Isoperiods maps using spectral families for the seismic microzonation of Lima Metropolitan Area, Peru

An isoperiod map is proposed using spectral families in Metropolitan Lima with the aim of improving the seismic microzonification of the city. For that purpose, empirical transfer functions were used in 170 locations along the city obtained using the H/V spectral ratio method with earthquakes and microtremors records. The earthquake records were obtained throughout the city from the Lima accelerographic network and microtremors were recorded only using broadband seismometers, due to the unreliable results provided by acelerometers according to previous studies. The empirical transfer functions were grouped into spectral families with which the isoperiod map is developed. From this map, seismic zones are delimited and the microzonation map is generated. Moreover, local isoperiod maps for the districts of La Molina and Bellavista are presented and compared with previous research. These districts have different geotechnical typefaces and have been cataloged as places with a strong amplification due to soil effects by seismic history and recent studies. In addition to an isoperiod map, isoamplitudes and soil thickness maps were constructed for Lima metropolitan and they were the basis for proposing new classification of soils. Firstly, Zone I or hill Zone, represented as Rock, does not show any amplification in the frequency band between 0.1 a 1.0 seconds. Then, Zone II or Transition Zone that has a relative amplification less than four times in the band of 0.1 to 0.2 seconds, and soil thicknesses colluvial less than 10 meters. Zone III or Low Zone A that has relative amplification values up to 7 times in the band between 0.2 and 0.5 seconds, whose thicknesses of its soils colluvial and strata of poorly graded sand between 10 to 25 m thick. And, finally, Zone IV or Zone B that has relative amplification values up to 6 times between 0.5 to 1.4 sec, which covers the central and deepest part of the valley, consisting mostly of fine and sandy soils of great power up to 35 m. The results aim to contribute to future revisions of the seismic code. Furthermore, the methodology is intended to be the basis of a different approach to the soils dynamics evaluation that can produce a more accurate microzonation map of the metropolitan city.