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Profiling the Quito basin (Ecuador) using seismic ambient noise

Abstract : Quito, the capital of Ecuador, with more than 2.5 M inhabitants, is exposed to a high seismic hazard due to its proximity to the Pacific subduction zone and active crustal faults, both capable of generating significant earthquakes. Furthermore, the city is located in an intermontane piggy-back basin prone to seismic wave amplification. To understand the basin’s seismic re sponse and characterize its geological structure, 20 broad and medium frequency band seismic stations were deployed in Quito’s urban area between May 2016 and July 2018 that continuously recorded ambient seismic noise. We first compute horizontal-to-vertical spectral ratios to determine the resonant frequency distribution in the entire basin. Secondly, we cross-correlate seismic stations operating simultaneously to retrieve inter-stations surface-wave Green’s func tions in the frequency range of 0.1 - 2 Hz. We find that Love waves traveling in the basin’s longitudinal direction (NNE-SSW) show much clearer correlograms than those from Rayleigh waves. We then compute Love wave phase-velocity dispersion curves and invert them to obtain shear-wave velocity profiles throughout the city. The inversions highlight a clear difference in the basin’s structure between its northern and southern parts. In the center and northern areas, the estimated basin depth and mean shear-wave velocity are about 300 m and 1700 m.s−1, respectively, showing resonance frequency values between 0.6 and 0.7 Hz. On the contrary, the basement’s depth and shear-wave velocity in the southern part are about 1000 m and 2600 m.s−1, having a low resonance frequency value of around 0.3 Hz. This difference in structure between the center-north and the south of the basin explains the spatial distribution of low frequency seismic amplifications observed during the Mw 7.8 Pedernales earthquake in April 2016 in Quito.
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Contributor : Françoise Courboulex Connect in order to contact the contributor
Submitted on : Tuesday, December 28, 2021 - 9:00:32 PM
Last modification on : Saturday, April 2, 2022 - 3:38:04 AM
Long-term archiving on: : Tuesday, March 29, 2022 - 6:31:39 PM


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D Pacheco, E Mercerat, Françoise Courboulex, L Bonilla, A Laurendeau, et al.. Profiling the Quito basin (Ecuador) using seismic ambient noise. Geophysical Journal International, Oxford University Press (OUP), 2022, 228 (2), pp.1419-1437. ⟨10.1093/gji/ggab408⟩. ⟨hal-03442293⟩



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