Estimation of S-wave velocity profiles in the Matsumoto basin, Japan, from microtremor array exploration and seismic interferometry

Microtremor exploration was performed around seismic recording stations at five sites in Lima city, Peru in order to know the site amplification at these sites. The Spatial Autocorrelation (SPAC) method was applied to determine the observed phase velocity dispersion curve, which was subsequently inverted in order to estimate the 1-D S-wave velocity structure. From these results, the theoretical amplification factor was calculated to evaluate the site effect at each site. S-wave velocity profiles at alluvial gravel sites have S-wave velocities ranging from ∼500 to ∼1500 m/s which gradually increase with depth, while Vs profiles at sites located on fine alluvial material such as sand and silt have Swave velocities that vary between ∼200 and ∼500 m/s. The site responses of all Vs profiles show relatively high amplification levels at frequencies larger than 3 Hz. The average transfer function was calculated to make a comparison with values within the existing amplification map of Lima city. These calculations agreed with the proposed site amplification ranges.

Download Full-text

Application of passive and active seismic methods to subsurface investigation of Just-Tegoborze landslide (Outer Carpathians, Poland)

10.5194/egusphere-egu2020-12652 ◽

2020 ◽

Author(s):

Paulina Harba ◽

Krzysztof Krawiec

Keyword(s):

Wave Velocity ◽

Seismic Noise ◽

Slip Surface ◽

Seismic Refraction ◽

Seismic Interferometry ◽

Geological Medium ◽

S Wave ◽

Passive Seismic ◽

Outer Carpathians ◽

Velocity Changes

The study presents the results of seismic measurements on the Just-Tegoborze landslide located in Outer Carpathians in the southern region of Poland. The aim of the study was to investigate the landslide geological subsurface and define S-wave velocity changes within geological medium using passive seismic interferometry (SI) and active multichannel analysis of surface waves (MASW). Additionally, seismic refraction and numerical slip surface calculations were carried out in order to combine the results.Measurements of SI were conducted based on local high-frequency seismic noise generated by heavy vehicles passing state road which intersects Just-Tegoborze landslide. Seismic noise registration was made using three-component broadband seismometers installed along a seismic profile. Measurements were repeated in a few series in different season and hydration conditions.Seismic sections show different velocity layers within the landslide medium. Comparing them with geological cross-section of the studied area, we can distinguish the main lithological boundaries. First near-surface seismic layers may correspond to clayey colluvium and clayey-rock colluvium. The deepest seismic layer probably correlates to less weathered flysch bedrock made of shales and sandstones. It can be identified as the main slip surface of the studied landslide.S-wave velocities within seismic profiles significantly varies between each measurement series of SI. It can be observed a decrease of S-wave velocity in March and July which is connected to seasonal weather and hydration conditions. Strong increase of hydration during melting snow cover in March and after heavy rainfalls in July resulted in loss of rigidity what presumably led to drop of S-wave velocity. Changes in hydration could also cause the variation of the course of the less weathered flysch bedrock boundary.Presented results of passive seismic interferometry measurements show that study of seismic noise can be applicable to subsurface identification of an active landslide. The example of Just-Tegoborze site indicates that based on seismic interferometry it is possible to observe changes in elastic properties of geological medium. It is worth to underline that SI and MASW complement each other in retrieving the information of Rayleigh surface wave. Combining the results with seismic refraction and numerical calculations allows to better image the landslide geological subsurface. Such observations may be helpful in assessing landslide threat.

Download Full-text

A comprehensive comparison between the refraction microtremor and seismic interferometry methods for phase-velocity estimation

Geophysics ◽

10.1190/geo2016-0654.1 ◽

2017 ◽

Vol 82 (6) ◽

pp. EN99-EN108 ◽

Cited By ~ 7

Author(s):

Zongbo Xu ◽

T. Dylan Mikesell ◽

Jianghai Xia ◽

Feng Cheng

Keyword(s):

Surface Wave ◽

Surface Waves ◽

Wave Velocity ◽

Velocity Estimation ◽

Seismic Interferometry ◽

S Wave ◽

Noise Sources ◽

Surface Wave Dispersion ◽

Near Surface ◽

Refraction Microtremor

Passive-source seismic-noise-based surface-wave methods are now routinely used to investigate the near-surface geology in urban environments. These methods estimate the S-wave velocity of the near surface, and two methods that use linear recording arrays are seismic interferometry (SI) and refraction microtremor (ReMi). These two methods process noise data differently and thus can yield different estimates of the surface-wave dispersion, the data used to estimate the S-wave velocity. We have systematically compared these two methods using synthetic data with different noise source distributions. We arrange sensors in a linear survey grid, which is conveniently used in urban investigations (e.g., along roads). We find that both methods fail to correctly determine the low-frequency dispersion characteristics when outline noise sources become stronger than inline noise sources. We also identify an artifact in the ReMi method and theoretically explain the origin of this artifact. We determine that SI combined with array-based analysis of surface waves is the more accurate method to estimate surface-wave phase velocities because SI separates surface waves propagating in different directions. Finally, we find a solution to eliminate the ReMi artifact that involves the combination of SI and the [Formula: see text]-[Formula: see text] transform, the array processing method that underlies the ReMi method.

Download Full-text

High-Resolution Crustal S-wave Velocity Model and Moho Geometry Beneath the Southeastern Alps: New Insights From the SWATH-D Experiment

Frontiers in Earth Science ◽

10.3389/feart.2021.641113 ◽

2021 ◽

Vol 9 ◽

Author(s):

Amir Sadeghi-Bagherabadi

Keyword(s):

High Resolution ◽

Wave Velocity ◽

Depth Map ◽

Velocity Model ◽

Velocity Profiles ◽

Dispersion Curves ◽

Crystalline Basement ◽

S Wave ◽

Basement Depth ◽

External Dinarides

We compiled a dataset of continuous recordings from the temporary and permanent seismic networks to compute the high-resolution 3D S-wave velocity model of the Southeastern Alps, the western part of the external Dinarides, and the Friuli and Venetian plains through ambient noise tomography. Part of the dataset is recorded by the SWATH-D temporary network and permanent networks in Italy, Austria, Slovenia and Croatia between October 2017 and July 2018. We computed 4050 vertical component cross-correlations to obtain the empirical Rayleigh wave Green’s functions. The dataset is complemented by adopting 1804 high-quality correlograms from other studies. The fast-marching method for 2D surface wave tomography is applied to the phase velocity dispersion curves in the 2–30 s period band. The resulting local dispersion curves are inverted for 1D S-wave velocity profiles using the non-perturbational and perturbational inversion methods. We assembled the 1D S-wave velocity profiles into a pseudo-3D S-wave velocity model from the surface down to 60 km depth. A range of iso-velocities, representing the crystalline basement depth and the crustal thickness, are determined. We found the average depth over the 2.8–3.0 and 4.1–4.3 km/s iso-velocity ranges to be reasonable representations of the crystalline basement and Moho depths, respectively. The basement depth map shows that the shallower crystalline basement beneath the Schio-Vicenza fault highlights the boundary between the deeper Venetian and Friuli plains to the east and the Po-plain to the west. The estimated Moho depth map displays a thickened crust along the boundary between the Friuli plain and the external Dinarides. It also reveals a N-S narrow corridor of crustal thinning to the east of the junction of Giudicarie and Periadriatic lines, which was not reported by other seismic imaging studies. This corridor of shallower Moho is located beneath the surface outcrop of the Permian magmatic rocks and seems to be connected to the continuation of the Permian magmatism to the deep-seated crust. We compared the shallow crustal velocities and the hypocentral location of the earthquakes in the Southern foothills of the Alps. It revealed that the seismicity mainly occurs in the S-wave velocity range between ∼3.1 and ∼3.6 km/s.

Download Full-text