Characteristics of Seismicity inside and outside the Salton Sea Geothermal Field

Cheng, Yifang; Chen, Xiaowei

doi:10.1785/0120170311

Cited by 22 publications

(17 citation statements)

References 27 publications

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“…The final thresholds employed are T = 5, R = 0.009 (Figure ), where interevent distances below those thresholds were identified as clusters. Based on time and distance thresholds, we automatically group events into individual clusters following Cheng and Chen (). The clustering resulted in 74 clusters.…”

Section: Methodsmentioning

confidence: 99%

Multiscale Analysis of Spatiotemporal Relationship Between Injection and Seismicity in Oklahoma

2018

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Many previous studies have suggested that wastewater disposal is the most probable factor affecting increased seismicity in Oklahoma since 2009. While this relationship is clear at the state scale, a systematic quantitative analysis of the spatiotemporal relationships between injection and seismicity is needed. We first apply multiscale analyses to assess the temporal correlation between injection rate and seismicity rate at a range of different grid sizes, which demonstrate clear temporal correlations within the two main seismic regions at variable time delays. The time delay variability decreases with larger grid sizes, whereby the average time delay ranges from 150 to 220 days. The average time delay at large scales is consistent with inferred large‐scale diffusive migration away from areas of high injection rates with diffusivities of 0.5 to 2.0 m2/s. The inferred large‐scale diffusivities are consistent with an expected range of diffusivity within the Arbuckle Group where wastewater disposals are occurring. However, individual earthquake clusters have diffusivities that are about one to two orders lower than the large‐scale models. We interpret this as a manifestation of a two‐layered diffusion model with high diffusivity within the injection layer above basement, which facilitates stress transfer at a larger spatial footprint, triggering seismic slip at multiple seismogenic faults within the crystalline basement with low diffusivity, similar to fluid‐driven clusters in other tectonic regions.

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Section: Methodsmentioning

confidence: 99%

Multiscale Analysis of Spatiotemporal Relationship Between Injection and Seismicity in Oklahoma

2018

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“…Therefore, we infer that within the hydrothermal reservoir temperature and pressure conditions at the time of deformation and alteration of the formation being analyzed in this study, the stiffer zones (zones B and D) were more brittle than the less-stiff zones (zones A and C), thus facilitating the preferential localization of greater fracturing in these stiffer zones. Our observations here suggest an influence of mechanical stratigraphy on the brittle Furthermore, the exploration of geothermal energy systems has been associated with induced seismicity (Diehl et al 2017;Wiemer et al 2017;Cheng and Chen 2018;Zbinden et al 2020). However, carbonate minerals (calcite and dolomite), are more mechanically susceptible to earthquake nucleation at higher temperatures and pressures such as those relevant for hydrothermal reservoirs (e.g., Carpenter et al 2014;Kolawole et al 2019).…”

Section: Reservoir Targetsmentioning

confidence: 54%

Mechanical Zonation of Rock Properties and the Development of Hydrothermal Fluid Circulation Pathways: Implications for Enhanced Geothermal Systems

Kolawole

Ispas²,

Kolawole

et al. 2020

Preprint

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Oil and gas operations in sedimentary basins have revealed significant temperatures at depth, raising the possibility of major geothermal resource potential in the sedimentary sequences. The efficient development of such a resource may require enhancement by hydraulic stimulation. However, effective stimulation relies on an initial assessment of in-situ mechanical properties and a Discrete Fracture Network (DFN) model of the rock response. Here, we examine the distribution of mechanical properties (unconfined compressive strength, UCS ; ultrasonic velocity-derived Poisson ratio, ν; and, scratch-derived fracture toughness, K s ) along the cored interval of a sedimentary formation with a known geothermal anomaly in the Permian Basin, U.S. Our results reveal the mechanical heterogeneity of the rock, demonstrated by four distinct alternating mechanical zones, which include: (1.) mechanically weaker 0.17 m-thick Zone-A and 0.18 m-thick Zone-C with mean UCS = 110 MPa, ν = 0.25, K s = 1.89 MPa·√m; and (2.) mechanically stronger 0.41 m-thick Zone-B and 0.15 m-thick Zone-D which show mean UCS = 166 MPa, ν = 0.22, and K s = 2.87 MPa·√m. Although X-ray Diffraction analyses of the samples suggest that the entire rock matrix is dominated by dolomite, the stronger zones show a higher abundance of quartz (>30%) and relatively lower phyllosilicate mineral content (<2%) than the weaker zones. Further, we observe that the mechanically stronger zones have the greatest occurrences of hydrothermal alterations (anhydrite veins and nodules ), indicating that the cored interval had experienced hydrothermal fluid circulation in the past. We infer that the denser clustering of fractures in the stronger zones which facilitated the hydrothermal vein development was due to the influence of mechanical stratigraphy on the brittle deformation and alteration of the sedimentary-hosted hydrothermal reservoir. Thus, we suggest that the stronger zones represent viable targets for hydraulic stimulation of a geothermal reservoir, both for the emplacement of new fractures and the linkage of pre-existing fractures. Our findings in this study provide an analog for hydraulic stimulation of viable geothermal reservoir targets at higher in-situ temperatures and higher geothermal gradients.

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“…Such variations can be caused by exogenous geological or anthropogenic processes introducing short but intense seismogenic episodes compared long term tectonic processes. This can be the case, for example, of episodic volcanic (Roberts et al, ), natural geothermal (Cheng & Chen, ; Gaeta et al, ), or human‐induced (Ellsworth, ; Martínez‐Garzón et al, ; Schoenball & Ellsworth, ; Trugman et al, ) seismicity, or even tectonic seismicity in the presence of seasonal variations (Ueda & Kato, ). A clear observation of such bimodality arising from the separation of tectonic and episodic fluid induced microseismicty was reported by Vasylkivska and Huerta () in Oklahoma earthquakes.…”

Section: Discussionmentioning

confidence: 99%

Topological Properties of Epidemic Aftershock Processes

Ardanuy¹

2020

JGR Solid Earth

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Earthquakes in seismological catalogs and acoustic emission events in lab experiments can be statistically described as point events in linear Hawkes processes, where the spatiotemporal rate is a linear superposition of background intensity and aftershock clusters triggered by preceding activity. Traditionally, statistical seismology interpreted these models as the outcome of epidemic branching processes, where one‐to‐one causal links can be established between mainshocks and aftershocks. Declustering techniques are used to infer the underlying triggering trees and relate their topological properties with epidemic branching models. Here, we review how the standard Epidemic Type Aftershock Sequence (ETAS) model extends from the Galton‐Watson branching processes and bridges two extreme cases: Poisson and scale‐free power law trees. We report the statistical laws expected in triggering trees regarding some topological properties. We find that the statistics of such topological properties depend exclusively on two parameters of the standard ETAS model: the average branching ratio nb and the ratio between exponents α and b characterizing the production of aftershocks and the distribution of magnitudes, respectively. In particular, the classification of clusters into bursts and swarms proposed by Zaliapin and Ben‐Zion (2013b, https://doi.org/10.1002/jgrb.50178) appears naturally in the aftershock sequences of the standard ETAS model depending on nb and α/b. On the other hand swarms can also appear by false causal connections between independent events in nontectonic seismogenic episodes. From these results, one can use the memory‐less Galton‐Watson as a null model for empirical triggering processes and assess the validity of the ETAS hypothesis to reproduce the statistics of natural and artificial catalogs.

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Characteristics of Seismicity inside and outside the Salton Sea Geothermal Field

Cited by 22 publications

References 27 publications

Multiscale Analysis of Spatiotemporal Relationship Between Injection and Seismicity in Oklahoma

Multiscale Analysis of Spatiotemporal Relationship Between Injection and Seismicity in Oklahoma

Mechanical Zonation of Rock Properties and the Development of Hydrothermal Fluid Circulation Pathways: Implications for Enhanced Geothermal Systems

Topological Properties of Epidemic Aftershock Processes

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