Poster

[NS-P-01] Statistical analysis of the Vs30 structure of Almeria city (Southeast of Spain) inferred from topographic slope method

*Fernando López¹, Manuel Navarro², Pedro Martínez-Pagán³, Antonio García-Jerez², Jaruselsky Pérez-Cuevas⁴, Takahisa Enomoto⁵ (1. Civil Protection Service of Junta de Andalucía, Almería, Spain (Spain), 2. Department of Chemistry and Physics, University of Almería, 04120 Almería, Spain (Spain), 3. Department of Mining and Civil Engineering, Universidad Politécnica de Cartagena, 30203 Cartagena, Spain (Spain), 4. Engineering Sciences, Pontificia Universidad Católica Madre y Maestra, 2748 Santo Domingo, Dominican Republic (Dominican Republic), 5. Department of Building Engineering, University of Kanagawa, Yokohama, Japan (Japan))

The topographic slope method is an innovative, fast and very low-cost technique to estimate the average S-wave velocity in the upper 30 m (Vs30) from the morphological characteristics of the surface. An indirect classification of the shallow urban geological structure of Almeria city (SE of Spain) has been carried out in terms of Vs30 values, based on the relationship between this quantity and the slope of the ground, obtained through a Digital Elevation Model (DEM). The relationship between measured Vs30 values and topographic slope has been fitted assuming a log-normal distribution and considering two functional forms: a) linear relationship between measured values of log(Vs30) and topographic slope; b) fit also including linear dependence on the geologic units. The measured values of Vs30 were derived from previous research using Spatial Autocorrelation Surveys (SPAC) at ten open spaces and from 7.1 km of linear active seismic transects using Multichannel Analysis of Surface Waves (MASW), all performed in the study area. The statistical comparison of the results obtained from the two models shows the weightiness of including indicator variables for the geologic units in the correlation. The average reliability evaluated by multiple R-squared varies between 79.1% using linear relationship between measured log(Vs30) values and topographic slope and 86.9% including indicator variables for the geologic units.

The comparison of the residuals obtained from the model proposed by Wald and Allen (2007), using the corresponding coefficients associated with tectonically active regions, with those obtained in this work for local samples of Vs30 values and including geologic units highlights the importance of using site specific correlations. Thus, the mean absolute values of the residuals are reduced from 74.7 m/s in the first case to 29.0 m/s in the second one.