Three-dimensional S-wave Velocity Structure Research Articles

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

Three-dimensional S-wave velocity structure of the upper crust in the Guangdong-Hong Kong-Macao Greater Bay Area: insights into the basins structure and genesis of hot springs

Three-dimensional S-wave velocity structure of the upper crust in the Guangdong-Hong Kong-Macao Greater Bay Area: insights into the basins structure and genesis of hot springs

The lithospheric S-wave velocity structure beneath the NE Tibetan Plateau and its surrounding craton basins

It is essential to investigate the spatial distribution of the lithosphere and asthenosphere in detail, to further obtain the understanding of the effect of plate collision and the process of orogenic movement. From the joint inversion of receiver functions and surface waves, the three-dimensional S-wave velocity structure results down to 200 km depth in the study area were obtained at 1,843 seismic stations. Analysis was performed on the sedimentary thickness, crustal thickness, lower crustal wave velocity, and lithospheric thickness. According to the crustal thickness, we evaluated the distribution of low-velocity zones in the lower crust. The results show that there are low-velocity bodies in the lower crust in the Qinling tectonic belt, but they are not connected, indicating that they may not be able to be used as a channel for material extrusion from the NE Tibetan Plateau at the crustal scale. According to the section results and the depth distribution of the lithosphere-astenosphere boundary, a relatively thick lithosphere exists below the Sichuan Basin and Ordos Basin, and the lithosphere in the east of the study area is relatively thin with a thickness of about 60–80 km, indicating that the lithosphere in the east of the study area has been severely destructed and restructured. The delamination has been observed in the lithosphere under the Songpan-Ganzi Block, showing characteristics of vertical movement of asthenosphere materials. There is a relatively thick low-velocity zone at the top of the mantle lithosphere of the NE plateau; however, it does not exist under the relatively stable Sichuan Basin and the Ordos Block. Compared with the Sichuan Basin and the Ordos Basin at both sides, the Qinling tectonic belt has a low-velocity zone at the depth of 100–160 km, which may be asthenosphere material. In combination with the polarization direction characteristics of the SKS wave, it is clearly observed that asthenospheric material movement exists in an approximate east-west direction beneath the Qinling tectonic belt. Therefore, the asthenosphere beneath the Qinling tectonic belt may serve as an important channel for material extrusion in the NE Tibetan Plateau.

Urban near-surface imaging from ambient noise tomography using dense seismic networks

It is of scientific and engineering significance to extract surface wave signals from urban ambient noise for fine-scale three-dimensional velocity structure imaging of underground medium. A series of issues such as ambient noise characteristics in urban environment, observation system design and resolution of small-scale imaging, have put forward a lot of new requirements and challenges to traditional methods and technologies. We utilized the dense array with its aperture extend below hundred meters in Hangzhou urban area, to carry out the ambient noise data acquisition experiments within one day. Based on the time-frequency analysis of noise cross-correlations, we conducted surface wave travel time tomography. Finally, the phase velocity slices were inverted to build a three-dimensional S-wave velocity structure, and the profiles were compared with the drilling data for validations. We concluded that these geometry and processing parameters adopted in the urban environment are feasible for near-surface tomography and can meet the demands of three-dimensional geological survey in cities efficiently.

3D mantle structure of Central Asia from Rayleigh wave group velocity dispersion

The mantle structure in Central Asia was investigated by surface-wave tomography from dispersion of the fundamental mode of the Rayleigh wave group velocities along more than 3200 earthquake-station paths within 40° N to 60° N and 80° E to 132° E. The velocities were processed by the frequency-time analysis at periods from 10 to 250s to obtain their dispersion curves. Then group velocity maps were computed separately for each period, at different sampling intervals: at every 5s for the short periods from 10 to 30s, at 10s for periods between 30 and 100s, and at 25s for the longest periods of 100 to 250s. Resolution was estimated according to the effective averaging radius (R) and presented likewise in the form of maps. To estimate the depths of the revealed inhomogeneties, locally averaged dispersion curves were calculated using the group velocity maps, with reference to the radius R, and were then inverted to S-wave velocity-depth profiles. The resulting three-dimensional S-wave velocity structure to depths of about 700km revealed large lateral inhomogeneties through the entire depth range. This pattern may be due to the history of the major tectonic structures, as well as to ongoing processes in the mantle.

Estimating deep S-wave velocity structure in the Los Angeles Basin using a passive surface-wave method

This article summarizes a passive surface-wave method that uses only two sensors and its application to the estimation of deep S-wave velocity structure. Three-dimensional S-wave velocity structure to a depth of several kilometers has a large effect on long-period ground motion in tectonic basins, such as the Los Angeles (LA) Basin. Recent studies of long-period ground motion in the LA Basin (e.g., Hatayama and Kalkan, 2012) show that observed ground motion in some areas cannot be explained by the S-wave velocity models in current use. Most studies of basin velocity structure rely on geologic information, surface and borehole geophysical data, and observed earthquake records to deduce or measure seismic velocities. Geophysical data and seismic stations commonly used for velocity analysis are sparsely distributed and most well data are too shallow to characterize deep S-wave velocity structure. To establish more accurate basin velocity structure, there is a need for more densely distributed deep S-wave velocity data.

Three-dimensional S-wave velocity structure in eastern Tibet from ambient noise Rayleigh and love wave tomography

We apply ambient noise tomography to continuous three-component broadband seismic data between January 1, 2008 and December 31, 2008 from the regional networks of 76 stations deployed by China Earthquake Administration. Ambient noise cross-correlations were performed to produce the Green’s functions of each station-pair. Within the period from 6 to 50 s, Rayleigh and Love wave dispersion curves were measured using the multiple filter analysis method. Then three-dimensional (3-D) S-wave velocity structures from the surface down to 70 km are inverted from both Rayleigh and Love wave dispersion results. The obtained S-wave velocity maps show strong lateral variations and correlate well with the distinct geological and tectonic features in the study area. The Sichuan basin displays low velocity in shallow depth due to thick sedimentary deposits but high velocity in the mid-lower crust; the eastern Tibetan plateau is clearly featured with a low-velocity zone in its mid-to-lower crust which is consistent with the crustal flow model proposed to explain the mechanism of uplift and pattern of deformation for the Tibetan plateau. Meanwhile, our results also exhibit that the crustal thickness decreased from the eastern Tibetan plateau to the Sichuan basin.