Journal of Geology & Geophysics
Open Access

Seismic Data and Shear Wave Splitting in Local Earthquakes

Souhila Benfedda^{* *}Correspondence: Souhila Benfedda, Department of Physics, Institute of Earth Sciences, University of Évora, Évora, Portugal, Email:

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Description

Seismic data, acquired through the study of local earthquakes, provides a significance into the Earth's interior. One of the advanced techniques employed in seismic studies is shear wave splitting analysis, which unveils the complexities of subsurface structures and seismic anisotropy. This article will delve into the scientific intricacies of seismic data and the application of shear wave splitting to unravel the secrets concealed within the Earth's crust.

Seismic data, gathered from the vibrations of the Earth during seismic events, serves as a powerful tool for probing the Earth's internal structure. Earthquakes generate seismic waves, including compressional waves (P-waves) and shear waves (S-waves), which travel through the Earth at different velocities. Seismic sensors record the arrival times and amplitudes of these waves, providing valuable information about the subsurface.

Seismic anisotropy and shear wave splitting

Seismic anisotropy refers to the directional dependence of seismic wave velocities within the Earth. Shear wave splitting is a phenomenon observed in S-waves, where a single incoming shear wave splits into two polarized waves with different arrival times. This splitting is caused by the anisotropic properties of the subsurface materials through which the seismic waves travel.

Key concepts

Fast and slow directions: Shear wave splitting results in two distinct shear wave arrivals–a faster wave (fast shear wave) and a slower wave (slow shear wave). The orientation of these waves provides information about the direction of anisotropy in the subsurface.

Crystalline alignment: Anisotropy often arises from the alignment of minerals or structural elements within rocks. The orientation of these aligned features influences the propagation of seismic waves, leading to shear wave splitting.

Shear wave splitting parameters

Splitting time: The time delay between the arrival of the fast and slow shear waves is a critical parameter. It provides information about the thickness and orientation of anisotropic layers within the Earth.

Fast direction: The azimuthal direction of the fast shear wave is a key parameter in shear wave splitting analysis. It indicates the orientation of the anisotropic structures responsible for the observed splitting.

Amplitude ratios: The relative amplitudes of the split shear waves offer insights into the degree of anisotropy. Changes in amplitude ratios can indicate variations in the properties of subsurface materials.

Applications of shear wave splitting in local earthquakes

Crustal structure imaging: Shear wave splitting aids in imaging the crustal structure beneath seismically active regions. Variations in splitting parameters can highlight changes in the composition and alignment of subsurface materials.

Stress and strain analysis: By examining shear wave splitting patterns, scientists can infer information about the stress and strain conditions within the Earth's crust. This is particularly valuable for understanding tectonic processes and seismicity in local earthquake-prone regions.

Reservoir-induced seismicity studies: Shear wave splitting has proven useful in studying induced seismicity associated with reservoirs. Changes in seismic anisotropy patterns can indicate alterations in subsurface stress and fluid migration, providing insights into potential seismic hazards.

Volcano monitoring: Shear wave splitting is employed in monitoring volcanic regions, offering clues about magma movement and volcanic structure. Changes in splitting parameters can be indicative of volcanic processes and potential eruption risks.

Challenges and advances in shear wave splitting analysis

Despite its utility, shear wave splitting analysis faces challenges such as data quality issues, uncertainties in the subsurface structure, and the complexity of anisotropic patterns. Advances in computational methods, improved seismic instrumentation, and refined analytical techniques contribute to overcoming these challenges, enhancing the reliability of shear wave splitting results. Seismic data and shear wave splitting analysis constitute a sophisticated approach to unraveling the mysteries of the Earth's subsurface during local earthquakes. The insights gained from this technique provide a deeper understanding of the Earth's interior, aiding in the interpretation of tectonic processes, structural complexities, and seismic hazards. As technology advances and our analytical capabilities improve, shear wave splitting continues to be a valuable tool in the seismic scientific tools.