scholarly journals Three-dimensional shear-wave quality factor, Qs(f), model for south-central Gulf of California, Mexico obtained from inversion of broadband data

2021 ◽  
Vol 60 (2) ◽  
pp. 140-160
Author(s):  
Sanjay Kumar ◽  
Anand Joshi ◽  
Raul R. Castro ◽  
Sandeep Singh ◽  
Shri Krishna Singh
Keyword(s):  
Quality Factor ◽  
Shear Wave ◽  
Gulf Of California ◽  
Wave Attenuation ◽  
Three Dimensional ◽  
Ocean Bottom ◽  
Inversion Algorithm ◽  
Attenuation Relations ◽  
South Central ◽  
Dependent Relation

Abstract          We apply an iterative inversion scheme, initially developed by Hashida and Shimazaki (1984) and later modified by Joshi et al., (2010), to estimate three - dimensional shear - wave quality factor, Qs(f), of south-central Gulf of California, Mexico. An area of 230 km x 288 km in this region is divided into 108 rectangular blocks of different Qs(f). We use 25 well-located earthquakes recorded at three broadband stations of the regional network RESBAN operated by CICESE (Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California) and three Ocean Bottom Seismographs (OBS) of the Sea of Cortez Ocean Bottom Array (SCOOBA) experiment.  This dataset permits us to obtain Qs(f) estimates of different blocks using the modified inversion algorithm. Qs(f) is obtained at various frequencies in 0.16 - 7.94 Hz range. We found that the estimated Qs structure correlates with geological and tectonic models of the region proposed in previous studies. A regional frequency-dependent relation using all 1944 values of shear-wave quality factor is obtained at 18 different frequencies in all blocks can be approximated by a function of the form Qs(f) = 20 f 1.2. This relation is typical in a tectonically active region with high S-wave attenuation and is similar to attenuation relations reported by other authors for the Imperial Valley, California region.

scholarly journals Three-dimensional shear wave structure beneath the Philippine Sea from land and ocean bottom broadband seismograms

2006 ◽  
Vol 111 (B6) ◽  
pp. n/a-n/a ◽  
Author(s):  
Takehi Isse ◽  
Kazunori Yoshizawa ◽  
Hajime Shiobara ◽  
Masanao Shinohara ◽  
Kazuo Nakahigashi ◽  
...  
Keyword(s):  
Shear Wave ◽  
Three Dimensional ◽  
Wave Structure ◽  
Ocean Bottom ◽  
Philippine Sea ◽  
Broadband Seismograms

Shear‐Wave Attenuation Study in the South Region of the Gulf of California, Mexico

2019 ◽  
Vol 109 (2) ◽  
pp. 600-609 ◽  
Author(s):  
Raúl R. Castro ◽  
Shri K. Singh ◽  
Anand Joshi ◽  
Sandeep Singh
Keyword(s):  
Shear Wave ◽  
Gulf Of California ◽  
Wave Attenuation ◽  
The South

scholarly journals Lorentz force induced shear waves for magnetic resonance elastography applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Guillaume Flé ◽  
Guillaume Gilbert ◽  
Pol Grasland-Mongrain ◽  
Guy Cloutier
Keyword(s):  
Magnetic Resonance ◽  
Shear Wave ◽  
Lorentz Force ◽  
Wave Attenuation ◽  
Shear Waves ◽  
Estimation Method ◽  
Biological Tissues ◽  
Magnetic Resonance Elastography ◽  
Motion Generation ◽  
Wave Source

AbstractQuantitative mechanical properties of biological tissues can be mapped using the shear wave elastography technique. This technology has demonstrated a great potential in various organs but shows a limit due to wave attenuation in biological tissues. An option to overcome the inherent loss in shear wave magnitude along the propagation pathway may be to stimulate tissues closer to regions of interest using alternative motion generation techniques. The present study investigated the feasibility of generating shear waves by applying a Lorentz force directly to tissue mimicking samples for magnetic resonance elastography applications. This was done by combining an electrical current with the strong magnetic field of a clinical MRI scanner. The Local Frequency Estimation method was used to assess the real value of the shear modulus of tested phantoms from Lorentz force induced motion. Finite elements modeling of reported experiments showed a consistent behavior but featured wavelengths larger than measured ones. Results suggest the feasibility of a magnetic resonance elastography technique based on the Lorentz force to produce an shear wave source.

scholarly journals Characteristics of relocated hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its aftershocks with a three-dimensional seismic velocity structure

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Saeko Kita
Keyword(s):  
Seismic Velocity ◽  
Three Dimensional ◽  
Double Difference ◽  
Earthquake Catalog ◽  
Seismic Structure ◽  
Depth Limit ◽  
High Attenuation ◽  
South Central ◽  
Collision Zone ◽  
Hidaka Collision Zone

AbstractI relocated the hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its surrounding area, using a three-dimensional seismic structure, the double-difference relocation method, and the JMA earthquake catalog. After relocation, the focal depth of the mainshock became 35.4 km. As previous studies show, in south-central Hokkaido, the Hidaka collision zone is formed, and anomalous deep and thickened forearc crust material is subducting at depths of less than 70 km. The mainshock and its aftershocks are located at depths of approximately 10 to 40 km within the lower crust of the anomalous deep and thickened curst near the uppermost mantle material intrusions in the northwestern edge of this Hidaka collision zone. Like the two previous large events, the aftershocks of this event incline steeply eastward and appear to be distributed in the deeper extension of the Ishikari-teichi-toen fault zone. The highly inclined fault in the present study is consistent with a fault model by a geodetic analysis with InSAR. The aftershocks at depths of 10 to 20 km are located at the western edge of the high-attenuation (low-Qp) zone. These kinds of relationships between hypocenters and materials are the same as the 1970 and 1982 events in the Hidaka collision zone. The anomalous large focal depths of these large events compared with the average depth limit of inland earthquakes in Japan could be caused by the locally lower temperature in south-central Hokkaido. This event is one of the approximately M7 large inland earthquakes that occurred repeatedly at a recurrence interval of approximately 40 years and is important in the collision process in the Hidaka collision zone.

scholarly journals Three-Dimensional Inversion of Borehole-Surface Resistivity Method Based on the Unstructured Finite Element

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Zhi Wang ◽  
Sinan Fang
Keyword(s):  
Numerical Solution ◽  
Surface Topography ◽  
Current Source ◽  
Three Dimensional ◽  
Surface Resistivity ◽  
Normal Equation ◽  
Inversion Algorithm ◽  
Field Source ◽  
Resistivity Method ◽  
Borehole Surface

The electromagnetic wave signal from the electromagnetic field source generates induction signals after reaching the target geological body through the underground medium. The time and spatial distribution rules of the artificial or the natural electromagnetic fields are obtained for the exploration of mineral resources of the subsurface and determining the geological structure of the subsurface to solve the geological problems. The goal of electromagnetic data processing is to suppress the noise and improve the signal-to-noise ratio and the inversion of resistivity data. Inversion has always been the focus of research in the field of electromagnetic methods. In this paper, the three-dimensional borehole-surface resistivity method is explored based on the principle of geometric sounding, and the three-dimensional inversion algorithm of the borehole-surface resistivity method in arbitrary surface topography is proposed. The forward simulation and calculation start from the partial differential equation and the boundary conditions of the total potential of the three-dimensional point current source field are satisfied. Then the unstructured tetrahedral grids are used to discretely subdivide the calculation area that can well fit the complex structure of subsurface and undulating surface topography. The accuracy of the numerical solution is low due to the rapid attenuation of the electric field at the point current source and the nearby positions and sharply varying potential gradients. Therefore, the mesh density is defined at the local area, that is, the vicinity of the source electrode and the measuring electrode. The mesh refinement can effectively reduce the influence of the source point and its vicinity and improve the accuracy of the numerical solution. The stiffness matrix is stored with Compressed Row Storage (CSR) format, and the final large linear equations are solved using the Super Symmetric Over Relaxation Preconditioned Conjugate Gradient (SSOR-PCG) method. The quasi-Newton method with limited memory (L_BFGS) is used to optimize the objective function in the inversion calculation, and a double-loop recursive method is used to solve the normal equation obtained at each iteration in order to avoid computing and storing the sensitivity matrix explicitly and reduce the amount of calculation. The comprehensive application of the above methods makes the 3D inversion algorithm efficient, accurate, and stable. The three-dimensional inversion test is performed on the synthetic data of multiple theoretical geoelectric models with topography (a single anomaly model under valley and a single anomaly model under mountain) to verify the effectiveness of the proposed algorithm.

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