Rupture Directivity of the Strongest 2016–2017 Central Italy Earthquakes

Calderoni, Giovanna; Rovelli, A.; Giovambattista, Rita Di

doi:10.1002/2017jb014118

Cited by 49 publications

(60 citation statements)

References 45 publications

(75 reference statements)

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“…However, in the integral of the squared velocity spectra of equation , the increase of amplitude is partially compensated by a decrease of duration, and the resulting azimuthal effect due to directivity is less evident being masked in the estimate fluctuations. Moreover, the integral is made over the entire frequency band, whereas directivity affects only frequencies above the corner frequency (e.g., see Figure 2 of Calderoni et al, ). Figure shows that, when a systematic trend is observed, the azimuth of the largest values of Brune stress drop corresponds to the fault strike but can be reversed (to the northwest like in panel a or to the southeast like in panel b), indicating along‐fault ruptures that propagate unilaterally to opposite directions in the two cases.…”

Section: Discussionmentioning

confidence: 99%

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M_w 6.1 L'Aquila Earthquake

2019

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We investigate the variability of Brune stress drop (Δσ) and apparent stress (τ a ) of 23 earthquakes occurred in a small crustal volume adjacent to the hypocenter of the destructive M w 6.1 L'Aquila earthquake. Their magnitude range is 2.7 ≤ M w ≤ 4.1. Interevent variability of stress drop and apparent stress results in a factor of 10, well beyond the individual-event uncertainty. Radiation efficiency η sw = τ a /Δσ varies mostly between 0.1 and 0.2, but in the days immediately before and after the main shock, η sw tends to be smaller decreasing to values as low as 0.06. This may be the consequence of ruptures migrating in those days into a focal volume with higher dynamic strength. The temporal change of η sw is tentatively interpreted as a spatial variation due to the earthquake migration into the locked portion of the fault that originated the main shock. Consistently, no variation in stress drop and apparent stress is observed between foreshocks and aftershocks but the smallest and largest Δσ result in a good correlation with the largest and smallest b-values, respectively, imaged by other authors in the rupture nucleation volume.

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Section: Discussionmentioning

confidence: 99%

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M_w 6.1 L'Aquila Earthquake

2019

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“…An important result of this study is the correlation between f c and n, which is clearly evident from the P wave focal-sphere results in Figure 5. This correlation across the focal sphere is likely to be important to model, if one attempts to extract the rupture velocity, V R , from f c data (as tentatively suggested by Calderoni et al, 2017).…”

Section: A Note On Correlation Between Parameters and Uncertaintiesmentioning

confidence: 99%

Improved Model Fitting for the Empirical Green's Function Approach Using Hierarchical Models

Houtte

Denolle

2018

JGR Solid Earth

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Stress drops calculated from source spectral studies currently show larger variability than what is implied by empirical ground motion models. One of the potential origins of the inflated variability is the simplified model‐fitting techniques used in most source spectral studies. This study examines a variety of model‐fitting methods and shows that the choice of method can explain some of the discrepancy. The preferred method is Bayesian hierarchical modeling, which can reduce bias, better quantify uncertainties, and allow additional effects to be resolved. Two case study earthquakes are examined, the 2016 MW7.1 Kumamoto, Japan earthquake and a MW5.3 aftershock of the 2016 MW7.8 Kaikōura earthquake. By using hierarchical models, the variation of the corner frequency, fc, and the falloff rate, n, across the focal sphere can be retrieved without overfitting the data. Other methods commonly used to calculate corner frequencies may give substantial biases. In particular, if fc was calculated for the Kumamoto earthquake using an ω‐square model, the obtained fc could be twice as large as a realistic value.

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“…Building on the results of Calderoni et al (2015) and Pacor et al (2016) for the L'Aquila, Italy, earthquake sequence, Calderoni et al (2017) used azimuthal variations in S wave spectra to demonstrate that along-strike directivity is a common feature of normal faulting earthquakes in the central Appennines.…”

Section: Related Workmentioning

confidence: 99%

Directivity Modes of Earthquake Populations with Unsupervised Learning

et al. 2020

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We present a novel approach for resolving modes of rupture directivity in large populations of earthquakes. A seismic spectral decomposition technique is used to first produce relative measurements of radiated energy for earthquakes in a spatially compact cluster. The azimuthal distribution of energy for each earthquake is then assumed to result from one of several distinct modes of rupture propagation. Rather than fitting a kinematic rupture model to determine the most likely mode of rupture propagation, we instead treat the modes as latent variables and learn them with a Gaussian mixture model. The mixture model simultaneously determines the number of events that best identify with each mode. The technique is demonstrated on four datasets in California, each with compact clusters of several thousand earthquakes with comparable slip mechanisms. We show that the datasets naturally decompose into distinct rupture propagation modes that correspond to different rupture directions, and the fault plane is unambiguously identified for all cases. We find that these small earthquakes exhibit unilateral ruptures 63–73% of the time on average. The results provide important observational constraints on the physics of earthquakes and faults.

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Rupture Directivity of the Strongest 2016–2017 Central Italy Earthquakes

Cited by 49 publications

References 45 publications

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M_w 6.1 L'Aquila Earthquake

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M_w 6.1 L'Aquila Earthquake

Improved Model Fitting for the Empirical Green's Function Approach Using Hierarchical Models

Directivity Modes of Earthquake Populations with Unsupervised Learning

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Rupture Directivity of the Strongest 2016–2017 Central Italy Earthquakes

Cited by 49 publications

References 45 publications

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, Mw 6.1 L'Aquila Earthquake

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, Mw 6.1 L'Aquila Earthquake

Improved Model Fitting for the Empirical Green's Function Approach Using Hierarchical Models

Directivity Modes of Earthquake Populations with Unsupervised Learning

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Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M_w 6.1 L'Aquila Earthquake

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M_w 6.1 L'Aquila Earthquake