Rayleigh Wave Ellipticity Research Articles

Joint estimation ofS-wave velocity and damping ratio of the near-surface from active Rayleigh wave surveys processed with a wavefield decomposition approach

SUMMARYThe use of surface wave measurements to derive an S-wave velocity profile of the subsurface has become a widely applied procedure; however, their potential use to reconstruct the S-wave material damping properties of the subsoil is generally overlooked, due to the difficulties in obtaining consistent surface wave amplitude information from field data and translating them into robust estimates of the dissipative properties of the near-surface. In this work, we adapt a wavefield decomposition technique for the processing of elastic surface wave data to the extraction of the complete set of properties of Rayleigh waves generated by a controlled source and propagating in dissipative geomaterials. Retrieved information includes multimodal phase velocity and ellipticity as well as the frequency-dependent attenuation coefficient. We exploit the key advantages of wavefield decomposition processing (joint interpretation of multicomponent recordings, coupled estimation of wave propagation parameters, modelling of multiple superimposing modes) to maximize the robustness of the retrieval of Rayleigh wave properties, especially of the dissipative ones. For the subsequent interpretation of Rayleigh wave dispersion, ellipticity and attenuation data we implement a joint Monte Carlo inversion yielding a coupled estimate of S-wave velocity and damping ratio profile for the subsurface; we incorporate a series of geophysical constraints to narrow down the searched parameter space to realistic soil models. We apply this processing and inversion scheme to a bespoke synthetic data set and to a field survey for the characterization of a strong motion station; in both cases, we succeed in retrieving Rayleigh wave multimodal dispersion, ellipticity and attenuation curves. From the inversion of data from the simulated seismogram we are able to reconstruct the properties of the synthetic model. As for the real case, we determine an S-wave velocity and damping ratio model for the soil column below the station, through which we are able to model the inelastic earthquake local response observed at the site. Basing on the results obtained for the real case, we argue that one of the advantages brought by our processing method—the possibility to process active Rayleigh wave data acquired by a 2-D array illuminated by different source positions—may play a key role in allowing to retrieve dissipative properties of the near-surface closer to the material damping of the soil materials, and less influenced by scattering determined by possible discontinuities in the subsurface.

Sedimentary and crustal structure of eastern North China from joint inversion of Rayleigh wave phase velocity and ellipticity and its implication for magmatism

Understanding the tectonic evolution of the North China Craton and its destruction mechanism requires the knowledge of eastern North China's fine crustal velocity structure. Using the two-year record of 342 ChinArray stations deployed in eastern North China, we obtain the Rayleigh wave phase velocity via ambient noise interferometry and Rayleigh wave ellipticity from ∼1000 teleseismic events. High-resolution sedimentary thickness and crustal 3D S-wave velocity structure are obtained by jointly inverting these observations. The results show that the Bohai Bay Basin is infilled with thick sediments and the Central Bohai Sea is the current depocenter with sedimentary thickness up to about 6 km. The crust and uppermost mantle beneath the Bohai Bay Basin are characterized by low velocity, indicating a high internal temperature of the crust. An upwelling of mantle thermal material under the crust of the Bohai Bay Basin continuously modifies the crust, suggesting that bottom-up thermochemical erosion is likely the primary control factor of crustal modification and thinning in this area. The uplift areas around the basin generally exhibit high velocity with weaker crustal modification, showing the heterogeneity of craton modification. Moreover, localized low-velocity zones observed beneath the Chifeng Volcanos, Dalainor Volcanos, and Kuandian Volcanos indicate the residual magmatism beneath these Quaternary volcanos. Furthermore, the magmatism beneath the Chifeng and Dalainor Volcanos shares a common magmatic source.

Extraction and applications of Rayleigh wave ellipticity in polar regions

AbstractSeismic Rayleigh wave ellipticity measurements are the horizontal-to-vertical ratio of the Rayleigh wave particle motion, and are sensitive to the subsurface structure beneath a seismic station. H/V ratios measured from the ambient vibrations of the Earth are being increasingly used in glaciological applications to determine glacier and ice sheet thickness, seismic velocities and firn properties. Using the newly developed degree-of-polarisation (DOP-E) method which exploits the polarisation properties of seismic noise, we identify and extract Rayleigh waves from seismic stations in Greenland, and relate them to sea ice processes and the geology of the upper crust. Finally, we provide some suggestions for future applications of DOP-E method to gain greater insight into seasonal and long-term variability of sea ice formation and breakup as well as the monitoring of ice sheet thickness, subglacial environment and firn layers in the poles.

Site characterization study with microtremor data: A case study at the West Borneo NPP potential site

ABSTRACTA site characterization using a microtremor measurement study was conducted at the West Borneo nuclear power plant (NPP) potential site as a preliminary feasibility study. This study measured the natural resonant frequency of soil and estimated the subsurface VS as prior information for the design planning of an NPP building foundation. The single station microtremor data were processed using the horizontal‐to‐vertical spectral ratio (HVSR) method to obtain the f0 and A0 values, and the array data were processed using the spatial autocorrelation (SPAC) method. The study area was classified based on the f0 and A0 values. Due to the unavailability of borehole data and limited array data, the HVSR curve was used to estimate the VS profile. The HVSR curve VS estimation was calculated using Rayleigh wave ellipticity inversion. The inversion results were constrained by VS profiles from SPAC and regional geology data to ensure that the inverted model was rational. It was demonstrated that the constrained inversion process could generate a rational subsurface model for Pantai Gosong's coastline. Based on the result, the feasible bedrock for the NPP building foundation was found at a depth of 40 m in the coastline area.

Combining Dense Seismic Arrays and Broadband Data to Image the Subsurface Velocity Structure in Geothermally Active South‐Central Utah

AbstractSouth‐central Utah is characterized by Quaternary volcanism, current geothermal activity, and unusually high surface heat flux across the region. Additionally, there are three operating geothermal power plants in this region, known as the Sevier thermal area. This setting is very similar to that found in the Coso geothermal area. However, the source and lateral extent of subsurface heat in Utah is poorly understood. We use temporally separated geophone arrays combined with regional broadband data to perform ambient noise seismic tomography to study the subsurface shear velocity structure in the region. We find good recovery of ocean‐seism excited Rayleigh wave signals between the periods of 5 and 10 s. For each period, we measure the Rayleigh wave phase velocity and ellipticity across the region using the beamforming methodology and horizontal to vertical (H/V) amplitude ratio. Finally, we combine spline‐based 1D shear velocity models inverted using Rayleigh wave phase velocity and H/V measurements on a 2D, beamforming discretized grid to construct a final 3D model. The final 3D model has many similarities to imaged velocity models at the Coso geothermal area. We find a strong correlation between low velocity anomalies and high surface heat flux and geothermal activity. Additionally, we find a laterally continuous low‐velocity anomaly between 5 and 15 km depth, which may represent elevated temperature of hundreds of degrees Celsius, partial melt, and/or the presence of water, and a common heat source across the region which likely originates from the mantle.

Seismic Hazard Potential in Yogyakarta Based on HVSR Curve Estimation

In 2006, the Special Region of Yogyakarta was shaken by a destructive earthquake. The United States Geological Survey (USGS) recorded that the earthquake had a magnitude of 6.3 Mw at a depth of 12.5 km below the surface that was triggered by strike slip fault activity. The severe damage occurred in Bantul district and Klaten district, where the Klaten area location were far from the earthquake epicenter. This proves that the magnitude and the earthquake source distance are not the only parameters for seismic hazard potential, but rather the presence of local site effects and building conditions. The present study aims to determine the characteristics of the soil and estimate the seismic hazard potential by using HVSR method. Horizontal to Vertical Spectral Ratio (HVSR) is one method that can be used to obtain the subsurface information from single station measurements. Furthermore, the inversion of Rayleigh wave ellipticity curve is used to obtain 1-D of shear wave velocity (Vs). The parameters from HVSR calculation and Rayleigh wave inversion were mapped to understand the subsurface structure beneath the Yogyakarta area. Based on the soil classification to Vs, Yogyakarta area is categorized to SD (Stiff soil/soft soil) and SC (Very dense soil and soft rock). The results of the mapping analysis indicated that Bantul district is an area with the highest potential of seismic hazard.

3D Shear Wave Velocity Model of Salt Lake Valley via Rayleigh Wave Ellipticity across a Temporary Geophone Array

Abstract We construct a 3D shear velocity model of the Salt Lake Valley using Rayleigh waves excited by the 31 March 2020 Mw 6.5 central Idaho earthquake recorded on a 168-station temporary nodal geophone network and the 49-station permanent regional network. The temporary array—deployed in response to the March 18 Mw 5.7 Magna earthquake—serendipitously recorded clear surface waves between 10 and 20 s period from the Idaho event at ∼500 km epicentral distance, from which we measure both Rayleigh wave phase velocity and ellipticity (H/V ratio). In addition, we employ multicomponent earthquake coda cross correlation to extend the measurements down to 5 s period. Because Rayleigh wave ellipticity features outstanding shallow sensitivity, we invert for a 3D upper crust VS model of the Salt Lake Valley. Our model shows basin structure in general agreement with and complements the current Community Velocity Model, which is mostly constrained by borehole and gravity measurements. Our model thus provides critical information for future earthquake hazard assessment studies, which require detailed shallow velocity structure.

Seismic Site Characterization Using Ambient Noise and Earthquake HVSR in the Easternmost Part of Shillong Plateau, India

This study provides site characterization results using passive seismic techniques for the easternmost part of Shillong plateau of Northeastern India. The prime objective of this research is to generate the Horizontal-to-Vertical Spectral Ratios (HVSR) from earthquakes and ambient microtremor data for generation of 1-D shear wave velocity profiles to reveal the basement depths and fundamental resonance frequencies underneath three stations of Shillong plateau. The earthquake waveforms are recorded for a period of eighteen months (i.e. December 2018 to June 2020) using broadband seismometer; while the ambient microtremor data is collected from a three component highly sensitive velocity meter. The earthquake HVSRs and noise HVSRs are consistent with each other and range from ∼3.6 Hz to ∼14.5 Hz. The Rayleigh wave ellipticity are generated from the corresponding HVSR curves for inversion to determine compressional and shear wave velocity structure. We report that the compressional and shear wave velocity profiles match fairly well for both earthquakes and ambient microtremor data. Overall, Vs30 lies in the range of 480 m/s to 2600 m/s at all locations in the easternmost part of Shillong plateau; while the sedimentary layer velocity lies between 450 m/s and 1100 m/s. The thickness of the sedimentary layer is assessed from the velocity profiles and using an empirical formula makes a good match and varies from 11.3 m to 31.2 m.

Seismic characterization of Iranian strong motion stations in Kermanshah province (Iran) using single-station Rayleigh wave ellipticity inversion of ambient noise measurements

Seismic characterization of Iranian strong motion stations in Kermanshah province (Iran) using single-station Rayleigh wave ellipticity inversion of ambient noise measurements

Sedimentary and Crustal Structure of the Western United States From Joint Inversion of Multiple Passive Seismic Datasets

AbstractAccurate seismic images of the crust are essential for assessing seismic hazards and elucidating tectonic processes that shape surface landforms. Although California and Nevada have been studied extensively using various seismic datasets and tomographic methods, the region lacks a seismic model that can accurately define both the shallow (<8 km) and deeper crust. We take the advantage of recent increases in seismic data coverage to build a new 3D shear wave speed model by jointly inverting Rayleigh wave ellipticity, phase velocity, and teleseismic P waveforms. In the Great Valley, the new model reveals an asymmetric basement, steeply dipping in the west and gently dipping in the east. Beneath its western margin, in the Coast Ranges, we resolve a wedge‐shaped, low‐velocity zone in the upper‐middle crust, interpreted as Franciscan Complex. Our images confirm that uplift of the western Great Valley and an eastward shift of its depositional center are caused by wedging and underthrusting of the complex during subduction. Across the Basin and Range, the resolved crust has an average thickness of 38 km in the southern half of the northern Basin and Range, about 5 km thicker than neighboring regions. The thickened crust overlaps with major volcanic centers of the mid‐Cenozoic ignimbrite flare‐up. This spatial correlation may suggest magmatic intrusions and underplating contributed to crustal growth and thickening prior to Miocene Basin and Range extension. Overall, the new model is consistent with active source studies in the region but provides a more comprehensive view of shallow and deep structures across this large and tectonically complex region.

The shallow structure of Mars at the InSight landing site from inversion of ambient vibrations

Orbital and surface observations can shed light on the internal structure of Mars. NASA’s InSight mission allows mapping the shallow subsurface of Elysium Planitia using seismic data. In this work, we apply a classical seismological technique of inverting Rayleigh wave ellipticity curves extracted from ambient seismic vibrations to resolve, for the first time on Mars, the shallow subsurface to around 200 m depth. While our seismic velocity model is largely consistent with the expected layered subsurface consisting of a thin regolith layer above stacks of lava flows, we find a seismic low-velocity zone at about 30 to 75 m depth that we interpret as a sedimentary layer sandwiched somewhere within the underlying Hesperian and Amazonian aged basalt layers. A prominent amplitude peak observed in the seismic data at 2.4 Hz is interpreted as an Airy phase related to surface wave energy trapped in this local low-velocity channel.

Sedimentary and crustal velocity structure of Trans-North China Orogen from joint inversion of Rayleigh wave phase velocity and ellipticity and some implication for Syn-rift volcanism

We present a high-resolution 3-D shear wave velocity model of the crust and uppermost mantle beneath the Trans-North China Orogen and its adjacent regions derived from a joint inversion of Rayleigh wave phase velocity and ellipticity computed from ambient noise data. The 3-D velocity model reveals large lateral variations in sedimentary and crustal structure across the study area. In addition to the large velocity contrast between the North China Basin and the Ordos Basin located in the east and west sides of the orogen, we found a northward thinning of sediments within the Weihe-Shanxi Rift System that sits in the middle of the orogen, suggesting that the rifting has likely propagated from the Weihe Rift in the south to the Shanxi Rift in the north during the Oligocene-Pliocene. While the north-south trending rift is underlaid by a low Vs across the entire range in the upper and middle crust, only the north segment, which houses the Datong volcanic complex, exhibits a substantial low velocity structure in the lower crust and the uppermost mantle. The center of the low velocity anomaly extends into the uppermost mantle at a location approximately 150 km west to the volcanic complex, which is speculated for a nearly horizontal channel in the lower crust for the upwelling of the hot materials from the asthenosphere. These observations suggest that Shanxi Rift in the north is a more active segment within the rift system, which is manifested by the Quaternary syn-rift Datong volcanic complex.

Rayleigh-wave ellipticity in weakly heterogeneous layered media

SUMMARY We derive approximate expressions for the ellipticity (i.e. horizontal-to-vertical or vertical-to-horizontal ratio) of Rayleigh waves propagating in a layered medium. The approximation is based on the generalized energy equation for Rayleigh waves, which has been used previously to obtain perturbational results for ellipticity. For a medium with weakly heterogeneous layers, we obtain an approximation from the perturbational result by taking the background medium to be homogeneous. The generalized energy equation also requires an auxiliary function and we discuss how the various possible functions are related to the homogeneous Rayleigh-wave eigenfunction. The analysis reveals that, within the weak approximation, the product of ellipticity and squared phase velocity is linearly related to squared shear wave velocity in the subsurface. We show the accuracy of the approximation with a simple layer-over-half-space model and then demonstrate its utility in a linear inversion scheme for shear wave velocity.

Seismic site classification from HVSR data using the Rayleigh wave ellipticity inversion: A case study in Singapore

Shear wave velocity (Vs) profile is one of the critical geotechnical measurements of soil layers for seismic hazard assessment and liquefaction potential evaluation. Enhancing the effectiveness of in-situ Vs profiling by reducing time and cost is of great interest. For that reason, this study aims at assessing Vs profile generation from a single-station three-component geophone with additional borehole log data for constraining parameter space. Based on multichannel analysis of surface waves (MASW), and microtremor array Measurements (MAM) conducted previously at seven sites located in Bukit Timah Granite, Singapore, this study utilized HVSR signals for Rayleigh wave ellipticity (ellipticity curve) inversion with additional inversion constraint using borehole log data. The resulting Vs profiles and reference Vs profiles from MASW and MAM were quantitatively compared using average Vs of 30 m (Vs30). The profiles generated from ellipticity curve inversion revealed a good agreement with Vs reference profiles. Vs30 based site classification results also indicated a good fit of two test results. Therefore, HVSR measurements for further ellipticity curve inversion, with already available borehole log data for constraint, is considered as a promising cost and time-effective site classification approach.

Shallow Crustal Shear Velocity and Vp/Vs Across Southern California: Joint Inversion of Short‐Period Rayleigh Wave Ellipticity, Phase Velocity, and Teleseismic Receiver Functions

AbstractNear‐surface seismic velocity structure plays a critical role in ground motion amplification during large earthquakes. In particular, the local Vp/Vs ratio strongly influences the amplitude of Rayleigh waves. Previous studies have separately imaged 3D seismic velocity and Vp/Vs ratio at seismogenic depth, but lack regional coverage and/or fail to constrain the shallowest structure. Here, we combine three datasets with complementary sensitivity in a Bayesian joint inversion for shallow crustal shear velocity and near‐surface Vp/Vs ratio across Southern California. Receiver functions–including with an apparent delayed initial peak in sedimentary basins, and long considered a nuisance in receiver function imaging studies–highly correlate with short‐period Rayleigh wave ellipticity measurements and require the inclusion of a Vp/Vs parameter. The updated model includes near‐surface low shear velocity more in line with geotechnical layer estimates, and generally lower than expected Vp/Vs outside the basins suggesting widespread shallow fracturing and/or groundwater undersaturation.

Ambient noise and ERT data provide insights into the structure of co-seismic rock avalanche deposits in Sichuan (China)

The post-seismic history of the 2008 Mw7.9 Wenchuan earthquake shows that marginally stable deposits of large co-seismic landslide dams can pose persistent debris flow hazards for the downstream areas. Here, we combine analyses of single-station recordings of ambient noise with electrical resistivity tomography (ERT) surveys to explore the potential of drawing information on structure and geometry of the deposit of a large rock avalanche triggered by the Mw 7.9 2008 Wenchuan earthquake, which dammed the Yangjia stream in the Sichuan Province (China). The substantial thickness and heterogeneity of this kind of deposits limit the application of standard geophysical techniques, like active seismic surveys, which require highly energetic sources and long linear geophone arrays to reach adequate investigation depths. Passive single-station methods, relying on ambient noise recordings to determine site resonance properties, controlled by the contrast between soft surface layers and a stiffer substratum, offer the opportunity of investigating subsoil properties down to larger depths. In particular, we use a recently developed technique, which isolates the contribution of Rayleigh waves to ambient noise and draws information on sub-soil properties from the inversion of Rayleigh wave ellipticity curves plotted as function of frequency. In this framework, the ERT data can support the ellipticity curve inversion, typically affected by highly non-univocal solutions, by providing constraints for defining of the thickness of the uppermost surficial layers. The results allowed inferring the overlap of different layers within the 2008 rock avalanche deposit, as well as estimating lateral variations in their thickness and S-wave (Vs) velocities.

Determining the hydrothermal flow media using seismicity properties in Kaliulo geothermal field, Semarang, Central Java, Indonesia

Geothermal system requires specific geological condition that allow deep circulation of ground water to extract heat from the heat source. Faults and fractures play a major role in the localization and evolution of hydrothermal flow on several scales. The research aim was to obtain the permeability pattern of hydrothermal fluid base on response of micro seismic waves to subsurface structures. In one dimensional structure, average Horizontal to Vertical (H/V) spectral ratios can be assumed to measure the ellipticity of fundamental mode Rayleigh wave. Hence the shape of H/V ratios can be used to estimate the shear-wave velocity profile. The poisson’s ratio value of the hot spring corresponds to the physical properties of rock containing fluids. The thickness of the sand deposit and the soft layer indicated in the hot spring zone. We interpreted that we have warm springs in the research area comes up by the fracture or fault zone and permeable zone of sand soil. The mixing waters flow to the earth’s surface through the structure.

Multi-drive level Vibroseis test to evaluate the non-linear response of soft soils

In this paper we present the results of a seismic experiment using data produced by an active Vibroseis source and varying the drive force level, during a standard seismic reflection survey. We observed a clear non-linear response that can be linked to the presence of shallow soft sediment layers. The variation of the applied vibration force induces a change in both propagation velocity and attenuation of the Rayleigh waves, and this implies that such parameters are non-linear functions of the wave energy. We analyze the soil non-linear behavior with respect to the estimated induced strain, in order to compare the collected data against the observed reduction of shear modulus and damping values as usually measured in laboratory experiments and reported in the literature. The use of multi-component receivers allowed us also to identify the Rayleigh wave ellipticity and hence the resonance frequency of the studied site. Using active source data, rather than passive micro-tremors of unknown origin, for these applications is a novel approach. Thus, we propose an alternative and efficient method to characterize the non-linear key parameters of the soil seismic response, based on the use of controlled sources of widespread use in exploration seismics. This approach may pave the way to the development of utterly new site characterization techniques.

Rayleigh-wave H/V ratio measurement from ambient noise cross-correlations and its sensitivity to VP: a numerical study

SUMMARY The promise of passive seismology has increasingly been realized in recent years. Given the expense in installing and maintaining seismic station networks, it is important to extract as much information from the measurements as possible. In this context, the ellipticity or H/V amplitude ratio of Rayleigh waves can prove to be a valuable observable in ambient noise seismology due to its complimentary sensitivity to subsurface structure, compared to phase and group-velocity dispersion, as well as its potential for constraining VP structure in addition to VS. However, the suitability of the Rayleigh H/V ratio in noise-based studies depends on the accurate interpretation of measurements made on multicomponent ambient-noise cross-correlations. We present a synthetic study that critically examines measurements commonly interpreted as the Rayleigh-wave H/V ratio, under realistic scenarios of spatially distributed and non-uniform noise sources. Using the surface wave terms of Green’s function in a laterally homogeneous medium, we rigorously model multicomponent cross-correlations for arbitrary noise-source distributions and extract from them standard estimates of the H/V ratio. Variation of these measurements as a function of VP is studied empirically, by brute-force simulation. We find that the measurements depart significantly from the theoretical Rayleigh-wave H/V for the medium in question, when noise sources are strongly directional or anisotropic. Love waves, if present in the cross-correlations, also have the potential to significantly bias interpretation. Accurate interpretation of the H/V ratio measurement thus rests on carefully modelling these effects. However, the sensitivity to VP structure is comparable to that of the classic Rayleigh-wave H/V. We also propose a new measurement for cross-correlations that has slightly greater sensitivity to VP. Finally, uncertainty analysis on synthetic tests suggests that simplistic interpretations of Rayleigh-wave ellipticity are only effective (in resolving VP structure) when the Love-wave contamination is negligible and measurement uncertainties are less than 10 per cent.

Site Characterization of Swiss Strong-Motion Stations: The Benefit of Advanced Processing Algorithms

ABSTRACTSince 2009, 91 new strong-motion stations were built for the renewal of the Swiss Strong Motion Network. Another nine stations will be installed until 2022. For each new station, an extensive site characterization study is performed to model the 1D seismic-velocity profile and, for some sites, the liquefaction potential. Geophysical (passive and active surface-wave methods) and geotechnical cone penetration test (CPT) with additional pore-pressure measurement (CPTu) and seismic CPT (SCPT) methods are used. Analyzing the passive and active recordings with a variety of established and advanced methods, the fundamental frequency of the site, the polarization of the wavefield, the Love- and Rayleigh-wave phase-velocity dispersion curves, and the Rayleigh-wave ellipticity function are retrieved. The liquefaction potential is assessed using CPTu. SCPT measurements are sometimes used to determine the shallow underground structure. The benefits of the combination of different appropriate methods are shown for two examples—the borehole station SBUS in Buochs and the upcoming borehole station SCME in Collombey-Muraz. At both the sites, the CPTu measurements show an elevated liquefaction potential. Combining the passive and active data, the dispersion curves for Love and Rayleigh waves and Rayleigh-wave ellipticity curves are retrieved over a wide-frequency range and inverted for the S-wave velocity profile, in which the shallow part is constrained by the active or SCPT data, the intermediate part by the dispersion curves of the passive methods, and the deepest part by the ellipticity information. For Buochs, the 1D SH-wave amplification functions modeled for the velocity profiles are compared with the empirical amplification for earthquake recordings. Finally, an overview of the site characterization results for 52 of the newly installed seismic stations is given.