Browsing by Author "Venegas-Aravena, Patricio"

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    Fractal Spatial Distributions of Initial Shear Stress and Frictional Properties on Faults and Their Impact on Dynamic Earthquake Rupture
    (2024) Venegas-Aravena, Patricio; Crempien, Jorge G. F.; Archuleta, Ralph J.
    We investigate the influence of the heterogeneous slip-weakening distance ( D-C ) in dynamic rupture simulations, in which D-C is proportional to the fault irregularities. Specifically, we compare a heterogeneous fractal D-C distribution to a uniform D-C over the entire fault when the initial shear stress is also heterogeneous. We find that even small changes in the average value of D-C ( < 1 mm) can lead to significant differences in the rupture evolution; that is, the average D-C and the way D(C )is distributed determines if the rupture is a runaway, self-arrested, or nonpropagating. We find that the self-arrested ruptures differ from runaway ruptures in the amount of area characterized by large slips (asperities). Self-arrested ruptures match the Somerville et al. (1999) asperity criteria in which - 25% of ruptured area radiate - 45% of the total seismic moment. This criterion is not satisfied for runaway ruptures. For runaway ruptures, - 50% of the ruptured area radiates about 70% of the seismic moment, indicating that the ruptured area is not linearly proportional to the seismic moment. Self-arrested ruptures are characterized by dynamic shear stress drops (SDs) in the range - 2.9 -5.5 MPa, whereas for runaway ruptures the dynamic SDs increase to values between -12 and 20 MPa. Self-arrested ruptures generated by fractal distributed D-C resemble the rupture properties of observed earthquakes. In addition, results show that the conditions for self-arrested ruptures are connected to the decrease of residual energy at rupture boundaries.
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    Heterogeneous self-arrested ruptures leading to spatial variability of radiated energy and Doppler effect of the observed corner frequency
    (2023) Venegas-Aravena, Patricio
    The study of the strong ground motion is of utmost relevance because the amplitude of seismic waves and their frequency content could severely damage structures. As both the amplitude and the frequency content directly depend on the seismic source, a proper description and simulations of the earthquakes’ rupture process are required. This means that realistic source models should incorporate a heterogeneous distribution of rupture parameters that generates self-arrested ruptures. One of these models is a heterogeneous energy-based (HE-B) method, which can describe the kinematic rupture process based on the distribution of residual energy (Eres). This parameter defnes zones in faults where the accumulated energy is larger than the dissipated energy. In this context, this study presents the spatial variations of radiated energy, corner frequency, and stress drop at far-feld distances as a consequence of the heterogeneous distribution of positive residual energy. It is found that the rupture of asperities, determined by large values of Eres, strongly shifts the frequency content and generates a Doppler efect of the frequency content. That is, the location in the far-feld in direction where the asperity is being ruptured generates traveling waves characterized by an increase of the observed corner frequency, which corresponds to the corner frequency measured by the observer. This implies that diferent station measures diferent frequency content implying diferent estimations of the source parameters. Besides, the variability of the observed corner frequency could break the scaling between the corner frequency and the magnitude. Nevertheless, it is also found that the average observed corner frequency, when considering all the points or stations, is almost the same as that obtained for the seismic source. A similar property is found for radiated energy and stress drop. These results show that the ground motion at a given location varies depending on the heterogeneities of the section of the fault being ruptured.
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    The effect of spatial frictional heterogeneities on the dynamic rupture process on faults
    (2021) Venegas-Aravena, Patricio; Jorge G.F. Crempien; Ralph Archuleta