Evidence of soil amplification and damage in Centro, Tabasco, southern México due to distant large earthquakes

There are only a few worldwide cases where distant earthquakes have caused damage. One such example is the municipality of Centro located in Tabasco, Southeast Mexico, approximately 360 km from the Mesoamerican trench, where a strong ground shaking was felt during the M_w8.2 earthquake of September 08, 2017. In this study, for 20 sites shear-wave velocity profiles were determined using Multichannel Analysis of Surface Wave and V_P profiles using Seismic Refraction techniques. Also V_S30 (shear-wave velocity up to a depth of 30 m) values were obtained for the same sites. The distribution of the V_S30 values in the study area varied from 120 m/s to 570 m/s and it was observed that sites where damage to buildings were reported lie near areas with V_S30 < 270 m/s. Additionally, the transfer functions of the 20 sites were estimated using the Thomson-Haskell method. The fundamental frequencies (f₀) obtained through transfer functions had values varying from 0.9 ≤ f₀ ≤ 2.0 Hz. These transfer functions were convolved with the signal that represents the record in the bottom of the soil column in the study area to obtain synthetic accelerograms in the municipality of Centro. The only accelerograph station located in the study area (VHSA station) was used as a reference site. The horizontal-to-vertical spectral ratio of the VHSA location was used for site characterization to assess the effects of regional events. The study concludes that several factors contribute to the susceptibility of Centro municipality to distant seismic events. These factors include low shear-wave velocity (V_s), low fundamental frequency (f₀), local site conditions, the presence of buildings on former lake zones, low seismic wave attenuation, and the regions’ overall vulnerability to regional earthquakes.