Browsing by Author "Fortuño Jara, Catalina Pía"

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    Rupture parameter sensitivity of low frequency ground motion response spectra using synthetic scenarios in North Chile
    (SPRINGER, 2021) Fortuño Jara, Catalina Pía; Llera Martin, Juan Carlos de la; Gonzalez, Gabriel; Gonzalez, Juan; Aguirre Aparicio, Paula
    This research performs a sensitivity analysis of response spectrum values for various physical earthquake parameters, which are used to generate synthetic seismograms consistent with the expected seismicity in north Chile. Sensitivity analyses are based on the earthquake scenario and slip distribution model of the 2014, M-w 8.1 Pisagua earthquake, and seven other physically plausible interplate events for north Chile. A finite-fault rupture model, and slip distribution of the Pisagua earthquake, were obtained using inversion of InSAR and GPS data. Three other rupture models based on previous studies of interplate locking for north Chile and capable of generating M-w 8.3-8.6 earthquakes with an estimated maximum slip of 9.2 m, were incorporated in the analyses. Also, four additional scenarios with moment magnitudes in the range M-w 8.6-8.9 were generated by concatenating these physical scenarios into larger rupture areas within the north segment. Using these scenarios, synthetic ground motions were built at four observation sites: Pisagua, Iquique, Tocopilla, and Calama. Response sensitivity was studied for three key rupture parameters: mean rupture velocity, slip rise-time, and rupture directivity. Responses selected were peak ground displacement (PGD), spectral pseudo-velocities, S-v, and spectral displacements, S-d. First and second order variations of PGD, S-v, and S-d relative to the source parameters were computed and used together with a Taylor series expansion to propagate uncertainty into the responses as a function of v(r) and rise-time t(r). To study the effect of rupture directivity, three different foci locations were considered for each scenario: north, south, and at the centroid of the slip model. Response PGD values show no clear trends with rupture velocity, v(r); however, the variability increases as the system period increases. The effect of the slip rise-time is significant, and as t(r) increases, the spectral responses tend to decrease, suggesting that shorter slip rise-times lead to higher seismic demands in long period structures. The results obtained for the directivity analysis suggest that two factors control the expected waveforms and spectral responses: first, the direction of the rupture relative to the location of each site, and the hypocentral distance.
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    Sensitivity of synthetic seismograms for different seismic scenarios in north Chile
    (National Information Centre of Earthquake Engineering, 2017) Fortuño Jara, Catalina Pía; Llera Martin, Juan Carlos de la; González López, Gabriel; González, Juan; Aguirre Aparicio, Paula
    This research studies the sensitivity of spectral response values to various physical earthquake scenario parameters, the latter used to generate synthetic low frequency seismograms in North Chile. Ten earthquake scenarios have been defined using seed information from the slip model of the 2010, Maule earthquake, and different physically plausible interplate locking models in the region. Firstly, the Maule 2010 finite fault rupture model was resituated in the existing seismic gap in north Chile using a curved geometry according to the Slab 1.0 model. From this seed model, one synthetic scenario with constant moment magnitude Mw 8.8 was generated with the same slip distribution as the original 2010 slip model. Three other models with variations in the slip distribution were considered. In addition, three physically plausible fault rupture models based on previous studies of interplate locking were used. Each of these scenarios was capable of generating Mw 8.2 – 8.4 earthquakes with a maximum slip of 7.5 m, approximately. Patches of major slip were located along the coast line approximately in front of the cities of Arica, Iquique, and Tocopilla, respectively. Also, three additional scenarios with moment magnitudes in the range Mw 8.5 – 8.7 were built by connecting these physical scenarios into larger rupture areas. These combined interplate locking models represented the activation of two or more asperities, similar to the experience of the 2010 Maule earthquake. Using these scenarios we built low frequency synthetic seismograms at four control sites: Arica, Iquique, Tocopilla, and Calama. The sensitivity of these results was studied by deterministic analyses on some key rupture parameters, such as mean rupture velocity and slip rise-time. Sensitivity analysis used peak ground displacement (PGD) and acceleration (PGA), pseudo-acceleration spectra, Sa, and displacement spectra, Sd. The range of values considered for mean rupture velocity was vr = 2.2-3.0 km/s. Four points were considered in the vicinity of each specified velocity to compute sensitivities. First and second order derivatives of PGD, PGA, Sd, and Sa relative to the source parameters were then used to build a Taylor series expansion to predict PGD, Sa and Sd as a function of vr. This allows to consider uncertainty in this parameter and propagate such uncertainty into spectral response values. An analogous procedure was considered for rise-time tr in the range from 2 to 10s.
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    Synthetic hybrid broadband seismograms based on InSAR coseismic displacements
    (2012) Fortuño Jara, Catalina Pía; Llera Martin, Juan Carlos de la; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    El terremoto de Maule del 2010 movilizó un área de aproximadamente 540 por 200 km de la zona de subducción del centro de Chile, produciendo desplazamientos superficiales de hasta 3-4 metros hacia el oeste. Los acelerogramas registrados, fundamentales para describir solicitaciones sísmicas, comúnmente poseen ruido de baja frecuencia que debe ser eliminado mediante pro- cesos de corrección, perdiéndose usualmente información sobre los desplazamientos residuales. Este trabajo, propone calcular sismogramas de amplio espectro consistentes con desplazamientos cosísmicos, para mejorar la caracterización de la demanda sísmica para periodos largos. El proced- imiento realizado, consiste en cuatro fases: analisis InSAR, inversión sísmica, funciones de Green y registros sintéticos. En primer lugar, se obtienen interferogramas mediante procesamiento SAR e InSAR, para estimar los desplazamientos superficiales en el área afectada. Esta información, es usada para construir un modelo discretizado del plano de falla, estimando el deslizamiento en cada elemento, y luego, la respuesta dinámica en un sitio, es calculada usando funciones de Green y un enfoque matricial de la teoría de propagación de ondas.
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    Synthetic Hybrid Broadband Seismograms Based on InSAR Coseismic Displacements
    (2014) Fortuño Jara, Catalina Pía; Llera Martin, Juan Carlos de la; Wicks, Charles W.; Abell, José A.
    Conventional acceleration records do not properly account for the observed coseismic ground displacements, thus leading to an inaccurate definition of the seismic demand needed for the design of flexible (long period) structures. Large coseismic displacements observed during the 27 February 2010 Maule earthquake suggest that this effect should be included in the design of flexible structures by modifying the design ground motions and spectra considered. Consequently, Green's functions are used herein to compute synthetic low-frequency seismograms that are consistent with the coseismic displacement field obtained from interferometry using synthetic aperture radar (SAR) images. In this case, the coseismic displacement field was determined by interfering twenty SAR images of the Advanced Land Observation Satellite (ALOS)/PALSAR satellite taken between 12 October 2007 and 28 May 2010. These images cover the region affected by the 2010 M-w 8.8 Maule earthquake. Synthetic broadband seismograms are built by superimposing the low-pass filtered synthetic low-frequency seismograms with high-frequency strong-motion data. The broadband seismograms generated are then consistent with the coseismic displacement field and the high-frequency content of the earthquake. A sensitivity analysis is performed using three different fault and slip parameters, the rupture velocity, the corner frequency, and the slip rise time. Results show that the optimal corner frequency of the low-pass filter f(c) = 1/T-c, leads to a trade-off between acceleration and displacement accuracy. Furthermore, spectral response for long periods, say T >= 8 s, is relatively insensitive to the value of T-c, whereas shorter periods are strongly dependent on both the slip rise time and T-c. In general, larger displacements consistent with coseismic data are obtained using this technique instead of digitally processing the acceleration ground-motion records.