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Determination of the seismic structure of the Earth based on joint analysis of gravimetric and seismometric data – a case study

Karkowska Kamila, Wilde-Piórko Monika, Dykowski Przemysław, Sękowski Marcin, Polkowski Marcin

Geology, Geophysics and Environment

2024

Vol. 50, no. 1

5--22

The evolution of the Earth’s surface is driven by external and internal forces, the latter of which can only be studied indirectly. Knowledge about the structure of the Earth’s interior is very important for modeling and predicting the processes occurring at the surface. This study presents a new concept of joint analysis of the gravimetric and seismometric recordings of earthquakes for determining the seismic structure of the Earth down to the depth of 1250 km. The proposed method allows the use of gravimetric data without the known full transfer function of the instrument. Group velocity dispersion curves of the fundamental mode of Rayleigh waves up to the period of 550 s are measured based on the joint analysis of the recordings of superconducting gravimeter and broadband seismometers operating at the same location in five testing sites in Europe, allowing for the exploration of a broader response for incoming seismic waves. Averaged dispersion curves for earthquakes around the world for each site are inverted by the weighted linear inversion and Monte Carlo methods to estimate the distribution of shear-wave seismic velocity in the Earth’s mantle. A comparison of the deterministic and probabilistic inversion methods can excellently demonstrate surface waves’ ability to determine the Earth’s mantle structure. The inversion results are compared with the global ak135 seismic model (Kennett et al. 1995) to verify the proposed method.

Reflected wave least squares reverse time migration with angle illumination compensation

Zhou Huamin, Chen Shengchang, Zhou Liming, Ren Haoran, Wu Rushan, Xiao Guoqiang

Acta Geophysica

2019

Vol. 67, no. 6

1551--1561

High-quality seismic data imaging plays an important role in the lithological interpretation of subsurface structures. However, high-quality imaging remains a challenging task. Based on the linear inversion theory of reflected wave equations, this paper proposes reflected wave least squares reverse time migration with angle illumination compensation to better balance the amplitude of seismic imaging. We use the reflected wave migration equation to unify forward and backward propagation, which helps to obtain an image with correct phase and symmetric waveform. Under the assumption that the spectrum of seismic wavefield remains unchanged, the Poynting vector method is used to efficiently calculate the propagation direction of seismic waveform and seismic illumination in the angle domain. During iteration, angle-domain illumination is used as a preconditioner to compensate for the amplitude of the iterated gradient terms based on the angle value. In this manner, we can enhance the imaging energy of steeply inclined structures. To improve the stability of linear inversion, the spatial derivative of the image is used as a regularized constraint term. Numerical tests show that the proposed method can suppress imaging noise as well as improve resolution and amplitude fidelity of the images. Furthermore, the inversed result can be used to estimate underground reflectivity, which is important for the further development of seismic inversion technology.