Ing. Osiris de Leon
Commission of Natural Sciences and Environment of the Academy of Sciences
On January 12th, 2010, a 7.0 magnitude earthquake with an epicenter 15 km SW of the city of Port-au-Prince and a hypocenter at 10 km depth, produced 316,000 deaths, 350,000 wounded, and destroyed 300,000 homes that left 1,500,000 homeless. This is the worst global seismic tragedy of the past 50 years. All the collapsed buildings in Haiti were raised on soft clayey soils of bad seismic response, which were deposited on ancient marine channel. In comparison, the buildings raised on Tertiary limestone of the southern slope of the city suffered no damage. This includes the precariously built structures near the epicenter, which lacked any engineering design from the impoverished people who live on the rocky slopes. Buildings with apparently robust structures, and designed with engineering standards, such as the national palace, the cathedral and the Montana hotel, collapsed when the soft soils amplified the vibration and the seismic energy of the earthquake. A similar situation happened in Mexico City, in September 1985, when amplified shear seismic waves, arriving from an epicenter 320 km away, caused buildings to collapse over the soft soils of the ancient Texcoco lake, while buildings over hard rock remained intact. Some reports refers that this Mexican earthquake produced near 40,000 deaths.
Most construction projects do not perform soil dynamic studies. Furthermore, the ministry of public works only requires a few mechanical boreholes that include standard penetration tests (SPT) and testing laboratories (grain size and Atterberg limits) to determine the bearing capacity of soils and settlement. This level of analysis does not meet the necessary standard to safely build in areas where earthquake hazards exist. In the same way, few architectural designs took seismic response into consideration when engineering building projects. The low shear-strength (which may be related to low shear velocity) foundations of many locations were given no differential treatment, in comparison to locally more rigid rock foundations. These engineering deficiencies lead to more seismic disasters around the world. Future engineering seismic design must be in accordance with shear-wave velocity measurements made at building site to avoid or reduce disasters, as seen in Haiti, Mexico city and other Latin American and Caribbean countries. IANAS should include in agenda, as a social and security priority, the Latin American and Caribbean seismic risk along tectonic border lines, and recommendations for revisions of old structures in seismic zones, mainly schools, hospitals, houses and bridges, taking as main consideration the soil types, the seismic properties of them, as well as the structural design used.
Osiris de Leon Graduated of Geological Engineering at the Pontificia Universidad Católica Madre y Maestra, 1979. For 12 years was Counselor Scientist of the National Commission for the Environment of the Dominican Republic. Since 1998 he is a member of the Board of Directors of the Academy of Sciences of the Dominican Republic, during six years he was the Coordinator of the Commission of Natural Sciences and Environment of the Academy of Sciences, and actually is the Dominican Focal Point for the Water Program of the Inter-American Network of Academies of Sciences, IANAS. Among his main publications are cited: Environmental issues of Aggregates Extraction of Rivers in the Dominican Republic and Alternative Sources of Quarry in a Dry Land (Geological and Mining Institute of Spain), Mining and Environment, Big Mining and the Environment in the Dominican Republic; the Landmines order in the Dominican Republic (CYTED Publications, 2002), Geology of the Sierra de Bahoruco; Geological Conferences; Geological and hydrogeological aspects of the Southwest Region; Diagnosis of Dominican environmental situation; and Water and Sanitation in the Dominican Republic (IANAS 2012). He has given internationals conferences about mining and environment in different countries of the region.