Seismic Hazard And Site Response Analyses For Rio Caribe
Authors: Sullya J.P. , Gajardo E. , Paga M. , Fermindez A. , Cascanteb G. 
Published: October 2008

An evaluation of seismic hazard was performed for the Proposed Rio Caribe ollkhore development in order to verifi the seismic parameters for the engineering design. A compilation of the historical and instrumental data suggested that the seismic enviromnentis different from thatassumed in the API RP2A code. A series of sensitivity analyses for the seismic response were performed to evaluate uncertainties in the response taking into account both seismic and geotechnical variations. The results ofthese analyses are presented in this paper and applied to provide a more realistic design acceleration for the offshore platform.

GEOLOGY AND REGIONAL TECTONICS

The north-west region of Venezuela, in the area of study, is Traversed by a complicated series of faults, being close to the boundary between the South America and Caribbean plates. A recent interpretation of the tectonics of the area is presented in Fig, 1. As a result of the interaction between the two a forementioned plates, a 100lan wide fault zone has developed with the principal faults being El Pilar and San Sebastihn.

SEISMIC HAZARD EVALUATION

The seismic hazard is defined as the level or value of the parameter representing ground movement (maximum acceleration, for example) that has a specific probability of being exceeded during a particular defined period of time. Usually, what is obtained is the annual probability of Exceed ence, from which the relevant value for any other time span can be determined. The inverse of the annual probability of exceede nwcau be considered to be equivalent to the average return period, expressed in years,

In general terms, the seismic hazard at a location depends on the following factors:location and geometryof the seismic source zones with respect to the area of interestfrequency of occurrence (recurrence) of earthquakes of different magnitudes in each of the source zones up to and including the maximum value possibleattenuation relationships governing the decay of amplitude with distance between the source and study Site.

The basic methodology employed for the evaluation of seismic hazard incorporates the uncertainties associated with the location of each registered event, the recurrence time for earthquakes of diffiig magnitudes and the dispersion inherent in the attenuation relationships. The informationrequiredin order to evaluate the seismic hazard includes the following:definitionof sourcezones (type, geometry and location)maximum magnitude possible for each source zoneseismic recurrence relationship for each source zonemagnitude-fault rupture length characteristics .attenuation laws for each source in the direction of the site under study

Various probability relationships are required:the probability of occurrence of an earthquake of certain magnitude during a defined period of time, commonly known as the rate of occurrence or averageannual number of events of magnitude, M, for a particular source zonethe probability that the fault rupture surface occurs at a specificdistancefrcxnthe study site, determined from the geometry and rupture length-magnituderelationshipthe probabilitythat the levelof excitation (movement of the soiI surface), resulting from an event of certain magnitude at a certain distance