Seismic Hazard and Ground Motion Characterization at the Itoiz Dam (Northern Spain)

Abstract

Abstract-This paper presents a new hazard-consistent ground motion characterization of the Itoiz dam site, located in Northern Spain. Firstly, we propose a methodology with different approximation levéis to the expected ground motion at the dam site. Secondly, we apply this methodology taking into account the particular characteristics of the site and of the dam. Hazard calculations were performed following the Probabilistic Seismic Hazard Assessment method using a logic tree, which accounts for different seismic source zonings and different ground-motion attenuation relationships. The study was done in terms of peak ground acceleration and several spectral accelerations of periods coinciding with the fundamental vibration periods of the dam. In order to estímate these ground motions we consider two different dam conditions: when the dam is empty (T = 0.1 s) and when it is filled with water to its máximum capacity (T = 0.22 s). Additionally, seismic hazard analysis is done for two return periods: 975 years, related to the project earthquake, and 4,975 years, identified with an extreme event. Soil conditions were also taken into account at the site of the dam. Through the proposed methodology we deal with different forms of characterizing ground motion at the study site. In a first step, we obtain the uniform hazard response spectra for the two return periods. In a second step, a disaggregation analysis is done in order to obtain the controlling earthquakes that can affect the dam. Subsequently, we characterize the ground motion at the dam site in terms of specific response spectra for target motions defined by the expected valúes SA (7) of T = 0.1 and 0.22 s for the return periods of 975 and 4,975 years, respectively. Finally, synthetic acceleration time histories for earthquake events matching the controlling parameters are generated using the discrete wave-number method and subsequently analyzed. Because of the short relative distances between the controlling earthquakes and the dam site we considered finite sources in these computations. We conclude that directivity effects Special issue on Deformation and Gravity Change: Indicators of Isostasy, Tectonics, Volcanism and Climate Change PAGEOPH.should be taken into account as an important variable in this kind of studies for ground motion characteristics.

Surface dynamic deformation estimates from local seismicity: the Itoiz reservoir, Spain

“…The largest earthquakes reported for the Itoiz region have magnitudes between 4.8 and 5.5, generating intensities between V and IV in the Pamplona region (Ruiz et al 2006a). Based on the probabilistic seismic hazard assessment performed for the Itoiz dam region by Rivas-Medina et al, (2012), using earthquake databases for the region including events occurring in different active fault systems near the Itoiz dam, an M w 5.5 earthquake in the region near the dam can be expected.…”

“…In the western part of the Pyrenees, the seismicity during the second half of the last century appears relatively sparse with small to moderate magnitudes (up to M=5.5) and shallow depths (e.g. Rivas-Medina et al 2012;Souriau et al 2014). However, at least six destructive earthquakes have been reported in this area (e.g.…”

“…Martínez-Solares and Mezcua 2003;Benito et al 2008). Rivas-Medina et al (2012) obtained from PSHA analysis, peak ground accelerations for the Itoiz dam site of PGA=0.10g for 975 years of return period (RP) and PGA=0.17g for 4,975 years RP. They also estimated maximum spectral accelerations SA(0.1s)=0.27g for 975 years RP and SA(0.1s)=0.44g for 4,975 years RP.…”

Control Spectra for Quito

“…Comparisons between control spectra or specific response spectra obtained with empirical GMPEs (ground motion prediction equations) and a seismic code spectrum have been made in other cities or seismic zones as mentioned in Gaspar-Escribano et al (2008), Hao and Gaull (2009) and Nunziata et al (2011), inter alia. Control spectra or specific response spectra are also used to estimate the seismic hazard and risk in cities or specific sites (Rivas-Medina et al, 2011, 2014a.…”