A method for determining significant structures in a cloud of earthquakes

Jones, R. H.; Stewart, R. C.

doi:10.1029/96jb03739

Cited by 143 publications

(108 citation statements)

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“…Hypocenters typically cluster into well-defined smallscale geometrical patterns (e.g. Philips et al, 2002) and the enhanced use of such data sets has made significant progress in recent years applying location collapsing methods (Jones and Stewart, 1997) as well as relative relocation techniques (Waldhauser and Ellsworth, 2000).…”

Section: Discussionmentioning

confidence: 99%

Seismic detection of CO2 leakage along monitoring wellbores

Bohnhoff

Zoback

Chiaramonte

et al. 2010

International Journal of Greenhouse Gas Control

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A pilot carbon dioxide (CO 2 ) sequestration experiment was carried out in the Michigan Basin in which ~10,000 tonnes of supercritical CO 2 was injected into the Bass Island Dolomite (BILD) at 1050 m depth. A Passive Seismic Monitoring (PSM) network was operated before, during and after the ~17 day injection period. The seismic monitoring network consisted of two arrays of eight, three-component sensors, deployed in two monitoring wells at only a few hundred meters from the injection point. 225 microseismic events were detected by the arrays. Of these, only one event was clearly an injectioninduced microearthquake. It occurred during injection, approximately 100 m above the BILD formation. No events, down to the magnitude -3 detection limit, occurred within the BILD formation during the injection. The observed seismic waveforms associated with the other 224 events were quite unusual in that they appear to contain dominantly compressional (P) but no (or extremely weak) shear (S) waves, indicating that they are not associated with shear slip on faults. The microseismic events were unusual in two other ways. First, almost all of the events occurred prior to the start of injection into the BILD formation. Second, hypocenters of the 94 locatable events cluster around the wells where the sensor arrays were deployed, not the injection well. While the temporal evolution of these events show no 2 correlation with the BILD injection, they do correlate with CO 2 injection for enhanced oil recovery (EOR) into the 1670 m deep Coral Reef formation that had been going on for ~2.5 years prior to the pilot injection experiment into the BILD formation. We conclude that the unusual microseismic events reflect degassing processes associated with leakage up and around the monitoring wells from the EOR-related CO 2 injection into the Coral Reef formation, ~700 m below the depth of the monitoring arrays. This conclusion is also supported by the observation that as soon as injection into the Coral Reef formation resumed at the conclusion of the BILD demonstration experiment, seismic events (essentially identical to the events associated with the Coral Reef injection prior to the BILD experiment) again started to occur close to a monitoring arrays. Taken together, these observations point to vertical migration around the casings of the monitoring wellbores. Detection of these unusual microseismic events was somewhat fortuitous in that the arrays were deployed at the depth where the CO 2 undergoes a strong volume increase during transition from a supercritical state to a gas. Given the large number of pre-existing wellbores that exist in depleted oil and gas reservoirs that might be considered for CO 2 sequestration projects, passive seismic monitoring systems could be deployed at appropriate depths to systematically detect and monitor leakage along them.

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Section: Discussionmentioning

confidence: 99%

Seismic detection of CO2 leakage along monitoring wellbores

Bohnhoff

Zoback

Chiaramonte

et al. 2010

International Journal of Greenhouse Gas Control

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“…The orientations of Fenton Hill planes found with this technique are consistent with known stress fields. The collapsing method (Jones and Stewart, 1997) shifts hypocenters toward the center of mass of nearby events and is able to resolve numerous geometrical features that are otherwise obscured by location error. This method has been generalized into a joint hypocenter (JHD) method (Fehler et al, 2000).…”

Section: Soultz-sous-forêts Francementioning

confidence: 99%

Induced Microearthquake Patterns in Hydrocarbon and Geothermal Reservoirs: Six Case Studies

Phillips

Rutledge

Fehler

2002

The Mechanism of Induced Seismicity

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The injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs. By deploying sensors downhole, data sets have been collected that consist of a few hundred to well over 10,000 induced events. We find that most induced events cluster into well-defined geometrical patterns. In many cases, we must apply highprecision, relative location techniques to observe these patterns. At three sedimentary sites, thin horizontal strands of activity are commonly found within the location patterns. We believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress. At a massive carbonate and two crystalline sites, combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns. In addition, the fine-scale seismicity patterns often evolve systematically with time.At sedimentary sites, migration of seismicity toward the injection point has been observed and may result from slip-induced stress along fractures that initially have little resolved shear. In such cases, triggering events may be critical to generate high levels of seismic activity. At one crystalline site, the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures. We hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs.Running Head: Microearthquake Patterns in Reservoirs

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“…The method of Jones and Stewart [1997] moves events with overlapping uncertainty ellipsoids within their individual uncertainty ellipsoids towards the centroid of all overlapping events in an iterative process that results in the simplest pattern of events that is still consistent with the location and confidence ellipsoid data. This method reduces the smearing effects due to pick uncertainty and errors in the velocity model on a cloud of events, while not formally increasing the absolute location accuracy.…”

Section: Data Processing and Resultsmentioning

confidence: 99%

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

Horning¹

2017

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This thesis investigates the evolution of the oceanic lithosphere in a broad sense from formation to subduction, in a focused case at the ridge, and in a focused case proximal to subduction. In general, alteration of the oceanic lithosphere begins at the ridge through focused and diffuse hydrothermal flow, continues off axis through low temperature circulation, and may occur approaching subduction zones as bending related faulting provides fluid pathways. In Chapter 2 I use a dataset of thousands of microearthquakes recorded at the Rainbow massif on the Mid-Atlantic Ridge to characterize the processes which are responsible for the long-term, high-temperature, hydrothermal discharge found hosted in this oceanic core complex. I find that the detachment fault responsible for the uplift of the massif is inactive and that the axial valleys show no evidence for faulting or active magma intrusion. I conclude that the continuous, low-magnitude seismicity located in diffuse pattern in a region with seismic velocities indicating ultramafic host rock suggests that serpentinization may play a role in microearthquake generation but the seismic network was not capable of providing robust focal mechanism solutions to constrain the source characteristics. In Chapter 3 I find that the Juan de Fuca plate, which represents the young/hot end-member of oceanic plates, is lightly hydrated at upper crustal levels except in regions affected by propagator wakes where hydration of lower crust and upper mantle is evident. I conclude that at the subduction zone the plate is nearly dry at upper mantle levels with the majority of water contained in the crust. Finally, in Chapter 4 I examine samples of cretaceous age serpentinite sampled just before subduction at the Puerto Rico Trench. I show that these upper mantle rocks were completely serpentinized under static conditions at the Mid-Atlantic Ridge. Further, they subsequently underwent 100 Ma of seafloor weathering wherein the alteration products of serpentinization themselves continue to be altered. I conclude that complete hydration of the upper mantle is not the end point in the evolution of oceanic lithosphere as it spreads from the axis to subduction. Chapter 1: IntroductionThe total water content of the oceanic lithosphere is the sum of the free water in pore spaces in the sedimentary cover and highly porous upper crust, chemically bound water in sediment clay minerals, chemically bound water in the upper and lower crust resulting from the precipitation of secondary hydrous alteration products, free water in fault zones, and bound water of hydrous minerals in the uppermost mantle resulting from serpentinization of peridotite. This thesis is focused on characterizing the location, extent, and timing of the processes that result in this alteration of the lithosphere.In Chapter 2 I focus on the alteration that occurs in the near axis region at an oceanic core complex located on the slow spreading Mid-Atlantic Ridge. At the Rainbow massif long-lived high-T hydrothermal venting h...

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A method for determining significant structures in a cloud of earthquakes

Cited by 143 publications

References 19 publications

Seismic detection of CO2 leakage along monitoring wellbores

Seismic detection of CO2 leakage along monitoring wellbores

Induced Microearthquake Patterns in Hydrocarbon and Geothermal Reservoirs: Six Case Studies

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

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