Depth dependence of source parameters at Monticello, South Carolina

1983 ◽  
Vol 73 (6A) ◽  
pp. 1735-1751
Author(s):  
J. B. Fletcher ◽  
J. Boatwright ◽  
W. B. Joyner
Keyword(s):  
South Carolina ◽  
Stress Drop ◽  
Strong Dependence ◽  
Source Parameters ◽  
Failure Process ◽  
The Other ◽  
Depth Range ◽  
S Wave ◽  
S Waves ◽  
Stress Drops

Abstract Three estimates of stress differences, which include Brune stress drop, stress drop from rms of acceleration (arms), and the apparent stress, have been determined for 13 earthquakes at Monticello, South Carolina, a site of reservoir-induced seismicity. Data for nine of the events come from digitally recorded three-component seismograms at four or five stations that were deployed around the Monticello Reservoir in May and early June 1979. The data from the other four events come from a strong-motion accelerograph located on the dam abutment at the southwest end of the reservoir. Estimates of the seismic moment (Mo) range from 4.6 × 1017 to 3.4 × 1020 dyne-cm (S waves) and radiated energy from about 1011 to 3 × 1016 dyne-cm (S waves). Brune stress drops ranged from 0.5 bars to about 90 bars and show a strong dependence on depth (focal depths range from 0.07 to 1.4 km) and a moderate dependence on Mo. Arms stress drops from the direct S-wave span a similar range of values and also exhibit a strong dependence on depth. Apparent stresses are usually lower than the other estimates of stress differences by a factor of 2 to 4. Seismic stress differences are highest in the topmost 0.2 to 0.3 km, a depth range for which the in situ measurements of stress and pore pressure suggest that the rock is in a state of incipient failure. In this depth range, where the four largest events occurred, the stress drops are of the same order as the ambient shear stress. These data suggest that at Monticello, where pore fluids have a strong influence on the failure process, the largest stresses released seismically are in regions most conducive to failure and that the seismic efficiencies for events at Monticello are larger than have been reported for other tremors in different tectonic settings.

Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination

2021 ◽  
Author(s):  
Itzhak Lior ◽  
Anthony Sladen ◽  
Diego Mercerat ◽  
Jean-Paul Ampuero ◽  
Diane Rivet ◽  
...  
Keyword(s):  
Early Warning ◽  
Stress Drop ◽  
Source Parameters ◽  
Simulated Data ◽  
Earthquake Early Warning ◽  
Body Waves ◽  
Ocean Bottom ◽  
Correlated Noise ◽  
S Wave ◽  
Earthquake Source Parameters

<p>The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves’ apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.</p>

Source dimensions and stress drops of small earthquakes near Parkfield, California

1984 ◽  
Vol 74 (1) ◽  
pp. 27-40
Author(s):  
M. E. O'Neill
Keyword(s):  
Stress Drop ◽  
Small Region ◽  
Static Stress ◽  
Depth Range ◽  
Zero Crossing ◽  
Source Dimensions ◽  
Duration Magnitude ◽  
Short Period ◽  
Static Stress Drop ◽  
Stress Drops

Abstract Source dimensions and stress drops of 30 small Parkfield, California, earthquakes with coda duration magnitudes between 1.2 and 3.9 have been estimated from measurements on short-period velocity-transducer seismograms. Times from the initial onset to the first zero crossing, corrected for attenuation and instrument response, have been interpreted in terms of a circular source model in which rupture expands radially outward from a point until it stops abruptly at radius a. For each earthquake, duration magnitude MD gave an estimate of seismic moment MO and MO and a together gave an estimate of static stress drop. All 30 earthquakes are located on a 6-km-long segment of the San Andreas fault at a depth range of about 8 to 13 km. Source radius systemically increases with magnitude from about 70 m for events near MD 1.4 to about 600 m for an event of MD 3.9. Static stress drop ranges from about 2 to 30 bars and is not strongly correlated with magnitude. Static stress drop does appear to be spatially dependent; the earthquakes with stress drops greater than 20 bars are concentrated in a small region close to the hypocenter of the magnitude 512 1966 Parkfield earthquake.

Stress Drop Derived from Spectral Analysis Considering the Hypocentral Depth in the Attenuation Model: Application to the Ridgecrest Region, California

2021 ◽  
Author(s):  
Dino Bindi ◽  
Hoby N. T. Razafindrakoto ◽  
Matteo Picozzi ◽  
Adrien Oth
Keyword(s):  
Stress Drop ◽  
Spectral Decomposition ◽  
Epicentral Distance ◽  
Source Parameters ◽  
S Wave ◽  
Qualitative Comparison ◽  
Ground Shaking ◽  
Attenuation Model ◽  
Hypocentral Distance ◽  
The Impact

ABSTRACT We investigate the impact of considering a depth-dependent attenuation model on source parameters assessed through a spectral decomposition. In particular, we evaluate the effect of considering the hypocentral depth as an additional variable for the attenuation model, using as the target the tendency of the average stress drop to increase with depth, as observed in recent studies. We analyze the Fourier spectra of S-wave windows for about 1900 earthquakes with a magnitude above 2.5 recorded in the Ridgecrest region, southern California. Two different parameterizations of the attenuation term are implemented in the spectral decomposition, either as a function of the hypocentral distance alone or as a function of both epicentral distance and depth. The comparison of the spectral attenuation curves shows that, although the hypocentral model describes, on average, the range of values spanned by the attenuation curve for different depths, systematic differences with distance, depth, and frequency are observed. These differences are transferred to the source spectra and, in turn, to the source parameters extracted from the best-fitting ω−2 models. In particular, stress drops for events deeper than 7 km are, on average, almost double even when depth is introduced explicitly in the attenuation model. The increase of stress drop with depth is confirmed also after accounting for the increase of the shear velocity with depth, which absorbs about 30%–40% of the total increase. Moreover, a qualitative comparison with a model for the gradient of the effective normal stress confirms the reliability of the observed trend. Finally, the coherent spatial patterns shown by a simplified 2D tomographic representation of the spectral residuals highlights the impact on ground-shaking variability of the lateral variability of the crustal attenuation properties in the region.

scholarly journals Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination

2021 ◽  
Author(s):  
Itzhak Lior ◽  
Anthony Sladen ◽  
Diego Mercerat ◽  
Jean-Paul Ampuero ◽  
Diane Rivet ◽  
...  
Keyword(s):  
Early Warning ◽  
Stress Drop ◽  
Source Parameters ◽  
Simulated Data ◽  
Earthquake Early Warning ◽  
Body Waves ◽  
Ocean Bottom ◽  
Correlated Noise ◽  
S Wave ◽  
Earthquake Source Parameters

Abstract. The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves' apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.

Stress-Drop Estimates for Induced Seismic Events in the Fort Worth Basin, Texas

2021 ◽  
Author(s):  
Seong Ju Jeong ◽  
Brian W. Stump ◽  
Heather R. DeShon ◽  
Louis Quinones
Keyword(s):  
Stress Drop ◽  
Source Parameters ◽  
Fluid Pressure ◽  
Corner Frequency ◽  
Mean Stress ◽  
Fort Worth ◽  
Induced Earthquakes ◽  
Fort Worth Basin ◽  
Generalized Inversion Technique ◽  
Stress Drops

ABSTRACT Earthquakes in the Fort Worth basin (FWB) have been induced by the disposal of recovered wastewater associated with extraction of unconventional gas since 2008. Four of the larger felt earthquakes, each on different faults, prompted deployment of local distance seismic stations and recordings from these four sequences are used to estimate the kinematic source characteristics. Source spectra and the associated source parameters, including corner frequency, seismic moment, and stress drop, are estimated using a modified generalized inversion technique (GIT). As an assessment of the validity of the modified GIT approach, corner frequencies and stress drops from the GIT are compared to estimates using the traditional empirical Green’s function (EGF) method for 14 target events. For these events, corner-frequency residuals (GIT−EGF) have a mean of −0.31 Hz, with a standard deviation of 1.30 Hz. We find consistent mean stress drops using the GIT and EGF methods, 9.56 and 11.50 MPa, respectively, for the common set of target events. The GIT mean stress drop for all 79 earthquakes is 5.33 MPa, similar to estimates for global intraplate earthquakes (1–10 MPa) as well as other estimates for induced earthquakes near the study area (1.7–9.5 MPa). Stress drops exhibit no spatial or temporal correlations or depth dependency. In addition, there are no time or space correlations between estimated FWB stress drops and modeled pore-pressure perturbations. We conclude that induced earthquakes in the FWB occurring on normal faults in the crystalline basement release pre-existing tectonic stresses and that stress drops on the four sequences targeted in this study do not directly reflect perturbations in pore-fluid pressure on the fault.

scholarly journals Source Properties of Moderate-Magnitude Earthquakes Along the Alpine Fault, New Zealand

2021 ◽  
Author(s):  
◽  
Ilma Del Carmen Juarez Garfias
Keyword(s):  
New Zealand ◽  
Stress Drop ◽  
Boundary Zone ◽  
The South ◽  
S Waves ◽  
The North ◽  
Alpine Fault ◽  
Central Segment ◽  
Stress Drops ◽  
Moderate Magnitude

<p><b>The Alpine Fault is a major active continental transform fault that is late in its typical cycle of large earthquakes. Extensive paleoseismic research has revealed that the central segment of the Alpine Fault ruptures in M7+ earthquakes every 291±23 years and last ruptured in 1717 AD. The paleoseismic results also reveal that some places along the fault, which coincide with pronounced along-strike changes in fault characteristics, act as conditional barriers to rupture. The geometry, seismicity rates and geology of the Alpine Fault change along three principal segments (North Westland, Central and South Westland segments) but it is unclear whether source properties (e.g. stress drop) of near-fault seismicity also vary between those fault segments, and whether these properties have some influence on conditional segmentation of the Alpine Faultduring large earthquake rupture.</b></p> <p>To examine whether source properties of earthquakes can influence or elucidate the conditional segmentation of Alpine Fault earthquakes, we have computed stress drops of moderate-magnitude earthquakes occurring on and close to the Alpine Fault. We use an empirical Green’s function (EGF) approach and require each EGF earthquake to be highly correlated (cross-correlation ≥0.8) with its respective mainshock. We use data from dense, temporary seismometer networks, including DWARFS (Dense WestlandArrays Researching Fault Segmentation), a new two-part network designed to constrain seismogenic behaviour near key transitional boundaries. Our results investigate the spatial variability of these source properties along the length of the Alpine Fault, focusing on whether earthquakes at the rupture segment boundaries behave differently to those in the middle of previously identified rupture segments.</p> <p>We analyse individual P- and S-wave measurements of corner frequency and stress drop for 95 earthquakes close to (within 5 km) and on the Alpine Fault. Overall, the calculated stress drops range between 1–352 MPa and show good agreement with other studies both within New Zealand and worldwide. The stress drop values obtained for the three Alpine segment are: 1–143 MPa (median values of 8 and 9 MPa for P- and S-waves, respectively) for the South Westland/Central segment boundary zone, 2–309 MPa (median values of 17 and 39 MPa for P- and S-waves, respectively) for the Central segment and 1–352 MPa (median values of 15 and 19 MPa for P- and S-waves, respectively) for the North Westland/Central segment boundary zone. There are no marked differences in stress drop values along the North Westland and Central segments, but those values are slightly higher than along the South Westland segment.</p> <p>This may indicate a bigger difference in fault geometry, slip and seismicity rate compare with other segments, or that the South Westland segment is weaker than the other segments. We see no clear dependence of stress drop values on depth, magnitude or focal mechanism.</p>

Simultaneous inversion for Q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock

1991 ◽  
Vol 81 (2) ◽  
pp. 553-575 ◽  
Author(s):  
Michael Fehler ◽  
W. Scott Phillips
Keyword(s):  
Hydraulic Fracturing ◽  
Stress Drop ◽  
Source Parameters ◽  
Low Frequency ◽  
Seismic Energy ◽  
P Wave ◽  
Corner Frequency ◽  
Spectral Amplitude ◽  
Seismic Zone ◽  
Stress Drops

Abstract An inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low-frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite. Assuming a ω−2 source model, the inversion fits the P-wave spectra of microearthquake waveforms to determine individual values of corner frequency and low-frequency spectral amplitude for each event and one average frequency-independent Q for all source-receiver paths. We also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra. The waveforms analyzed were recorded by a borehole seismometer. The P-wave Q was found to be 1070. For Q values as low as 600 and as high as 3000, the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a Q of 1070. Average stress drop was 3.7 bars. Seismic moments obtained from spectra ranged from 1013 to 1018 dyne-cm. The low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes. Spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock. Stress drops were found to be larger near the edges of the seismic zone, in regions that had not been seismically active during previous injections. The seismic moments determined from spectra were used to obtain a coda length-to-moment relation. Then, moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal-to-noise ratio. The constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions. The slope is so high that the seismic energy release is dominated by the large number of small events. In the absence of information about the number of events smaller than we studied, we cannot estimate the total seismic energy released by the hydraulic injection.

scholarly journals Stress drop–magnitude dependence of acoustic emissions during laboratory stick-slip

2020 ◽  
Vol 224 (2) ◽  
pp. 1371-1380
Author(s):  
Aglaja Blanke ◽  
Grzegorz Kwiatek ◽  
Thomas H W Goebel ◽  
Marco Bohnhoff ◽  
Georg Dresen
Keyword(s):  
Grain Size ◽  
Stress Drop ◽  
Source Parameters ◽  
Corner Frequency ◽  
Strong Increase ◽  
Stick Slip ◽  
Fault Roughness ◽  
Average Grain Size ◽  
Seismic Stress ◽  
Stress Drops

SUMMARY Earthquake source parameters such as seismic stress drop and corner frequency are observed to vary widely, leading to persistent discussion on potential scaling of stress drop and event size. Physical mechanisms that govern stress drop variations are difficult to evaluate in nature and are more readily studied in controlled laboratory experiments. We perform two stick-slip experiments on fractured (rough) and cut (smooth) Westerly granite samples to explore fault roughness effects on acoustic emission (AE) source parameters. We separate large stick-slip events that generally saturate the seismic recording system from populations of smaller AE events which are sensitive to fault stresses prior to slip. AE event populations show many similarities to natural seismicity and may be interpreted as laboratory equivalent of natural microseismic events. We then compare the temporal evolution of mechanical data such as measured stress release during slip to temporal changes in stress drops derived from AEs using the spectral ratio technique. We report on two primary observations: (1) In contrast to most case studies for natural earthquakes, we observe a strong increase in seismic stress drop with AE size. (2) The scaling of stress drop with magnitude is governed by fault roughness, whereby the rough fault shows a more rapid increase of the stress drop–magnitude relation with progressing large stick-slip events than the smooth fault. The overall range of AE sizes on the rough surface is influenced by both the average grain size and the width of the fault core. The magnitudes of the smallest AE events on smooth faults may also be governed by grain size. However, AEs significantly grow beyond peak roughness and the width of the fault core. Our laboratory tests highlight that source parameters vary substantially in the presence of fault zone heterogeneity (i.e. roughness and narrow grain size distribution), which may affect seismic energy partitioning and static stress drops of small and large AE events.

scholarly journals Source Properties of Moderate-Magnitude Earthquakes Along the Alpine Fault, New Zealand

2021 ◽  
Author(s):  
Ilma Del Carmen Juarez Garfias
Keyword(s):  
New Zealand ◽  
Stress Drop ◽  
Boundary Zone ◽  
The South ◽  
S Waves ◽  
The North ◽  
Alpine Fault ◽  
Central Segment ◽  
Stress Drops ◽  
Moderate Magnitude

<p><b>The Alpine Fault is a major active continental transform fault that is late in its typical cycle of large earthquakes. Extensive paleoseismic research has revealed that the central segment of the Alpine Fault ruptures in M7+ earthquakes every 291±23 years and last ruptured in 1717 AD. The paleoseismic results also reveal that some places along the fault, which coincide with pronounced along-strike changes in fault characteristics, act as conditional barriers to rupture. The geometry, seismicity rates and geology of the Alpine Fault change along three principal segments (North Westland, Central and South Westland segments) but it is unclear whether source properties (e.g. stress drop) of near-fault seismicity also vary between those fault segments, and whether these properties have some influence on conditional segmentation of the Alpine Faultduring large earthquake rupture.</b></p> <p>To examine whether source properties of earthquakes can influence or elucidate the conditional segmentation of Alpine Fault earthquakes, we have computed stress drops of moderate-magnitude earthquakes occurring on and close to the Alpine Fault. We use an empirical Green’s function (EGF) approach and require each EGF earthquake to be highly correlated (cross-correlation ≥0.8) with its respective mainshock. We use data from dense, temporary seismometer networks, including DWARFS (Dense WestlandArrays Researching Fault Segmentation), a new two-part network designed to constrain seismogenic behaviour near key transitional boundaries. Our results investigate the spatial variability of these source properties along the length of the Alpine Fault, focusing on whether earthquakes at the rupture segment boundaries behave differently to those in the middle of previously identified rupture segments.</p> <p>We analyse individual P- and S-wave measurements of corner frequency and stress drop for 95 earthquakes close to (within 5 km) and on the Alpine Fault. Overall, the calculated stress drops range between 1–352 MPa and show good agreement with other studies both within New Zealand and worldwide. The stress drop values obtained for the three Alpine segment are: 1–143 MPa (median values of 8 and 9 MPa for P- and S-waves, respectively) for the South Westland/Central segment boundary zone, 2–309 MPa (median values of 17 and 39 MPa for P- and S-waves, respectively) for the Central segment and 1–352 MPa (median values of 15 and 19 MPa for P- and S-waves, respectively) for the North Westland/Central segment boundary zone. There are no marked differences in stress drop values along the North Westland and Central segments, but those values are slightly higher than along the South Westland segment.</p> <p>This may indicate a bigger difference in fault geometry, slip and seismicity rate compare with other segments, or that the South Westland segment is weaker than the other segments. We see no clear dependence of stress drop values on depth, magnitude or focal mechanism.</p>

Stress Drops and Directivity of Induced Earthquakes in the Western Canada Sedimentary Basin

2019 ◽  
Vol 109 (5) ◽  
pp. 1635-1652 ◽  
Author(s):  
Joanna M. Holmgren ◽  
Gail M. Atkinson ◽  
Hadi Ghofrani
Keyword(s):  
Stress Drop ◽  
Sedimentary Basin ◽  
Source Parameters ◽  
Corner Frequency ◽  
Source Spectrum ◽  
Western Canada ◽  
Induced Earthquakes ◽  
Western Canada Sedimentary Basin ◽  
Stress Drops ◽  
Canada Sedimentary Basin

Abstract The Western Canada sedimentary basin (WCSB) has experienced an increase in seismicity during the last decade due primarily to hydraulic fracturing. Understanding the ground motions of these induced earthquakes is critical to characterize the increase in hazard. Stress drop is considered an important parameter in this context because it is a measure of the high‐frequency content of the shaking. We use the empirical Green’s function (EGF) method to determine S‐wave corner frequencies and stress drops of 87 earthquakes of moment magnitude (M) 2.3–4.4 in the WCSB. The EGF method is an effective technique to isolate earthquake source effects by dividing out the path and site components in the frequency domain, using a smaller collocated earthquake as an EGF. The corner frequency of the target event is determined for an assumed spectral ratio shape, from which the stress drop is computed. Assuming a fixed velocity, we find that the average stress drop for induced earthquakes in the WCSB for small‐to‐moderate events is 7.5±0.5  MPa, with a total range from 0.2 to 370 MPa. However, because of the dependence of stress drop on model conventions and constants, we consider the absolute stress‐drop value meaningful only for comparison with other results using the same underlying models. By contrast, corner frequency is a less‐ambiguous variable with which to characterize the source spectrum. The range of corner frequencies obtained in this study for events of M 4.0±0.5 is 1.1–5.8 Hz. Significant rupture directivity is observed for more than one‐third of the earthquakes, with station corner frequencies varying by about a factor of 4 with azimuth. This emphasizes the importance of having suitable station coverage to determine source parameters. We model directivity where evident using a Haskell source model and find that the rupture azimuths are primarily oriented approximately north–south throughout the region.

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