Seismic microzonation study of Santo Domingo, Santiago de los Caballeros and Barahona metropolitan cities (Dominican Republic) using combined methods of reflection/refraction of surface waves and microtremor records

The Dominican Republic has high seismicity, due to the position of the Hispaniola Island, right in the interaction between the North American and Caribbean tectonic plates. More specifically, on the northern edge of the Caribbean plate, where seismicity is especially intense, causing the entire island to be affected by a high seismic hazard. In this tectonic context, a seismic data acquisition campaign has been carried out in several cities of the Dominican Republic to determine site effects and to carry out seismic microzonation studies. These studies have been carried out within the framework of the research projects MICROSIS-I (seismic microzoning in urban areas of the Dominican Republic, based on active and passive seismic) and “KUK ÀHPÁN: Integrated Regional Study of Structure and Evolution 4D of the Lithosphere in Central America”. Implications in the Calculation of Seismic Hazard and Risk”).

In the present study, a campaign of urban noise recording the horizontal-to-vertical (H/V) components spectral ratio and the spatial autocorrelation (SPAC) methods was carried out, in order to extract valuable information about the fundamental frequency peaks and geological shallow structure Vs30 and the bedrock interface under the investigated urban areas of Santo Domingo (East) Santiago de los Caballeros and Barahona cities.

Investigations were performed on 10x10 km dense grid with two broad band 120s seismic stations, five short period (1s) three components short period seismic stations and 36 single channel seismic stations provided with 4.5 Hz vertical component seismometers.

The computed H/V curves suggest the existence of multiple interfaces within the geological structure below the studied cities. The fundamental frequency of resonance varies between 0.3–10.1 Hz. Some H/V curves in the South of Santo Domingo, the bedrock sites are generally characterized by flat spectra whatever the geological nature of bedrock interface. The observed resonance peaks were interpreted according with the available geological information.

In addition of those studies, a Multichannel Analysis of Surface Waves (MASW) experiment of some 40 km has been carried out with a land streamer of 16 three component 4.5 Hz geophones and an active source of surface waves providing Rayleigh and Love waves along de main geological structures identified in the both studied cities. The combination of that methodology, the SPAC and the H/V methods, provided the Shear-wave velocity (VS) and time-averaged shear-wave velocity to 30 m depth (VS30). Values obtained from the above methods were combined and plotted for averaging the site’s Vs30 and layered models and the bedrock interface.

With these new results, we performed a step forward toward the understanding of ground motion propagation in the studied cities and future studies will be done to constrain the bedrock depth in order to build realistic velocity profiles for those cities.