Regional and local seismic hazard mapping for seismic risk mitigation of Santiago de los Caballeros (Dominican Republic)

In order to propose methodological solutions for reducing seismic risk in Caribbean urban zones, efforts concentrate on applying research activities. For example, elaborating seismic risk scenarios allows a better assessment of the consequences of an earthquake affecting the organization of social structures, in order to highlight sensitive sectors where considering seismic risk must be given priority. Because of its primary objectives, the SYSMIN II program in Dominican Republic takes place in this context. In this paper, we show how methodologies developed during seismic microzonation studies in the French West Indies, were suitable to be applied to the case of Hispaniola, the second island in the Greater Antilles. The north of Hispaniola is threatened by the eventual rupture of a major seismogenic fault zone, named Septentrional. The town of Santiago de los Caballeros in the Dominican Republic is particularly exposed because of its close location to this fault (<10 km). The paper gathers results obtained from the seismic hazard and microzonation studies developed in the city of Santiago: i) quantification of regional seismic hazard dominated by the Septentrional fault, ii) a new geological mapping of superficial formations at the scale 1:10.000, and iii) mapping of zones of homogeneous seismic response and liquefaction susceptibility. These interpretations are based on field geotechnical and geophysical measures, but also on the geological expertise achieved over several years in the Cibao region by the consortium IGME-BRGM-INYPSA. On the French West Indies, the volcanic origin of the geological formations punctuated by sedimentary episodes, gives a particular signature to the amplification phenomena of seismic vibrations due to site effects. The investigations carried out in Santiago revealed a new issue: surprisingly minor site effects (based on the H/V method of ambient noise) in the plastic continental argillaceous unit that represents the main layer for foundations in the whole city area.