Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama

Abstract

The City of David constitutes one of the most important commercial centers of the Republic of Panama. However, it is located on a coastal plane, close to an area with high seismic activity and has been affected by significant earthquakes (18 July 1934, Mw = 7.4 and 12 March 1962, Mw = 6.7). The goal of this study is to estimate the seismic effects and to classify the soil in the City of David. The experimental work entailed the measurement of environmental noise for H/V spectral ratio (HVSR) analyzed at 22 stations. A series of microtremor refraction studies (ReMi) at six stations distributed from north to south of the city was also performed. The stations were distributed around urban areas of the city, which are characterized by the presence of water supply, sewerage, buildings, roads, etc. The spectral analysis of environmental noise allowed the generation of three different types of maps: First, predominant frequency maps (f0) with zones composed mainly of rigid and semi-rigid soils in the southern end of the city and rigid soils in the central and northern regions. Secondly, maximum H/V amplitude maps (A0) which evidence a low range of HVSR amplitude in the city, ranging from 1.1 to 3.8. Finally, liquefaction vulnerability (Kg) maps, with values less than 2 Hz−1, representative of a low liquefaction risk. Soil classification using ReMi and calculation of the corresponding Vs30 reveal type D soils, which correlate well with results obtained using HVSR analyses. A comparison between HVSR and ReMi shows that HVSR curves that exhibit clear peaks tend to be related to ReMi stations that presented relatively large shear-wave velocity contrasts at some depth. The results from this research are intended to aid the decision-making process related to the future development of the city, as well as government level maintenance and mitigation plans.

Estudio Sísmico de Zonas Portuarias de David Mediante las Técnicas de Razón Espectral H/V (HVSR) y Refracción de Microtremores (ReMi)

“…En cada punto o estación de monitoreo, se generaron 20 archivos con 24 señales de ruido, cada una con una duración de 32 segundos, utilizando un intervalo de muestreo de 2 milisegundos. [6].…”

“…Los resultados como parte de este estudio [6] pueden ser importantes para la construcción de nuevas obras civiles, ya que el conocimiento de las propiedades físicas de los suelos permite evitar que estas experimenten la resonancia ante la ocurrencia de sismos importantes, sobre todo en la zona sur de la ciudad, donde se desarrollan importantes actividades portuarias. Con los mapas de distribución espacial sobre las frecuencias predominantes del sector Sur de David (zona portuaria), los rangos del parámetro sugieren que las edificaciones superiores a los 2 niveles podrían sufrir daños por eventos sismológicos considerados por el efecto de resonancia.…”

“…Con los mapas de distribución espacial sobre las frecuencias predominantes del sector Sur de David (zona portuaria), los rangos del parámetro sugieren que las edificaciones superiores a los 2 niveles podrían sufrir daños por eventos sismológicos considerados por el efecto de resonancia. Los resultados de este estudio han sido publicados y explicados ampliamente en [6].…”