Soil classification based on spectral ratios where Central American accelerographic stations are located. Cases of El salvador, Nicaragua and Costa Rica

摘要

This research applies a common soil classification for sites where most of the Central American accelerographic stations are located. It is very necessary to adopt a uniform classification procedure for all sites, because usually the information provided by local agencies (accelerographic network administrators) is incomplete or based on subjective interpretations read from maps or observation of the surface geology. Moreover, precise knowledge of the soil type in which accelerograms are recorded is essential to validate the records for future researches. It was considered the information provided by each local agency to assign the soil type for each site, as well as the USGS (U.S. Geological Survey) Vs30 map and it was followed the procedure proposed by Zhao et al. (2006) based on the calculation of spectral average ratios of the horizontal component on the vertical, obtained from all available records at each station. Finally, it is assigned a score to each site according to coincidence or not of different mentioned classification criteria. 134 station sites were studied, which received the following qualification: A (26%), B (32%), C (17%) and D (25%), being A the best category and D the worst one. Only few stations were classified as S I (rock) and S IV (soft soil). Comparing the spectral ratios obtained by other authors for Japan, the amplifications obtained in the present study tend to be lower in almost the whole range of periods for the four considered soil types.