In situ study of the physical mechanisms controlling induced seismicity at Monticello Reservoir, South Carolina

Zoback, Mark D.; Hickman, Stephen H.

doi:10.1029/jb087ib08p06959

Cited by 127 publications

(52 citation statements)

References 38 publications

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“…Incidentally, neither (11) nor the notion that r/is controlled by the two factors rl/5¾ and overshoot is original to this paper. Equation (11), in fact, can easily be shown to be the same as equation (16) [Zoback and Hickman, 1982]. Thus, if these data are accepted at face value, the apparent stresses are comparable to the maximum shear stresses, implying seismic efficiencies near 1, in contradiction to (7).…”

Section: Control Of •1 By P•/pd and Overshootmentioning

confidence: 67%

On relating apparent stress to the stress causing earthquake fault slip

McGarr¹

1999

J. Geophys. Res.

244

153

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Abstract. Apparent stress ra is defined as ra -r/5, where 5 is the average shear stress loading the fault plane to cause slip and r/is the seismic efficiency, defined as E•/W, where E• is the energy radiated seismically and I,V is the total energy released by the earthquake. The results of a recent study in which apparent stresses of mining-induced earthquakes were compared to those measured for laboratory stick-slip friction events led to the hypothesis that r•/• -< 0.06. This hypothesis is tested here against a substantially augmented data set of earthquakes for which 5 can be estimated, mostly from in situ stress measurements, for comparison with r•. The expanded data set, which includes earthquakes artificially triggered at a depth of 9 km in the German Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland (KTB) borehole and natural tectonic earthquakes, covers a broad range of hypocentral depths, rock types, pore pressures, and tectonic settings. Nonetheless, over ---14 orders of magnitude in seismic moment, apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of ---0.06, consistent with the hypothesis proposed before. This behavior of ra and r/can be expressed in terms of two parameters measured for stick-slip friction events in the laboratory: the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot. Typical values for these two parameters yield seismic efficiencies of ---0.06. In contrast to efficiencies for laboratory events for which r/is always near 0.06, those for earthquakes tend to be less than this bounding value because E• for earthquakes is usually underestimated due to factors such as band-limited recording. Thus upper bounds on r•/• appear to be controlled by just a few fundamental aspects of frictional stick-slip behavior that are common to shallow earthquakes everywhere. Estimates of 5 from measurements of r• for suites of earthquakes, using r•/• -< 0.06, are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths. IntroductionStick-slip friction experiments in the laboratory are thought to be mechanically similar to crustal earthquakes [e.g., Brace and Byerlee, 1966; Dieterich, 1979] and, to the extent that this is so, can provide insights into natural earthquake processes. Studying earthquake phenomena in the laboratory environment is, in many ways, more effective than pursuing the same investigations in the field.To relate stick-slip friction experiments in the laboratory to eters seismic moment, radiated energy, and apparent stress are all useful because none has any model dependence; laboratory measurements of any of these quantities can be related directly to corresponding measurements from earthquake seismograms.The significance of apparent stress is illustrated in Figure 1, which shows the various stress changes that occur during an earthquake as a function of fault slip. In the laboratory the apparent stress is estimated from ...

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Section: Control Of •1 By P•/pd and Overshootmentioning

confidence: 67%

On relating apparent stress to the stress causing earthquake fault slip

McGarr¹

1999

J. Geophys. Res.

244

153

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“…The fracture density (number of fractures per meter) is greater in these wells than in any of the other wells studied (compare Figures 6, 16, and 19). At Monticello Reservoir, the current local stress field has been determined by in situ stress measurements using the hydrofracture technique [Zoback and Hickman, 1982] and from earthquake focal mechanisms [Talwani et al, 1978]. In Monticello !…”

Section: Mojave Desert Wellsmentioning

confidence: 99%

The distribution of natural fractures and joints at depth in crystalline rock

Seeburger¹,

Zoback²

1982

J. Geophys. Res.

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This paper presents the results of studies of the natural fracture distribution encountered in 10 test wells drilled in three areas of the United States. Seven of the wells were drilled to depths of 200-250 m, while three were drilled to depths of about 1 kin. Using an ultrasonic borehole televiewer, fracture depths, strikes, and dips were determined. Steeply dipping fractures were found throughout each of the wells, and in general, few horizontal fractures were observed. Statistically significant fracture pole concentrations were found for each well which were basically invariant with depth, although some variation of fracture orientation with depth was found in two wells. The significant fracture orientations were not found to be the same in wells only several kilometers apart in a given region. In none of the wells did the number of observable fractures decrease markedly with increasing depth. No simple relationship of fracture orientation or fracture density with major structural features such as the San Andreas fault were observed, and no simple relation between the significant fracture orientations and either past or present regional stress fields could be determined.

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“…The reservoir itself is located within the Charlotte belt gneiss, a region characteriLed by low relief and chemical weathering (Secor et al 1982) and by frequent intrusion of migmatitic bodies, granite, and granodiorite. As pointed out by Zoback & Hickman (1982), the induced earthquakes at Monticello appear to be caused by a reduction of the effective normal stress on the fault planes due to an increased pore pressure at the subsurface involving a physical mechanism proposed earlier by Hubbert & Rubey (1959). The composite focal mechanisms, obtained by Talwani (1 979) for spatially localized zones, generally indicate thrust faulting under and around the reservoir.…”

Section: Introductionmentioning

confidence: 94%

Determination of focal mechanism solutions for four earthquakes from Monticello, South Carolina, and crustal structure by waveform modelling

Saikia

Herrmann

1987

Geophysical Journal International

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We investigate the effect of thin near-surface crustal layers on seismic waveforms by modelling digital seismograms available from Monticello, South Carolina, a site for reservoir-induced seismicity. The epicentral distances to all stations used in this study are less than 5.0 km and the depths of the earthquakes are less than 2.0 km. These near-source seismograms are rich in frequencies as high as 50 Hz and are sensitive to crustal velocity layers as thin as 0.1 km. Velocity profiles from two boreholes (Secor et al.) were used as the starting models and modified as required by the comparison of synthetic seismograms with the observed data. The frequency-wavenumber (F-K) integration technique of Bouchon was used to calculate the synthetic response of these crustal models. Inclusion of some near-surface low-velocity layers over a crustal model produces many reverberations observed after the direct S arrival. The final model differs from the crustal model of Fletcher and Moos & Zoback by about 20-30 per cent and produces small travel time residuals.Having determined the velocity model we then determine the focal mechanisms of four small earthquakes whose magnitudes are less than 2.5 using both the search and the least squares inversion algorithms of Saikia & Herrmann. The amplitudes of direct P, SV, SH and some reverberating S waves from all components were used to analyse the focal mechanisms. The inferred mechanisms suggest that the area is characterized by reverse faulting. The P-axes are consistent with ENE compressional stress. The synthetic seismograms predicted for these events match the observed seismograms remarkably well in both the peak amplitudes of P and S waves and various amplitude ratios among different components.

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In situ study of the physical mechanisms controlling induced seismicity at Monticello Reservoir, South Carolina

Cited by 127 publications

References 38 publications

On relating apparent stress to the stress causing earthquake fault slip

On relating apparent stress to the stress causing earthquake fault slip

The distribution of natural fractures and joints at depth in crystalline rock

Determination of focal mechanism solutions for four earthquakes from Monticello, South Carolina, and crustal structure by waveform modelling

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