Jorge Aguirre

Inversion of Source Parameters and Site Effects from Strong Ground Motion Records using Genetic Algorithms

The low-frequency flat levels and corner frequencies of the aftershocks of the Kobe earthquake, together with the site effects of the recording stations, are inverted by using genetic algorithms. All records were corrected by the quality factor, Q, of propagation-path, and for each aftershock, a different omega-squared model was assumed such that the low-frequency flat levels and corner frequencies would minimize the standard deviation of the site effects at all stations. It was observed that site effects for rock sites showed significant amplification at high frequencies. This amplification was found to correlate with spectral ratios of records located at 70-m depth and at the surface for one of the stations. After estimating the seismic moment and the stress drop, it was observed that the relation of the seismic moment, M0, versus the corner frequency, fo, followed the scaling law M0 fo 3 . Large values of stress drop were found around asperities on the fault zone and at depth.

Source Characterization of Mexican Subduction Earthquakes from Acceleration Source Spectra for the Prediction of Strong Ground Motions

For the source characterization of Mexican subduction earthquakes we used records from the Guerrero Accelerograph Array for earthquakes occurr- ing during the last 15 years with seismic moments ranging from 6:37E23 to 1:15E28 dynecm. After removing the path and site effects, we obtained the flat level from the source acceleration spectra versus seismic moment and compared it with the relationship proposed by Dan et al. (2001). A new alternative method for characterizing size and stress drop of asperities in source modeling is to use the re- lationship between acceleration source spectral level and seismic moment. We found that the relationship proposed by Dan et al. works appropriately for predicting the flat level of the acceleration spectra for the Mexican subduction earthquakes. To contrast these results we analyzed the aftershocks of the Tokachi-oki, Japan, earthquake of 26 September 2003 and aftershocks. After removing the path and site effects, the flat level of the acceleration spectra in high frequencies clearly and system- atically is underestimated by Dans relation. Even Dans relation has been obtained based on data from different subduction zones in the world; our results show that it is not always applicable. We also found that the fault areas estimated from Brunes formula (Brune, 1970) and the corner frequencies obtained from data of this regional array gave a good es- timation of the size of the biggest asperity. These sizes are well predicted by the re- lationship for subduction earthquakes from the source inversion results given by Somerville et al. (2002). The relationships presented in this work are useful for the source characterization of Mexican subduction earthquakes for the prediction of strong ground motions. That is made from the relationship between acceleration source spectral level and seismic moment. The asperities with area and stress drop (effective stress) are characterized from the acceleration source spectral levels, total source area, and seismic moment.

Simulation of Accelerograms, Peak Ground Accelerations, and MMI for the Tecomán Earthquake of 21 January 2003

Abstract The Tecoman, Mexico, earthquake (21 January 2003, 20:06) shows directivity in the area in which it spread (the Colima graben). The presence of soft soils and the location of 8 out of 10 major urban zones in the area are important factors concerning the acceleration, peak ground acceleration (PGA), and Modified Mercalli Intensity (MMI) caused by this earthquake. Data are not available due to the lack of instrumentation in the area. In this paper we simulate acceleration time histories whose main contribution is to reflect a model that considers the source, the path, and the site effects. In order to reach this objective, we used the source model generated by Ramirez-Gaytan and Aguirre (2008) for the Tecoman earthquake. The PGA and MMI were estimated from the waveforms in 25 points within the state of Colima and eight more outside. Thus, the maximum accelerations obtained are compared with four different ground-motion prediction equations (GMPEs). Our results show an expected and reasonable behavior in agreement with the considerations of each one of the statistical methods compared. In the end, we generated an isoseismal map for the region. This map is overlaid by the isoseismal map for this earthquake generated by other authors (who used traditional methods to determine MMI). First, we conclude that the empirical Green’s function method can be successfully applied to simulate the acceleration waveforms in sites without instrumentation during the mainshock. Second, the simulated records can be successfully used in seismic risk studies.

Reliability of Envelope Inversion for the High-Frequency Radiation Source Process Using Strong Motion Data: Example of the 1995 Hyogoken Nanbu Earthquake

This article presents an application of a procedure to invert the high- frequency radiation process at the source during the 1995 Hyogo-ken Nanbu earth- quake using the envelopes of acceleration waveforms from 16 stations. The inversion uses genetic algorithms that compare observed ground motions with synthetic ones calculated using empirical Greens functions. Before the inversion, the reliability of the solutions for models with different grid sizes is checked. It is found that the resolution of the high-frequency radiation is strongly dependent on the number of reliable data and, for this case, it is shown that a coarse grid model with 60 parameters provides reliable results. With use of this model, the inversion of the high-frequency radiation distribution for the 1995 Hyogo-ken Nanbu earthquake was performed, and results showed four distinct zones of high-frequency radiation. The first zone is located in subfault 1 near a step-over from subfault 1 to the Nojima fault and the starting point of the rupture. The second zone is located in subfault 2 near the lower limit of the slip inverted from low-frequency data by many authors. The third and fourth zones are located in subfault 3, one of them coinciding with the bifurcation of the fault plane into two fault planes (Sekiguchi et al., 2000). It is concluded that the procedure applied in this article successfully inverts the high-frequency radiation distribution for the 1995 Hyogo-ken Nanbu earthquake. Resolution is restricted to the coarse grid model with 60 parameters because of the limited number of stations, according to the resolution test. The results of the reso- lution test done in this work can not be generalized; however, they show that it is very important to check the resolution before doing this kind of inversion.

Lagrangian model, simulation and control of a spherical robot

The derivation of the Lagrangian for different configurations of spherical robots is explored through the use of the Euler Lagrange equations and additional constrains for the generalized velocities. The degrees of freedom are specified with rotation matrices and linear displacement vectors, allowing to determine the necessary elements for all the models in a procedural way, and to obtain the dynamics of the system. One of the thus obtained models is used for simple velocity control tests with two approaches, using the torque and velocity of the rotatory actuators as control inputs, with successful results for a simplified system with one degree of freedom, and satisfactory results for the general system.

Sismicidad y seguridad estructural en las construcciones: lecciones aprendidas en México

Resumen Con la motivacion de los eventos teluricos recientes, se revisa el ambiente sismico en el que Mexico esta inmerso, asi como su sismicidad. Se revisan tambien los mecanismos y regiones de generacion de los temblores. Se mencionan algunos de los parametros que determinan la intensidad y la magnitud de estos asi como la forma de hacer predicciones mediante las funciones de atenuacion con los datos provenientes de las estaciones sismologicas. Se muestra ademas como los colapsos de las estructuras tras el sismo del 19 de septiembre de 2017 en la Ciudad de Mexico se alinean en la zona de transicion entre la vieja area lacustre del valle de Mexico y la zona de lomas. En la parte estructural se presentan los criterios basicos de diseno y como los reglamentos de construccion intentan establecer cual debe ser el desempeno de las estructuras ante acciones de distinta intensidad y frecuencia. Se da un ejemplo de la relacion que existe entre resistencia, dano y desempeno estructural. Se presentan algunos danos observados y se hacen algunas reflexiones sobre los aspectos que influyen en la seguridad de las construcciones y que deberian mejorarse.