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Site Effects Modelling and Urban Exposure Models

Over the past year, TREQ has made significant progress in the risk and hazard assessment for the selected cities: Santiago (Dominican Republic), Quito (Ecuador) and Cali (Colombia). This includes compiling and preparing existing PSHA models for hazard calculations; and the development of detailed exposure and vulnerability models.

Urban Hazard Assessment

For Santiago de los Caballeros, Dominican Republic, the project team worked with local experts from the National Geological Survey (SGN) and the Autonomous University (UASD) at compiling, reviewing, and preparing a new seismic catalogue to be used in hazard calculations for Hispaniola. The team has also prepared the national database of active faults, using the information compiled in the CCARA project and additional information provided by SGN (i.e. data and reports). The project is now using the catalogue and fault data to construct the national probabilistic seismic hazard model for the Dominican Republic. A preliminary version has been completed, and construction of the final model is underway.

For Cali, Colombia, the project improved the national model proposed by Arcila et al. (2020) by adding a new fault located underlying the city (i.e. Cauca-Cali-Patia fault), consistent with the seismic zonations used in the microzonation study for Cali (Ingeominas-Dagma, 2005), and the Colombian building code (AIS, 2009). For Quito, Ecuador, the project selected the model of Beauval et al. (2018), composed of shallow and subduction seismic sources characterized using an ISC-based catalogue and active shallow fault sources considering geodetic slip-rates assuming a 50% of aseismic slip.

Now, the project is consolidating the available geological, geophysical, and geotechnical data for each of the three cities needed to compute site-response (amplification of ground shaking in surficial sediments (or soil) during an earthquake). Future versions of the OpenQuake engine will support the calculation of site response through detailed site/soil amplification functions and their corresponding uncertainty.

Urban Risk Assessment

GEM has already developed exposure datasets at the subnational level in the Dominican Republic, Colombia and Ecuador. However, the risk assessment activities planned within the context of TREQ require exposure datasets at urban scale. To this end, GEM has focused on the development of high-resolution exposure models. These have been established with support from the municipal governments in each city, namely, Oficina de Planeamiento Territorial (Santiago de los Caballeros), Oficina de Planeación y la Secretaría de Gestión del Riesgo de Emergencias y Desastres (Cali), and Dirección Metropolitana de Gestión del Riesgo (Quito).

The exposure models were developed using dedicated databases from each city. These databases include the most recent information from the census, cadaster, and urban planning offices. As a result, they feature better estimates for the number of occupants, building counts, replacement costs and vulnerability classification of structures. In close collaboration GEM and the USGS are validating the exposure models by means of assessing the potential impacts of earthquake scenarios at a neighborhood level. The objective is to use recorded/estimated damage and economic losses from relevant historical scenarios to assess the accuracy of the exposure and hazard model data. The risk metrics that are being analyzed in each city include building damage, economic losses and fatalities.