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Abundant heterogeneity has been documented on faults in nature across a wide range of length scales, including structural, mineralogical, and roughness variations. The role of complex heterogeneity on fault mechanics and frictional stability is not well established, and experiments investigating heterogeneity have typically incorporated a single source of heterogeneity. Here, we conduct rock friction experiments on rough, bimaterial faults that are creeping, or steadily sliding, to explore the role of lithological heterogeneity on fault mechanics and stability. When strong asperities juxtapose weak gouge, stable sliding occurs with a low friction coefficient, µ. Encounters of strong diabase asperities on talc gouge lined faults initiate dramatic increases in µ and transitions to unstable sliding characterized by frequent stick-slip events (StSE). Seismic moments and stress drops of StSE decrease with increasing asperity abundance. Stress is concentrated at asperities during encounters, increasing with decreasing asperity abundance and leading to extensive mechanical damage. Interactions between strong, velocity weakening asperities provide a model to explain the nucleation of seismic and aseismic slip events on nominally stable, creeping faults. 

Abstract: The datasets provided here are from the paper “Lee, J., Tsai, V. C., Trugman, D. T., Hirth, G., & Chatterjee, A. (2025). Fault network geometry modulates earthquake source spectra across scales. Geophysical Research Letters, 52, e2025GL115592. https://doi.org/10.1029/2025GL115592".   They include earthquake stress-drop and fault misalignment (Rm) measurements from Southern California (Shearer et al., 2022), Japan (Oth, 2013) and Italy (Kemna et al., 2021). The SCARDEC datasets provide estimated corner frequencies, moment-rate roughness (Radiated Energy Enhancement Factor; REEF) and mean Kagan angles computed within proximity of each event (count#). For more details, please refer to the paper.   Kemna, K. B., Verdecchia, A., & Harrington, R. M. (2021). Spatio-temporal evolution of earthquake static stress drop values in the 2016–2017 central Italy seismic sequence. Journal of Geophysical Research: Solid Earth, 126, e2021JB022566. https://doi.org/10.1029/2021JB0225 Oth, A. (2013). On the characteristics of earthquake stress release variations in Japan. Earth and Planetary Science Letters, 377–378, 132–141. https://doi.org/10.1016/j.epsl.2013.06.037 Shearer, P. M., Abercrombie, R. E., & Trugman, D. T. (2022). Improved stress drop estimates for M 1.5 to 4 earthquakes in southern California from 1996 to 2019. Journal of Geophysical Research: Solid Earth, 127, e2022JB024243. https://doi.org/10.1029/2022JB024243 Vallée, M., Charléty, J., Ferreira, A. M. G., Delouis, B., & Vergoz, J. (2011). SCARDEC: A new technique for the rapid determination of seismic moment magnitude, focal mechanism and source time functions for large earthquakes using body-wave deconvolution. Geophysical Journal International, 184(1), 338–358. https://doi.org/10.1111/j.1365-246X.2010.04836.x 

Abstract Understanding the generation of damaging, high‐frequency ground motions during earthquakes is essential both for fundamental science and for effective hazard preparation. Various theories exist regarding the origin of high‐frequency ground motions, including the standard paradigm linked to slip heterogeneity on the rupture plane, and alternative perspectives associated with fault complexity. To assess these competing hypotheses, we measure ground motion amplitudes in different frequency bands for 3 ≤ M ≤ 5.8 earthquakes in Southern California and compare them to empirical ground motion models. We utilize a Bayesian inference technique called the Integrated Nested Laplace Approximation (INLA) to identify earthquake source regions that produce higher or lower ground motions than expected. Our analysis reveals a strong correlation between fault complexity measurements and the high‐frequency ground motion event terms identified by INLA. These findings suggest that earthquakes on complex faults (or fault networks) lead to stronger‐than‐expected ground motions at high frequencies. 

We develop a linear viscous constitutive relationship for pressure solution constrained by models of deformed metasedimentary rocks and observations of exposed rocks from ancient subduction zones. We include pressure and temperature dependence on the solubility of silica in fluid by parameterizing a practical van’t Hoff relationship. This general flow law is well suited for making predictions about interseismic behavior of subduction zones. We apply the flow law to Cascadia, where thermal structure, geometry, relative plate velocity, and Global Positioning System velocity field are well constrained. Results are consistent with the temperature conditions at which resolvable ductile strain is recorded in subducted mudstones (at depths near the updip limit of the seismogenic zone) and with relative plate motion accommodated completely by viscous deformation (at depths near the downdip limit of the seismogenic zone). The flow law also predicts the observed forearc tapering of slip rate deficit with depth. 

Abstract Before large volumes of crystal poor rhyolites are mobilized as melt, they are extracted through the reduction of pore space within their corresponding crystal matrix (compaction). Petrological and mechanical models suggest that a significant fraction of this process occurs at intermediate melt fractions (ca. 0.3–0.6). The timescales associated with such extraction processes have important ramifications for volcanic hazards. However, it remains unclear how melt is redistributed at the grain‐scale and whether using continuum scale models for compaction is suitable to estimate extraction timescales at these melt fractions. To explore these issues, we develop and apply a two‐phase continuum model of compaction to two suites of analog phase separation experiments—one conducted at low and the other at high temperatures, T, and pressures, P. We characterize the ability of the crystal matrix to resist porosity change using parameterizations of granular phenomena and find that repacking explains both data sets well. A transition between compaction by repacking to melt‐enhanced grain boundary diffusion‐controlled creep near the maximum packing fraction of the mush may explain the difference in compaction rates inferred from high T + P experiments and measured in previous deformation experiments. When upscaling results to magmatic systems at intermediate melt fractions, repacking may provide an efficient mechanism to redistribute melt. Finally, outside nearly instantaneous force chain disruption events occasionally recorded in the low T + P experiments, melt loss is continuous, and two‐phase dynamics can be solved at the continuum scale with an effective matrix viscosity. 

Key Points Changes in hydraulic diffusivity and pressurization factor during thermal pressurization (TP) balance each other in low permeability and low porosity fault rocks Hydraulic diffusional length scales as time 0.7 when considering TP parameters that depend on temperature and pressure The constant case model should be considered with ambient initial conditions and not time‐averaged ones 

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. 

Type II and IV twins with irrational twin boundaries are studied by high-resolution transmission electron microscopy in two plagioclase crystals. The twin boundaries in these and in NiTi are found to relax to form rational facets separated by disconnections. The topological model (TM), amending the classical model, is required for a precise theoretical prediction of the orientation of the Type II/IV twin plane. Theoretical predictions also are presented for types I, III, V, and VI twins. The relaxation process that forms a faceted structure entails a separate prediction from the TM. Hence, faceting provides a difficult test for the TM. Analysis of the faceting by the TM is in excellent agreement with the observations.