scholarly journals Shear velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations

2010 ◽  
Vol 115 (B5) ◽  
Author(s):  
Y. Behr ◽  
J. Townend ◽  
S. Bannister ◽  
M. K. Savage
Keyword(s):  
New Zealand ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity

scholarly journals Shear velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations

2021 ◽  
Author(s):  
Y Behr ◽  
John Townend ◽  
S Bannister ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Love Wave ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Receiver Function ◽  
Shear Velocity ◽  
Moho Depth ◽  
Noise Correlation ◽  
Linear Pattern ◽  
Noise Field

Ambient noise correlation has been successfully applied in several cases to regions with dense seismic networks whose geometries are well suited to tomographic imaging. The utility of ambient noise correlation-based methods of seismic imaging where either network or noise field characteristics are less ideal has yet to be fully demonstrated. In this study, we focus on the Northland Peninsula of New Zealand using data from five seismographs deployed in a linear pattern parallel to the direction from which most of the ambient noise arrives. Shear wave velocity profiles computed from Rayleigh and Love wave dispersion curves using the Neighborhood Algorithm are in good agreement with the results of a previous active source refraction experiment and a teleseismic receiver function and surface wave analysis. In particular, we compute a path-averaged Moho depth of ̃28 km along a ̃250 km profile. The use of both Rayleigh and Love wave measurements enables us to estimate the degree of radial anisotropy in the crust, yielding values of 2-15%. These results demonstrate that ambient noise correlation methods provide useful geophysical constraints on lithospheric structure even for nonoptimal network geometries and noise field characteristics. © 2010 by the American Geophysical Union.

scholarly journals Shear velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations

2021 ◽  
Author(s):  
Y Behr ◽  
John Townend ◽  
S Bannister ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Love Wave ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Receiver Function ◽  
Shear Velocity ◽  
Moho Depth ◽  
Noise Correlation ◽  
Linear Pattern ◽  
Noise Field

Ambient noise correlation has been successfully applied in several cases to regions with dense seismic networks whose geometries are well suited to tomographic imaging. The utility of ambient noise correlation-based methods of seismic imaging where either network or noise field characteristics are less ideal has yet to be fully demonstrated. In this study, we focus on the Northland Peninsula of New Zealand using data from five seismographs deployed in a linear pattern parallel to the direction from which most of the ambient noise arrives. Shear wave velocity profiles computed from Rayleigh and Love wave dispersion curves using the Neighborhood Algorithm are in good agreement with the results of a previous active source refraction experiment and a teleseismic receiver function and surface wave analysis. In particular, we compute a path-averaged Moho depth of ̃28 km along a ̃250 km profile. The use of both Rayleigh and Love wave measurements enables us to estimate the degree of radial anisotropy in the crust, yielding values of 2-15%. These results demonstrate that ambient noise correlation methods provide useful geophysical constraints on lithospheric structure even for nonoptimal network geometries and noise field characteristics. © 2010 by the American Geophysical Union.

Inferring shear-velocity structure of the upper 200 m using cultural ambient noise at the Ngatamariki geothermal field, Central North Island, New Zealand

2016 ◽  
Vol 4 (3) ◽  
pp. SJ87-SJ101 ◽  
Author(s):  
Francesco Civilini ◽  
Aasha Pancha ◽  
Martha Kane Savage ◽  
Steven Sewell ◽  
John Townend
Keyword(s):  
New Zealand ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Geothermal Field ◽  
S Wave ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Spatially Correlated ◽  
Geothermal Wells

We have determined subsurface structure using the refraction microtremor (ReMi) method at the Ngatamariki geothermal field, Central North Island, New Zealand. The local geology is such that refraction and reflection studies are hindered by energy scattering and attenuation in the near-surface layers. The ReMi method uses surface waves from ambient noise and active sources to determine S-wave velocities in the shallow subsurface. We have deployed two lines of 72-channel, 10 Hz vertical geophones with 10 m spacing, and we were able to model near-surface S-wave velocity to depths of 57–93 m for 2D profiles and as much as 165 m for 1D profiles. Shear-velocity anomalies were detected on one line that were spatially correlated with a fault. The location of the fault was previously inferred from stratigraphic offset in the geothermal wells, suggesting that the ReMi method can provide important constraints on near-surface geology in noisy geothermal settings.

Near-surface Structure of Downtown Jinan, China: Application of Ambient Noise Tomography with a Dense Seismic Array

2019 ◽  
Vol 24 (4) ◽  
pp. 641-652
Author(s):  
Feng Liang ◽  
Zhihui Wang ◽  
Hailong Li ◽  
Kai Liu ◽  
Tao Wang
Keyword(s):  
Surface Wave ◽  
Human Activities ◽  
High Frequency ◽  
Urban Areas ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Ambient Noise Tomography ◽  
Surface Wave Dispersion ◽  
Near Surface

Urban geophysics ups the ante in the world of applied geophysics, which requires innovative thinking and seemingly off-the-wall approaches, if for no other reason than the settings. Ambient-noise-tomography (ANT) can play a pivotal role in yielding subsurfa2ce information in urban areas, which is capable of dealing with challenges related to these scenarios ( e.g., human activities and low signal-to-noise ratio). In this study, the ANT was conducted to investigate the near-surface shear-velocity structure in the surrounding area of the Baotu Spring Park in downtown Jinan, Shandong Province, China. Quiet clear Rayleigh waves have been obtained by the cross-correlation, which indicates that strong human activities, such as moving vehicles and municipal engineering constructions, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surface-wave tomographic method with period-dependent ray-tracing was used to invert all surface-wave dispersion data in the period band 0.2-1.5 s simultaneously for 3D variations of shear-velocity (Vs) structure. Our results show a good correspondence to the geological features with thinner Quaternary sediments, the geological structural characteristic of the limestone surrounded by the igneous which has the highest velocity than that of the limestone in the study area, and several concealed faults of which specific location has been detected at depth. The results demonstrate that it is possible to successfully use ANT with high-frequency signal in an urban environment provided a detailed planning and execution is implemented.

scholarly journals High-resolution 3D shallow crustal structure in Long Beach, California: Application of ambient noise tomography on a dense seismic array

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. Q45-Q56 ◽  
Author(s):  
Fan-Chi Lin ◽  
Dunzhu Li ◽  
Robert W. Clayton ◽  
Dan Hollis
Keyword(s):  
Phase Velocity ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Seismic Array ◽  
Clear Correlation ◽  
Long Beach ◽  
Ambient Noise Tomography ◽  
Station Pair ◽  
Dense Seismic Array

Ambient noise tomography has proven to be effective in resolving shallow earth structure. We applied ambient noise tomography on a dense seismic array in Long Beach, California. The array was composed of more than 5200 stations with an average spacing close to 100 m. Three weeks of passive ambient noise were crosscorrelated between each station pair, which resulted in more than 13.5 million crosscorrelations within the area. Clear fundamental-mode Rayleigh waves were observed between 0.5 and 4 Hz, which were most sensitive to structure above 1-km depth. For each station pair, we applied frequency-time analysis to determine the phase traveltime dispersion, and, for each frequency, we applied eikonal tomography to determine the Rayleigh wave phase velocity map. The eikonal tomography accounted for ray bending by tracking the wavefront and allowed uncertainties to be estimated through statistical analysis. The compilation of phase velocity maps was then used to invert for 3D shear velocity structure. The inverted model showed clear correlation with the known geologic features such as the shallow south–north velocity dichotomy and a deeper fast anomaly associated with the Newport-Inglewood fault zone. Our results can potentially be used to complement traditional active source studies.

Studies of seismic velocities in subduction zones from continuous OBS data

2020 ◽  
Author(s):  
Weiwei Wang ◽  
Martha Savage ◽  
Alec Yates ◽  
Shu-Huei Hung ◽  
Yinhe Luo ◽  
...  
Keyword(s):  
New Zealand ◽  
Shear Wave ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Okinawa Trough ◽  
Phase Velocities ◽  
Velocity Changes ◽  
S Period ◽  
Shear Wave Velocity Structure

<p>In recent years, Ocean Bottom Seismometers (OBSs) have become widely used to expand the coverage of seismic networks onto the ocean. This study takes advantage of offshore observations at the northern end of the Hikurangi margin and southwestern Okinawa Trough to study the tectonics in both regions.</p><p>In the Hikurangi subduction zone, slow slip events (SSEs) have been observed, which are caused by the subduction of the Pacific Plate under New Zealand. The behaviour of SSEs and how they influence the physical properties of Earth materials are open to question. From 2014 to 2015, 15 OBSs were deployed offshore Gisborne, New Zealand on the Hikurangi margin. Ambient noise data from the OBSs are used to study velocity changes related to SSEs. Single station cross-component correlations and auto-correlations are computed, from which coda waves are used to monitor the velocity changes before, during and after the SSEs in 2014 and 2015 to analyse the slow earthquake behaviour and its relation to stress changes. Different rotation on horizontal components is tested by rotating horizontal components to N-E direction and parallel-perpendicular to the coastline. The dv/v computed by different components or rotation show different changes. The averaged dv/v displays a 0.1% velocity decrease during the SSE in October 2014.</p><p>The southwestern Okinawa Trough tapers towards Taiwan. How the back-arc crust accommodates the narrowing processing remains to be understood. At various times between 2010 and 2017, 22 OBSs on a small scale (~0.2°×0.3°) were deployed in Southwestern Okinawa Trough offshore northeast Taiwan. Ambient noise recorded on vertical velocity and pressure sensors is used to retrieve Scholte waves for studying shear wave velocity structure. Phase velocities are forward-modeled according to a model proposed by Kuo et al. 2015 and shear strength and density results from ODP1202. Phase velocity dispersion curves are measured from cross-correlations and unwrapped according to the modeled phase velocities. The fundamental mode phase velocities averaged from different station pairs are 0.62 km/s at 3 s period and 1.56 km/s at 6.5 s period. A 3D inversion will be conducted for a shear wave velocity structure from the basin center to the edge.</p>

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