Spectral Characteristics of Ground Motion from Induced Earthquakes in the Fort Worth Basin, Texas, Using the Generalized Inversion Technique

2020 ◽  
Vol 110 (5) ◽  
pp. 2058-2076 ◽  
Author(s):  
SeongJu Jeong ◽  
Brian W. Stump ◽  
Heather R. DeShon
Keyword(s):  
Seismic Hazard ◽  
Spectral Characteristics ◽  
Vertical Component ◽  
Sedimentary Basins ◽  
Fort Worth ◽  
Induced Earthquakes ◽  
Fort Worth Basin ◽  
Inversion Technique ◽  
Generalized Inversion ◽  
Generalized Inversion Technique

ABSTRACT A generalized inversion technique (GIT) is applied to local seismic data from 90 induced earthquakes (ML 2.0–3.9) in the Fort Worth Basin (FWB) of north Texas to separate path, site, and source characteristics and to improve local seismic hazard assessment. Seismograms from three earthquake sequences on spatially separated basement faults are recorded on 66 temporary stations. Because of the lack of hard-rock recording sites within the sedimentary basin, we developed a site correction method for the appropriate GIT process. At about 30 km distance from the hypocenters, we observed a change in spectral attenuation and thus focus data analysis within this distance range. The estimated quality factors for S and P waves result in a QS that is larger than QP which we interpret as a result of concentrations of crustal pore fluids or partial fluid-saturated material along the path; an interpretation consistent with fluid-rich sedimentary rocks in the FWB. Strong site amplifications as much as five times on horizontal components reflect the thick sediments in the basin. A limited number of sites exhibit amplification or deamplification on the vertical component that limits the use of horizontal-to-vertical spectral ratio methods for characterizing the site effect relative to the site effects estimated by GIT. Stress drops for all earthquakes range from 1.18 and 21.73 MPa with a mean of 4.46 MPa, similar to values reported for tectonic intraplate events. The stress-drop values suggest that strong motion and seismic hazard from the injection-induced earthquake in the FWB are comparable to those for tectonic earthquakes. The strong site amplification and fluid effects on propagation attenuation may be crucial factors to take into account for estimating seismic hazards of induced earthquakes in sedimentary basins.

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.

Attribute illumination of basement faults, examples from Cuu Long Basin basement, Vietnam and the Midcontinent, USA

2014 ◽  
Vol 2 (1) ◽  
pp. SA119-SA126 ◽  
Author(s):  
Ha T. Mai ◽  
Olubunmi O. Elebiju ◽  
Kurt J. Marfurt
Keyword(s):  
Sedimentary Basins ◽  
Fort Worth ◽  
North Texas ◽  
Fort Worth Basin ◽  
Diagenetic Alteration ◽  
Basement Faults ◽  
The Usa ◽  
Lead Zinc ◽  
Granite Basement ◽  
Osage County

Geometric attributes such as coherence and curvature have been very successful in delineating faults in sedimentary basins. Albeit not a common exploration objective, fractured and faulted basement forms important reservoirs in Southern California, Mexico, India, Yemen, and Vietnam. Basement faulting controls hydrothermally altered dolomite in the Appalachian Basin of the USA, and is suspected to play a role in diagenetic alteration of carbonates in the Fort Worth Basin of north Texas where copper has been found in some wells, as well as in Osage County, Oklahoma, not far from the classic Mississippi type lead-zinc deposits. Because of the absence of stratified, coherent reflectors, illumination of basement faults is more problematic than illumination of faults within the sedimentary column. To address these limitations, we make simple modifications to well-established vector attributes including structural dip, azimuth, and amplitude gradients, in combination with variance, and most positive and most negative principal curvature to provide greater interpreter interaction. Using these methods, we can better illuminate fracture “sweet spots” and estimate their intensity and orientation. We apply these methods to better characterize faults in the granite basement of the Cuu Long Basin, Vietnam, and the granite and rhyolite-metarhyolite basement of Osage County, Oklahoma, USA. Cuu Long forms an important unconventional reservoir. In Osage County, we suspect basement control of shallower fractures in the Mississippi chat deposits.

scholarly journals Determination of path attenuation and site characteristics of the North-west Himalayan region and adjoining regions within the Indian Territory using Generalized inversion method

2020 ◽  
Vol 63 (6) ◽  
Author(s):  
Nelliparanbil Harinarayan ◽  
Abhishek Kumar
Keyword(s):  
Seismic Hazard ◽  
Predominant Frequency ◽  
Site Class ◽  
North West ◽  
The North ◽  
Generalized Inversion ◽  
Site Characteristics ◽  
Generalized Inversion Technique ◽  
Recording Station

North-west Himalayas and its adjoining regions have been experiencing deadly earthqaukes from time to time and are home for a large portion of population of Indian subcontinent. Knowledge of regional path attenuation and site parameters are prerequisite while attempting seismic hazard studies towards minimizing damages during future earthqaukes for a region. Present work focuses on the determination of path attenuation and site characteristics of earthqaukes recording stations, located in the north-west Himalayas and its adjoining regions, within India. It is done using two- step generalized inversion technique. In the first step of inversion, non-parametric attenuation curves are developed by constraining attenuation to be a smooth decaying function with hypocentral distance. Qs = (105 ± 11)f (0.94 ± 0.08) as S wave quality factor is obtained indicating that the region is seismically active having high degree of heterogeneities in the crustal medium. In the second step of generalized inversion, site amplification curve, at each recording station, is computed as the ratio of site spectral amplitude of horizontal and vertical components. In addition, based on Horizontal to vertical spectral ratio (HVSR) method, predominant frequency of each recording station is calculated. Values of predominant frequencies based on HVSR and generalized inversion are found matching for each of the recording station. Based on obtained predominant frequency, site class of 101 recording stations, which at present are absent, are determined in this work. Determined path attenuation as well as site parameters can be collectively used for developing regional ground motion models and subsequently for seismic hazard studies for the selected region.

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