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1. High-precision Aftershock Locations and Fault Planes of the 2016-2017 Central Italy Sequence

   https://doi.org/10.5281/zenodo.5091137  

   Waldhauser, Felix; Michele, Maddalena; Chiaraluce, Lauro; Stefano, Raffaele Di; Schaff, David (January 2021, Zenodo)

   The earthquake catalog includes high-precision hypocenter relocations for 390,334 earthquakes recorded during the 2016-2017 Amatrice (Central Italy)  earthquake sequence. The relative locations were computed by double-difference inversion of a  combination of INGV phase picks and cross-correlation differential  times measured from correlated seismograms with correlation coefficients > 0.7. Planes of normal faults (idx=1-5) are derived from PCA analysis of 2 months of aftershock  locations in the CAT4 catalog following large events. Surfaces of detachment faults (idx=7-10) are derived from mapping out the location of correlated earthquakes.  Citation: Waldhauser, F., Michele, M., Chiaraluce, L., Di Stefano, R., & Schaff, D. P. (2021). Fault planes, fault zone structure and detachment fragmentation resolved with highprecision aftershock locations of the 2016-2017 central Italy sequence. Geophysical Research Letters, 48, e2021GL092918. https://doi.org/10.1029/2021GL092918 

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2. Fault Network Geometry Modulates Earthquake Source Spectra Across Scales

   https://doi.org/10.1029/2025GL115592  

   Lee, Jaeseok; Tsai, Victor C; Trugman, Daniel T; Hirth, Greg; Chatterjee, Avigyan (June 2025, Geophysical Research Letters)

   Abstract Earthquake source spectra provide unique insights into the earthquake rupture process. Motivated by previous research suggesting that complex fault geometries enhance high‐frequency seismic radiation, we study the influence of fault network geometry on earthquake source spectra using multiple independent observations. At regional scales, we examine correlations of stress drop measurements with surface fault trace misalignment in Southern California, Japan, and Central Italy. At a global scale, we examine correlations of moment‐rate function complexity of large earthquakes with focal mechanism variability, a proxy for local fault complexity. Despite significant scatter in the observations, we find overall consistent positive correlations. The concept that elastic interactions of discrete fault structures during the earthquake rupture process generates high‐frequency ground motions offers a coherent framework for interpreting our observations. These findings suggest that variations in fault complexity explain why some earthquakes produce stronger high‐frequency ground motions than others. 

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3. To Heal or Not to Heal?: 2. The Moment–Recurrence Time Behavior of Repeating Earthquakes in the 2011 Prague, Oklahoma Aftershock Sequence Is Consistent With Laboratory Healing Rates

   https://doi.org/10.1029/2024JB030548  

   Okamoto, Kristina K; Savage, Heather M; Cochran, Elizabeth S; Brodsky, Emily E; Abercrombie, Rachel (September 2025, Journal of Geophysical Research: Solid Earth)

   Abstract The timing and failure conditions of an earthquake are governed by the interplay between fault reloading and restrengthening. The moment‐recurrence time behavior of repeating earthquakes can give observational estimates of fault healing rates; however, it is difficult to link these observed healing rates to laboratory studies of frictional healing in part because of uncertainty in lithology. Here, we study the 2011 Prague earthquake sequence, which includes repeating earthquakes in the Arbuckle group and the granitic basement, and compare them to laboratory experiments on samples of the Arbuckle and Troy granite (representative of the basement rock) (Okamoto et al., 2025,https://doi.org/10.1029/2024JB030573). We find three spatially distinct groups of repeating earthquakes with different moment‐recurrence behavior: (a) constant moment‐recurrence time in the Arbuckle group, (b) scattered moment‐recurrence time at the intersection of the foreshock‐mainshock fault in the granitic basement, and (c) moment‐predictable behavior outside of the foreshock‐mainshock fault intersection also in the granitic basement. Our observation of stagnant healing for repeating sequences in the Arbuckle group is consistent with laboratory observations of low healing rates for moderately high pore fluid pressures in Arbuckle samples. For the moment‐predictable group, the source radius that is required in order to match healing rates is consistent with source radius estimations when taking into account reasonable attenuation of theP‐pulse width. Overall, we observe diverse healing behaviors in the seismic families that are consistent with laboratory healing rates, providing seismic evidence that contact‐scale frictional mechanisms are relevant to large‐scale earthquake dynamics. 

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4. Improved Observations of Deep Earthquake Ruptures Using Machine Learning

   https://doi.org/10.1029/2023JB027334  

   Shi, Qibin; Denolle, Marine A. (December 2023, Journal of Geophysical Research: Solid Earth)

   Abstract Elevated seismic noise for moderate‐size earthquakes recorded at teleseismic distances has limited our ability to see their complexity. We develop a machine‐learning‐based algorithm to separate noise and earthquake signals that overlap in frequency. The multi‐task encoder‐decoder model is built around a kernel pre‐trained on local (e.g., short distances) earthquake data (Yin et al., 2022,https://doi.org/10.1093/gji/ggac290) and is modified by continued learning with high‐quality teleseismic data. We denoise teleseismic P waves of deep Mw5.0+ earthquakes and use the clean P waves to estimate source characteristics with reduced uncertainties of these understudied earthquakes. We find a scaling of moment and duration to beM₀ ≃ τ⁴, and a resulting strong scaling of stress drop and radiated energy with magnitude ( and ). The median radiation efficiency is 5%, a low value compared to crustal earthquakes. Overall, we show that deep earthquakes have weak rupture directivity and few subevents, suggesting a simple model of a circular crack with radial rupture propagation is appropriate. When accounting for their respective scaling with earthquake size, we find no systematic depth variations of duration, stress drop, or radiated energy within the 100–700 km depth range. Our study supports the findings of Poli and Prieto (2016,https://doi.org/10.1002/2016jb013521) with a doubled amount of earthquakes investigated and with earthquakes of lower magnitudes. 

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5. False Positives in the Identification of Dynamic Earthquake Triggering

   https://doi.org/10.1029/2025JB031566  

   Hardebeck, Jeanne L; DeSalvio, Nicolas D; Fan, Wenyuan; Barbour, Andrew J (July 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Dynamic earthquake triggering is commonly identified through the temporal correlation between increased seismicity rates and global earthquakes that are possible triggering events. However, correlation does not imply causation. False positives may occur when unrelated seismicity rate changes coincidently occur at around the time of candidate triggers. We investigate the expected false positive rate in Southern California with globalM ≥ 6 earthquakes as candidate triggers. We compute the false positive rate by applying the statistical tests used by DeSalvio and Fan (2023),https://doi.org/10.1029/2023jb026487to synthetic earthquake catalogs with no real dynamic triggering. We find a false positive rate of ∼3.5%–8.5% when realistic earthquake clustering is present, consistent with the 95% confidence typically used in seismology. However, when this false positive rate is applied to the tens of thousands of spatial‐temporal windows in Southern California tested in DeSalvio and Fan (2023),https://doi.org/10.1029/2023jb026487, thousands of false positives are expected. The expected false positive occurrence is large enough to explain the observed apparent triggering following 70% of large global earthquakes (DeSalvio & Fan, 2023,https://doi.org/10.1029/2023jb026487), without requiring any true dynamic triggering. Aside from the known triggering from the nearby El Mayor‐Cucapah, Mexico, earthquake, the spatial and temporal characteristics of the reported triggering are indistinguishable from random false positives. This implies that best practice for dynamic triggering studies that depend on temporal correlation is to estimate the false positive rate and investigate whether the observed apparent triggering is distinguishable from the correlations that may occur by chance. 

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