SEISMIC PRESSURES IN OFFSHORE AREAS: NUMERICAL RESULTS

Abstract

THE PURPOSE OF THIS STUDY IS TO OBTAIN NUMERICAL ESTIMATIONS OF SEISMIC PRESSURES IN OFFSHORE AREAS CONSIDERING THE EFFECT OF SEABED CONFIGURATIONS AND MATERIALS. ACCORDING TO THE BOUNDARY ELEMENT METHOD, BOUNDARY ELEMENTS ARE USED TO IRRADIATE WAVES AND FORCE DENSITIES ARE DETERMINED. FROM THIS HYPOTHESIS, HUYGENS´ PRINCIPLE IS IMPLEMENTED SINCE THE DIFFRACTED WAVES ARE CONSTRUCTED AT THE BOUNDARY FROM WHICH THEY ARE RADIATED. APPLICATION OF BOUNDARY CONDITIONS ALLOWS US TO DETERMINE A SYSTEM OF INTEGRAL EQUATIONS OF FREDHOLM TYPE OF SECOND KIND. VARIOUS MODELS WERE ANALYZED, THE FIRST ONE IS USED TO VALIDATE THE PROPOSED FORMULATION. OTHER MODELS OF IDEAL SEABED CONFIGURATIONS ARE DEVELOPED TO ESTIMATE THE SEISMIC PRESSURE PROFILES AT SEVERAL LOCATIONS. THE INFLUENCE OF P- AND SV-WAVE INCIDENCE WAS ALSO HIGHLIGHTED. IN GENERAL TERMS, MATERIALS WITH HIGHER WAVE PROPAGATION VELOCITIES GENERATE A LESSER PRESSURE FIELD. THE DIFFERENCE BETWEEN THE MAXIMUM PRESSURE VALUES OBTAINED FOR A MATERIAL WITH SHEAR WAVE VELOCITY OF β=3000 M/S IS APPROXIMATELY 9 TIMES LOWER THAN THOSE OBTAINED FOR A MATERIAL WITH β=90 M/S, FOR THE P WAVE INCIDENCE, AND 2.5 TIMES FOR THE CASE OF SV WAVES. THESE RESULTS ARE RELEVANT BECAUSE THE SEABED MATERIAL HAS DIRECT IMPLICATIONS ON THE PRESSURE FIELD OBTAINED.