Chino Hills Research Articles

Instantaneous Physics‐Based Ground Motion Maps Using Reduced‐Order Modeling

AbstractPhysics‐based simulations of earthquake ground motion are useful to complement recorded ground motions. However, the computational expense of performing numerical simulations hinders their applicability to tasks that require real‐time solutions or ensembles of solutions for different earthquake sources. To enable rapid physics‐based solutions, we present a reduced‐order modeling approach based on interpolated proper orthogonal decomposition (POD) to predict peak ground velocities (PGVs). As a demonstrator, we consider PGVs from regional 3D wave propagation simulations at the location of the 2008 MW 5.4 Chino Hills earthquake using double‐couple sources with varying depth and focal mechanisms. These simulations resolve frequencies ≤1.0 Hz and include topography, viscoelastic attenuation, and S‐wave speeds ≥500 m/s. We evaluate the accuracy of the interpolated POD reduced‐order model (ROM) as a function of the approximation method. Comparing the radial basis function (RBF), multilayer perceptron neural network, random forest, and k‐nearest neighbor, we find that the RBF interpolation gives the lowest error (≈0.1 cm/s) when tested against an independent data set. We also find that evaluating the ROM is 107–108 times faster than the wave propagation simulations. We use the ROM to generate PGV maps for 1 million different focal mechanisms, in which we identify potentially damaging ground motions and quantify correlations between focal mechanism, depth, and accuracy of the predicted PGV. Our results demonstrate that the ROM can rapidly and accurately approximate the PGV from wave propagation simulations with variable source properties, topography, and complex subsurface structure.

Soil–Structure Interaction Effects on a Regional Scale through Ground-Motion Simulations and Reduced Order Models: A Case Study from the 2008 Mw 5.4 Chino Hills Mainshock

ABSTRACT We demonstrate the effects of soil–structure interaction (SSI) for three idealized building typologies on a regional scale, using a simulated earthquake scenario of the 2008 Mw 5.4 Chino Hills mainshock in southern California as an example. All the three buildings lie on shallow foundations, and they are subject to three-component simulated ground motions. To carry out this task, we develop a reduced order model (ROM) for each building typology that accounts for the effects of SSI on the building system in the time domain. We specifically use ensemble Kalman inversion (EnKI) to extract the soil impedance values from fully coupled soil–foundation–structure interaction simulations; and we interpolate the EnKI results to derive analytical functions that span the range of applicability of the soil impedance model. We then verify our ROMs by comparing results to fully coupled soil–foundation–structure interaction simulations, also known as direct modeling methods. We finally populate the simulation grid across southern California with the verified building ROMs, and interpret the responses in the form of maps that represent urban-scale effects of SSI on the seismic demand parameters such as maximum displacement, acceleration, and interstory drift. We also identify areas where the effects of SSI, given the resonant characteristics of a specific building, the foundation typology, and the local site conditions, lead to higher seismic demand relative to the fixed-base response.

Applications of Nonergodic Site Response Models to ShakeAlert Case Studies in the Los Angeles Area

ABSTRACT In this study, we explore whether the Parker and Baltay (2022) site response models for the Los Angeles (LA) basin region can improve ground-motion forecasts in the U.S. Geological Survey ShakeAlert earthquake early warning system (hereafter ShakeAlert). We implement the peak ground acceleration and peak ground velocity site response models of Parker and Baltay (2022) in ShakeAlert via the earthquake information to ground-motion (hereafter eqinfo2GM) module, which predicts ground motions from the estimated earthquake parameters of magnitude, rupture length, and location. The nonergodic site response models for the greater LA area were developed using ground motions from 414 M 3–7.3 earthquakes in southern California. We test nonergodic ground-motion forecasts for five earthquakes in the LA area: the 1994 M 6.7 Northridge earthquake, the 2008 M 5.4 Chino Hills earthquake, the 2019 M 7.1 Ridgecrest earthquake, the 2020 M 4.5 South El Monte earthquake, and a synthetic M 7.8 earthquake on the southern San Andreas fault from the ShakeOut scenario, which was the basis of a statewide emergency response exercise. From the test results, we find that with the nonergodic site response applied, ShakeAlert not only alerts larger areas but can also result in longer warning times in LA region. In addition, the modified Mercalli intensity (MMI) ground-motion predictions generated by the ShakeAlert eqinfo2GM module are improved in accuracy when compared with the corresponding ShakeMap ground-truth MMI when the nonergodic site response model is applied.

Ground motion simulation and validation of the 2008 Chino Hills earthquake in scattering media

SUMMARYWe simulate 0–2.5 Hz deterministic wave propagation in 3-D velocity models for the 2008 Chino Hills, CA, earthquake using a finite-fault source model and frequency-dependent anelastic attenuation. Small-scale heterogeneities are modeled as 3-D random fields defined using an elliptically anisotropic von Kármán autocorrelation function with its parameters constrained using Los Angeles basin borehole data. We superimpose the heterogeneity models on a leading deterministic community velocity model (CVM) of southern California. We find that models of velocity and density perturbations can have significant effects on the wavefield at frequencies as low as 0.5 Hz, with ensemble median values of various ground motion metrics varying up to ±50 per cent compared to those computed using the deterministic CVM only. In addition, we show that frequency-independent values of the shear-wave quality factor (Qs0) parametrized as Qs0 = 150Vs (Vs in km s–1) provides the best agreement with data when assuming the published moment magnitude (Mw) of 5.4 (M0 = 1.6 × 1017 Nm) for the finite-fault source model. This model for Qs0 trades off with Qs0 = 100Vs assuming Mw = 5.5 (M0 = 2.2 × 1017 Nm), which represents an upper bound of the Mw estimates for this event. We find the addition of small-scale heterogeneities provides limited overall improvement to the misfit between simulations and data for the considered ground motion metrics, because the primary sources of misfit originate from the deterministic CVM and/or the finite-fault source description.

Prioritizing Ground‐Motion Validation Metrics Using Semisupervised and Supervised Learning

Research Article| June 26, 2018 Prioritizing Ground‐Motion Validation Metrics Using Semisupervised and Supervised Learning Naeem Khoshnevis; Naeem Khoshnevis aCenter for Earthquake Research and Information, The University of Memphis, 3890 Central Avenue, Memphis, Tennessee 38152, nkhshnvs@memphis.edu Search for other works by this author on: GSW Google Scholar Ricardo Taborda Ricardo Taborda bDepartment of Civil Engineering,, and Center for Earthquake Research and Information, The University of Memphis, 3890 Central Avenue, Memphis, Tennessee 38152, ricardo.taborda@memphis.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Naeem Khoshnevis aCenter for Earthquake Research and Information, The University of Memphis, 3890 Central Avenue, Memphis, Tennessee 38152, nkhshnvs@memphis.edu Ricardo Taborda bDepartment of Civil Engineering,, and Center for Earthquake Research and Information, The University of Memphis, 3890 Central Avenue, Memphis, Tennessee 38152, ricardo.taborda@memphis.edu Publisher: Seismological Society of America First Online: 26 Jun 2018 Online Issn: 1943-3573 Print Issn: 0037-1106 © Seismological Society of America Bulletin of the Seismological Society of America (2018) 108 (4): 2248–2264. https://doi.org/10.1785/0120180056 Article history First Online: 26 Jun 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Naeem Khoshnevis, Ricardo Taborda; Prioritizing Ground‐Motion Validation Metrics Using Semisupervised and Supervised Learning. Bulletin of the Seismological Society of America 2018;; 108 (4): 2248–2264. doi: https://doi.org/10.1785/0120180056 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract It has become common practice to validate ground‐motion simulations based on a variety of time and frequency metrics scaled to quantify the level of agreement between synthetics and data or other reference solutions. There is, however, no agreement about the importance or weight that it ought to be given to each metric. This leads to their selection often being subjective, either based on intended applications or personal preferences. As a consequence, it is difficult for simulators to identify what modeling improvements are needed, which would be easier if they could focus on a reduced number of metrics. We present an analysis that looks into 11 ground‐motion validation metrics using semisupervised and supervised machine learning techniques. These techniques help label and classify goodness‐of‐fit results with the objective of prioritizing and narrowing the choice of these metrics. In particular, we use a validation dataset of a series of physics‐based ground‐motion simulations done for the 2008 Mw 5.4 Chino Hills, California, earthquake. We study the relationships that exist between 11 metrics and carry out a process where these metrics are understood as part of a multidimensional space. We use a constrained k‐means method and conduct a subspace clustering analysis to address the implicit high‐dimensional effects. This allows us to label the data in our dataset into four validation categories (poor, fair, good, and excellent) following previous studies. We then develop a family of decision trees using the C5.0 algorithm, from which we select a few trees that help narrow the number of metrics leading to a validation prediction into the four referenced categories. These decision trees can be understood as rapid predictors of the quality of a simulation, or as data‐informed classifiers that can help prioritize validation metrics. Our analysis, although limited to the particular dataset used here, indicates that among the 11 metrics considered, the acceleration response spectra and total energy of velocity are the most dominant ones, followed by the peak ground response in terms of acceleration and velocity. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lean Enablers for Clinical Laboratories

Research in Medical & Engineering Sciences Lean Enablers for Clinical Laboratories Bohdan W Oppenheim1*, Michael H Kanter2, Onie Bueno3, Vincent L Dizon4, Louie M Farnacio5, Paulette L Medina6, Mike M Moradian7, Chiemi Tabata8 and Michael S Tiffert9 1PhD, Professor of Systems Engineering, Associate Director for Healthcare Systems Engineering, Loyola Marymount University, Los Angeles 2MD, CPPS, Regional Medical Director of Quality & Clinical Analysis, Southern California Permanente Medical Group (SCPMG), Executive Vice President, Chief Quality Officer, The Permanente Federation 3Director of Operations, Bacteriology and Molecular Microbiology, SCPMG, Regional Reference Laboratories, Chino Hills 4MBA MT(ASCP) DLM SBB. Director of Operations, Chemistry Services, Kaiser Permanente SCPMG Regional Reference Laboratories 5Director of Laboratory Services, Kaiser Permanente Southern California Regional Reference Laboratory 6Assistant Director of Operations, RRL Bacteriology, Kaiser Permanente SCPMG Regional Reference Lab 7PhD, Director of Operations, Molecular Genetic Pathology Regional Laboratory, Kaiser Permanente SCPMG Regional Reference Laboratories 8Assistant Director of Operations, RRL Automated Chemistry, Kaiser Permanente SCPMG, Regional Reference Laboratories 9MS, Section Manager, Cytogenetics, Regional Genetics Laboratory, Kaiser Permanente SCPMG, Regional Reference Laboratories *Corresponding author: Dr. Bohdan W Oppenheim, Professor of Systems Engineering, Associate Director for Healthcare Systems Engineering, Loyola Marymount University, Los Angeles, USA Submission: October 23, 2017; Published: November 27, 2017 DOI: 10.31031/RMES.2017.02.000543 ISSN : 2576-8816Volume2 Issue4

Close and Connected: The Effects of Proximity and Social Ties on Citizen Opposition to Electricity Transmission Lines

To meet reliability and renewable energy goals, new high-voltage transmission line (HVTL) projects are being built in the United States and worldwide. The siting of HVTLs, often considered a locally unwanted land use (LULU), can be difficult due to the negative externalities they create. Based on a survey of 358 residents of Chino Hills, California, we find that respondents’ main concerns in regard to an HVTL project were health risks and harm to property values. Regression modeling finds that citizens who live close to the project, and are more connected to each other, are more likely to oppose the project. Psychosocial perceptions of project risks are also an important predictor of opposition. A high level of perceived risk moderates the effects of distance on opposition attitudes and behaviors. Trust in the project sponsor is a significant independent predictor of opposition, and moderates the relationship between distance and opposition.

Fetal citizens? Birthright citizenship, reproductive futurism, and the “panic” over Chinese birth tourism in southern California

In September 2012, residents of Chino Hills, California—a wealthy suburb of Los Angeles—exposed a maternity hotel in their city. Subsequently, controversy erupted as protesting residents argued that Chinese birth tourism is an immigration loophole, where foreigners took advantage of jus soli birthright citizenship guaranteed by the Fourteenth Amendment to the U.S. Constitution. This paper uses this controversy as a springboard to explore how temporalities—both the past and the future—come to shape politics in the present. Considering reproductive futurism in the contexts of citizenship and migrations, this paper argues that the figure of the fetal citizen emerges as the defining site of struggle between preserving, or exposing, the fantasy of a national future. Reports of panic over Chinese birth tourism, then, show how “backwards” racialized citizenship is continually brought to this present struggle, especially vis-a-vis discourses of the “worthy immigrant” and “anchor babies”, to determine who may give birth to citizens in the U.S.

Probabilistic point source inversion of strong‐motion data in 3‐D media using pattern recognition: A case study for the 2008Mw5.4 Chino Hills earthquake

AbstractDespite the ever increasing availability of computational power, real‐time source inversions based on physical modeling of wave propagation in realistic media remain challenging. We investigate how a nonlinear Bayesian approach based on pattern recognition and synthetic 3‐D Green's functions can be used to rapidly invert strong‐motion data for point source parameters by means of a case study for a fault system in the Los Angeles Basin. The probabilistic inverse mapping is represented in compact form by a neural network which yields probability distributions over source parameters. It can therefore be evaluated rapidly and with very moderate CPU and memory requirements. We present a simulated real‐time inversion of data for the 2008Mw5.4 Chino Hills event. Initial estimates of epicentral location and magnitude are available ∼14 s after origin time. The estimate can be refined as more data arrive: by ∼40 s, fault strike and source depth can also be determined with relatively high certainty.

Memory‐Efficient Simulation of Frequency‐DependentQ

Memory‐variable methods have been widely applied to approximate frequency‐independent quality factor Q in numerical simulation of wave propagation. The frequency‐independent model is often appropriate for frequencies up to about 1 Hz but at higher frequencies is inconsistent with some regional studies of seismic attenuation. We apply the memory‐variable approach to frequency‐dependent Q models that are constant below, and follow a power‐law above, a chosen transition frequency. We present numerical results for the corresponding memory‐variable relaxation times and weights, obtained by nonnegative least‐squares fitting of the Q ( f ) function, for a range of exponent values; these times and weights can be scaled to an arbitrary transition frequency and a power‐law prefactor, respectively. The resulting memory‐variable formulation can be used with numerical wave‐propagation solvers based on methods such as finite differences (FDs) or spectral elements and may be implemented in either conventional or coarse‐grained form. In the coarse‐grained approach, we fit effective Q for low‐ Q values (<200) using a nonlinear inversion technique and use an interpolation formula to find the corresponding weighting coefficients for arbitrary Q . A 3D staggered‐grid FD implementation closely approximates the frequency–wavenumber solution to both a half‐space and a layered model with a shallow dislocation source for Q as low as 20 over a bandwidth of two decades. We compare the effects of different power‐law exponents using a finite‐fault source model of the 2008 M w 5.4 Chino Hills, California, earthquake and find that Q ( f ) models generally better fit the strong‐motion data than the constant Q models for frequencies above 1 Hz. Online Material: Figures comparing finite difference and frequency–wavenumber seismograms for an elastic layered‐model point source simulation. Median spectral acceleration centered at 1 s and Fourier amplitude centered at 0.25 and 2.25 Hz for strong ground motion recordings and synthetics from the Chino Hills earthquake.

Ground-Motion Simulation and Validation of the 2008 Chino Hills, California, Earthquake Using Different Velocity Models

Abstract We present a set of ground‐motion simulations of the 2008 M w 5.4 Chino Hills earthquake using different seismic‐velocity models available for southern California. The simulations are tailored for a maximum frequency of 4 Hz and a minimum shear‐wave velocity of 200 m/s. We use the community models developed by the Southern California Earthquake Center, CVM‐S and CVM‐H. In the case of CVM‐H, we use two available alternatives, with and without considering the geotechnical layers (GTL). We compare the simulation results obtained with the models against each other and validate the synthetics with recordings obtained at more than 300 stations. The comparisons are used to gain insight into the sensitivity of the results to differences in the models and to make conclusions about the strengths of each model’s description of the crustal structure and the GTL in the region. The validation is done using a goodness‐of‐fit (GOF) criterion. We find the GOF values show a better match at frequencies below 1 Hz, within the basins, and below 0.5 Hz in general. The models, however, do not converge at frequencies lower than 0.5 Hz, and the areas where each model leads to better results do not always coincide. The synthetics start to deviate significantly from observations at frequencies above 1 and 2 Hz, although very good agreement with data can still be found at individual locations, even at the higher frequencies. CVM‐S yields the best results at frequencies up to 0.25 Hz. Our results reveal significant sensitivity of the ground motion to the differences in the structural representation of basins and shallow layers in the models. This indicates the models need to be cross referenced. We close by offering suggestions on the type of improvements that could be adopted in the future.

Health monitoring of an instrumented SRMF building using earthquake data

SUMMARYThis paper is a study of a six‐story welded steel moment‐resisting frame instrumented by California Strong Motion Instrumentation Program. Several earthquakes had shaken the building, and its response of strong motion data recorded during the earthquakes were made available. In particular, the Whittier Narrows (October 1987), Sierra Madre (June 1991), Northridge (January 1994) and Chino Hills (July 2008) earthquakes were considered in the studies reported here.The paper investigates the capability of input–output system identification methods, namely eigensystem realization algorithm with data correlation, and observer Kalman filter identification, in identifying dynamic characteristics of typical office building structures subjected to strong ground motion. It explores the possibility to extend the above system identification procedures to near‐real‐time estimation of the building response under future earthquakes in order to estimate the likelihood of brittle damage in welded beam to column connections. The modal identification results are compared with those obtained using the spectral analysis and the deterministic‐stochastic subspace identification method to verify the accuracy of the identified modal parameters. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Response of an arch dam to non-uniform excitation generated by a seismic wave scattering model

Non-uniform ground motions are generated based on a single record available at a site and seismic wave scattering analysis. The Chino Hills 2008 earthquake records at the Pacoima Dam site are used to indicate the accuracy of the method. Dynamic analysis of the Pacoima dam-reservoir-foundation under uniform and non-uniform ground motions is carried out using the EACD-3D2008 software, and the results are compared to recorded responses at different locations on the dam. There is good agreement between computed and recorded displacements of the dam for non-uniform excitation. For uniform excitation, the displacements are underestimated in comparison with those obtained from recorded excitation. Significant intensification of stresses, especially near the foundation, and different patterns of stress distribution are observed for non-uniform excitation in comparison with uniform excitation. For uniform excitation maximum stresses occur in the crown cantilever near the crest, but for non-uniform excitation the maximum stresses occur along the sides and near the foundation.

Ground‐Motion Simulation and Validation of the 2008 Chino Hills, California, Earthquake

We present a simulation of the 2008 M w 5.4 Chino Hills earthquake for a maximum frequency up to 4 Hz and a minimum shear‐wave velocity down to 200 m/s and perform a validation study comparing data obtained from seismic networks with simulation synthetics on more than 300 recording stations. The simulation was done using a parallel‐computing code for earthquake simulations that implements a finite‐element solution to anelastic wave propagation in heterogeneous media. The source model corresponds to that of an independent inversion study, and the material model used is a community velocity model (CVM) developed by the Southern California Earthquake Center (SCEC). Our results for the goodness‐of‐fit measure of the synthetics indicate that, from a regional perspective, the simulation starts to deviate from the data at frequencies above 1 and 2 Hz. At particular locations or station clusters, however, the synthetics yield very good results, even at frequencies between 2 and 4 Hz. The best results are obtained between 0.1 and 0.25 Hz over the entire region and up to 1 Hz within the major basins. These and other results from comparisons at boreholes, biases of the peak surface response, and the differences in the strong‐phase duration of the waveforms and the arrival time of P waves suggest a strong sensitivity to seismic velocities. In particular, the CVM used seems to misrepresent the shallow soil deposits and overestimate seismic velocities in the upper layers outside the basins. These observations are helpful in identifying regions where the velocity model may need to be revised. Overall, this study shows that extending the maximum frequency for deterministic earthquake simulations beyond 1 Hz is an effort worth pursuing.

Multi-GPU Implementation of a 3D Finite Difference Time Domain Earthquake Code on Heterogeneous Supercomputers

We have developed a highly scalable 3D Finite Difference GPU code for use in earthquake engineering and disaster management through regional petascale earthquake simulations. This MPI-CUDA code is based on a widely-used wave propagation code called AWP-ODC and restructured for high throughput and efficiency on a heterogeneous computing architecture. We present an effective communication reduction technique for leveraging GPUs with minimal PCI-e overhead, and a novel overlapping method to fully hide data communication latency between GPUs. The optimization concept used in this work can be extended to general stencil computing on a structured grid. The benchmarks demonstrated sustained 100 TFlops in single precision for 49 billion mesh points using 952 GPUs on the NCCS Titan Phase 5 system, which is a 77-fold speedup compared to the CPU version of the code. This multi-GPU implementation has been validated and used for a large-scale verification wave propagation simulation of Mw5.4 Chino Hills earthquake using 128 GPUs.

Modal Pushover-Based Scaling of Two Components of Ground Motion Records for Nonlinear RHA of Structures

The modal-pushover-based-scaling (MPS) procedure, currently restricted to scale one component of ground motion records, is extended herein to scale two horizontal components. The accuracy and efficiency of the MPS procedure is evaluated here by applying it to an existing nine-story building, symmetric in plan. The computer model developed for the building is validated against motions of the building recorded during the Chino Hills earthquake (2008). It is demonstrated that nonlinear response history analysis (RHA) of the building for a small set of records scaled by the MPS procedure provided a highly accurate estimate of the engineering demand parameters (EDPs), accompanied by significantly reduced record-to-record variability of the responses. Furthermore, the MPS procedure is shown to be much superior to the procedure specified in the ASCE/SEI 7-05 standard for scaling two components of ground motion records.

Seismic response evaluation of retrofitted Vincent Thomas bridge under spatially variable ground motions

In this study, a three dimensional finite element (FE) model of the Vincent Thomas bridge is developed using a widely used software. In order to show the appropriateness of the model, the eigenproperties of the bridge model are evaluated and compared with the results of system identification from ambient vibration and the 2008 Chino Hills earthquake response data. A new simulation technique is developed to generate spectrum-compatible spatial variable ground motions. The response of Vincent Thomas bridge under spatially varying ground motion is evaluated by nonlinear time history analysis. Using spatially variable motions, it is found out that the response in some locations on the bridge girder, may be under-predicted even if the motion with maximum intensity is uniformly applied at all supports.

Rupture process and energy budget of the 29 July 2008 Mw 5.4 Chino Hills, California, earthquake

The source model of the 2008 Mw 5.4 Chino Hills, California, earthquake is constrained using near‐field seismic body waves recorded by the California Integrated Seismic Network (CISN). Finite fault inversions are preformed for the two fault models based on the nodal planes derived from the CISN moment tensor solution. The northeast dipping plane (strike = 289°; dip = 62°), which has a similar strike as the nearby Whittier fault, is chosen as the causative fault because it fits the data significantly better. Our inversion result indicates that the majority of the Chino Hills earthquake rupture occurred in a compact area. In particular, 48% of the total seismic moment (1.6 × 1017 Nm) was released by the failure of a 1.8 km2 asperity located east of the hypocenter in a short time window from 0.4 to 0.8 s after the rupture initiation. The average slip is approximately 0.5 m but the maximum slip is 1.8 m. The average rupture velocity is 1.9 km/s. The static stress drop calculated using the slip model is up to 80 MPa and the average stress drop changes from 19 to 38 MPa, depending on the average schemes. The weighted average slip velocity is 6.5 m/s for entire rupture and is 11 m/s for the east asperity. The inferred available energy and radiated energy are 8 × 1013 J and 2.5 × 1013 J, respectively. Radiation efficiency is then 0.31, which is moderately low compared with previous earthquakes but consistent with the inferred high average fracture energy density, ranging from 6.5 to 14.8 MJ/m2.

Locating earthquakes with surface waves and centroid moment tensor estimation

Traditionally, P wave arrival times have been used to locate regional earthquakes. In contrast, the travel times of surface waves dependent on source excitation and the source parameters and depth must be determined independently. Thus surface wave path delays need to be known before such data can be used for location. These delays can be estimated from previous earthquakes using the cut‐and‐paste technique, Ambient Seismic Noise tomography, and from 3D models. Taking the Chino Hills event as an example, we show consistency of path corrections for (&gt;10 s) Love and Rayleigh waves to within about 1 s obtained from these methods. We then use these empirically derived delay maps to determine centroid locations of 138 Southern California moderate‐sized (3.5 &gt; Mw&gt; 5.7) earthquakes using surface waves alone. It appears that these methods are capable of locating the main zone of rupture within a few (∼3) km accuracy relative to Southern California Seismic Network locations with 5 stations that are well distributed in azimuth. We also address the timing accuracy required to resolve non‐double‐couple source parameters which trades‐off with location with less than a km error required for a 10% Compensated Linear Vector Dipole resolution.

Earthquake Centroid Locations Using Calibration from Ambient Seismic Noise

Earthquakes occur in complex geology, making it difficult to determine their source parameters and locations because of uncertainty in path effects. We can avoid some of these problems by applying the cut-and-paste (CAP) method, which allows for timing shifts between phases, assuming a 1D model, and determines source parameters. If the travel times or lags of the phases due to path effects are known relative to a reference model, we can locate the events’ centroid with surface waves without knowledge of the 3D velocity structure. Here, we use ambient seismic noise for such a calibration. We cross correlate the seismic stations near the earthquake with stations 100–300 km away to obtain the 10–100-s surface wave Green’s functions. The new method is tested in southern California to locate the 2008 Chino Hills earthquake, which proves consistent with the epicenter location from P waves. It appears possible to use the location offset between the high-frequency P-wave onset relative to the centroid to provide a fast estimate of directivity.