A systematic analysis of basin effects on surface ground motion
"Basin effects" refers to trapped and reverberating earthquake waves in soft sedimentary deposits overlying convex depressions of the basement bedrock, which significantly alter frequency content, amplitude, and duration of seismic waves. This has played an important role on shaking duration and intensity in past earthquakes such as the M_w 8.0 1985 Michoa'can, Mexico, M_w 6.9 1995 Kobe, Japan, and M_w 7.8 2015 Gorkha, Nepal. Although the phenomenon has been understood and addressed in the literature, it has not been fully incorporated in seismic hazard analysis, and Ground Motion Prediction Equations (GMPE). In this study, we perform an extensive parametric study on the characteristics of surface ground motion associated with basin effects using finite element simulations. We use an elastic medium subjected to vertically propagating SV plane waves and utilize idealized basin shapes to examine the effects of basin geometry and material properties. We specifically study the effects of four dimensionless parameters, the width-to-depth (aspect) ratio, the rock-to-soil material contrast, a dimensionless frequency that quantifies the depth of the basin relative to the dominant incident wavelength, and a dimensionless distance quantifying distance of the basin edges relative to the dominant wavelength. Our results show that basin effects can be reasonably characterized using at least three independent parameters, each of which can significantly alter the resultant ground motion. To demonstrate the application of dimensional analysis applied here, we investigate the response of the Kathmandu Valley during the 2015 M_w 7.8 Gorkha Earthquake in Nepal using an idealized basin geometry and soil properties. Our results show that a simplified model can capture notable characteristics of the ground motion associated with basin effects which suggests that such studies can provide useful insights, relevant to the parameterization of basin effects in GMPEs and design code provisions.
© 2020 Elsevier Ltd. Received 11 February 2020, Revised 26 October 2020, Accepted 31 October 2020, Available online 28 December 2020. This work was partially supported by the Terrestrial Hazard Observation and Reporting (THOR) Center at Caltech. THOR, a joint venture by the Division of Geological and Planetary Sciences and the Division of Engineering and Applied Sciences, is made possible by an endowed gift from Foster and Coco Stanback. Their support is hereby acknowledged. CRediT authorship contribution statement: Peyman Ayoubi: Analysis, writing and editing. Kami Mohammadi: Conceptualization, Analysis, writing, review and editing. Domniki Asimaki: Supervision, review. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Submitted - Ayoubi_2020_Basin_Parametric_Study_Arxiv.pdf