Improved approach for stress drop estimation and its application to an induced earthquake sequence in Oklahoma

2020 ◽  
Vol 223 (1) ◽  
pp. 233-253
Author(s):  
X Chen ◽  
R E Abercrombie
Keyword(s):  
Stress Drop ◽  
Source Parameters ◽  
High Stress ◽  
Temporal Variations ◽  
Earthquake Source ◽  
Average Stress ◽  
Corner Frequency ◽  
Resolution Limit ◽  
Spectral Fitting ◽  
Spatio Temporal

SUMMARY We calculate source parameters for fluid-injection induced earthquakes near Guthrie, Oklahoma, guided by synthetic tests to quantify uncertainties. The average stress drop during an earthquake is a parameter fundamental to ground motion prediction and earthquake source physics, but it has proved hard to measure accurately. This has limited our understanding of earthquake rupture, as well as the spatio-temporal variations of fault strength. We use synthetic tests based on a joint spectral-fitting method to define the resolution limit of the corner frequency as a function of the maximum frequency of usable signal, for both individual spectra and the average from multiple stations. Synthetic tests based on stacking analysis find that an improved stacking approach can recover the true input stress drop if the corner frequencies are within the resolution limit defined by joint spectral-fitting. We apply the improved approach to the Guthrie sequence, using different wave types and signal-to-noise criteria to understand the stability of the calculated stress drop values. The results suggest no systematic scaling relationship of stress drop for M ≤ 3.1 earthquakes, but larger events (M ≥ 3.5) tend to have higher average stress drops. Some robust spatio-temporal variations can be linked to the triggering processes and indicate possible stress heterogeneity within the fault zone. Tight clustering of low stress drop events at the beginning stage of the sequence suggests that pore pressure influences earthquake source processes. Events at shallow depth have lower stress drop compared to deeper events. The largest earthquake occurred within a cluster of high stress drop events, likely rupturing a strong asperity.

Earthquake stress drop: what can we resolve from observations, and what can we infer about earthquake triggering processes

2020 ◽  
Author(s):  
Xiaowei Chen ◽  
Rachel Abercrombie ◽  
Qimin Wu
Keyword(s):  
Stress Drop ◽  
Signal To Noise Ratio ◽  
Earthquake Source ◽  
Average Stress ◽  
Corner Frequency ◽  
Spatiotemporal Variations ◽  
Resolution Limit ◽  
Signal To Noise ◽  
Spectral Fitting ◽  
Noise Ratio

<p>The average stress drop during an earthquake is a parameter fundamental to ground motion prediction and earthquake source physics, but it has proved hard to measure accurately. This has limited our understanding of earthquake rupture, as well as the spatiotemporal variations of fault strength. In this study, we investigate the resolution limits of spectral analysis based on synthetic spectra with similar magnitude range, average stress drop and frequency bands to a fluid-injection induced earthquake sequence in Oklahoma near Guthrie.</p><p>Synthetic tests using joint spectral fitting method define the resolution limit of corner frequency as a function of maximum frequency for both individual spectra and averaged spectra from multiple stations. Synthetic tests based on stacking analysis find that the improved stacking approach can recover the true input stress drop if the corner frequencies are within the resolution limit defined by joint spectral fitting.</p><p>The improved approach is applied to the Guthrie sequence, different wave types and different signal-to-noise criteria are examined to understand the stability of the stress drop distributions. The results suggest no systematic scaling relationship for stress drop for M≤ 3.1 earthquakes, but larger events M≥3.5 tend to have higher average stress drops. Results with lower signal-to-noise ratio requirement and direct P-wave tend to have higher scaling factor compared to results with high signal-to-noise ratio and S-waves.</p><p>Comparison of results from several different methods suggest that the average stress drop is well resolved and not subject to tradeoff with attenuation. Some robust spatiotemporal variations can be linked to triggering processes and indicate possible stress heterogeneity within the fault zone. Tight clustering of low stress drop events at the beginning stage of the sequence suggests that pore pressure influences earthquake source processes. Events at shallow depth have much lower stress drop compared to deeper events. The largest earthquake occurred within a cluster of high stress drop events, and involved cascading failure of several sub-events.   </p>

Spatio-temporal variations of source parameters in the nucleation zone of the 6 April 2009, Mw 6.1 L'Aquila Earthquake

2020 ◽  
Author(s):  
Rita Di Giovambattista ◽  
Giovanna Calderoni ◽  
Antonio Rovelli
Keyword(s):  
Stress Drop ◽  
Main Shock ◽  
Source Parameters ◽  
Dynamic Strength ◽  
Temporal Variations ◽  
Apparent Stress ◽  
L’Aquila Earthquake ◽  
Focal Volume ◽  
Spatio Temporal ◽  
The Individual

<p>We present the results of Brune stress drop (∆σ) and apparent stress (τa) variability of  earthquakes located in a small zone adjacent to the hypocenter of the damaging Mw 6.1 L'Aquila earthquake. Their magnitude ranges between  2.7 and 4.1. Interevent variability of stress drop and apparent stress results in a factor of 10, well beyond the individual‐event uncertainty. Radiation efficiency ηsw = τa/∆σ varies mostly between 0.1 and 0.2, but decreases in the days immediately before and after the main shock to values as low as 0.06. This may be related to the migration of the events occurring in those days into a focal volume with higher dynamic strength. The temporal change of ηsw might be interpreted as a spatial variation due to the earthquake migration into the locked portion of the fault originating the main shock. Furthermore, no variation in stress drop and apparent stress can be observed between foreshocks and aftershocks but the smallest and largest ∆σ result in a good correlation with the largest and smallest b‐values respectively, as already documented in literature in the rupture nucleation volume of large earthquakes.</p>

scholarly journals Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes

2021 ◽  
Author(s):  
Serge A. Shapiro ◽  
Carsten Dinske
Keyword(s):  
Stress Drop ◽  
Induced Seismicity ◽  
Quantitative Characteristic ◽  
High Stress ◽  
Operation Time ◽  
Average Stress ◽  
Induced Earthquakes ◽  
Effective Stresses ◽  
Seismicity Rates

AbstractSometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.

Earthquake source properties from analysis of dynamic ruptures and far-field seismic waves in a damage-breakage model

2020 ◽  
Vol 224 (3) ◽  
pp. 1793-1810
Author(s):  
Ittai Kurzon ◽  
Vladimir Lyakhovsky ◽  
Yehuda Ben-Zion
Keyword(s):  
Seismic Waves ◽  
Source Parameters ◽  
Dominant Frequency ◽  
Earthquake Source ◽  
Corner Frequency ◽  
Far Field ◽  
Rupture Directivity ◽  
Rupture Velocity ◽  
S Waves ◽  
Dominant Frequencies

SUMMARY We present results on earthquake source properties using simulations of dynamic rupture and radiated seismic waves in a continuum damage-breakage rheological model. The source properties are derived by (1) calculation of source parameters directly from the simulated ruptures and (2) observational processing of the far-field radiated waves. The seismic potency, moment, damage-related source term, rupture velocity and effective rigidity are estimated directly from the simulated sources, while the radiation pattern, dominant frequency, directivity, rupture velocity and seismic potency are calculated through analysis of the radiated waves. The potencies calculated directly from the sources are used to validate those estimated by wave analysis. The effective rigidity at the rupture zone during failure is about four times smaller than that of the intact surrounding rocks. Rupture velocity can be estimated by far-field measurements for sources with unidirectional ruptures with prominent rupture directivity. The dominant frequencies for P and S waves $f_d^S/f_d^P$ reflect clearly the rupture duration and have a ratio in the range 0.87–1.12. Seismic potencies obtained through processing the P or S waves have an overall ±15 per cent difference from the source reference values. The calculated values of the coefficient ${\rm{\kappa }}$, relating rupture length to corner or dominant frequency, have strong dependency on the source geometry. Using a strain-rate dependent ${\rm{\kappa }}$, we obtain much weaker dependencies of strain-drop on the dominant frequencies, $\Delta {\rm{\varepsilon }} \propto {( {{f_d}} )^{3/4}}$, than the classical cube-dependency between stress drop and corner frequency, and corresponding weak dependency of average slip on dominant frequency, ${\rm{\bar{D}}} \propto {( {{f_d}} )^{1/2}}$. The obtained analysis procedure and relations can be used to reduce the uncertainty of source properties derived from far-field seismic waves.

The characteristic of source spectra and stress drop of earthquakes in the Bucaramanga nest

2020 ◽  
Author(s):  
Wenzheng Gong ◽  
Xiaofei Chen
Keyword(s):  
Focal Mechanism ◽  
Stress Drop ◽  
Source Parameters ◽  
Time Function ◽  
Corner Frequency ◽  
Ratio Method ◽  
Source Time Function ◽  
Spectra Analysis ◽  
Source Spectra ◽  
Very High

<p>Spectra analysis is helpful to understand earthquake rupture processes and estimate source parameters like stress drop. Obtaining real source spectra and source time function isn’t easy, because the station recordings contain path effect and we usually can’t get precise path information. Empirical Green’s function (EGF) method is a popular way to cancel out the path effect, main two of which are the stacking spectra method (Prieto et al, 2006) and the spectral ratio method (Viegas et al, 2010; Imanishi et al, 2006). In our study, we apply the latter with multitaper spectral analysis method (Prieto et al, 2009) to calculate relative source spectra and relative source time function. Target event and EGFs must have similar focal mechanism and be collocated, so we combine correlation coefficient of wave at all stations and focal mechanism similarity to select proper EGFs.</p><p>The Bucaramanga nest has very high seismicity, so it’s suitable to calculate source spectra by using EGF method. We calculate the source spectra and source time function of about 1540 earthquakes (3-5.7ml, 135-160km depth) at Bucaramanga nest in Colombia. Simultaneously we also estimate corner frequency by fitting spectral source model (Brune, 1970; Boatwright, 1980) and stress drop using simple model (Eshelby, 1957) of earthquakes with multiple station recordings or EGFs. We obtain about 30000 events data with 12 stations from National Seismological Network of Colombia (RSNC).</p><p>The result show that the source spectra of most earthquakes fitted well by omega-square model are smooth, and the source spectra of some have obvious ‘holes’ near corner frequency, and the source time function of a few earthquakes appear two separate peeks. The first kind of earthquakes are style of self-arresting ruptures (Xu et al. 2015), which can be autonomously arrested by itself without any outside interference. Abercrombie (2014) and Wen et al. (2018) both researched the second kind of earthquakes and Wen think that this kind of earthquakes are style of the runaway ruptures including subshear and supershear ruptures. The last kind of earthquakes maybe be caused by simultaneous slip on two close rupture zone. Stress drop appear to slightly increase with depth and are very high (assuming rupture velocity/s wave velocity is 0.9). We also investigate the high-frequency falloff n, usually 2, of Brune model and Boatwright model by fitting all spectra, and find that the best value of n for Boatwright model is 2 and for Brune model is 3.5.</p>

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.

Source mechanism and surface-wave attenuation studies for Tibet earthquake of July 14, 1973

1979 ◽  
Vol 69 (3) ◽  
pp. 737-750
Author(s):  
D. D. Singh ◽  
Harsh K. Gupta
Keyword(s):  
Surface Wave ◽  
Stress Drop ◽  
Wave Attenuation ◽  
Source Parameters ◽  
High Stress ◽  
The Body ◽  
P Wave ◽  
Slip Angle ◽  
Apparent Stress ◽  
Crust And Upper Mantle

abstract Focal mechanism for Tibet earthquake of July 14, 1973 (M = 6.9, mb = 6.0) has been determined using the P-wave first motions, S-wave polarization angles, and surface-wave spectral data. A normal faulting is obtained with a plane having strike N3°W, dip 51°W, and slip angle 81°. The source parameters have been estimated for this event using the body- and surface-wave spectra. The seismic moment, fault length, apparent stress, stress drop, seismic energy release, average dislocation, and fault area are estimated to be 2.96 × 1026 dyne-cm, 27.4 km, 14 bars, 51 bars, 1.4 × 1022 ergs, 157 cm, and 628 km2, respectively. The high stress drop and apparent stress associated with this earthquake indicate that the high stresses are prevailing in this region. The specific quality factor Q is found to vary from 21 to 1162 and 22 to 1110 for Rayleigh and Love waves, respectively. These wide ranges of variation in the attenuation data may be due to the presence of heterogeneity in the crust and upper mantle.

A Study on the Largest Hydraulic-Fracturing-Induced Earthquake in Canada: Observations and Static Stress-Drop Estimation

2020 ◽  
Author(s):  
Bei Wang ◽  
Rebecca M. Harrington ◽  
Yajing Liu ◽  
Honn Kao ◽  
Hongyu Yu
Keyword(s):  
Hydraulic Fracturing ◽  
Stress Drop ◽  
Risk Mitigation ◽  
Source Parameters ◽  
B Value ◽  
Corner Frequency ◽  
Maximum Magnitude ◽  
Maximum Earthquake Magnitude ◽  
Tectonic Earthquakes ◽  
Maximum Earthquake

ABSTRACT On 17 August 2015, an Mw 4.6 earthquake occurred northwest of Fort St. John, British Columbia, possibly induced by hydraulic fracturing (HF). We use data from eight broadband seismometers located ∼50  km from the hypocenter to detect and estimate source parameters of more than 300 events proximal to the mainshock. Stress-drop values estimated using seismic moment and corner frequency from single-event spectra and spectral ratios range from ∼1 to 35 MPa, within the typical range of tectonic earthquakes. We observe an ∼5-day delay between the onset of fluid injection and the mainshock, a b-value of 0.78 for the sequence, and a maximum earthquake magnitude larger than the prediction based on the total injection volume, suggesting that the Mw 4.6 sequence occurred on a pre-existing fault and that the maximum magnitude is likely controlled by tectonic conditions. Results presented here show that pre-existing fault structures should be taken into consideration to better estimate seismic hazard associated with HF operations and to develop schemes for risk mitigation in close proximity to HF wells.

scholarly journals ANALISIS PARAMETER SUMBER SPEKTRAL GEMPABUMI VTA (VULKANO TEKTONIK-A) TERHADAP AKTIVITAS VULKANIK GUNUNG SINABUNG

2019 ◽  
Vol 5 (1) ◽  
pp. 18-23
Author(s):  
Tri Kusmita ◽  
Kirbani Brotopuspito ◽  
Hetty Triastuty
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Source Parameters ◽  
Radiation Energy ◽  
Angular Frequency ◽  
Moment Magnitude ◽  
Corner Frequency ◽  
Volcanic Earthquake ◽  
Seismic Volumes ◽  
The Relationship

The source parameters describe the different physical properties of seismic volumes under the volcanoes. Source parameters that can be used to distinguish seismic events that are generated by different types of volcanoes activities. Temporary changes of the spectral source parameters provided a description of the main events during the eruption process.  Source parameters are calculated by correlating the relationship between source frequency at spectral displacement (corner frequency) and source parameters based on spectral sources of the Brune model (1970). The angular frequency obtained by applying the FFT algorithm to the VTA spectral displacement. The source parameters analyzed from this VTA earthquake are the spectral slope, seismic moment, stress drop, length of rupture, moment magnitude and radiation energy. Based on the obtained corner frequency (12 Hz-13 Hz), seismic moment, moment magnitude and energy radiation respectively were at 0.2 -1.9 x 1012 Nm, 0.7 - 2 Mw, and 0.1 - 9.5 x 1015 erg. The length of rupture were from 144.2 to 243.1 m, the spectra slope has 2.1 - 7.8 dB/cm, and stress drop are 0.1 - 7,6 bar. From the results of this study, it can be concluded that the changes of spectra characteristic and fluctuate of source patrameters value of VTA earthquakes was asosiated with the different  volcanic activity of Sinabung. Keywords: spectral, VTA, source parameter, volcanic earthquake

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.

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