USGS Science⌕ Search
Home/Archive/USGS

USGS · 70222608

Ground motions in urban Los Angeles from the 2019 Ridgecrest earthquake sequence

Filippos Filippitzis·Monica Kohler·Tom Heaton·Robert Graves·Robert W. Clayton·Richard G. Guy·J. J. Bunn·K. M. Chandy
View original source ↗Export metadata ↓

Abstract

We study ground-motion response in urban Los Angeles during the two largest events (M7.1 and M6.4) of the 2019 Ridgecrest earthquake sequence using recordings from multiple regional seismic networks as well as a subset of 350 stations from the much denser Community Seismic Network. In the first part of our study, we examine the observed response spectral (pseudo) accelerations for a selection of periods of engineering significance (1, 3, 6, and 8 s). Significant ground-motion amplification is present and reproducible between the two events. For the longer periods, coherent spectral acceleration patterns are visible throughout the Los Angeles Basin, while for the shorter periods, the motions are less spatially coherent. However, coherence is still observable at smaller length scales due to the high spatial density of the measurements. Examining possible correlations of the computed response spectral accelerations with basement depth and Vs30, we find the correlations to be stronger for the longer periods. In the second part of the study, we test the performance of two state-of-the-art methods for estimating ground motions for the largest event of the Ridgecrest earthquake sequence, namely three-dimensional (3D) finite-difference simulations and ground motion prediction equations. For the simulations, we are interested in the performance of the two Southern California Earthquake Center 3D community velocity models (CVM-S and CVM-H). For the ground motion prediction equations, we consider four of the 2014 Next Generation Attenuation-West2 Project equations. For some cases, the methods match the observations reasonably well; however, neither approach is able to reproduce the specific locations of the maximum response spectral accelerations or match the details of the observed amplification patterns.

Explore related subjects

Earthquake SpectraArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 33.53223722395908° to 35.97800618085566° latitude; -118.77868652343751° to -116.971435546875° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Filippos Filippitzis, Monica Kohler, Tom Heaton, Robert Graves, Robert W. Clayton, Richard G. Guy, J. J. Bunn, K. M. Chandy. 2021-04-28. Ground motions in urban Los Angeles from the 2019 Ridgecrest earthquake sequence. https://doi.org/10.1177/87552930211003916

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

An examination of the reasons for, and variability of, the differences between response spectra and pseudo response spectra

For many decades, it has been common practice to overlook the differences between response spectra and pseudo response spectra. This practice stems from analyses indicating that the average difference between response spectra and pseudo response spectra is negligible for a viscous damping ratio of 5%, which is near-universally adopted. As others have shown, the differences depend strongly on the damping ratio, earthquake magnitude, and oscillator period, with larger differences for larger damping, smaller magnitudes, and longer periods. To quantify the full statistical distribution of the ratio of the absolute acceleration response spectrum (SA) to the pseudo absolute acceleration response spectrum (PSA), we fit empirical ratios with the generalized gamma distribution. Data for magnitudes from 4.0 to 5.5 give 95% prediction intervals for the ratio of 1.00–1.02 at 1 s and 1.01–2.24 at 10 s for 5% damping. For 30% damping, these intervals increase to 1.14–2.01 at 1 s and 1.62–11.8 at 10 s, respectively. Further, we demonstrate how the shape of the ground-motion Fourier amplitude spectrum interacts with the natural period of the oscillator to control the differences in the response spectra type. Routinely treating the two measures of acceleration response spectra as interchangeable may lead to unacceptable inconsistencies when the response spectra of individual records are important or when larger damping ratios are used, such as in direct displacement-based design. If one must convert between them, the uncertainty of the conversion should be accounted for during analysis.

Earthquake Spectra↗
USGS2026

Accounting for biases in the analysis of building damage data for the 2023 M7.8 Türkiye/Syria earthquake sequence

In the aftermath of a large earthquake, several practical constraints affect the systematic collection of data for assessing building damage. The available data are therefore typically incomplete, frequently missing key information such as the type of construction, age and geographic location. Moreover, the observations often favour certain locations and damage grades. In the absence of robust methods, using such data directly for characterising the building stock or conducting fragility assessments can introduce systematic bias. Using the 2023 M7.8 Türkiye/Syria earthquake sequence as a case study, we propose a statistical model that enables joint inference over the inventory and fragility of the building stock while explicitly accounting for sources of data error and missing information. The results show higher-than-expected vulnerability amongst several building types, particularly mid- and high-rise reinforced concrete buildings, which performed extremely poorly during the 2023 earthquake sequence. The proposed Bayesian framework provides rigorous uncertainty quantification that can be propagated to future applications.

Earthquake Spectra↗
USGS2026

Suite of regional seismic velocity models for the U.S. Atlantic and Gulf Coastal Plains (CPVMv2.0): Incorporating epistemic uncertainty in velocity models

The U.S. Atlantic and Gulf Coastal Plain (CP) sediments are kilometers-thick, low-velocity deposits underlain by high-velocity bedrock that create regional patterns of amplification and attenuation of ground motions. Capturing these effects is challenging because of the limited subsurface information available, particularly the shear wave velocity ( V S ) structure down to bedrock (or assumed reference rock condition) and the associated uncertainties. This paper introduces a new suite of regional velocity models for the CPs, called CPVMv2.0, which builds upon previous efforts integrating geology, V S measurements, and sediment thickness in the region. CPVMv2.0 uses 750 measured V S profiles and identifies nine surficial-geologic-age-based and geography-based groups (with alternative physiographic-province-based subgroupings) to create surface-based median V S profiles. This suite of new models also includes six subsurface-based median profiles developed using geologic age boundaries from depth-dependent stratigraphic sequences extracted from the U.S. Geological Survey National Crustal Model. In addition to quantifying aleatory variability in sediment velocity, weathered-rock velocity, bedrock velocity, and the depth to the top of weathered rock and bedrock, CPVMv2.0 provides alternative profile models that allow for the characterization of the epistemic uncertainty. This is a unique and relevant feature of CPVMv2.0. Our suite of models was validated using measured and estimated fundamental resonant frequencies as well as other V S models in the region. CPVMv2.0 enables the incorporation of crustal velocities (and their associated variability and uncertainty) into physics-based ground-motion simulations in the eastern United States and into the development of new ground-motion models aiming to characterize systematic site effects via V S30 , depths to V S isosurfaces, and/or sediment thickness in the region.

U.S. Atlantic and Gulf Coastal Plains↗