The Spectral Decay Parameter Kappa in Northeastern Sonora, Mexico

Fernández, Avelina I.; Castro, Raúl R.; Huerta, Carlos I.

doi:10.1785/0120090049

Cited by 39 publications

(18 citation statements)

References 17 publications

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“…For very hard rock, the question arises: what is the minimum value of κ 0 ? Some of the possible reasons for this scatter in existing κ 0 -V s30 data are differences in measurement, the range of frequencies used and the region , as well as possible differences in rock hardness (Rebollar 1990) and the degree of fracturing and erosion (Fernández et al 2010). In this study, we have been consistent in terms of measurement method, frequency range, type of rock and region.…”

Section: Correlation With the Deeper Basin Structuresupporting

confidence: 67%

Understanding the physics of kappa (κ): insights from a downhole array

et al. 2015

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S U M M A R YAt high frequencies, the acceleration spectral amplitude decreases rapidly; this has been modelled with the spectral decay factor κ. Its site component, κ 0 , is used widely today in ground motion prediction and simulation, and numerous approaches have been proposed to compute it. In this study, we estimate κ for the EUROSEISTEST valley, a geologically complex and seismically active region with a permanent strong motion array consisting of 14 surface and 6 downhole stations. Site conditions range from soft sediments to hard rock. First, we use the classical approach to separate local and regional attenuation and measure κ 0 . Second, we take advantage of the existing knowledge of the geological profile and material properties to examine the correlation of κ 0 with different site characterization parameters. κ 0 correlates well with V s30 , as expected, indicating a strong effect from the geological structure in the upper 30 m. But it correlates equally well with the resonant frequency and depth-to-bedrock of the stations, which indicates strong effects from the entire sedimentary column, down to 400 m. Third, we use our results to improve our physical understanding of κ 0 . We propose a conceptual model of κ 0 with V s , comprising two new notions. On the one hand, and contrary to existing correlations, we observe that κ 0 stabilizes for high V s values. This may indicate the existence of regional values for hard rock κ 0 . If so, we propose that borehole measurements (almost never used up to now for κ 0 ) may be useful in determining these values. On the other hand, we find that material damping, as expressed through travel times, may not suffice to account for the total κ 0 measured at the surface. We propose that, apart from material damping, additional site attenuation may be caused by scattering from small-scale variability in the profile. If this is so, then geotechnical damping measurements may not suffice to infer the overall crustal attenuation under a site; but starting with a regional value (possibly from a borehole) and adding damping, we might define a lower bound for site-specific κ 0 . More precise estimates would necessitate seismological site instrumentation.

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Section: Correlation With the Deeper Basin Structuresupporting

confidence: 67%

Understanding the physics of kappa (κ): insights from a downhole array

et al. 2015

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“…García, Romacho, and Jiménes (2004) determined values from 0.01 s to 0.04 s for southern Spain, and the result presented in this paper is even higher than the average k of 0.04 s calculated for northeastern Sonora, Mexico, which is a tectonically active region (Fernández, Castro, and Huerta, 2010).…”

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confidence: 56%

Near-surface wave attenuation (kappa) of Far West Rand micro-events

Brandt

2017

J. South. Afr. Inst. Min. Metall.

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Brandt (2015) and Birch, Cichowicz, and Grobbelaar (2015) recently undertook studies to determine the quality factor Q and attenuation parameter , which describe the attenuation of seismic waves with distance, for South African earthquakes and mining-related seismic events, respectively. Brandt (2015) derived an attenuation relation of Q( f ) 400f 0.7 , whereas Birch, Cichowicz, and Grobbelaar (2015) estimated the relation Q( f ) = 327f 0.81 for the Kaapvaal Craton. However, both these studies determined Q without knowledge of the near-surface attenuation, which is quantified by the factor k (kappa). The general decrease in amplitude of seismic waves caused by attenuation may be described by using the quality factor Q, as was proposed over 50 years ago (e.g. Havskov and Ottemöller, 2010b):where A 0 is the initial amplitude, A(t) the amplitude after the waves have travelled for time t, f represents the frequency, and Q( f) is the general frequency-dependent quality factor. Q has been observed to have strong regional variations in the crust and a frequency dependence of the form(e.g. Kvamme and Havskov, 1989;Kvamme, Hansen, and Bungum, 1995;Malagnini, Herrmann, and Koch, 2000) when f > 1 Hz and Q( f ) is nearly constant for 0.1 Hz < f < 1.0 Hz (e.g. Stein and Wysession, 2003). The frequency dependence is often found to be stronger with increasing tectonic activity and is thought to be related to the decrease in homogeneity within the crust (e.g. Kvamme and Havskov, 1989;Birch, Cichowicz, and Grobbelaar, 2015). Q is also thought to be mostly constant along the ray path for local seismology observations, with the exception of the near-surface layers (1-3 km), which generally have a much lower Q than the rest of the path and tend to filter out high-frequency energy between 5-25 Hz (e.g. Havskov and Ottemöller, 2010b). The attenuation term in Equation [1] may be separated into surface and deeper crust effects: [3] with k representing the near-surface attenuation. The parameter k describes the asymptotic high-frequency slope of the spectrum of a seismogram. A low value for k corresponds to a seismogram with abundant high-frequency energy, whereas a high value corresponds to a minimal amount of highfrequency energy (Kilb et al., 2012). Kappa varies with region (stable continental area vs. Kappa, near-surface attenuation, mining-related seismic event, spectral analysis.

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“…Gentili and Franceschina (2011) use an inversion scheme to determine κ dependence with distance and find it to be concave, which they then model with a piecewise linear function with two different slopes. Fernández et al (2010), on the other hand, derive a convex dependence with distance, whereas Kilb et al (2012) find no significant correlation with distance, albeit for distances < 40 km. Tsai and Cheng (2000) propose an alternative model where κ depends primarily on the source, secondarily on the site, and only slightly on distance.…”

Section: Introductionmentioning

confidence: 85%

“…This significant difference even for the rock estimates leads us to consider the variation of κ 0 for rock sites, which is of particular interest nowadays in the context of empirical GMPEs and host-to-target adjustment methods between rock and hard rock sites. Rebollar et al (1991) compared κ 0 values for rock sites found across literature and concluded that their large variability is due not only to rock type but also to rock hardness; Tselentis (1993) reiterated this point, whereas Fernández et al (2010) added the degree of fracturing and erosion as another factor. The results mentioned by Tselentis (1993) (Anderson and Hough, 1984;Rebollar, 1990;Rebollar et al, 1991), are reproduced in Figure 14; to them we add recent results from the same basic method of Anderson and Hough (1984): Margaris and Hatzidimitriou (2002), Douglas et al (2010), Van Houtte et al (2011), and the present study.…”

Section: Comparisons With Literaturementioning

confidence: 99%

A Study on the Variability of Kappa ( ) in a Borehole: Implications of the Computation Process

Ktenidou¹,

Gelis²,

Bonilla³

2013

Bulletin of the Seismological Society of America

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Knowledge of the acceleration spectral shape is crucial to various applications in engineering seismology. Spectral amplitude decays rapidly at high frequencies. Anderson and Hough (1984) introduced the empirical factor κ to model this attenuation. This is the first time κ is studied in a vertical array consisting of more than two stations. We use 180 earthquakes recorded at a downhole array with five stations in soils and rock to investigate the effect of soil conditions on κ. Given that κ computation processes vary across literature when following the classic AndersonHough method, we investigate its variability with the different assumptions that can be made when applying the method. The estimates of κ 0 range between 0.017 and 0.031 s at the surface and between 0.004 and 0.024 s at rock. This variability due to the assumptions made is larger than the error of each estimate and larger than the average difference in values between sediment and rock. For this data set, part of it can be attributed to the type of distance used. Given this variability, κ 0 values across literature may not always be comparable; this may bias the results of applications using κ 0 as an input parameter, such as ground-motion prediction equations. We suggest ways to render the process more homogeneous. We also find that κ at rock level is not well approximated by surface records from which we deconvolved the geotechnical transfer function. Finally, we compute κ on the vertical component and find a dependence of the vertical-to-horizontal κ ratio on site conditions.

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The Spectral Decay Parameter Kappa in Northeastern Sonora, Mexico

Cited by 39 publications

References 17 publications

Understanding the physics of kappa (κ): insights from a downhole array

Understanding the physics of kappa (κ): insights from a downhole array

Near-surface wave attenuation (kappa) of Far West Rand micro-events

A Study on the Variability of Kappa ( ) in a Borehole: Implications of the Computation Process

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