HR: 0800h
AN: S11A-0272    [Abstracts]
TI: Structural Seismic Risk at David City, Panama
AU: Camacho, E
EM: ecamacho@cableonda.net
AF: Instituto de Geociencias, Universidad de Panama, Panama, 0830-01104, Panama
AU: Battlo, J
EM: jbattlo@igc.cat
AF: Institut Geologic de Catalunya, Balmes 209-211, Barcelona, E08006, Spain
AU: * Novelo-Casanova, D A
EM: dnovelo@geofisica.unam.mx
AF: Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AU: Tapia, A
EM: aalaint@hotmail.com
AF: Instituto de Geociencias, Universidad de Panama, Panama, 0830-01104, Panama
AU: Lindhom, C
EM: conrad@norsar.no
AF: NORSAR, P.O.Box 53, Kjeller, N2027, Norway
AB: At the southwest margin of the Isthmus of Panama, the Cocos, Nazca and Panama Microplate join in a triple junction. In this tectonic setting, the Panama Fracture Zone (PFZ) which bounds the Nazca and Cocos plate, subducts in an oblique and shallow manner. This zone is one of the most active seismic areas of Central America. On July 18, 1934, the largest earthquake in Panama in historical times (Ms= 7.7) occurred in its northern region. This event caused extensive damage to towns located in the border of Panama and Costa Rica and during the two subsequent days, six aftershocks with magnitude greater than 6.0 were recorded. David City, with 130,000 inhabitants is the most important urban center in southwestern Panama and lies at the northern end of the PFZ. This city was impacted by the strong destructive earthquakes (Ms>7.0) that took place in 1879 and 1934, both with epicenters located on the northern terminus of the PFZ. In this work, we collected and digitized historical seismograms to measure the centroid moment tensor (CMT) from the main 1934 earthquake. Additionally, we gathered new macroseismic information to create improved and more complete isoseismals maps of the 1879 and 1934 events. We determined the probabilistic seismic hazard for David City using records of historical and recent seismicity and the characteristics of local faults. The hazard computation results are presented as peak iso-acceleration curves for rock/hard soil for a recurrence time of 500 years. An elastic response spectrum was obtained with a uniform exceedance probability of 10% in 50 years with one degree of freedom and 5% of damping. Our results indicate maximum peak ground acceleration (PGA) in downtown David of 3.8 and 4.5 m/s2 with a probability annual exceedance of 0.002 and 0.001, respectively. Structural vulnerability was determined analyzing the quality and construction design of housing, buildings, and critical facilities as well as the type of soil where these structures were located. Soil was classified as soft, intermediate, and hard from in-situ dynamic standard penetration test (SPT) measurements. For proper interpretation, all our observations were incorporated in a Geographical Information System (GIS). From a combined analysis of seismic hazard and vulnerability results, we identified six areas with different levels of structural seismic risk increasing from north to south along the David River. Central David has intermediate level risk. The highest risk is measured southwest and south of the city. The southern areas increase their risk due to the thickness of their sedimentary soils, low quality of housing construction and high population density.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2007 Fall Meeting