Assessing bedrock weathering patterns from P-wave and S-wave velocity profiles and their relationships to landscape positions.

Christina R. Kitamikado, Seulgi Moon, & Alan K. Yong

Submitted August 13, 2021, SCEC Contribution #11349, 2021 SCEC Annual Meeting Poster #063

P-wave and S-wave velocities (VP and VS) have historically been used to determine the geologic substrate, which directly influences localized earthquake ground-motions. Thus, knowledge about seismic site conditions is an important factor for estimating earthquake hazards. Previous studies have shown that subsurface processes, such as bedrock weathering, can mechanically weaken rocks, which results in the reduction of seismic velocities that would be reflected in VP and VS profiles. Recent studies of the critical zone have found that physical properties of bedrock affected by weathering vary depending on their landscape positions, such as on a ridge top or a valley bottom, likely due to topographically induced stress and hydrologic flow. However, no large spatial-scale studies have shown clear evidence for variations in near surface seismic velocity related to landscape positions. In this study, we examine whether we can infer subsurface weathering patterns and controls using dense VP and VS measurements that are widely available in Japan. We consider 1,613 strong-motion seismic stations and choose 649 stations that have paired borehole VP and VS measurements with maximum depth to 700 meters. Then, we examine the correlation between VP and VS profiles and various geomorphometrics, such as curvature and slope, and landscape position, as well as lithology. Our analyses show that there is good potential to improve understanding about relationships among near-surface seismic velocity distribution, subsurface critical zone structures, and topographic attributes. Therefore, these improvements can in-turn be directed at advancing our understanding about the influence of subsurface processes on seismic site conditions.

Key Words
Geomorphology, S-Wave, P-Wave, Critical Zone, Velocity Profiles

Citation
Kitamikado, C. R., Moon, S., & Yong, A. K. (2021, 08). Assessing bedrock weathering patterns from P-wave and S-wave velocity profiles and their relationships to landscape positions.. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology