Non-double-couple microearthquakes at Long Valley caldera, California, provide evidence for hydraulic fracturing

Foulger, G. R.; Julian, Bruce R.; Hill, David P.; Pitt, A. M.; Malin, Péter; Shalev, E.

doi:10.1016/s0377-0273(03)00420-7

Cited by 124 publications

(89 citation statements)

References 52 publications

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“…Involvement of fluids, slip along curved faults, and fractal faulting are some possible causes that lead to earthquakes with non-DC radiation patterns in the upper crust [Frohlich, 1994]. Shortperiod non-DC events are commonly observed within geothermal areas, such as in Iceland [Foulger and Long, 1984] and California [Ross et al, 1999;Foulger et al, 2004]. Tensile faulting was reported from a geothermal field in West Bohemia, Czech Republic [Vavrycuk , 2002], mixed tensile and shear faulting found at Hengill-Grensdalur ], and vertical dipole radiation patterns identified inside the Long Valley caldera [Foulger et al, 2004].…”

Section: Seismic Source Mechanismsmentioning

confidence: 99%

Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland

et al. 2016

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Seismicity was monitored beneath the Krafla central volcano, NE Iceland, between 2009 and 2012 during a period of volcanic quiescence, when most earthquakes occurred within the shallow geothermal field. The highest concentration of earthquakes is located close to the rock‐melt transition zone as the Iceland Deep Drilling Project‐1 (IDDP‐1) wellbore suggests and decays quickly at greater depths. We recorded multiple swarms of microearthquakes, which coincide often with periods of changes in geothermal field operations, and found that about one third of the total number of earthquakes are repeating events. The event size distribution, evaluated within the central caldera, indicates average crustal values with b = 0.79 ± 0.04. No significant spatial b value contrasts are resolved within the geothermal field nor in the vicinity of the drilled melt. Besides the seismicity analysis, focal mechanisms are calculated for 342 events. Most of these short‐period events have source radiation patterns consistent with double‐couple (DC) mechanisms. A few events are attributed to non‐shear‐faulting mechanisms with geothermal fluids likely playing an important role in their source processes. Diverse faulting styles are inferred from DC events, but normal faulting prevails in the central caldera. The best fitting compressional and tensional axes of DC mechanisms are interpreted in terms of the principal stress or deformation rate orientations across the plate boundary rift. Maximum compressive stress directions are near‐vertically aligned in different study volumes, as expected in an extensional tectonic setting. Beneath the natural geothermal fields, the least compressive stress axis is found to align with the regional spreading direction. In the main geothermal field both horizontal stresses appear to have similar magnitudes causing a diversity of focal mechanisms.

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Section: Seismic Source Mechanismsmentioning

confidence: 99%

Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland

et al. 2016

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“…In 1997, a swarm of earthquakes in the south moat of Long Valley caldera, west of Casa Diablo Hot Springs was recorded by a network of 69 digital, 3C seismic stations (Foulger et al, 2004). Wellconstrained moment tensors obtained for several of these earthquakes have mechanisms that are close to double couples, but contain a net volume increase.…”

Section: Interpreting Moment Tensors and Hypocenter Locations Jointlymentioning

confidence: 99%

“…High-resolution relative hypocenter locations for the entire sequence of several hundred earthquakes clearly define a failure plane that bisects the dilatational polarity fields of the earthquake radiation patterns. This fact rules out shear faulting and requires that the primary failure mechanism is tensile cracking, probably caused by hydraulic fracturing (Foulger et al, 2004).…”

Section: Interpreting Moment Tensors and Hypocenter Locations Jointlymentioning

confidence: 99%

“…moments Mulcahy, 1976a, 1976b;Julian et al, 1998). Net forces may be significant components of earthquake mechanisms in geothermal and hydrocarbon reservoirs, and including them in source studies may contribute to understanding the volumetric components of geothermal and other reservoir-related earthquakes (Foulger et al, 2004).…”

Section: Confidence Bounds For Moment Tensorsmentioning

confidence: 99%

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Earthquakes and errors: Methods for industrial applications

Foulger

Julian

2011

GEOPHYSICS

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The high accuracies and realistic confidence assessments demanded for seismic monitoring of hydraulic fracturing work require specialist experimental approaches. These include seismic network design based on quantitative modeling, high-quality instrument deployments, and accurate and detailed crustal models. Confidence estimates must take into account uncertainties about crustal structure, which may dominate error budgets. Earthquake size should be expressed in terms of scalar seismic moment or the associated moment magnitude M W , which is related to fundamental physical source processes, and not as traditional earthquake magnitudes. Representing earthquake mechanisms in terms of seismic moment tensors allows for processes such as volume changes and complex types of shearing that are important in hydrocarbon and geothermal reservoirs. Traditional fault-plane solutions are based on simplifying assumptions such as shear slip on a planar faults, and isotropic crustal structures, which may introduce large uncertainties. Quantitative assessment of confidence regions for moment-tensor source mechanisms, a newly emerging field, is important for distinguishing computational artifacts from real physical phenomena. We review methods currently available for realistic error estimation for earthquake locations and moment tensors, with particular emphasis on surface sensor arrays in geothermal areas.

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“…In addition, focal mechanisms for spasmodic burst earthquakes beneath Mammoth Mountain in 1997 recorded on a dense, temporary array of three-component seismometers were interpreted to reflect crack opening and fluid transport within a fracture mesh in the brittle crust [Foulger et al, 2004].…”

Section: Lessons Learnedmentioning

confidence: 99%

Natural and industrial analogues for release of CO2 from storagereservoirs: Identification of features, events, and processes and lessonslearned

Lewicki¹,

Birkhölzer²,

Tsang³

2006

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. We thank J. Apps and A. Cortis for constructive review of this report. 2 EXECUTIVE SUMMARYThe injection and storage of anthropogenic CO 2 in deep geologic formations is a potentially feasible strategy to reduce CO 2 emissions and atmospheric concentrations. While the purpose of geologic carbon storage is to trap CO 2 underground, CO 2 could migrate away from the storage site into the shallow subsurface and atmosphere if permeable pathways such as well bores or faults are present. Large-magnitude releases of CO 2 have occurred naturally from geologic reservoirs in numerous volcanic, geothermal, and sedimentary basin settings. Carbon dioxide and natural gas have also been released from geologic CO 2 reservoirs and natural gas storage facilities, respectively, due to influences such as well defects and injection/withdrawal processes. These systems serve as natural and industrial analogues for the potential release of CO 2 from geologic storage reservoirs and provide important information about the key features, events, and processes (FEPs) that are associated with releases, as well as the health, safety, and environmental consequences of releases and mitigation efforts that can be applied.We describe a range of natural releases of CO 2 and industrial releases of CO 2 and natural gas in the context of these characteristics. Based on this analysis, several key conclusions can be drawn, and lessons can be learned for geologic carbon storage. First, CO 2 can both accumulate beneath, and be released from, primary and secondary reservoirs with capping units located at a wide range of depths. Both primary and secondary reservoir entrapments for CO 2 should therefore be well characterized at storage sites. Second, many natural releases of CO 2 have been correlated with a specific event that triggered the release, such as magmatic fluid intrusion or seismic activity. The potential for processes that could cause geomechanical damage to sealing cap rocks and trigger the release of CO 2 from a storage reservoir should be evaluated. Third, unsealed fault and fracture zones may act as fast and direct conduits for CO 2 flow from depth to the surface. Risk assessment should therefore emphasize determining the potential for and nature of CO 2 migration along these structures. Fourth, wells that are structurally unsound have the potential to rapidly release large quantities of CO 2 to the atmosphere. Risk assessment should therefore be focused on the potential for both active and abandoned wells at storage sites to transport CO 2 to the surface, particularly at sites with depleted oil or gas reservoirs where wells are abundant. Fifth, the style of CO 2 release at the surface varies widely between and within different leakage sites. In rare circumstances, the release of CO 2 can be a self-enhancing and/or eruptive process; this possibility should be assessed in the case of CO 2 leakage from storage reservoirs. Sixth, the hazard to human health has been small in most cases of large surface releases of CO 2 . This could be due to imp...

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Non-double-couple microearthquakes at Long Valley caldera, California, provide evidence for hydraulic fracturing

Cited by 124 publications

References 52 publications

Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland

Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland

Earthquakes and errors: Methods for industrial applications

Natural and industrial analogues for release of CO2 from storagereservoirs: Identification of features, events, and processes and lessonslearned

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