Effects of Realistic Surface Topography on Seismic Ground Motion in the Yangminshan Region of Taiwan Based Upon the Spectral-Element Method and LiDAR DTM

Abstract

We combine light detection and ranging (LiDAR) digital terrain model (DTM) data and an improved mesh implementation to investigate the effects of highresolution surface topography on seismic ground motion based upon the spectralelement method. In general, topography increases the amplitude of shaking at mountain tops and ridges, whereas valleys usually have reduced ground motion, as has been observed in both records from past earthquakes and numerical simulations. However, the effects of realistic topography on ground motion have not often been clearly characterized in numerical simulations, especially the seismic response of the true ground surface. Here, we use LiDAR DTM data, which provide two-meter resolution at the free surface, and a spectral-element method to simulate three-dimensional (3D) seismic-wave propagation in the Yangminshan region in Taiwan, incorporating the effects of realistic topography. A smoothed topographic map is employed beneath the model surface in order to decrease mesh distortions due to steep ground surfaces. Numerical simulations show that seismic shaking in mountainous areas is strongly affected by topography and source frequency content. The amplification of ground motion mainly occurs at the tops of hills and ridges whilst the valleys and flat-topped hills experience lower levels of ground shaking. Interaction between small-scale topographic features and high-frequency surface waves can produce unusually strong shaking. We demonstrate that topographic variations can change peak ground acceleration (PGA) values by 50% in mountainous areas, and the relative change in PGA between a valley and a ridge can be as high as a factor of 2 compared to a flat surface response. This suggests that high-resolution, realistic topographic features should be taken into account in seismic hazard analysis, especially for densely populated mountainous areas.

Spectral-Element Simulations of Seismic Waves Generated by the 2009 L'Aquila Earthquake

“…In addition, these studies highlight the ability of the SEM to accommodate such complexity in simulations at very high resolution (e.g., Lee, Chan, et al, 2009). In general, surface topography can cause complex wave propagation phenomena, with seismic energy reflected and scattered by mountain ridges (as shown by several studies, e.g., Massa et al, 2010, and references therein; Monteiller et al, 2013).…”

“…In general, surface topography can cause complex wave propagation phenomena, with seismic energy reflected and scattered by mountain ridges (as shown by several studies, e.g., Massa et al, 2010, and references therein; Monteiller et al, 2013). In particular, ground motions amplify on hilltops and along ridges (e.g., Çelebi, 1987;Kawase and Aki, 1990;Bouchon and Barker, 1996;Komatitsch and Vilotte, 1998;Lee, Chan, et al, 2009), with multiple reflections prolonging seismic shaking (e.g., Lee et al, 2008). Remarkable variations in PGV and acceleration values have been attributed to topography, highlighting its role for seismic-hazard assessment (e.g., Komatitsch and Vilotte, 1998;Lee, Chan, et al, 2009; Pischiutta et al (2010), and our simulation volume features relevant topographic relief.…”

“…Several studies document the importance of including realistic descriptions of surface topography to accurately reproduce seismic-wave propagation and surface ground motion (e.g., Kawase and Aki, 1990;Bouchon and Barker, 1996;Spudich et al, 1996;Komatitsch and Vilotte, 1998;Komatitsch et al, 2004;Lee et al, 2008;Lee, Chan, et al, 2009;Monteiller et al, 2013). In addition, these studies highlight the ability of the SEM to accommodate such complexity in simulations at very high resolution (e.g., Lee, Chan, et al, 2009).…”

“…In particular, ground motions amplify on hilltops and along ridges (e.g., Çelebi, 1987;Kawase and Aki, 1990;Bouchon and Barker, 1996;Komatitsch and Vilotte, 1998;Lee, Chan, et al, 2009), with multiple reflections prolonging seismic shaking (e.g., Lee et al, 2008). Remarkable variations in PGV and acceleration values have been attributed to topography, highlighting its role for seismic-hazard assessment (e.g., Komatitsch and Vilotte, 1998;Lee, Chan, et al, 2009; Pischiutta et al (2010), and our simulation volume features relevant topographic relief. As a consequence, inclusion of topography in our models turns out to be of fundamental importance for properly simulating observed ground motions.…”

Frequency‐Scaled Curvature as a Proxy for Topographic Site‐Effect Amplification and Ground‐Motion Variability

“…However, the complexity of the phenomenon (i.e., frequency and source dependencies, intrinsic 3D effects) makes it difficult to provide general models able to predict motion patterns in realistic topographic configurations. Recently, 3D numerical simulations of ground motions have been useful to estimate site effects on realistic, intricate topographies (Lee, Chan, Komatitsch, et al, 2009;Chaljub et al, 2010;Maufroy et al, 2012;De Martin et al, 2013). Nonetheless, this kind of sophisticated simulations remains computationally expensive and thus unsuitable for common seismic-hazard studies.…”