Energy partition of seismic coda waves in layered media: theory and application to Pinyon Flats Observatory

Margerin, Ludovic; Campillo, Míchel; Tiggelen, Bart van; Hennino, R.

doi:10.1111/j.1365-246x.2008.04068.x

Cited by 91 publications

(78 citation statements)

References 34 publications

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“…Furthermore, the duration to reach the same decay rate seems to become longer as hypocentral distance increases. Although the energies of P and S modes and those of vertical and horizontal components obviously have different physical meanings [e.g., Margerin et al, 2009], the observed same decay rate at short lapse time and the dependence of the duration on hypocentral distance are qualitatively consistent with the establishment of equipartition shown in Figure 7a.…”

Section: Energy Partitioningsupporting

confidence: 71%

Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan

Yamamoto¹,

Sato²

2010

J. Geophys. Res.

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[1] Volcanoes are one of the most heterogeneous fields in the Earth's crust, and the understanding of such inhomogeneities may provide us important information on various volcanic processes. In the previous studies on the seismic wave propagation at active volcanoes, the diffusion model has been widely used to model the energy transportation and the contribution of P and S waves and their mode conversion have not been well recognized partly due to lack of dense observations capturing spatiotemporal pattern of energy propagation. In this study, we present observational evidence of mode conversions and multiple scattering at Asama volcano, Japan, revealed by an active seismic experiment with a dense seismic network. The observed spatial distribution of propagating energy emitted from the explosive P source shows a wavefront of direct P wave and a pattern exhibiting two slopes which is indicative of multiple scattering and conversion scattering of two modes having different scattering coefficients. These facts suggest that the radiative transfer theory is more preferable than the diffusion theory to explain the observed characteristics. We thus modeled the energy propagation using the radiative transfer theory assuming multiple isotropic scattering including conversion scatterings and quantitatively estimated scattering parameters. Estimated total scattering coefficients for P-to-S and S-to-S scattering are about three times larger than that of P-to-P scattering, and the mean free path of S wave is about 1 km for an 8-16 Hz band. These results suggest that the mode conversion and multiple scattering have an indispensable effect on the seismic energy propagation in heterogeneous volcanic environments.Citation: Yamamoto, M., and H. Sato (2010), Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan,

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Section: Energy Partitioningsupporting

confidence: 71%

Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan

Yamamoto¹,

Sato²

2010

J. Geophys. Res.

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“…In the auto-correlation approach, we can determine the velocity structure immediately below the observed site because of the direct correspondence of the imaginary part of the Green's function to the spectral energy density . As a pioneering work, Margerin et al (2009) showed that after sufficient lapse time from the onset of the S-wave the late coda can be considered to be in the diffuse field regime. Then, Kawase et al (2011) extended the idea of DFC to the stack of horizontal-to-vertical ratios of earthquakes (EHVR) and provided a simple theoretical formula assuming equipartition of energy in the incident waves at the bedrock (i.e., equipartition inside the half-space).…”

Section: Introductionmentioning

confidence: 99%

Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

Kawase

Mori

Nagashima

2018

Earth Planets Space

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We have been discussing the validity of using the horizontal-to-vertical spectral ratios (HVRs) as a substitute for S-wave amplifications after Nakamura first proposed the idea in 1989. So far a formula for HVRs had not been derived that fully utilized their physical characteristics until a recent proposal based on the diffuse field concept. There is another source of confusion that comes from the mixed use of HVRs from earthquake and microtremors, although their wave fields are hardly the same. In this study, we compared HVRs from observed microtremors (MHVR) and those from observed earthquake motions (EHVR) at one hundred K-NET and KiK-net stations. We found that MHVR and EHVR share similarities, especially until their first peak frequency, but have significant differences in the higher frequency range. This is because microtremors mainly consist of surface waves so that peaks associated with higher modes would not be prominent, while seismic motions mainly consist of upwardly propagating plain body waves so that higher mode resonances can be seen in high frequency. We defined here the spectral amplitude ratio between them as EMR and calculated their average. We categorize all the sites into five bins by their fundamental peak frequencies in MHVR. Once we obtained EMRs for five categories, we back-calculated EHVRs from MHVRs, which we call pseudo-EHVRs (pEHVR). We found that pEHVR is much closer to EHVR than MHVR. Then we use our inversion code to invert the one-dimensional S-wave velocity structures from EHVRs based on the diffuse field concept. We also applied the same code to pEHVRs and MHVRs for comparison. We found that pEHVRs yield velocity structures much closer to those by EHVRs than those by MHVRs. This is natural since what we have done up to here is circular except for the average operation in EMRs. Finally, we showed independent examples of data not used in the EMR calculation, where better ground structures were successfully identified from pEHVRs again. Thus we proposed here a simple empirical method to estimate S-wave velocity structures using single-station microtremor records, which is the most cost-effective method to characterize the site effects.Keywords: Site effect, Subsurface structure, Seismological bedrock, Horizontal-to-vertical ratio, Hybrid heuristic search, S-wave, P-wave © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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“…The partitioning between P and S energy is one observable that is difficult to measure (Shapiro et al 2000;Hennino et al 2001;Margerin et al 2009) in the field but can easily be simulated . According to Ryzhik et al (1996) the theoretical value for the S-to P-energy ratio for long lapse times tends to stabilize in infinite space at…”

Section: Discussionmentioning

confidence: 99%

The influence of crustal scattering on translational and rotational motions in regional and teleseismic coda waves

Gaebler

Sens‐Schönfelder²,

Korn

2015

Geophysical Journal International

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S U M M A R YMonte Carlo solutions to the radiative transfer equations are used to model translational and rotational motion seismogram envelopes in random elastic media with deterministic background structure assuming multiple anisotropic scattering. Observation and modelling of the three additional components of rotational motions can provide independent information about wave propagation in the Earth's structure. Rotational motions around the vertical axis observed in the P-wave coda are of particular interest as they can only be excited by horizontally polarized shear waves and therefore indicate the conversion from P to SH energy by multiple scattering at 3-D heterogeneities. To investigate crustal scattering and attenuation parameters in south-east Germany beneath the Gräfenberg array multicomponent seismogram envelopes of rotational and translational motions are synthesized and compared to seismic data from regional swarm-earthquakes and of deep teleseismic events. In the regional case a nonlinear genetic inversion is used to estimate scattering and attenuation parameters at high frequencies (4-8 Hz). Our preferred model of crustal heterogeneity consists of a medium with random velocity and density fluctuations described by an exponential autocorrelation function with a correlation length of a few hundred metres and fluctuations in the range of 3 per cent. The quality factor for elastic S-waves attenuation Q S i is around 700. In a second, step simulations of teleseismic P-wave arrivals using this estimated set of scattering and attenuation parameters are compared to observed seismogram envelopes from deep events. Simulations of teleseismic events with the parameters found from the regional inversion show good agreement with the measured seismogram envelopes. This includes ringlaser observations of vertical rotations in the teleseismic P-wave coda that naturally result from the proposed model of wave scattering. The model also predicts, that the elastic energy recorded in the teleseismic P coda is not equipartitioned, unlike the coda of regional events, but contains an excess of shear energy. The results confirm that scattering generating the teleseismic P-wave coda mainly occurs in the crustal part of the lithosphere beneath the receiver. Our observations do not require scattering of high frequency waves in the mantle, but weak scattering in the lithospheric mantle cannot be ruled out.

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Energy partition of seismic coda waves in layered media: theory and application to Pinyon Flats Observatory

Cited by 91 publications

References 34 publications

Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan

Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan

Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

The influence of crustal scattering on translational and rotational motions in regional and teleseismic coda waves

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