S24A-01
Historic Seismicity, Computed Peak Ground Accelerations, and Seismic Site Conditions for Northeast Mexico
In this study we present the historic seismicity, computed peak ground accelerations, and mapping of seismic site conditions for northeast Mexico. We start with a compilation of the regional seismicity in northeast Mexico (24- 31°N, 87-106°W) for the 1787-2006 period. Our study area lies within three morphotectonic provinces: Basin and Range and Rio Grande rift, Sierra Madre Oriental and Gulf Coastal Plain. Peak ground acceleration (PGA) maps were computed for three different scenarios: 1928 Parral, Chihuahua (MW = 6.5); 1931 Valentine, Texas (MW = 6.4); and a hypothetical earthquake located in central Coahuila (MW = 6.5). Ground acceleration values were computed using attenuation relations developed for central and eastern North America and the Basin and Range province. The hypothetical earthquake in central Coahuila is considered a critical scenario for the main cities of northeast Mexico. The damage associated with this hypothetical earthquake could be severe because the majority of the buildings were constructed without allowance for seismic accelerations. The expected PGA values in Monterrey, Saltillo and Monclova range from 30 to 70 cm/s2 (0.03 to 0.07g). This earthquake might also produce or trigger significant landslides and rock falls in the Sierra Madre Oriental, where several cities are located (e.g. suburbs of Monterrey). Additionally, the Vs30 distribution for the state of Nuevo Leon and the cities of Linares and Monterrey are presented. The Vs30 data was obtained using seismic refraction profiling correlated with borehole information. According to NEHRP soil classification, sites classes A, B and C are dominant. Sites with class D occupy minor areas in both cities. Due to the semi-arid conditions in northeast Mexico, we obtained the highest values of Vs30 in Quaternary deposits (alluvium) cemented by caliche. Similar values of Vs30 were obtained in Reno and Las Vegas, Nevada. This work constitutes the first attempt at understanding and characterizing soil velocity profiles, the areal distribution of different site classes, ground shaking amplification, and the nature of seismic hazards in northeast Mexico.
S24A-02
The Prediction of Damage to Buildings by Earthquake in the Residential Zones of Colima, México, From the Damage Probability Matrix and its Test by the 2003 Mw 7.5 Earthquake
The damage probability matrix was calculated for the Colima, México masonry (Zobin and Ventura-Ramírez, 1999) for three residential zones and for the earthquakes of intensity MM of VI to IX (Mercalli Modify Scale). The Mw 7.5 earthquake of 21 January 2003 that occurred within the Mexican subduction zone had tested this prediction. The macroseismic investigation of damage produced by the earthquake in Colima city was realized for 3,332 constructions within the area of study representing about 20 per cent of the total city area and covered with the different type of constructions. The 7-grade scale of damage was used to describe the damage distribution. The damage matrix, constructed for the area, showed that the damage distribution varied from 63 per cent for constructions with relatively slight damages (grades 1 to 3) for 29 per cent to constructions that had significant damages (grades 4 to 5) and 8 per cent for completely destructed or demolished masonry. The damage matrix, constructed for 12 subzones of the area of study, reflected two tendencies in the damage distributions: the predominance of slight damage to the recent constructions situated in the northern and eastern parts of the area and the predominance of significant damage to the older constructions in the southern and western parts of the area. It was observed a significant dependence of damage index upon the age of constructions and the type of masonry. The observed damage matrix was in a good accordance with the 1999 damage probability matrix (MM VII) for two zones of three where the prediction was done.
S24A-03
SEISMIC HAZARD MANAGEMENT IN MEXICO CITY
Mexico City is one of the largest cities in the world. More than 8.5 million residents and 4.5 million floating population are in the city itself, but with the surrounding suburbs the number of people that could be affected by natural and man-made hazards rises to approximately 20 million. The main risk to the city as a whole is a large magnitude earthquake. Since there is reason to prepare for a credible seismic scenario of Mw = 8.2, which would exceed the damages caused during the 1985 earthquake (Mw = 8.1), we founded the Metropolitan Geologic Service (MGS) in 1998. The MGS has developed geologic and seismic hazard maps for the city (http:www.proteccioncivil.df.gob.mx). The maps include three separate risk maps for low height (3 stories), medium height (10 stories) and tall buildings (10 stories). The maps were prepared by using the maximum horizontal accelerations documented during the 1985 earthquake, and wave propagation modeling for buildings of different resonant periods (T = 0.0, 1.0 and 2.0 sec). In all cases, the risk zones were adjusted to include documented damage during the 1957, 1979 and 1985 earthquakes. All three maps show a high risk zone in the north-central portion of the city, elongated in a N-S direction, which corresponds with a narrow graben where the thickness of alluvial sediments is particularly large, and where wave amplification is accentuated. Preparation of these maps, and others used for planning, has been facilitated by the ongoing elaboration of a Dynamic Geographical Information System, which is based on geo-scientific information, includes all types of risks, and incorporates vulnerability models. From the risk management standpoint, we have elaborated the Permanent Contingency Plan for Mexico City, which in its Earthquakes chapter includes plans for coordination and for organizing attention to the population in the event of a seismic disaster. This Permanent Plan follows the philosophy of Descartes' Method, has 11 processes (6 main and 5 support processes), and is coordinated by Center of Control of Operations under the overall direction of the Head of Government of the Federal District. We are also working on the definition of the Basic Elements for a New Paradigm in the Prevention of Disasters, to investigate the origins, causes and effects of disaster phenomena, and to plan and implement a suitable response from the Government to better protect the population.
S24A-04
Geo hazard studies and their policy implications in Nicaragua
Nicaragua, situated at the Central American Subduction zone and placed in the trajectory of tropical storms and hurricanes, is a frequent showplace of natural disasters which have multiplied the negative effects of a long term socioeconomic crisis leaving Nicaragua currently as the second poorest country of the Americas. In the last years, multiple efforts were undertaken to prevent or mitigate the affectation of the natural phenomena to the country. National and local authorities have become more involved in disaster prevention policy and international cooperation boosted funding for disaster prevention and mitigation measures in the country. The National Geosciences Institution (INETER) in cooperation with foreign partners developed a national monitoring and early warning system on geological and hydro-meteorological phenomena. Geological and risk mapping projects were conducted by INETER and international partners. Universities, NGOīs, International Technical Assistance, and foreign scientific groups cooperated to capacitate Nicaraguan geoscientists and to improve higher education on disaster prevention up to the master degree. Funded by a World Bank loan, coordinated by the National System for Disaster Prevention, Mitigation and Attention (SINAPRED) and scientifically supervised by INETER, multidisciplinary hazard and vulnerability studies were carried out between 2003 and 2005 with emphasis on seismic hazard. These GIS based works provided proposals for land use policies on a local level in 30 municipalities and seismic vulnerability and risk information for each single building in Managua, Capital of Nicaragua. Another large multidisciplinary project produced high resolution air photos, elaborated 1:50,000 vectorized topographic maps, and a digital elevation model for Western Nicaragua. These data, integrated in GIS, were used to assess: 1) Seismic Hazard for Metropolitan Managua; 2) Tsunami hazard for the Pacific coast; 3) Volcano hazard for Telica-Cerro Negro and El Hoyo volcanoes; and 4) Flood hazard map of Maravilla river. This study was realized between 2004 and 2006, through technical cooperation of Japan International Cooperation Agency with INETER, upon the request of the Government of Nicaragua. The results of the mapping and investigations are fed in a National GIS on Geohazards maintained by INETER and developed in the frame of a regional cooperation project with BGR, Germany, and other international institutions. Many maps, project reports and GIS coverage are made available on INETERīs Website to the general public. (www.ineter.gob.ni/geofisica/geofisica.html ).
S24A-05
Implementation of tsunami disaster prevention measures in the municipality of San Rafael del Sur, Nicaragua
The Nicaraguan Pacific coast presents considerable tsunami risk. On September 1, 1992, a tsunami caused enormous damage in the infrastructure and killed more than 170 people. A pilot project was conducted between 2006 and 2007 in the municipality of San Rafel del Sur, area of Masachapa, The project included multiple topics of tsunami prevention measures and considering the direct participation of the local population, as: -General education on disaster prevention, participative events; -Investigation of awareness level and information needs for different population groups; -Specific educational measures in the schools; -Publication of brochures, calendars, news paper articles, radio programs, TV spots -Development of local tsunami hazard maps, 1:5,000 scale; (based on previous regional tsunami hazard mapping projects and local participation) -Development of a tsunami warning plan; -Improvements of the national tsunami warning system. -Installation of sirens for tsunami warning -Installation of tsunami signs, indicating hazardous areas, evacuation routes, safe places; -Realization of evacuation drills in schools. Based on the experiences gained in Masachapa it is planned to run similar projects in other areas along the Nicaraguan Pacific coast. In the project participated the local municipality and local stakeholders of San Rafael del Sur, Ministry of Education, National Police, Nicaraguan Red Cross, Ministry of Health, Ministry of Tourism, Nicaraguan Geosciences Institute (INETER), National System for Disaster Prevention (SINAPRED), Swiss Agency for Development and Cooperation (SDC). It was financed by SDC and INETER.
S24A-06
Geophysical studies for the identification of basin effects in urban areas in Venezuela
Urban areas in northern Venezuela are subject to a moderate seismic hazard due to the interactions between the Caribbean and south American plates, which has been evidenced by historical damaging earthquakes as for example the 1812 and the 1967 earthquakes with a magnitude of 7.2 and 6.5, respectively. Strong damages in Caracas during the 1967 earthquake have been asociated to site effects produced by the sediment filled basin. This situation can be observed in most of the big cities in northern Venezuela, which initially developped on plain areas with quaternary basin fills of up to 500 m within mountainous areas, as for example Caracas, Maracay and Barquisimeto. In the mid- 1990ies FUNVISIS started to promote geophysical studies to investigate the shape and the properties of the basin fills in order to contribute to the earthquake disaster reduction. Methods applied for the investigations are gravimetry, microtremor measurements, seismic refraction, among others. In Caracas, a total of 350 m of cuaternary sediments with an average S-wave velocity of about 850 m/s have been derived by seismic investigations. The corresponding predominant periods from microtremor measurements amount up to 2.2 s. Integrating drilling information and 3D gravimetric modeling a detailed picture of the bedrock - sediment interface could be obtained. Results from numerical modelling as well as from experimental transfer function indicate amplifications point to amplifications of a factor of more than 10 related to the deep basin area. In Barquisimeto Metropolitan Area, sediment thickness reaches up to 500 m in the fast growing Cabudare area. Actually, modelling of a recent seismic refraction campaign is in progress, but predominant periods up to 3.0 s in the deepest part of the valley and gravity modelling point to the same order of cuaternary sediments. In other cities, as for example Carora and Mérida, geophysical studies are in progress, first with gravimetric and microtremor measurements which point to sediment with more than 150 m thickness. The subsoil information from geophysical studies will be used to define the distribution of microzones of equal seismic response in order to determine PSHA spectra. Contribution to projects FONACIT 200400738 and FONACIT-ECOS Nord 2004000347.
S24A-07
Methodology for the Caracas Seismic Microzonation Study
Currently, the Venezuelan Foundation for Seismological Research (FUNVISIS) is executing the Caracas Seismic Microzonation Study. Fundamental objectives are the selection of microzones of similar response and the determination of landslide susceptibility. Both result from a guided combination of damage data of 1967 Caracas earthquake, landslides inventory, geophysical investigations, seismic hazard analysis, geological information, geotechnical database, and earthquake engineering estimations of soil response and probable hillside behavior. Geophysical investigations include refraction seismic, microtremor and gravimeter measurements, for modeling the valley basin; sediment thickness to bedrock reaches 350 m. The model was calibrated with three deep drillings, in which accelerometers will be placed for future comparisons between surface and bedrock seismic motions. Probabilistic seismic hazard analysis was performed, leading to uniform hazard spectra for 475-year mean return period and deaggregation of magnitude-distance pairs, differentiated within the Caracas bedrock. A parametric one-dimensional dynamic soil response study was performed with varying sediment thickness (0-350 m), average shear wave velocity in the upper 30 m (150-500 m/s), and nonlinear soil properties; 144 representative soil profiles were analyzed. The mean amplification of spectral response values of ther surface regarding to the bedrock is obtained, in order to determine probable surface spectra using the bedrock PSHA spectra as input. The seismic effects of the basin are incorporated in an approximate way, from numerical simulations of the 2D and 3D seismic response and statistical data around the world. Finally, a set of microzones with similar average response spectrum is selected, by means of correlating their geological, geophysical and geotechnical properties with those of the parametric study. Hillside pre-seismic hazard is established from lithological properties, slope gradients and seasonal and rainfall wet indexes, estimating the static factor of safety. Newmark displacements and probability of failures are estimated using PSHA results and statistical correlations, leading to the qualification of the earthquake-induced landslide susceptibility. The results will allow updating the municipality ordinances, in order to improve the design and safety construction of new buildings and establish reinforcement priorities of the existing ones. Contribution to projects FONACIT 200400738 (with funds from IDB) and FONACIT-ECOS Nord 2004000347.
S24A-08
The role of seismic microzoning within the disaster prevention in Venezuela
Due to the experience of the strong rainfalls which experienced great parts of Venezuela in early 2005, a national commission for risk management (CNGR) was created, that is composed by representatives from the Ministry of Interior and Justice, the Ministry of Environment, Defense Ministry, Infrastructure Ministry, Habitát and Housing Ministry and Science and Tecnology Ministry. The participation of the different ministries, which are represented by institutions related to hidrometeorological research and slope stability, amongst others, enables to focuss the risk management from anintegrated point of view. Within this commission, FUNVISIS, the official agency for seismological investigations, represents the Science and Tecnology Ministry and is responsible for the actions to be taken to reduce the seismic risk. A plan to reduce the seismic hazard and vulnerability, presented by FUNVISIS, was approved by the commission, in order to establish state policies to minimize the impact to the comunities in case of the ocurrence of an earthquake. Therein, seismic microzoning studies are addressed as the methodology to follow in order to reduce the seismic risk, which includes the evaluation of regional conditions (fault ocurrences, source characteristics, attenuation) as well as the knowledge of the local conditions (wave propagation, geological conditions, site effects). The interdisciplinary methods used within the microzoning studies (joint work done by geologists, geophysicists, civil engineers, arquitects, teachers) enable to address the results of the studies in away that they can be assimilated by the communities that live in the respective urban areas as well as by the local governments. Recommendations to local buiding codes as well as training of the communities take an important part within the projects.