Abstract
In this paper, we describe recent studies for the geophysical and geomechanical characterization of soils in Hispaniola (Greater Antilles), an island threatened by the eventual rupture of major seismogenic fault systems. The investigations were performed for four different cities settled on complex geological formations in Haiti (Cap-Haïtien, Port-au-Prince) and the Dominican Republic (Santo Domingo, Santiago de los Caballeros). We present the complete methodology we implemented for mapping zones of homogeneous seismic response and for microzonation studies, but each main stage of investigation is described as it was conducted in one or two cities. Therefore, first we present our site-characterization technique applied to Santo Domingo and Santiago de los Caballeros, which is based on geotechnical data, geophysical multichannel analysis of surface waves, and ambient-noise recordings. Then we present the site-response analysis through numerical analysis with nonlinear soil models that we performed for the city of Cap-Haïtien. Finally, we describe the amplification factors for site-specific response spectra that we derived for the microzonation of Port-au-Prince. We argue for the implementation of a multidisciplinary approach built upon complementary field geological, geophysical, and geotechnical data rather than solely depending on geophysical measures for the characterization of VS30. In addition, we explore the compatibility of the soil classes recommended by the International Building Code (IBC) in the context of local seismic amplification.
Highlights
After the great disaster caused by the January 2010 Mw 7.1 Haiti earthquake in the region of Port-au-Prince, the evaluation of the seismic hazard in the whole Hispaniola Island became an imperative need
Even though we found significant site effects for the seven cities considered for microzonation, we selected the four cities where geological conditions permit a better illustration of the relevant aspects of the methodology we implemented
While all those soil types would be classified in the same class D by the 2009 provisions of the National Earthquake Hazards Reduction Program (NEHRP) [33], our microzonation study was capable of better characterizing the variability of local seismic response
Summary
After the great disaster caused by the January 2010 Mw 7.1 Haiti earthquake in the region of Port-au-Prince, the evaluation of the seismic hazard in the whole Hispaniola Island became an imperative need. The first step in microzonation studies is to identify areas that are expected to have homogeneous seismic response Such identification is based on a combined analysis of available geological, seismic, geotechnical, and geophysical information, a process we refer to as site characterization. In the case of Santo Domingo, out of the eight initial geological formations, the analysis led to the identification of 34 areas (shown in Figure 2) with similar enough characteristics to suspect a homogeneous site-effect signature. Other reasons behind the nonexistence of a significant peak could be the case of significant lateral heterogeneity giving rise to 2D/3D effects [25], or effects of sea-wave motion and strong winds [26] Even if these factors may play a role, the resulting almost-flat HVSR may be attributed to the low velocity contrast considering the sedimentary sequence in the eastern part of Santiago de los Caballeros. When used alone, the HVSR method might not provide the most reliable estimates; complementary approaches, combined with geological descriptions and geotechnical investigations, are recommended for characterizing different soil configurations
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