@article{ji_cabas_kottke_pilz_macedo_liu_2023, title={A DesignSafe earthquake ground motion database for California and surrounding regions}, volume={39}, ISSN={["1944-8201"]}, DOI={10.1177/87552930221141108}, abstractNote={This article presents a ground motion database for California and its close surroundings (i.e. areas near the border in Nevada, Oregon, and Arizona) from earthquakes between 1999 and 2021. This data set includes events with magnitudes larger than 3.2 and focal depths less than 40 km, and it is available on DesignSafe. Ground motion records and events included in this data set are collected from 65 different seismic networks and processed with an automated software tool called gmprocess, which was developed by the United States Geological Survey (USGS). Path measures such as rupture distance and epicentral distance are computed, 5%-damped spectral accelerations, duration metrics, and other ground motion intensity measures (IMs) are provided for records that pass the quality assurance check performed by the gmprocess toolkit. The quality of processed ground motions is also screened by using outlier detection algorithms and a multiple wave-train arrivals identification algorithm. In addition, site metadata are provided, including wave velocity information (from proxy-based time-averaged shear-wave velocity for the top 30 m, Vs30, and from P- and S-wave measured velocity profiles when available), predominant frequency measured from microtremor-based horizontal-to-vertical ratios (mHVSR), and site-specific (high-frequency spectral decay) κ 0 values computed from multiple ground motions recorded at sites when available. The final database contains 287,804 three-component ground motions recorded at 3709 stations from 2641 earthquakes with magnitudes and distances ranging from 3.2 to 7.2 and 0.15 to 335 km, respectively. This ground motion database contributes to advancing both engineering seismology studies and earthquake engineering applications in shallow crustal tectonic settings.}, number={1}, journal={EARTHQUAKE SPECTRA}, author={Ji, Chunyang and Cabas, Ashly and Kottke, Albert and Pilz, Marco and Macedo, Jorge and Liu, Chenying}, year={2023}, month={Feb}, pages={702–721} }
 @article{cabas_rodriguez-marek_green_ji_2022, title={Quantifying the Error Associated with the Elastic Halfspace Assumption in Site Response Analysis}, volume={148}, ISSN={["1943-5606"]}, DOI={10.1061/(ASCE)GT.1943-5606.0002893}, abstractNote={One of the fundamental decisions when performing one-dimensional (1D) site response analyses (SRA) involves the selection of the depth and dynamic properties of the elastic halfspace (EHS). This boundary condition assumes linear and homogenous material underlying the soil column for an infinite depth. This assumption implies that waves refracted into the EHS are fully absorbed, and as a result, energy from waves that are potentially reflected back toward the surface from deeper impedance contrasts in the actual geologic profile are not accounted for in the SRA. If a strong soil-rock seismic impedance contrast is present at the site of interest, the EHS boundary is typically set at that depth. However, the actual geologic profile below this impedance contrast may not be in accord with the assumed properties of the EHS, which can lead to systematic errors in the SRA. An analytical expression to quantify these errors is derived in this study, verified using an idealized three-layer profile, and compared to case studies of nine real sites in Charleston, South Carolina. Our results show that the presence of a single strong impedance contrast does not suffice as the sole condition to define the EHS boundary. Frequency-dependent errors in site amplification associated with the assumptions inherent to the EHS used in the SRA can be evaluated as a function of multiple impedance contrasts present in the profile. Smaller errors are associated with strong impedance contrasts at shallower layers and/or minimal impedance contrast among layer interfaces at depth. We also find that strong impedance contrasts located at great depths within deep soil deposits introduce nonnegligible errors to site response results.}, number={10}, journal={JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING}, author={Cabas, Ashly and Rodriguez-Marek, Adrian and Green, Russell A. and Ji, Chunyang}, year={2022}, month={Oct} }
 @article{ji_cabas_bonilla_gelis_2021, title={Effects of Nonlinear Soil Behavior on Kappa (kappa): Observations from the KiK-Net Database}, volume={111}, ISSN={["1943-3573"]}, DOI={10.1785/0120200286}, abstractNote={
 Soil nonlinear behavior is often triggered in soft sedimentary deposits subjected to strong ground shaking and has led to catastrophic damage to civil infrastructure in many past earthquakes. Nonlinear behavior in soils is associated with large shear strains, increased material damping ratio, and reduced stiffness. However, most investigations of the high-frequency spectral decay parameter κ, which captures attenuation, have focused on low-intensity ground motions inducing only small shear strains. Because studies of the applicability of the κ model when larger deformations are induced are limited, this article investigates the behavior of κ (both κr per record and site-specific κ0 estimates) beyond the linear-elastic regime. About 20 stations from the Kiban–Kyoshin network database, with time-average shear-wave velocities in the upper 30 m between 213 and 626  m/s, are used in this study. We find that the classification scheme used to identify ground motions that trigger soil nonlinear behavior biases estimates of κ0 in the linear and nonlinear regimes. A hybrid method to overcome such bias is proposed considering proxies for in situ deformation (via the shear-strain index) and ground shaking intensity (via peak ground acceleration). Our findings show that soil nonlinearity affects κr and κ0 estimates, but this influence is station dependent. Most κ0 at our sites had a 5%–20% increase at the onset of soil nonlinear behavior. Velocity gradients and impedance contrasts influence the degree of soil nonlinearity and its effects on κr and κ0. Moreover, we observe that other complexities in the wave propagation phenomenon (e.g., scattering and amplifications in the high-frequency range) impose challenges to the application of the κ0 model, including the estimation of negative values of κr.}, number={4}, journal={BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA}, author={Ji, Chunyang and Cabas, Ashly and Bonilla, Luis Fabian and Gelis, Celine}, year={2021}, month={Aug}, pages={2138–2157} }
 @article{ji_cabas mijares_cotton_pilz_bindi_2020, title={Within station variability in kappa: evidence of directionality effects}, volume={110}, ISSN={["1943-3573"]}, DOI={10.1785/0120190253}, abstractNote={
 One of the most commonly used parameters to describe seismic attenuation is the high-frequency spectral decay parameter Kappa (κr), yet the physics behind it remain little understood. A better understanding of potential factors that lead to large scatter in estimated values of κr constitutes a critical need for ground-motion modeling and seismic hazard assessment at large. Most research efforts to date have focused on studying the site-to-site and model-to-model variability of κ, but the uncertainties in individual κr estimations associated with different events at a selected site (which we refer to as the within-station variability of κr) remain uncharacterized. As a direct corollary, obtaining robust estimates of the site-specific component κ0, and their corresponding interpretation become a challenge. To understand the sources of the variability observed in κr (and κ0) at a single site, we select 10 Japanese Kiban–Kyoshin network (KiK-net) downhole arrays and investigate the systematic contributions from ground-motion directionality. We observe that κr estimated from a single horizontal component is orientation dependent. In addition, the influence of ground-motion directionality is a function of local site conditions. We propose an orientation-independent κr-value, which is not affected either by ground-motion directionality or by the events’ azimuths. In addition, we find that focal depth of events used in κr calculations affects the estimation of the regional attenuation component κR, which, in turn, influences the within-station variability in the κ0 model.}, number={3}, journal={Bulletin of the Seismological Society of America}, author={Ji, C. and Cabas Mijares, A. and Cotton, F. and Pilz, M. and Bindi, D.}, year={2020}, month={Apr}, pages={1247–1259} }