quantitative definition of completeness for DYFI data. The presented modeling technique is applicable to other Internet-based macroseismic intensity databases.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 4
    Publication Date: 2014-12-05
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2014-12-05
    Description: The Regional Earthquake Likelihood Models experiment in California tested the performance of earthquake likelihood models over a five-year period. First-order analysis showed a smoothed-seismicity model by Helmstetter et al. (2007) to be the best model. We construct optimal multiplicative hybrids involving the best individual model as a baseline and one or more conjugate models. Conjugate models are transformed using an order-preserving function. Two parameters for each conjugate model and an overall normalizing constant are fitted to optimize the hybrid model. Many two-model hybrids have an appreciable information gain (log probability gain) per earthquake relative to the best individual model. For the whole of California, the Bird and Liu (2007) Neokinema and Holliday et al. (2007) pattern informatics (PI) models both give gains close to 0.25. For southern California, the Shen et al. (2007) geodetic model gives a gain of more than 0.5, and several others give gains of about 0.2. The best three-model hybrid for the whole region has the Neokinema and PI models as conjugates. The best three-model hybrid for southern California has the Shen et al. (2007) and PI models as conjugates. The information gains of the best multiplicative hybrids are greater than those of additive hybrids constructed from the same set of models. The gains tend to be larger when the contributing models involve markedly different concepts or data. These results need to be confirmed by further prospective tests. Multiplicative hybrids will be useful for assimilating other earthquake-related observations into forecasting models and for combining forecasting models at all timescales.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 6
    Publication Date: 2015-12-02
    Description: The engineering seismology community has recently recognized the importance of validating the performance of predictive models for seismic hazard by independent observations, yielding a number of studies on the relative performance of ground-motion prediction equations. The validation of intensity prediction equations (IPEs) has attracted less attention. We fill this gap by validating eight Italian IPEs plus one global IPE using five sets of Italian macroseismic intensity data, of which three are prospective and two retrospective to the models. We implemented multiple scoring methods to validate the models and found that the simple score of mean absolute error is sufficient to measure the general model performance. Good models consistently perform well under multiple methods and datasets, showing robustness. Models with physical functional forms are found to perform better. The global IPE performed well for Italian data, implying insignificant regional differences for IPEs. This result encourages grouping intensity data collected from multiple geographic regions, both from the Internet and traditional surveys, into a larger dataset for the use of future model development and validation. Online Material: Table of selected earthquakes, figure showing data for intensity prediction equation (IPE) evaluation, figures for additional residual analyses, and figures showing evaluations based on other performance metrics.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 7
    Publication Date: 2011-12-01
    Description: Estimation of the recording completeness of seismic catalogs recorded with small networks in a heterogeneous observation volume, for example, in mines, is difficult. Local heterogeneities have a strong influence on the wave path and attenuation and must be taken into account. In order to analyze the spatially varying completeness of such catalogs in three dimensions, we present a new approach based on the probability-based magnitude of completeness (PMC) method of Schorlemmer and Woessner (2008). We demonstrate that the traditional approach of Schorlemmer and Woessner (2008) is insufficient in very complex and heterogeneous settings. To account for this problem, we extend the PMC method, taking into account the direction of incoming seismic waves. This allows us to analyze the influence of small heterogeneities on the recording completeness in high resolution. We compare the results with results obtained by a traditional Gutenberg–Richter frequency-magnitude analysis for the JAGUARS catalog: The Japanese German Underground Acoustic Emission Research in South Africa (JAGUARS) project recorded approximately 500,000 seismic events with magnitudes -5
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 8
    Publication Date: 2014-07-04
    Description: Seven competing models for forecasting medium-term earthquake rates in California are quantitatively evaluated using the framework of the Collaboratory for the Study of Earthquake Predictability (CSEP). The model class consists of contrasting versions of the Every Earthquake a Precursor According to Size (EEPAS) and Proximity to Past Earthquakes (PPE) modelling approaches. Models are ranked by their performance on likelihood-based tests, which measure the consistency between a model forecast and observed earthquakes. To directly compare one model against another, we run a classical paired t -test and its non-parametric alternative on an information gain score based on the forecasts. These test scores are complemented by several residual-based methods, which offer detailed spatial information. The experiment period covers 2009 June–2012 September, when California experienced 23 earthquakes above the magnitude threshold. Though all models fail to capture seismicity during an earthquake sequence, spatio-temporal differences between models also emerge. The overall best-performing model has strong time- and magnitude-dependence, weights all earthquakes equally as medium-term precursors of larger events and has a full set of fitted parameters. Models with this time- and magnitude-dependence offer a statistically significant advantage over simpler baseline models. In addition, models that down-weight aftershocks when forecasting larger events have a desirable feature in that they do not overpredict following an observed earthquake sequence. This tendency towards overprediction differs between the simpler model, which is based on fewer parameters, and more complex models that include more parameters.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
    Publication Date: 2014-07-02
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 10
    Publication Date: 2016-04-28
    Description: Finite-fault earthquake source inversions infer the (time-dependent) displacement on the rupture surface from geophysical data. The resulting earthquake source models document the complexity of the rupture process. However, multiple source models for the same earthquake, obtained by different research teams, often exhibit remarkable dissimilarities. To address the uncertainties in earthquake-source inversion methods and to understand strengths and weaknesses of the various approaches used, the Source Inversion Validation (SIV) project conducts a set of forward-modeling exercises and inversion benchmarks. In this article, we describe the SIV strategy, the initial benchmarks, and current SIV results. Furthermore, we apply statistical tools for quantitative waveform comparison and for investigating source-model (dis)similarities that enable us to rank the solutions, and to identify particularly promising source inversion approaches. All SIV exercises (with related data and descriptions) and statistical comparison tools are available via an online collaboration platform, and we encourage source modelers to use the SIV benchmarks for developing and testing new methods. We envision that the SIV efforts will lead to new developments for tackling the earthquake-source imaging problem.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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