Monograph records
https://feeds.library.caltech.edu/people/Asimaki-D/monograph.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 28 Nov 2023 16:55:29 +0000Geometrical Optics applied to 1D Site Response of Inhomogeneous Soil Deposits
https://resolver.caltech.edu/CaltechAUTHORS:20200220-090311459
Authors: Garcia-Suarez, Joaquin; Asimaki, Domniki; Seylabi, Elnaz E.
Year: 2020
DOI: 10.31224/osf.io/db7jv
The technique referred as Geometrical Optics entails considering the wave propagation in a heterogeneous medium as if it happened with infinitely small wavelength. This classic simplification allows to obtain useful approximate analytical results in cases where complete description of the waveform behavior is virtually unattainable, hence its wide use in Physics. This approximation is also commonly termed Ray Theory, and it has already been thoroughly applied in Seismology. This text presents an application of Geometrical Optics to 1D Site Response (1DSR): it is used herein to, first, explain and elucidate the generality of some previous observations and results; second, to partially settle an open question in 1DSR, namely "what are the equivalent homogeneous properties that yield the same response, in terms of natural frequencies and resonance amplitude, for a certain inhomogeneous site?", provided few assumptions.https://authors.library.caltech.edu/records/93zwy-z6k13Dimensional Analysis: Overview and applications to problems of Soil-Structure Interaction
https://resolver.caltech.edu/CaltechAUTHORS:20200220-144007826
Authors: Kusanovic, Danilo S.; Garcia-Suarez, Joaquin; Asimaki, Domniki
Year: 2020
DOI: 10.31224/osf.io/m3ycp
Dimensional Analysis is a long-established tool widely used in many branches of engineering and science. However, applications in geotechnical engineering, and in particular soil-structure interaction (SSI), have barely been explored, in spite of the method's potential to clarify parameter influence and shed light on the range of response regimes. The purpose of this text is twofold: (a) it intends to provide a brief introduction to Dimensional Analysis specifically tailored to geotechnical engineers by carefully choosing illustrative examples, (b) it uses Dimensional Analysis to study the parameter space in soil-building interaction problems, emphasizing modeling choices and using a finite-element model to demonstrate the concept of physical similarity. The suitability of using certain dimensionless parameters over others is discussed based on and their magnitude and sensitivity analysis.https://authors.library.caltech.edu/records/v9te7-1fr64Geotechnical Site Characterization via Deep Neural Networks: Recovering the Shear Wave Velocity Profile of Layered Soils
https://resolver.caltech.edu/CaltechAUTHORS:20201002-151457704
Authors: Ayoubi, Peyman; Seylabi, Elnaz; Asimaki, Domniki
Year: 2020
DOI: 10.31224/osf.io/jcw3t
The mechanical property of soils is a vital part of seismic hazard analysis of a site. Such properties are obtained by either in-situ (destructive) experiments such as crosshole or downhole tests, or by non-destructive tests using surface wave inversion methods. While the latter is more favorable due to the cost-efficiency, there are challenges mostly due to computational need, non-uniqueness of inversion results, and fine-tuning parameters. In this article, we use a deep learning framework to circumvent the above-mentioned limitations to output soil mechanical properties, requiring dispersion data as input. Our trained model performs with high accuracy on the test dataset and shows satisfactory performance compared to the ensemble Kalman inversion technique. We finally propose a framework to extend the method to higher dimensions by numerically solving the wave equation in a two-dimensional medium.https://authors.library.caltech.edu/records/t0nw9-et471Data-driven Accelerogram Synthesis using Deep Generative Models
https://resolver.caltech.edu/CaltechAUTHORS:20210111-160825629
Authors: Florez, Manuel A.; Caporale, Michaelangelo; Buabthong, Pakpoom; Ross, Zachary E.; Asimaki, Domniki; Meier, Men-Andrin
Year: 2021
DOI: 10.48550/arXiv.2011.09038
Robust estimation of ground motions generated by scenario earthquakes is critical for many engineering applications. We leverage recent advances in Generative Adversarial Networks (GANs) to develop a new framework for synthesizing earthquake acceleration time histories. Our approach extends the Wasserstein GAN formulation to allow for the generation of ground-motions conditioned on a set of continuous physical variables. Our model is trained to approximate the intrinsic probability distribution of a massive set of strong-motion recordings from Japan. We show that the trained generator model can synthesize realistic 3-Component accelerograms conditioned on magnitude, distance, and V_(s30). Our model captures the expected statistical features of the acceleration spectra and waveform envelopes. The output seismograms display clear P and S-wave arrivals with the appropriate energy content and relative onset timing. The synthesized Peak Ground Acceleration (PGA) estimates are also consistent with observations. We develop a set of metrics that allow us to assess the training process's stability and tune model hyperparameters. We further show that the trained generator network can interpolate to conditions where no earthquake ground motion recordings exist. Our approach allows the on-demand synthesis of accelerograms for engineering purposes.https://authors.library.caltech.edu/records/je98a-2c414Analytical 1D transfer functions for layered soils
https://resolver.caltech.edu/CaltechAUTHORS:20211206-445261197
Authors: Garcia-Suarez, Joaquin; Asimaki, Domniki
Year: 2021
DOI: 10.31224/osf.io/n43cv
Transfer functions are constantly used in both Seismology and Geotechnical Earthquake Engineering to relate seismic displacement at different depths within strata. In the context of Diffusive Theory, they also appear in the expression of the imaginary part of 1D Green's functions. In spite of its remarkable importance, their mathematical structure is not fully understood yet, except in the simplest cases of two or three layers at most. This incomplete understanding, in particular as to the effect of increasing number of layers, hinders progress in some areas, as researchers have to resort to expensive and less conclusive numerical parametric studies. This text presents the general form of transfer functions for any number of layers, overcoming the above issues. Owing to the formal connection between seismic wave propagation and other phenomena that, in essence, represent different instances of wave propagation in a linear-elastic medium, one can extend the results derived elsewhere [Garcia-Suarez, Joaquin. 2021. "Trace Spectrum of 1D Transfer Matrices for Wave Propagation in Layered Media." engrXiv. June 24. doi:10.31224/osf.io/ygt8z] in the context of longitudinal wave propagation in modular rods to seismic response of stratified sites. The knowledge of the general closed-form expression of the transfer functions allows to analytically characterize the long-wavelength asymptotics of the horizontal-to-vertical spectral ratio for any number of layers.https://authors.library.caltech.edu/records/z2knf-1zv93Monte Carlo Simulation to Study the Spatial Variation of Ground Motion Associated with Basin Heterogeneities
https://resolver.caltech.edu/CaltechAUTHORS:20220517-740389000
Authors: Ayoubi, Peyman; Asimaki, Domniki
Year: 2022
DOI: 10.31224/2285
Basin effects cause a complex wave interference inside a basin which can be attributed to basin versus bedrock material contrast and edge effect. This will have a significant impact on spatial variation, duration, and intensity of surface ground motion (SGM) during an earthquake. While important, the lack of sufficient information about material properties and stratigraphy of a basin prevents accurate simulation of the phenomena, particularly in high frequency regime. Stochastic analysis and the Monte Carlo technique are suitable approaches to address this issue, where basin material is represented by a correlated random field. In this study, We use a 2D finite element analysis of an idealized-shaped basin subjected to a vertically propagating SV plane wave and investigate the spatial variation of SGM associated with basin effects by assuming a correlated random field to represent basin material. We generate a random medium by adding perturbations to a homogeneous domain with various correlation lengths, coefficient of variations, and autocorrelation functions to evaluate their contribution to SGM. Our results show a difference between the output of homogeneous and stochastic models, where we conclude that the former would not represent basin response, especially in the high-frequency regime correctly. Among the parameters we consider, the coefficient of variation has the most influential impact on surface acceleration. We observe that increasing this parameter decreases the mean value of surface amplification while its standard deviation increases. In addition, correlation length affects the standard deviation of surface acceleration, but it does not significantly impact the mean amplification. As for the autocorrelation function, where we consider von Karman, Gaussian, and exponential, the results show that the trend of surface amplification does not change by choosing a different autocorrelation function. Finally, by comparing the 2D basin versus 1D layered medium, we show that one cannot accurately capture basin response by using a 1D analysis for seismic hazard quantification.https://authors.library.caltech.edu/records/wxn9d-5ya44A method to generate initial fault stresses for physics-based ground motion prediction consistent with regional seismicity
https://resolver.caltech.edu/CaltechAUTHORS:20220520-388187000
Authors: Oral, Elif; Ampuero, Jean Paul; Ruiz, Javier; Asimaki, Domniki
Year: 2022
DOI: 10.1002/essoar.10511188.2
Near-field ground motion is the major blind spot of seismic hazard studies, mainly because of the challenges in accounting for source effects. Initial stress heterogeneity is an important component of physics-based approaches to ground motion prediction that represent source effects through dynamic earthquake rupture modeling. We hypothesize that stress heterogeneity on a fault primarily originates from past background seismicity. We develop a new method to generate stochastic stress distributions as a superposition of residual stresses left by previous ruptures that are consistent with regional distributions of earthquake size and hypocentral depth. We validate our method on M_w 7 earthquake models suitable for California, by obtaining a satisfactory agreement with empirical earthquake scaling laws and ground motion prediction equations. To avoid the excessive seismic radiation produced by dynamic models with abrupt arrest at preset rupture borders,
we achieve spontaneous rupture arrest by incorporating a scale-dependent fracture energy adjusted with fracture mechanics theory. Our analyses of rupture and ground motion reveal particular signatures of the initial stress heterogeneity: rupture can locally propagate at supershear speed near the highly-stressed areas; the position of high-stress and low-stress areas due to initial stress heterogeneity determines how the peak ground motion amplitudes and polarization spatially vary along the fault, as low-stress areas slows down the rupture, decrease stress drop, and change the radiation distribution before the rupture arrest. We also find that the medium stratification amplifies the moment rate spectrum at frequencies above 2 Hz, which requires understanding the interaction between site effects and rupture dynamics; therefore, we highlight the need to consider a realistic fault medium on future studies of rupture dynamics. Our approach advances our understanding of the relations between dynamic features of earthquake ruptures and the statistics of regional seismicity, and our capability to model source effects for near-field ground motion prediction studies.https://authors.library.caltech.edu/records/h6c4h-7g059