Effects of topography and basins on seismic wave amplification: the Northern Chile coastal cliff and intramountainous basins

Abstract

Summary During earthquakes, structural damage is often related to soil conditions. Following the 01 April 2014 Mw 8.1 Iquique earthquake in Northern Chile, damage to infrastructure was reported in the cities of Iquique and Alto Hospicio. In this study, we investigate the causes of site amplification in the region by numerically analyzing the effects of topography and basins on observed waveforms in the frequency range 0.1–3.5 Hz using the spectral element method. We show that topography produces changes in the amplitude of the seismic waves (amplification factors up to 2.2 in the frequency range 0.1–3.5 Hz) recorded by stations located in steep areas such as the ca. 1 km-high coastal scarp, a remarkable geomorphological feature that runs north–south, that is, parallel to the coast and the trench. The modeling also shows that secondary waves—probably related to reflections from the coastal scarp—propagate inland and offshore, augmenting the duration of the ground motion and the energy of the waveforms by up to a factor of three. Additionally, we find that, as expected, basins have a considerable effect on ground motion amplification at stations located within basins and in the surrounding areas. This can be attributed to the generation of multiple reflected waves in the basins, which increase both the amplitude and the duration of the ground motion, with an amplification factor of up to 3.9 for frequencies between 1.0 and 2.0 Hz. Comparisons between real and synthetic seismic waveforms accounting for the effects of topography and of basins show a good agreement in the frequency range between 0.1 and 0.5 Hz. However, for higher frequencies, the fit progressively deteriorates, especially for stations located in or near to areas of steep topography, basin areas, or sites with superficial soft sediments. The poor data misfit at high frequencies is most likely due to the effects of shallow, small-scale 3D velocity heterogeneity, which is not yet resolved in seismic images of our study region.

The December 9, 2020, Mw 5.5 Kudara earthquake (Middle Baikal, Russia): internet questionnaire hard test and macroseismic data analysis

“…The increased intensity in Irkutsk can be explained, in particular, by the local site effects. Systematic local amplification within a relatively small area during strong earthquakes is largely believed to be related to the geological structure and the subsoil conditions (Celebi 1987 ; Bouckovalas and Kouretzis 2001 ; Sbarra et al 2012 ; Burjánek et al 2014 ; García-Pérez et al 2021 ). The city of Irkutsk is located in the wide valley of the Angara River on its four terraces above the floodplain with Quaternary deposits, represented by alluvial, deluvial and eluvial complexes of more than 10 m thickness.…”

Estimating Ground Motion Intensities Using Simulation-Based Estimates of Local Crustal Seismic Response

“…Incorporation of any such influence could only constrain the variability so the results described here might be considered as a lower bound on the stability of the A field. The primary factor influencing ground motion amplification in this study is the basin geometry or buried topography, although the impact of surface topography is also anticipated to significantly affect the amplification pattern (García-Pérez et al, 2021;Geli et al, 1988;Lee et al, 2009;Poursartip et al, 2020). The surface topography, often rich in high-resolution data, is the most straightforward to control, and it is expected to contribute to the observed variability.…”

A framework for seismic response analysis of dams using numerical source‐to‐structure simulation

“…Therefore, it has been widely used in the simulation of seismic wave propagation at the global and local scales. [10][11][12][13][14] With the development of the physics-based ground motion simulations, the source-to-structure simulation, which is also called the "end-to-end simulation" has attracted increasing research attention in recent years. 10,[15][16][17][18] However, the seismic analysis for dams based on the source-to-structure simulation is still in its infancy.…”

“…Among those, the SEM combines the flexibility of the FEM and the accuracy of pseudo‐spectral method, making it suitable for parallel computing due to its diagonal mass matrix. Therefore, it has been widely used in the simulation of seismic wave propagation at the global and local scales 10–14 …”