Browsing by Author "Fernández Soto, Claudio"

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    Reconnaissance observations by CIGIDEN after the 2015 Illapel, Chile earthquake and tsunami
    (National Information Centre of Earthquake Engineering, 2017) Rivera Jofré, Felipe Andrés; Jünemann Ureta, Rosita; Candia, Gabriel A.; Favier, Philomène; Fernández Soto, Claudio; Chacón de la Cruz, Matías Fernando Nicolás; Hube Ginestar, Matías Andrés; Chamorro Giné, Marcela Alondra; Aguirre Aparicio, Paula; Llera Martin, Juan Carlos de la; Poulos Campbell, Alan John; Illapel earthquake; Critical infrastructure
    This paper describes the reconnaissance work conducted by researchers from the National Research Center for Integrated Natural Disaster Management (CIGIDEN) between September 23rd and October 2nd in the area affected by the Mw 8.3 Illapel megathrust earthquake, which struck offshore the coast of the Coquimbo Region in central Chile on September 16th, 2015. A first team focused on the seismic performance and effects of the tsunami on public hospitals and on reinforced concrete (RC) buildings. A second team focused on the road network infrastructure. Field work included: (i) a survey on the physical and functional damages of the public hospitals in the Region; (ii) a visual inspection and preliminary damage assessment of 20 RC buildings in the largest cities of the region and an aftershock instrumentation of the Coquimbo hospital; and (iii) the inspection of bridges, pedestrian bridges, and rockfall along overstepped cut slopes of the road network. The overall limited impact of this megathrust earthquake may be explained in part by the long-term efforts made by the country to prepare for such events. Learnings from the 2010 Maule earthquake were evidenced in the successful evacuation along the coast of the country, and the overall good performance of engineered masonry structures, and of RC buildings designed after 2010.
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    Simulation of pulse-like ground motions during the 2015 Mw 8.3 Illapel earthquake with a new source model using corrected empirical Green's functions
    (SEISMOLOGICAL SOC AMER, 2022) Fernández Soto, Claudio; Nozu, Atsushi; Crempien de la Carrera, Jorge Gustavo Federico; Llera Martin, Juan Carlos de la
    Pulse-like near-source ground motions were observed by the local network during the 2015 Mw 8.3 Illapel, Chile earthquake. Such ground motions can be quite damaging to a wide range of infrastructures. The primary objective of this study is to provide a source model that can explain such ground motions. The isolated nature of the pulses indicated that the rupture of some small isolated region on the fault contributed to the generation of the pulse. Therefore, we considered such regions and termed them as Strong Motion Pulse Generation Areas (SPGAs). We used the corrected empirical Green's function (EGF) method because this method has been successfully applied to near-source pulse-like ground motions in previous studies. We simulated synthetic waveforms using the frequency dependent quality factor Q = 239f0:71 and empirical site amplification factors, which we obtained by applying a generalized inversion technique to local weakmotion data. The result indicated that the observed ground motions from the Mw 8.3 Illapel earthquake can readily be explained with a source model that involves two SPGAs with dimensions of several kilometers in spite of the huge rupture zone of the earthquake. The source model can reproduce velocity waveforms, acceleration Fourier amplitude spectra (FAS) and pseudoacceleration response spectra. It also reproduces the duration of strong ground motions quite accurately. No significant bias was found with respect to distance and frequency. In conclusion, the corrected EGF method is a very efficient tool to simulate near-source ground motions of a subduction earthquake when it is combined with higher stress-drop subevents whose sizes are adjusted to the observed pulse widths.
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    Strong ground motion simulation of the 2015 Illapel earthquake using corrected empirical Green’s functions
    (National Information Centre of Earthquake Engineering, 2017) Fernández Soto, Claudio; Aguirre Aparicio, Paula; Llera Martin, Juan Carlos de la; Candia, Gabriel A.; Nozu, A.
    The September 16th 2015 Illapel, Chile, earthquake (Mw 8.4) generated a good set of aftershock data that enabled us to develop and to validate a model for synthetic ground motion generation. This study presents a methodology to generate strong ground motions based on site amplification and phase characteristics of seismic waves, and also based on a source model that was newly developed for the earthquake. The methodology includes the superposition of corrected empirical Green’s functions that consider the three effects: source, path and site. The path effects incorporate the attenuation of seismic waves between the source and the recording stations, and include both geometric spreading and inelastic attenuation. Weak motion data obtained at the strong-motion stations was used to evaluate empirical site amplification factors. For this purpose, aftershocks recorded during the first three months after the main shock were used. Furthermore, the phase characteristics of the Green’s functions were determined based on the weak motion data recorded at the stations. The source model involves two SPGAs (strong-motion pulse generation areas). The locations of the SPGAs were basically determined based on the arrival times of the velocity pulses. The SPGA sizes were chosen according to the pulse duration. The methodology was validated using observed records in terms of velocity waveforms and Fourier spectra. According to the results, the velocity waveforms including pulses were well reproduced in a frequency range of interest to structural engineering (0.2 to 1 Hz). The agreement between the simulated and measured waveforms makes this model a strong platform to assess hazard at specific sites where detailed hazard assessment is required.