Study of Seismic Noise Excited by the Anthropogenic and Natural Causes Using Seismometers and Distributed Acoustic Sensing

• Main Author: Xiao, Han
• Other Authors: Tanimoto, Toshiro TT
• Format: Thesis
• Language: English
• Published: eScholarship, University of California 2022
• Subjects: Geophysics; Geology; Geotechnology; Greenland
• Online Access: https://escholarship.org/uc/item/05p6f7xh; https://escholarship.org/content/qt05p6f7xh/qt05p6f7xh.pdf

Seismic noise is the continuous vibration of the ground due to various non-earthquake causes and is generally regarded as an unwanted component of the signal recorded by a seismograph. Its primary sources include human activity, ocean waves, wind, and atmospheric phenomena. It has long been discarded in seismic analysis but it contains valuable information about its excitation sources and Earth structure. This thesis aims at exploring two main components of seismic noise: anthropogenic noise (human activity) and microseisms (ocean waves). It attempts to clarify noise source characteristics, excitation mechanisms, and propagation processes. By using seismic records from seismometers and Distributed Acoustic Sensing (DAS), and applying several processing techniques, we show discoveries on patterns of human behavior, SH-wave microseisms excitation mechanisms, and precise microseism source locations.First, in Chapter 2, in regards to the anthropogenic noise, we find seismic noise is positively correlated with human activity and economic development over 20 years. We choose an iconic event: the COVID-19 pandemic to study human response recorded in seismic noise records, on the ground that cities in mainland China and Italy imposed restrictions on travel and daily activities in response to COVID-19. It gives us an unprecedented opportunity to study the relationship between human behavior and seismic noise. In this study, we are primarily concerned with seismic noise with frequencies above 1 Hz, known as "cultural noise", mainly generated by local transportation systems. We demonstrate that seismic noise can provide an absolute real-time, anonymous characterization of human activity. In Chapter 3, with respect to the microseisms in the frequency band 0.05-0.5 Hz, we present body-wave microseisms caused by two remote low-pressure systems off the coast of southeastern Australia and southeastern Greenland, detected by a large, dense array (~350 stations) in China. We then use two years of data to study the noise sources ...