Crustal structure of northern Italy from the ellipticity of Rayleigh waves

Berbellini, Andrea; Morelli, A.; Ferreira, Ana M. G.

doi:10.1016/j.pepi.2016.12.005

Cited by 22 publications

(36 citation statements)

References 34 publications

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“…With respect to the model of Albano et al [18], we obtain a smaller and faster modeled poroelastic LOS displacement evolution at point 1. Possible reasons of this discrepancy are (1) the different assumed configurations used to model the ground displacements (here a 3D one is assumed, with respect to the 2D from previous work), (2) the different permeability profiles, and (3) the fact that we exclude the possibility of poroelastic induced afterslip. Given the different time scale of IC1 and IC3 and the reasonable agreement between IC3 and poroelastic rebound results for a locked fault (Figure 8(b)), we argue that a nonnegligible fraction of postseismic deformation at the surface occurred regardless of the poroelastic process and that even if the permeability layering here adopted is a coarse representation of the Emilia-Romagna subsoil, it is adequate to model both the order of magnitude and the time scale of the poroelastic effects.…”

Section: Discussionmentioning

confidence: 99%

“…The seismic sequence evolved along an about 50 km long, east-west-oriented thrust belt, including 8 events with M L ≥ 5 0 [1]. All the events occurred in the alluvial plain of the Po river, in the foredeep of the northern Apennines chain, where the subsoil is composed of Plio-Quaternary sediment layers placed just above the Emilia-Romagna blind thrust system [2][3][4]. This area is known to be characterized by active tectonic shortening, due to the northward movement of the Apennines at about 2 mm/yr with respect to the stable Adriatic microplate [5].…”

Section: Introductionmentioning

confidence: 99%

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Poroelasticity and Fluid Flow Modeling for the 2012 Emilia-Romagna Earthquakes: Hints from GPS and InSAR Data

et al. 2018

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The Emilia-Romagna seismic sequence in May 2012 was characterized by two mainshocks which were close in time and space. Several authors already modeled the geodetic data in terms of the mechanical interaction of the events in the seismic sequence. Liquefaction has been extensively observed, suggesting an important role of fluids in the sequence. In this work, we focus on the poroelastic effects induced by the two mainshocks. In particular, the target of this work is to model the influence of fluids and pore-pressure changes on surface displacements and on the Coulomb failure function (CFF). The fluid flow and poroelastic modeling was performed in a 3D half-space whose elastic and hydraulic parameters are depth dependent, in accordance with the geology of the Emilia-Romagna subsoil. The model provides both the poroelastic displacements and the pore-pressure changes induced coseismically by the two mainshocks at subsequent periods and their evolution over time. Modeling results are then compared with postseismic InSAR and GPS displacement time series: the InSAR data consist of two SBAS series presented in previous works, while the GPS signal was detected adopting a variational Bayesian independent component analysis (vbICA) method. Thanks to the vbICA, we are able to separate the contribution of afterslip and poroelasticity on the horizontal surface displacements recorded by the GPS stations. The poroelastic GPS component is then compared to the modeled displacements and shown to be mainly due to drainage of the shallowest layers. Our results offer an estimation of the poroelastic effect magnitude that is small but not negligible and mostly confined in the near field of the two mainshocks. We also show that accounting for a 3D fault representation with a nonuniform slip distribution and the elastic-hydraulic layering of the half-space has an important role in the simulation results.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Poroelasticity and Fluid Flow Modeling for the 2012 Emilia-Romagna Earthquakes: Hints from GPS and InSAR Data

et al. 2018

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“…The Rayleigh wave ellipticity may be inverted in terms of structure either alone (Yano et al 2009;Berbellini et al 2017) or in combination with phase or group velocity data (Lin et al 2012), as their more shallow sensitivity makes them a good complement to the more traditional velocity data. In addition, as it is assumed that the ellipticity depends on the local structure beneath the station, inversion of ellipticity can be done independently for several stations and does not require a tomographic inversion as velocity data do.…”

Section: Introductionmentioning

confidence: 99%

“…Ray theory is valid if the lateral variations occur over a large scale compared to the 108 V. Maupin wavelength, leading to the implicit assumption that the ellipticity is affected by the average structure over a significant area around the station. Inversions of ellipticity are on the other hand done individually beneath stations, without considering, also because this is unknown, what is the region around the station that is actually affecting the measurement at that station (Lin et al 2012;Berbellini et al 2017).…”

Section: Introductionmentioning

confidence: 99%

3-D sensitivity kernels of the Rayleigh wave ellipticity

Maupin

2017

Geophysical Journal International

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S U M M A R YThe ellipticity of the Rayleigh wave at the surface depends on the seismic structure beneath and in the vicinity of the seismological station where it is measured. We derive here the expression and compute the 3-D kernels that describe this dependence with respect to S-wave velocity, P-wave velocity and density. Near-field terms as well as coupling to Love waves are included in the expressions. We show that the ellipticity kernels are the difference between the amplitude kernels of the radial and vertical components of motion. They show maximum values close to the station, but with a complex pattern, even when smoothing in a finite-frequency range is used to remove the oscillatory pattern present in mono-frequency kernels. In order to follow the usual data processing flow, we also compute and analyse the kernels of the ellipticity averaged over incoming wave backazimuth. The kernel with respect to P-wave velocity has the simplest lateral variation and is in good agreement with commonly used 1-D kernels. The kernels with respect to S-wave velocity and density are more complex and we have not been able to find a good correlation between the 3-D and 1-D kernels. Although it is clear that the ellipticity is mostly sensitive to the structure within half-a-wavelength of the station, the complexity of the kernels within this zone prevents simple approximations like a depth dependence times a lateral variation to be useful in the inversion of the ellipticity.

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“…Surface‐wave polarization or ellipticity has been used to study shallow structure (e.g., Berbellini et al, ; Lin et al, ; Tanimoto & Rivera, ). Similarly, body‐wave polarization, that is, the direction of body‐wave particle motion measured at the free surface, has been demonstrated to be effective in studying near‐surface structure (e.g., Kruger, ; Park & Ishii, ).…”

Section: Introductionmentioning

confidence: 99%

Frequency‐Dependent P Wave Polarization and Its Subwavelength Near‐Surface Depth Sensitivity

Park

Tsai

Ishii

2019

Geophysical Research Letters

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Near-surface structure is crucial to assessing seismic hazards and understanding earthquakes and surface processes yet is a major challenge to robustly image. Recently, an approach based on body-wave polarization was introduced for constraining shallow seismic structure, but the depth sensitivity of the polarization measurement has remained unclear. Using waveform simulations based on a layer over a half space, we find that the depth sensitivity of P wave polarization peaks at the surface and decreases abruptly over a depth range shorter than its wavelength. A strong frequency dependence provides constraints on local 1-D structure, with frequencies between 0.1 and 10 Hz illuminating structure at depths of 10 m to several kilometers. Applying these results to teleseismic recordings in Japan provides constraints on structure at about 120 to 750 m, including a distinctive weak zone along the Median Tectonic Line in the Kii peninsula and Awaji Island.Plain Language Summary Shallow structure controls the level of ground shaking and hence is critical in assessing seismic hazards. Conventionally, drilling or local seismic surveys are performed to image the near surface, but their high cost has resulted in extremely sparse coverage of studied sites worldwide. Here we demonstrate that the directions of P waves that are naturally generated by local or distant earthquakes constrain the structure immediately below the seismometer where the P waves are recorded. Our finding suggests that frequency-dependent measurements of P wave directions is a promising tool for studying shallow structure that is noninvasive and cost effective. Application to data recorded in Japan reveals structure at about 120-to 750-m depth, including a weak zone along a segment of the Median Tectonic Line.Surface-wave polarization or ellipticity has been used to study shallow structure (e.g., Berbellini et al., 2017;Lin et al., 2014;Tanimoto & Rivera, 2008). Similarly, body-wave polarization, that is, the direction of bodywave particle motion measured at the free surface, has been demonstrated to be effective in studying near-Key Points:• The depth sensitivity of P wave polarization peaks at the surface and becomes negligible at a depth that is shallower than its wavelength • The frequency content and the near-surface shear wave speeds are the main factors that determine the depth sensitivity • P wave polarization is a useful tool for constraining shallow 1-D structure from about 10 m to several kilometers at 0.1 to 10 Hz Supporting Information:• Supporting Information S1

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Crustal structure of northern Italy from the ellipticity of Rayleigh waves

Cited by 22 publications

References 34 publications

Poroelasticity and Fluid Flow Modeling for the 2012 Emilia-Romagna Earthquakes: Hints from GPS and InSAR Data

Poroelasticity and Fluid Flow Modeling for the 2012 Emilia-Romagna Earthquakes: Hints from GPS and InSAR Data

3-D sensitivity kernels of the Rayleigh wave ellipticity

Frequency‐Dependent P Wave Polarization and Its Subwavelength Near‐Surface Depth Sensitivity

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