The search for hard-rock kappa (κ) in NGA-East: A semi-automated method for large, challenging datasets in stable continental regions

2021 ◽  
Vol 37 (1_suppl) ◽  
pp. 1391-1419
Author(s):  
Olga-Joan Ktenidou ◽  
Norman A Abrahamson ◽  
Walter J Silva ◽  
Robert B Darragh ◽  
Tadahiro Kishida
Keyword(s):  
Stress Drop ◽  
High Frequency ◽  
Frequency Resolution ◽  
Corner Frequency ◽  
Site Specific ◽  
Regional Stress ◽  
Automated Method ◽  
Stable Continental Region ◽  
Band Limited ◽  
Horizontal Ground Motion

This article describes the work undertaken within the Next Generation Attenuation (NGA)-East project with the aim of estimating κ0 (the site-specific component of the high-frequency decay parameter, κ) for rock sites in Central and Eastern North America (CENA), using the project’s shallow crustal dataset. We introduce a methodology to address the numerous challenges in CENA: a large dataset in a low-seismicity stable continental region, with poor magnitude and distance coverage, undesirable recording sensor characteristics (low sampling rates leading to poor high-frequency resolution), high uncertainty in the regional stress drop, and lack of site-specific velocity characterization. We use two band-limited κ estimation approaches, the acceleration and displacement spectrum (AS and DS), applied above and below the source corner frequency ( fc), respectively. For band-limited approaches, the key requirement is an estimate of fc, which—apart from the event magnitude readily available in the flatfile—also heavily depends on the highly uncertain stress drop. By considering lower and upper bounds on regional stress drop, we propose a new method to quickly and automatically screen such very large datasets to identify all possible recordings for which band-limited κ approaches can be used. Combining them produces better-quantify estimates of κ and its epistemic uncertainties for this challenging dataset. The mean κ0 values combining the two methods are 13 ± 23 ms for horizontal ground motion.

Source parameter analysis from strong motion records of the Friuli, Italy, earthquake sequence (1976-1977)

1987 ◽  
Vol 77 (4) ◽  
pp. 1127-1146
Author(s):  
Giuseppe De Natale ◽  
Raul Madariaga ◽  
Roberto Scarpa ◽  
Aldo Zollo
Keyword(s):  
Frequency Domain ◽  
Stress Drop ◽  
High Frequency ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Source Model ◽  
Parameter Analysis ◽  
Corner Frequency ◽  
Spectral Parameters ◽  
Single Station

Abstract Time and frequency domain analyses are applied to strong motion data recorded in Friuli, Italy, during 1976 to 1977. An inversion procedure to estimate spectral parameters (low frequency level, corner frequency, and high frequency decay) has been applied to displacement spectra using a simple earthquake source model with a single corner frequency. The data were digitized accelerograms from ENEA-ENEL portable and permanent networks. Instrument-corrected SH waves were selected from a set of 138 three-component, hand-digitized records and 28 automatically digitized records. Thirty-eight events with stations having 8 to 32 km epicentral distance were studied. Different stress drop estimates were performed showing high values (200 to 300 bars, on the average) with seismic moments ranging from 2.8 × 1022 to 8.0 × 1024 dyne-cm. The observation of systematic higher values of Brune stress drop (obtained from corner frequencies) with respect to other time and frequency domain estimates of stress release, and the evidence on time series of multiple rupture episodes suggest that the observed corner frequencies are most probably related to subevent ruptures rather than the overall fault size. Seven events recorded at more than one station show a good correlation between rms, Brune, and dynamic stress drops, and a constant scaling of this parameter as a function of the seismic moment. When single station events are also considered, a slight moment dependence of these three stress drop estimates is observed differently. This may be explained by an inadequacy of the ω−2 high-frequency decay of the source model or by high-frequency attenuation due to propagation effects. The high-frequency cutoff of acceleration spectra indicates the presence of an Fmax in the range of 5 to 14 Hz, except for the stations where local site effects produce spectral peaks.

Insights into downhole array spectra of hydraulic-fracturing induced seismicity in the Horn River Basin, British Columbia

2020 ◽  
Author(s):  
Adam Klinger ◽  
Max Werner
Keyword(s):  
British Columbia ◽  
Hydraulic Fracturing ◽  
Stress Drop ◽  
High Frequency ◽  
Source Parameters ◽  
Low Frequency ◽  
Corner Frequency ◽  
Downhole Array ◽  
Horn River Basin ◽  
Downhole Arrays

<p>Hydraulic fracturing underpins tight shale gas exploration but can induce seismicity. During stimulations, operators carefully monitor the spatio-temporal distribution and source parameters of seismic events to be able to respond to any changes and potentially reduce the chances of fault reactivation. Downhole arrays of geophones offer unique access to (sub) microseismic source parameters and can provide new insights into the processes that induce seismicity. For example, variations in stress drop might indicate changes in the seismic response to injection (e.g. pore pressure variations). However, borehole arrays of geophones and the high frequencies of small events also present new challenges for source characterization. Stress drop depends on the corner frequency, a parameter with great uncertainty that is sensitive to attenuation, especially for (sub-) microseismicity. Here, we explore the behavior of microseismic spectra measured along borehole arrays and the effect of attenuation on estimates of corner frequency. We examine a dataset of over 90,000 microseismic events recorded during hydraulic fracturing in the Horn River Basin, British Columbia. We only see clear phase arrivals for events M<sub>w</sub> > -1 and restrict our initial analysis to a subsample of M<sub>w</sub>> 0 events that vary in space and time.</p><p>Our first observation is that some stations in the borehole array show an unexpected increase in the displacement energy from the low frequency to the corner frequency in the P and SH phases as well as high-frequency energy spikes inconsistent with a smooth Brune source model. A shorter time window that only captures the direct arrival results in a flatter low frequency plateau and reduces the amplitude of the pulses but compromises the resolution. The spikes may be caused by high frequency coda energy. We also find that corner frequency estimates decrease with decreasing station depth along the array in both the P and SH phases, a likely result of high frequency attenuation along the downhole array. The findings suggest Brune corner frequencies of moment magnitudes < 0.5 may not be resolvable even with downhole arrays at close proximity. Our results will eventually contribute to a better characterization of microseismic source parameters measured in borehole arrays.</p><p> </p>

scholarly journals Evaluation of working memory in relation to cochlear implant consonant speech discrimination

2021 ◽  
Vol 37 (1) ◽  
Author(s):  
Mai M. El Ghazaly ◽  
Mona I. Mourad ◽  
Nesrine H. Hamouda ◽  
Mohamed A. Talaat
Keyword(s):  
Working Memory ◽  
Speech Perception ◽  
High Frequency ◽  
Word List ◽  
Frequency Discrimination ◽  
Frequency Resolution ◽  
Speech Discrimination ◽  
Place Of Articulation ◽  
Strong Positive Relationship ◽  
Speech And Language Development

Abstract Background Speech perception in cochlear implants (CI) is affected by frequency resolution, exposure time, and working memory. Frequency discrimination is especially difficult in CI. Working memory is important for speech and language development and is expected to contribute to the vast variability in CI speech reception and expression outcome. The aim of this study is to evaluate CI patients’ consonants discrimination that varies in voicing, manner, and place of articulation imparting differences in pitch, time, and intensity, and also to evaluate working memory status and its possible effect on consonant discrimination. Results Fifty-five CI patients were included in this study. Their aided thresholds were less than 40 dBHL. Consonant speech discrimination was assessed using Arabic consonant discrimination words. Working memory was assessed using Test of Memory and Learning-2 (TOMAL-2). Subjects were divided according to the onset of hearing loss into prelingual children and postlingual adults and teenagers. Consonant classes studied were fricatives, stops, nasals, and laterals. Performance on the high frequency CVC words was 64.23% ± 17.41 for prelinguals and 61.70% ± 14.47 for postlinguals. These scores were significantly lower than scores on phonetically balanced word list (PBWL) of 79.94% ± 12.69 for prelinguals and 80.80% ± 11.36 for postlinguals. The lowest scores were for the fricatives. Working memory scores were strongly and positively correlated with speech discrimination scores. Conclusions Consonant discrimination using high frequency weighted words can provide a realistic tool for assessment of CI speech perception. Working memory skills showed a strong positive relationship with speech discrimination abilities in CI.

scholarly journals High Frequency Resolution Technique of FFT.

2000 ◽  
Vol 66 (648) ◽  
pp. 2772-2777
Author(s):  
Yasuro HORI ◽  
Minoru SASAKI ◽  
Fumio FUJISAWA
Keyword(s):  
High Frequency ◽  
Frequency Resolution

A dynamic model for far-field acceleration

1982 ◽  
Vol 72 (4) ◽  
pp. 1049-1068
Author(s):  
John Boatwright
Keyword(s):  
Stress Drop ◽  
High Frequency ◽  
Dynamic Stress ◽  
The Body ◽  
Body Waves ◽  
Far Field ◽  
Rupture Velocity ◽  
Frequency Level ◽  
Average Change ◽  
Dynamic Stress Drop

abstract A model for the far-field acceleration radiated by an incoherent rupture is constructed by combining Madariaga's (1977) theory for the high-frequency radiation from crack models of faulting with a simple statistical source model. By extending Madariaga's results to acceleration pulses with finite durations, the peak acceleration of a pulse radiated by a single stop or start of a crack tip is shown to depend on the dynamic stress drop of the subevent, the total change in rupture velocity, and the ratio of the subevent radius to the acceleration pulse width. An incoherent rupture is approximated by a sample from a self-similar distribution of coherent subevents. Assuming the subevents fit together without overlapping, the high-frequency level of the acceleration spectra depends linearly on the rms dynamic stress drop, the average change in rupture velocity, and the square root of the overall rupture area. The high-frequency level is independent, to first order, of the rupture complexity. Following Hanks (1979), simple approximations are derived for the relation between the rms dynamic stress drop and the rms acceleration, averaged over the pulse duration. This relation necessarily depends on the shape of the body-wave spectra. The body waves radiated by 10 small earthquakes near Monticello Dam, South Carolina, are analyzed to test these results. The average change of rupture velocity of Δv = 0.8β associated with the radiation of the acceleration pulses is estimated by comparing the rms acceleration contained in the P waves to that in the S waves. The rms dynamic stress drops of the 10 events, estimated from the rms accelerations, range from 0.4 to 1.9 bars and are strongly correlated with estimates of the apparent stress.

The relations between the corner frequency, seismic moment and source dynamic parameters derived from the spontaneous rupture of a circular fault

2021 ◽  
Vol 228 (1) ◽  
pp. 134-146
Author(s):  
Jian Wen ◽  
Jiankuan Xu ◽  
Xiaofei Chen
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Dynamic Models ◽  
Scaling Law ◽  
Boundary Integral ◽  
Corner Frequency ◽  
Dynamic Parameters ◽  
Zone Size ◽  
Dynamic Rupture ◽  
Scaling Relationships

SUMMARY The stress drop is an important dynamic source parameter for understanding the physics of source processes. The estimation of stress drops for moderate and small earthquakes is based on measurements of the corner frequency ${f_c}$, the seismic moment ${M_0}$ and a specific theoretical model of rupture behaviour. To date, several theoretical rupture models have been used. However, different models cause considerable differences in the estimated stress drop, even in an idealized scenario of circular earthquake rupture. Moreover, most of these models are either kinematic or quasi-dynamic models. Compared with previous models, we use the boundary integral equation method to simulate spontaneous dynamic rupture in a homogeneous elastic full space and then investigate the relations between the corner frequency, seismic moment and source dynamic parameters. Spontaneous ruptures include two states: runaway ruptures, in which the rupture does not stop without a barrier, and self-arresting ruptures, in which the rupture can stop itself after nucleation. The scaling relationships between ${f_c}$, ${M_0}$ and the dynamic parameters for runaway ruptures are different from those for self-arresting ruptures. There are obvious boundaries in those scaling relations that distinguish runaway ruptures from self-arresting ruptures. Because the stress drop varies during the rupture and the rupture shape is not circular, Eshelby's analytical solution may be inaccurate for spontaneous dynamic ruptures. For runaway ruptures, the relations between the corner frequency and dynamic parameters coincide with those in the previous kinematic or quasi-dynamic models. For self-arresting ruptures, the scaling relationships are opposite to those for runaway ruptures. Moreover, the relation between ${f_c}$ and ${M_0}$ for a spontaneous dynamic rupture depends on three factors: the dynamic rupture state, the background stress and the nucleation zone size. The scaling between ${f_c}$ and ${M_0}$ is ${f_c} \propto {M_0^{ - n}}$, where n is larger than 0. Earthquakes with the same dimensionless dynamic parameters but different nucleation zone sizes are self-similar and follow a ${f_c} \propto {M_0^{ - 1/3}}$ scaling law. However, if the nucleation zone size does not change, the relation between ${f_c}$ and ${M_0}$ shows a clear departure from self-similarity due to the rupture state or background stress.

A Source Physics Interpretation of Nonself-Similar Double-Corner-Frequency Source Spectral Model JA19_2S

2022 ◽  
Author(s):  
Chen Ji ◽  
Ralph J. Archuleta
Keyword(s):  
Stress Drop ◽  
Wave Speed ◽  
Dynamic Stress ◽  
Corner Frequency ◽  
Rupture Velocity ◽  
Scaling Relation ◽  
Shear Wave Speed ◽  
Dynamic Stress Drop ◽  
Static Stress Drop ◽  
Frequency Source

Abstract We investigate the relation between the kinematic double-corner-frequency source spectral model JA19_2S (Ji and Archuleta, 2020) and static fault geometry scaling relations proposed by Leonard (2010). We find that the nonself-similar low-corner-frequency scaling relation of JA19_2S model can be explained using the fault length scaling relation of Leonard’s model combined with an average rupture velocity ∼70% of shear-wave speed for earthquakes 5.3 < M< 6.9. Earthquakes consistent with both models have magnitude-independent average static stress drop and average dynamic stress drop around 3 MPa. Their scaled energy e˜ is not a constant. The decrease of e˜ with magnitude can be fully explained by the magnitude dependence of the fault aspect ratio. The high-frequency source radiation is generally controlled by seismic moment, static stress drop, and dynamic stress drop but is further modulated by the fault aspect ratio and the relative location of the hypocenter. Based on these two models, the commonly quoted average rupture velocity of 70%–80% of shear-wave speed implies predominantly unilateral rupture.

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