The Analysis of Accelerograms for the Earthquake Resistant Design of Structures

In this paper, the analysis of ground motions (displacements, velocities and accelerations) has been performed focused to the seismic design. The relationships between the peak ground acceleration (PGA), the peak ground velocity (PGV), the peak ground displacement (PGD) and the bracketed duration, with the earthquake magnitude, are presented and their validity and applicability for seismic design is discussed. Finally, the dominant periods of the ground motions (displacement, velocity and acceleration) are obtained from their Fourier Spectrum. Their validity and applicability for the seismic design is discussed also. The results presented in this paper show that the relationships that exist between the important parameters: PGA, PGV, PGD and duration;and the earthquake magnitude, allow the prediction of the values for these parameters, in terms of the magnitude for future strong motions. These predictions can be very useful for seismic design. Particularly, the prediction of the magnitude associated to the critical acceleration, because the earthquakes with magnitude greater than this critical magnitude can produce serious damages in a structure (even its collapsing). The application of the relationships obtained in this paper must be very careful, because these equations are dependent on the source area, location and type of structure. The dominant periods of the ground motions (displacement, velocity and acceleration) that are computed and presented in this paper, are also important parameters for the seismic design, because recent studies have shown that the earthquake shaking is more destructive on structures having a natural period around some of these dominant periods. These parameters must also be handled with caution, because they show dependence with the source area, location and type of structure.

Determination of a Gravimetric Geoid Solution for Andalusia (South Spain)

The orthometric heights can be obtained without levelling by means of the ellipsoidal and geoidal heights. For engineering purposes, these orthometric heights must be determined with high accuracy. For this reason, the determination of a high-resolution geoid is necessary. In Andalusia (South Spain) a new geopotential model (EIGEN-GL04C) has been available since the publication of a more recent regional geoid. As a consequence, these new data bring about improvements that ought to be included in a new regional geoid of Andalusia. With this aim in mind, a new gravimetric geoid determination has been carried out, in which these new data have been included. Thus, a new geoid is provided as a data grid distributed for the South Spain area from 36 to 39 degrees of latitude and –7 to –1 degrees of longitude (extending to 3 × 6 degrees), in a 120 × 240 regular grid with a mesh size of 1.5’ × 1.5’ and 28800 points in the GRS80 reference system. This calculated geoid and previous geoids are compared to the geoid undulations obtained for 262 GPS/levelling points, distributed within the study area. The new geoid shows an improvement in accuracy and reliability, fitting the geoidal heights determined for these GPS-levelling points better than any previous geoid.

A Methodology for Filtering and Inversion of Gravity Data: An Example of Application to the Determination of the Moho Undulation in Morocco

In this paper, we perform a comprehensive explanation of the geophysical inversion of gravity data, as well as, how it can be used to determine the Moho undulation and the crustal structure. This inversion problem and the necessary assumptions to solve it will be described in this paper joint to the methodology used to invert gravity data (gravity anomalies). In addition, the application of this method to the determination of the Moho undulation will be performed computing the Moho undulation in the Moroccan area, as an example. Before the inversion, it is necessary the removing of the gravity effects for shallow and very deep structures, to obtain the deep gravity anomaly field that is associated to the deep structure and Moho undulation. These effects will be removed by a filtering process of the gravity anomaly field and by subtraction of the gravity anomalies corresponding to the very deep structure. The results presented in this paper will show that the inversion of gravity data is a powerful tool, to research the structure of the crust and the upper mantle. By means of this inversion process, the principal structural features beneath of Morocco area will be revealed.