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Detection and imaging of faults and other subsurface structures in urban settings

Institute of Geophysical and Geochemical Exploration (IGGE) of CAGS successfully performed a high density 2D and 3D combined survey in sub-center of Beijing in September, 2018, to get a high-resolution subsurface images and fault structures.

SmartSolo node seismic system is employed to minimize the impact on the environment and the local population. The subsurface fault structure in depth can be identified from the stacking profile.

LocationBeijing, China
Survey area483 m × 400 m
TargetFault detection (target depth: 600 m)
Survey2D + 3D High density seismic array
Channel countIGU-16 1C 5-Hz, 700 channels
SourceVibroseis,1600 VPs, sweep 10-130Hz, 12 s
Receiver interval5 m
Source interval10 m

Google Earth image of the survey area. The shot line is in red, and the color gradient indicates the fold density. (Shuiyu Luo, IGGE, 2018)

Geoscience Australia national geological survey

Geoscience Australia successfully completed a national Geological survey project (OSMT), to detect the deep crustal structures up to the depth of Moho interface through reflection profiling in 2017. The main object is to study the geodynamic evolution, assess mineral potential, and map natural hazard zones. The detailed information can be found at

http://www.ga.gov.au/about/projects/resources/seismic.

LocationSouth Lachlan, Australia
Survey line600 km
TargetDeep structure detection
Channel countIGU-16 1C 10 Hz, 5000 channels
SourceVibroseis, 24s sweep (20+ s listen), 4-96Hz
Receiver interval10 m
Source interval40 m

Australian natural gas exploration based on compressive sensing imaging (CSI)

SmartSolo is carrying out a practical exploration project in Australia based on compressed sensing technology, which is a popular research topic at present. SmartSolo nodal system is light, simple, and highly reliable. It is very suitable for being deployed in non-uniform spacing when the signal is processed using compressed sensing method. The production efficiency and HSE level are both improved.

LocationAustralia
Survey areaAbout 300 sq km
TargetNatural gas detection
Channel countIGU-16 1C 5Hz, 20000 chs
SourceVibroseis (EnviroVib)
Receiver intervalNominal 40m
Source intervalNominal 10m

Random receiver spacing in line

 

 

Pseudo-reflection profile through correlation of ambient noise

China University of Geoscience, Beijing, conducted a research on application of ambient noise imaging in August, 2018. This study attempts to apply the noise data to detect the shallow urban subsurface structure. Following result is from professor Lanbo Liu, 2018. As the result, correlation between first channel and all channels of the line and by correlation between two neighbor channels are very clear.

LocationBeijing, China
Survey line600 m
TargetFault detection
Channel countIGU-16 5 Hz, 200 channels
Receiver interval3 m

(Note: I replaced the old one by a more accurate setup of the array –Lanbo Liu)

Map view of fault strike (red line) and two survey lines (white line) along the road

S wave velocity inversion through Rayleigh wave dispersive curve

In June, 2018, Researchers from Jilin University got the S wave velocity from Rayleigh wave dispersive curve with 2 hours’ observation data, acquired by 10 IGU-16 1C (5 Hz) stations. The velocity curve is consistent with the logging data.

Layers indicated by S wave velocity (red curve) inversed from surface wave of ambient noise data (SPAC method) can be verified by the logging data. (Tian You, 2018)

Natural earthquake observation

In XinJiang, China, researchers from Institute of geology and geophysics of CAS deployed 50 pieces of IGU 3C 5-Hz along a 25 km long survey line to study the crustal thickness with receiver functions through earthquakes of large epicentral distance. The station interval was 500-m, which is denser than arrays using for this kind of study.

A number of earthquakes with magnitude above Mw 6.0 from Japan and Indonesia have been recorded. The signal has high SNR with the main frequency around 2 Hz.

Station survey Map

The vertical component data applied with low pass filter with corner frequency 10 Hz. The magnitude 6.5 earthquake occurred in Indonesian at 15:35:01, Aug 17th, 2018.The epicentral distance is about 6500 km.

Shear wave velocity inversion from ambient noise

In October, 2018, a field deployment of SmartSolo nodal system was successfully conducted to record ambient noise data in Henan, China. The purpose of the project is to monitor levee safety of hydraulic systems. The SmartSolo system is very convenient for this purpose.

LocationHenan, China
Graphics receivetriangle
Receiver point10 set
Receiver No10
Targetnatural source surface wave survey
Channel countIGU-16 1C 10 Hz,100 channels
Receive interval2 m

SmartSolo receivers were deployed in a triangular array.

 

The geometry of the triangular geometric receiver array

 

(Note: rotated -90 degrees, this is more conventional –Lanbo Liu)

S wave phase velocity dispersion curve extraction

 

 

 

 

 

 

 

SmartSolo receivers were deployed in a triangular array on the levees.

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