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Microseisms are the most energetic signals of Earth's ambient noise field. Locating the sources of microseisms helps us to understand arrivals on noise cross‐correlation functions (NCFs) and the asymmetric amplitude of Rayleigh waves on the positive and negative parts of the NCFs. Using a dense broadband seismic array in eastern China, we investigated temporal and spatial characteristics of Rayleigh wave microseisms in the frequency range of 45–155 mHz by conducting beamforming and Rayleigh wave amplitude‐azimuth variation analyses. Seasonal variations of incident direction are clearly observable at the primary microseisms frequency band (45–95 mHz) but are less prominent at the secondary microseisms frequency band (95–155 mHz). The beamforming and amplitude‐azimuth variation analyses also indicated that microseisms arriving at the array are dominantly from five back azimuthal bands. To locate the source areas of the observed microseisms, we combined noise data from two additional arrays in southern California and employed a multi‐array beamforming technique to constrain plausible microseisms' source areas. We found that microseisms of the five azimuthal bands were excited at the Southern Ocean, western coast of Europe, coastal areas of the North Pacific Ocean, the Kerguelen Islands in the southern Indian Ocean, and the Polynesia islands in the South Pacific Ocean, respectively.

We continuously monitor the long-term seismic velocity variation of one of the major ruptured faults of the devastating 2008 M w 7.using accurately controlled routinely operated signal system active source and seismic noise-based monitoring technique. Our measurements show that the temporal velocity change is not homogeneous and highly localized in the damaged fault zone and the adjacent areas. Velocity variations from the active and passive methods are quite consistent, which both are characterized by ±0.2 % seasonal variation, with peak and trough at winter and summer, respectively. The periodic velocity variation within fault zone exhibits remarkably positive correlation with barometric pressure with stress sensitivity in the order of 10 -6 Pa -1 , suggesting that the plausible mechanism might be the crack density variation of the shallow subsurface medium of the damaged fault zone in response to the cyclic barometric pressure loading.

Basin resonances can significantly amplify and prolong ground shaking, and accurate site‐amplification estimates are crucial for mitigating potential seismic hazards within metropolitan basins. In this work, we estimate the site amplification of long‐period (2–10 s) ground motions across northeast China for both surface waves and vertically incident shear waves. The spatial distribution of relatively large site amplifications correlates strongly with known sedimentary basins for both wave types. However, the site response of surface waves is typically twice as high as that of shear waves at most basin sites. We further show that these site‐amplification features can be well explained by predictions based on the local one‐dimensional structure at each site. Our results highlight the importance of accounting for surface‐wave contributions and demonstrate the usefulness of semi‐analytical theory for surface‐wave amplification, which may be broadly applicable in future seismic hazard analysis.