Browsing by Author "Deng, Sizhuang"
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Item Autocorrelation Analysis of the Seismic Data Recorded on Mars(2022-12-02) Deng, Sizhuang; Levander, AlanThere are eight planets in our solar system, which can be divided into two categories, terrestrial planets and Jovian planets. Mars, the last terrestrial planet away from the sun, is the target we want to investigate in this thesis. Mars has a very thin atmosphere and ice caps in its polar areas. Knowledge of the Martian interior informs theories for the formation and dynamic evolution of another terrestrial planet, hence providing information on the history of the solar system. On Earth, subsurface structure is discovered by analysis of seismic signals recorded by large seismograph arrays deployed worldwide. The InSight (Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport) lander carried one seismic station to Mars at the end of 2018, providing the opportunity to investigate the internal structure of Mars. As only one station is deployed on Mars to record seismic vibrations, some tomographic and imaging methods based on seismic array analysis are not suitable to investigate Mars data. In this thesis, we applied the autocorrelation method to retrieve two types of seismic phases, body-wave reflection signals and Mars orbiting surface wave signals. The body-wave reflection signal originated from subsurface interfaces of Mars can inform the depth range of these seismic boundaries, including Moho, olivine-wadsleyite transition and core-mantle boundary. As for Mars orbiting surface waves, it can be used to improve the velocity models of Martian upper mantle.Item Autocorrelation R2 on Mars(Wiley, 2022) Deng, Sizhuang; Levander, AlanA purpose of the Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport (InSight) mission is to reveal the Martian interior structure with seismic data. In this work, ambient noise autocorrelation of the continuously recorded vertical-component seismic signals has extracted the Rayleigh waves that propagate around Mars for one cycle, R2. The Mars orbiting surface waves are observed at a lag time of ∼6,000 s in the stacked autocorrelation series filtered between 0.005 and 0.01 Hz. Synthetic seismograms from a set of radially concentric velocity models were computed to find the best-fitting one as the starting model for a Monte Carlo inversion. The starting model was randomly perturbed iteratively to increase the correlation coefficients and reduce the absolute time shifts between the synthetic and observed R2. An S-wave low-velocity layer in the inverted velocity model extends to ∼400 km depth, consistent with Marsquake observations, geophysical inversion, and high-pressure experiments.Item Autocorrelation Reflectivity of Mars(Wiley, 2020) Deng, Sizhuang; Levander, AlanThe seismic structure of the Martian interior can shed light on the formation and dynamic evolution of the planet and our solar system. The deployment of the seismograph carried by the InSight mission provides a means to study Martian internal structure. We used ambient noise autocorrelation to analyze the available vertical component seismic data to recover the reflectivity beneath the Insight lander. We identify the noise that is approximately periodic with the Martian sol as daily lander operations and the diurnal variation in Martian weather and tides. To investigate the seismic discontinuities at different depths, the autocorrelograms are filtered and stacked into different frequency bands. We observe prominent reflection signals probably corresponding to the Martian Moho, the olivine-wadsleyite transition in the mantle, and the core-mantle boundary in the stacked autocorrelograms. We estimate the depths of these boundaries as ~35, 1,110–1,170, and 1,520–1,600 km, consistent with other estimates.