Geology applied to the study of seismic microzoning of Santiago de los Caballeros, Dominican Republic

Abstract

After the Haiti quake of 2010 an initiative started to better understand shaking effects in the Dominican Republic after natural earthquakes, in particular in the city of Santiago de los Caballeros, the second city in the country as far as inhabitants and economic wealth are concerned. Santiago has suffered several devastating earthquakes; in 1562 the city was rebuilt on a new site (the current location) further south from the responsible fault. It is well known that damage caused by an earthquake occurs associated to a number of factors, ground acceleration is one of them and is usually considered as the key to explain most of the damage. Ground acceleration varies from one point to another depending mainly on: distance to the source of the rupture, soil properties and topography. Regarding the distance, the further from the source the less acceleration is expected due to distance attenuation. On the other hand, different soil properties and different topographies will produce different responses to the propagating wave. Within the range of a few kilometres, the effect of distance attenuation might be far less relevant than the effect of the varying properties of soils. This paper gathers together 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, and iii) mapping of zones of homogeneous seismic response and liquefaction susceptibility.

Combined Geophysical and Geotechnical Approaches for Microzonation Studies in Hispaniola Island

“…The presence of a regular velocity gradient in these Quaternary clays, characterized by poor mechanical properties (a shear-wave velocity of 240 m/s), may explain the inability of the HVSR method to detect significant site effects. Moreover, the probable low velocity contrast between this clayey formation at depth and the bedrock, expected at around 100 m [22], may explain underestimation of the HVSR peak amplitude, as suggested in previous studies using the HVSR technique [23][24][25]. Modeling the ambient-noise wavefield, Reference [24] have observed that the amplitude of HVSR peaks also depends on the relative contribution of different types of seismic waves (body and surface waves).…”