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Dataset for Dc scaling manuscript. Please read the readme file before analyzing the datasets.

Quantifying the dynamics of sequestered CO2 plumes is critical for safe long-term storage, providing guidance on plume extent, and detecting stratigraphic seal failure. However, existing seismic monitoring methods based on wave reflection or transmission probe a limited rock volume and their sensitivity decreases as CO2 saturation increases, decreasing their utility in quantitative plume mass estimation. Here we show that seismic scattering coda waves, acquired during continuous borehole monitoring, are able to illuminate details of the CO2 plume during a 74-h CO2 injection experiment at the Frio-II well Dayton, TX. Our study reveals a continuous velocity reduction during the dynamic injection of CO2, a result that augments and dramatically improves upon prior analyses based on P-wave arrival times. We show that velocity reduction is nonlinearly correlated with the injected cumulative CO2 mass and attribute this correlation to the fact that coda waves repeatedly sample the heterogeneous distribution of cumulative CO2 in the reservoir zone. Lastly, because our approach does not depend on P-wave arrival times or require well-constrained wave reflections it can be used with many source-receiver geometries including those external to the reservoir, which reduces the risk introduced by in-reservoir monitoring wells. Our results provide an approach for quantitative CO2 monitoring and plume evolution that increases safety and long-term planning for CO2 injection and storage.

We investigate the role of pressure solution in deformation of upper- to mid-crustal rocks using aggregates of halite as a room temperature analog for fluid-assisted deformation processes in the Earth's crust. Experiments evaluate the effects of initial grain size distribution on macroscopic pressure solution rate of the aggregate and compare the results to theoretical models for pressure solution. We find that the grain size exponent deviates significantly from the theoretical value of 3 for diffusion-controlled pressure solution. Models typically assume mono-dispersed spherical particles in pseudo-regular packing. We infer that the discrepancy between experimentally determined grain size exponents and the theoretical values are a result of deviation of experimental (and natural) samples from regular packs of mono-dispersed spherical particles. Moreover, we find that compaction rates can vary by up to one order of magnitude as a function of the width of the grain size distribution for a given mean grain size. Wider size distributions allow for higher initial compaction rates, increasing the macroscopic compaction rate with respect to more narrow grain size distributions. Grain sizes in rocks, fault gouges, and hydrocarbon reservoirs are typically log-normal or power law distributed and therefore pressure solution rates may significantly exceed theoretical predictions. Spatiotemporal variations in pressure solution rates due to variations in grain size may cause the formation of low porosity zones, which could potentially focus deformation in these zones and produce pockets of high pore pressures, promoting nucleation of frictional instability and earthquake rupture.

Certain phenomena in nature occur in Goldilocks zones that provide just the right conditions. One such phenomenon in earthquake science seems to be the occurrence of slow slip preceding dynamic slip. For example, the slow slip before the 2011 Mw 9.0 Tohoku-Oki, Japan (Ito et al., 2013; Kato et al., 2012), 2014 Mw 8.2 Iquique, Chile (Meng et al., 2015; Ruiz et al., 2014) and 2015 Mw 8.4 Illapel, Chile (Huang and Meng, 2018) add to the growing number of such observations. Despite these accumulating evidences, a comprehensive understanding of such observations is lacking. Our quest is to understand the physics behind such phenomena by integrating laboratory and numerical simulations. One way to find the reasons for the slow-fast phenomena is to test the fault in a controlled setting. Several studies report the occurrence of transient deformation in rock frictional studies (Gu and Wong, 1994; Leeman et al., 2015, 2016; McLaskey and Yamashita, 2017). However, a thorough understanding of the possible parameters that can influence the slow transients is yet to be known. The primary goal of this work is to investigate the effect of material properties on the slow-fast transitional boundary. Here, we report the results of alternating slow and fast events at 23 MPa from the Brittle Rock DeformAtion Versatile Apparatus (BRAVA) at the National Institute of Geophysics and Volcanology (INGV). We show that a mixed slow-fast rupture sequences occur under a set of physical conditions in between those that produce distinct slow-slip events and fast earthquakes (Leeman et al., 2015, Leeman et al., 2016, Scuderi et al., 2016). The laboratory results of the slow-fast behavior at 33 MPa from the Biax machine at the Penn State University confirms that the same material can exhibit the dual mode deformation at a constant normal load. To depict a broad view of possible failure modes, we integrate the results from the double direct shear biaxial experiments with the dynamic fault modeling (Lapusta and Liu, 2009). The main goal of modeling is to understand the parameters that control the interval between the consecutive slow and fast events. Specifically, the ratio between time since previous event and time to next event, namely the recurrence ratio. We conducted a systematic parameter space study on the dependence of the recurrence ratio on the normal stress, characteristic slip distance, Poisson ratio, asperity size, asperity shape, ratio of friction parameters (a/b) and loading rate. Out of these seven parameters, we found that the loading rate controls the recurrence ratio. It is important to note that the bifurcation from slow-slip to period-two slow and fast ruptures in numerical simulations are only in those models that adequately capture the fault dynamics in three dimensions. Most importantly, the recurrence ratio of the laboratory events and the numerically simulated events are comparable. Overall, our findings highlight a range of possible slip behaviors emerging from the fundamental nature of the fault and provide clues into a potential long preparatory phase that precedes earthquake nucleation.