Implementation of seismic microzonation in municipa lity ordinances in Caracas, Venezuela

Michael Schmitz, FUNVISIS, mschmitz@funvisis.gob.ve, Florian Olbrich, FUNVISIS, Gustavo Coronel, IMME-UCV, Cecilio Morales, FUNVISIS, Ketty Mendes, FUNVISIS,

Roberto Uzcátegui, FUNVISIS, Maxlimer Vallée, FUNVISIS, Arisbel Arreaza, Libertador Municipality, Caracas

1. Abstract

Strong site effects, which caused the collapse of 4 buildings with 10 and more storeys during the Caracas 1967 earthquake, and the damage of a big number of them in the same deep sediment area, motivated the development of the Caracas Seismic microzoning project in the years 2005-2009. The main results of this project were the development of design response spectra for the different microzones within the sedimentary basin, as well as estimates of landslide hazard.Implementation of the results in municipality ordin ances is actually discussed with local authorities. They are aimed to address mitiga tion for new constructions by the application of the specific design spectra, for exi sting buildings via evaluation and retrofitting strategies, and for slope areas (infor mal, as well as formal developments) due to the identification of areas th at may not be developed or require detailed studies of slope stabilities.

NH51F-06. AGU 2013, Meeting of the Americas.

Marco Legal• Ley Orgánica de Ordenación

Urbanística (Gaceta Oficial Nº

33.868 del 16 de diciembre de

1987) y su respectivo Reglamento

extraordinario (Gaceta Oficial Nº

4.175 del 30 de Marzo de 1990) .

• La Ley de Gestión Integral de

Riesgos Socionaturales y

Tecnológicos (Gaceta Oficial Nº

39.095 del 9 de enero de 2009).

Marco Técnico • Norma Técnica Nacional para

Edificaciones Sismorresistentes

COVENIN 1756-2001 (COVENIN,

2001)

• Resultados del Proyecto de

Microzonificación Sísmica de

Caracas (FUNVISIS, 2009, Schmitz

et al., 2011)

2. Seismic hazard

In 1967, 4 modern high-rise buildings collapsed and more than 200 were damaged in a distinct area of the city, characterized by de ep sediments.

5. Seismic microzones and adjustment to cadastral l imits

As a result from geological, geophysical and seismi c engineering studies, a seismic microzoning map was derived, which allows t o define zones of similar seismic behaviour within the city (Schmitz et al., 2011)

8. Use of microzoning results in municipality ordin ances

Since 2011, after finishing the Caracas seismic mic rozoning study, considerations for the implementation of the results have been dis cussed with Libertador municipality, and since 2012 also with the other mu nicipalities Chacao, Sucre, Baruta and El Hatillo. Results maybe used for new b uildings in complement of the building code, as well as for existing buildings an d hillsides, within existing laws and technical regulations.

3. Caracas today

Caracas is a city of more than 3.5 million inhabita nts. High-rise buildings prevail within the sedimentary valley, and informal buildin gs with up to 6 storeys cover most of the surrounding slopes. 5 municipalities co mpose the Caracas Metropolitan Region.

The main seismic hazard is attributed to the San Se bastian fault system, which marks the plate boundary between the Caribbean and South America plates, is located just 5 km north of the city. Simulations of seismic hazard show decrease from north to south, with amplifications in the sed imentary basin, as for example for a severe scenario like the 1812 earthquake (Yam azaki et al., 2005).

12. ReferencesAmarís, E., Schmitz, M., Murphy, V., 2011. Sediment thickness as primary input for the Caracas Seismic Microzoning Project. 5th International Conference on Earthquake Geotechnical Engineering, Santiago de Chile, Paper Nr. MOSAM, 12 pp.

Hernández, J.J., 2009. Confiabilidad sísmica-estructural de edificaciones existentes de Caracas. Proyecto Pensar en Venezuela, C.I.V., Jornadas 18 y 19 de septiembre de 2009. Memorias, 115 pp.

Hernández, J.J., Schmitz, M., Delavaud, É., Cadet, H., Domínguez, J., 2011. Espectros de respuesta sísmica en microzonas de Caracas considerando efectos de sitio 1D, 2D Y 3D. Revista de la Facultad de Ingeniería UCV, 26 (2), 49–66.

López, O.A., Hernández, J.J., Del Re, G., Puig, J., Espinosa, L., 2007. Reducing Seismic Risk of School Buildings in Venezuela. Earthquake Spectra, 23 (4), 771–790.

Schmitz, M., Hernández, J.J., Morales, C., Domínguez, J., Rocabado, V., Valleé, M., Tagliaferro, M., Delavaud, É., Singer, A., Amarís, E., Molina, D., González, M., Leal, V. y el grupo de trabajo del proyecto de Microzonificación Sísmica de Caracas, 2011. Principales resultados y recomendaciones del proyecto de microzonificación sísmica en Caracas. Revista de la Facultad de Ingeniería UCV, 26 (2), 113–127.

Yamazaki, Y., Audemard, F., Altez, R., Hernández, J., Orihuela, N., Safina, S., Schmitz, M., Tanaka, I., Kagawa H., and JICA Study Team -Earthquake Disaster Group, 2005. Estimation of the seismic intensity in Caracas during the 1812 earthquake using seismic microzonation methodology. Revista Geográfica Venezolana, Número Especial 2005, 199-216.

4. Subsurface investigations

A series of geophysical measurements, including sei smic refraction, noise measurements and gravimetric modelling, together wi th geological (drillings, quaternary geology) and geotechnical investigations led to a d etailed subsurface model. Information of sedimentary thickness (Amaris et al., 2011) was used for modelling of the seismic response within the valley in 2-D and 3-D configura tions.

Seismic microzones were adjusted to the cadastral l imits in each of the municipalities in order to avoid ambiguities for th e application of the elastic response spectra (Hernandez et al., 2011)

6. Landslide hazard

A fast growing part of the city with more than half of its population comprises informal housing at steep hillsides surrounding the valley with earthquake or rainfall triggered landslide as the principal hazar d in these areas. Therefore, a methodology for the evaluation of the susceptibilit y to mass movements, including local calibrations, was applied (Hernández et al., 2008).

7. Active faults

Corridors are defined around the outcrops of the ac tive Tacagua – El Avila fault on the northern limit of the Caracas valley. Detail ed neotectonic investigations are required for construction permits within this corri dor.

Recommendations are given how to treat areas of hig h landslide hazard, and how to calculate the affected slope areas, as well as i ndications for response spectra that take into account topographic effects at hills ides.

9. Libertador municipality

Priorities for detailed building evaluation and pos sible retrofitting are defined based on the parametric studies of building behavio ur (Hernandez, 2009), as well as for the school buildings, based on a detailed st udy, including retrofitting plans for typical buildings (Lopez et al., 2007).

10. El Hatillo municipality

El Hatillo municipality is located in the hilly sou th eastern part of Caracas Metropolitan Region, with few contribution of sedim entary areas, but predominant bedrock and weathered bedrock with moderate landsli de hazard.

11. Chacao municipality

Chacao is the business district of Caracas with hig h-rise buildings in the area affected by the 1967 earthquake. The Local Urban De velopment Plan PDUL is actually in discussion and restrictions to building heights were introduces in areas of high sediment thickness in order to mitigate sei smic risk to high-rise buildings.