Vs30 Structure of Murcia City (Southeast Of Spain) from Mini-Array Observations and HVSR Measurements

To evaluate the site effects in Murcia city, a classification of the shallow urban geological structure has been carried out by using the average S-wave velocity in the upper 30 m (Vs30) and the fundamental period. The structure of the ground has been characterized by measurements of ambient noise using the Mini-Array and the HVSR methods at 50 places with different geotechnical properties on a 1000 x 1000 m square grid. The records were obtained using a total of six seismometers simultaneously, three of them distributed along a circle of 60 cm of radius with a fourth in the centre and the other two forming an irregular triangle of 5 - 10 m side, together with the Mini-Array centre. The dispersion curves obtained have a frequency range from 5 to 50 Hz and phase velocities between 215 and 760 m/s. The Vs30 values vary between 235.7 m/s and 816.9 m/s. The lowest values of Vs30 are found around the Segura river (southern part of the city) as the higher values are distributed along the northern part of the city. HVSR results show clear peaks between 1 and 4 Hz in most of the analysed sites.