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July 2000 - present
Publications
Publications (424)
Recent studies of Southern California have employed velocity and attenuation tomography to elucidate two aspects of crustal structure. Low-frequency velocity tomography reveals large-scale heterogeneity that can be approximated by a discrete set (𝐾 ≤ 10) of tectonic regions, each characterized by an isostatically balanced lithospheric column reflec...
The Statewide (formerly Southern) California Earthquake Center (SCEC) conducts multidisciplinary earthquake system science research that aims to develop predictive models of earthquake processes, and to produce accurate seismic hazard information that can improve societal preparedness and resiliency to earthquake hazards. As part of this program, S...
This report documents the assessment by the U.S. Geological Survey (USGS) Earthquake Rupture Forecast (ERF) Review Panel of the draft ERF for the conterminous United States (CONUS-ERF23) proposed for the 2023 update of the National Seismic Hazard Model (NSHM23). Panel members participated with the ERF Development Team in several verification and va...
We measured high-frequency (1–10 Hz) spectral amplitudes of more than fifty thousand P and S crustal phases from Southern California earthquakes and separately inverted the two datasets for three-dimensional and frequency-dependent models of total attenuation. The independent estimates of the P and S attenuation factors are nearly equal, decay with...
The main purpose of this article is to emphasize the importance of clarifying the probabilistic framework adopted for volcanic hazard and eruption forecasting. Eruption forecasting and volcanic hazard analysis seek to quantify the deep uncertainties that pervade the modeling of pre-, sin-, and post-eruptive processes. These uncertainties can be dif...
The main purpose of this article is to emphasize the importance of clarifying the probabilistic framework adopted for volcanic hazard and eruption forecasting. Eruption forecasting and volcanic hazard analysis seeks to quantify the deep uncertainties that pervade the modeling of pre-, sin- and post-eruptive processes. These uncertainties can be dif...
Earthquake ruptures and seismic sequences can be very complex, involving slip in various directions on surfaces of variable orientation. How is this geometrical complexity in seismic energy release, here called mechanism complexity, governed by tectonic stress? We address this question using a probabilistic model for the distribution of double coup...
We present a nonergodic framework for probabilistic seismic-hazard analysis (PSHA) that is constructed entirely of deterministic, physical models. The use of deterministic ground-motion simulations in PSHA calculations is not new (e.g., CyberShake), but prior studies relied on kinematic rupture generators to extend empirical earthquake rupture fore...
The first Uniform California Earthquake Rupture Forecast, Version 3–epidemic-type aftershock sequence (UCERF3-ETAS) aftershock simulations were running on a high-performance computing cluster within 33 min of the 4 July 2019 M 6.4 Searles Valley earthquake. UCERF3-ETAS, an extension of the third Uniform California Earthquake Rupture Forecast (UCERF...
We map crustal regions in Southern California that have similar depth variations in seismic velocities by applying cluster analysis to 1.5 million P and S velocity profiles from the three‐dimensional tomographic model CVM‐S4.26. We use a K‐means algorithm to partition the profiles into K sets that minimize the inter‐cluster variance. The regionaliz...
Seismic radiation from indigenous sources can be represented by the excess of model stress over actual stress, a second-order tensor field that Backus & Mulcahy named the stress glut. We prove a new representation theorem that exactly and uniquely decomposes any stress-glut (or strain-glut) density into a set of orthogonal tensor fields of increasi...
Seismic hazard models are important for society, feeding into building codes and hazard mitigation efforts. These models, however, rest on many uncertain assumptions and are difficult to test observationally because of the long recurrence times of large earthquakes. Physics-based earthquake simulators offer a potentially helpful tool, but they face...
To account for the randomness (aleatory variability) and limited knowledge (epistemic uncertainty) of earthquake processes, we must formulate and test seismic hazard models using the concepts of probability. Probabilistic seismic hazard analysis (PSHA) gives the chance that a specified seismic intensity will be exceeded at a particular site during...
Accurate models of crustal attenuation structure are important for simulating seismic wavefields at high frequencies (f > 1 Hz). In this study, we collected P and S waveforms from 160 regional earthquakes (3.3 ≤ M ≤ 5.7) recorded at 218 broadband stations of Southern California Seismic Network and measured spectral amplitudes of P and S waves in th...
Body-wave and normal-mode observations of Earth's inner core show cylindrical anisotropy consistent with an alignment of hexagonal close-packed iron (hcp-Fe) crystals along the rotation axis. We quantify the degree of alignment by comparing seismic observations longitudinally averaged over the outer 600 km of the inner core with stochastic rotation...
The Collaboratory for the Study of Earthquake Predictability (CSEP) is a global cyberinfrastructure for prospective evaluations of earthquake forecast models and prediction algorithms. CSEP’s goals are to improve our understanding of earthquake predictability, advance forecasting model development, test key scientific hypotheses and their predictiv...
We present highlights from the first decade of operation of the New Zealand Earthquake Forecast Testing Center of the Collaboratory for the Study of Earthquake Predictability (CSEP). Most results are based on reprocessing using the best available catalog, because the testing center did not consistently capture the complete real-time catalog. Tests...
The static coulomb stress hypothesis is a widely known physical mechanism for earthquake triggering and thus a prime candidate for physics-based operational earthquake forecasting (OEF). However, the forecast skill of coulomb-based seismicity models remains controversial, especially compared with empirical statistical models. A previous evaluation...
The proper scientific interpretation of the seismic hazard estimates requires a probabilistic framework that admits epistemic uncertainties on aleatory variables. This is not straightforward because, to subjectivists, all probabilities are epistemic, whereas to frequentists, all probabilities are aleatory.We illustrate the inadequacy of purely subj...
Computational science researchers running large-scale scientific workflow applications often want to run their workflows on the largest available compute systems to improve time to solution. Workflow tools used in distributed, heterogeneous, high performance computing environments typically rely on either a push-based or a pull-based approach for r...
Crustal seismic-velocity models and datasets play a key role in regional 3D numerical earthquake ground-motion simulation, full waveform tomography, and modern physics-based probabilistic earthquake-hazard analysis, as well as in other related fields, including geophysics and earthquake engineering. Most of these models and datasets, often collecti...
Probabilistic forecasting of earthquake-producing fault ruptures informs all major decisions aimed at reducing seismic risk and improving earthquake resilience. Earthquake forecasting models rely on two scales of hazard evolution: long-Term (decades to centuries) probabilities of fault rupture, constrained by stress renewal statistics, and short-Te...
We address the requirements that must be met by space-geodetic systems to place useful, new constraints on horizontal secular motions associated with the geological deformation of the earth's surface. Plate motions with characteristic speeds of about 50 mm/yr give rise to displacements that are easily observed by space geodesy. However, in order to...
To accommodate the relative motion across the North American-Pacific plate boundary predicted by global plate solutions, significant deformation on faults other than the San Andreas is necessary. In central California, this deformation is thought to include distributed compression perpendicular to the San Andreas as well as right-lateral strike-sli...
We, the ongoing Working Group on California Earthquake Probabilities, present a spatiotemporal clustering model for the Third Uniform California Earthquake Rupture Forecast (UCERF3), with the goal being to represent aftershocks, induced seismicity, and otherwise triggered events as a potential basis for operational earthquake forecasting (OEF). Spe...
We apply Jordan's self-consistent, second-order Born theory to compute the effective stiffness tensor for spatially stationary, stochastic models of 3-D elastic heterogeneity. The effects of local anisotropy can be separated from spatially extended geometric anisotropy by factoring the covariance of the moduli into a one-point variance tensor and a...
Full-3D waveform tomography is becoming a popular method for imaging Earth structure on local to global scales. It combines numerical simulations of wave propagation in heterogeneous media with adjoint techniques to construct seismogram sensitivity (Fréchet) kernels with respect to model parameters. The performance of this method is strongly determ...
This article reports on a workshop held to explore the potential uses of operational earthquake forecasting (OEF). We discuss the current status of OEF in the United States and elsewhere, the types of products that could be generated, the various potential users and uses of OEF, and the need for carefully crafted communication protocols. Although o...
S U M M A R Y A second-order Born approximation is used to formulate a self-consistent theory for the effective elastic parameters of stochastic media with ellipsoidal distributions of small-scale heterogeneity. The covariance of the stiffness tensor is represented as the product of a one-point tensor variance and a two-point scalar correlation fun...
A workshop on Operational earthquake forecasting and decision making was convened in Varenna, Italy, on June 8-11, 2014, under the sponsorship of the EU FP 7 REAKT (Strategies and tools for Real-time EArthquake risK reducTion) project, the Seismic Hazard Center at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), and the Southern Californi...
The 2014 Working Group on California Earthquake Probabilities (WGCEP 2014) presents time-dependent earthquake probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Building on the UCERF3 time-independent model published previously, renewal models are utilized to represent elastic-rebound-implied probabilities. A new m...
We derive time-dependent, renewal-model earthquake probabilities for the case in which the date of the last event is completely unknown, and compare these with the time-independent Poisson probabilities that are customarily used as an approximation in this situation. For typical parameter values, the renewal-model probabilities exceed Poisson resul...
The Regional Earthquake Likelihood Models experiment in California tested the performance of earthquake likelihood models over a five-year period. First-order analysis showed a smoothed-seismicity model by Helmstetter et al. (2007) to be the best model. We construct optimal multiplicative hybrids involving the best individual model as a baseline an...
Nearly half of the national seismic risk is located in Southern California, and about one‐fourth is concentrated in Los Angeles County alone (Federal Emergency Management Agency [FEMA], 2000). To assess the seismic hazards that drive this risk, we must forecast the strong ground motions that are likely to be produced by large fault ruptures. The st...
We cannot yet predict large earthquakes in the short term with much reliability and skill, but the strong clustering exhibited in seismic sequences tells us that earthquake probabilities are not constant in time; they generally rise and fall over periods of days to years in correlation with nearby seismic activity. Operational earthquake forecastin...
The 2014 Undergraduate Studies in Earthquake Information Technology (USEIT) Analysis Team studied and analyzed eighteen earthquake scenarios with similar magnitudes to the October 1989 magnitude 6.9 Loma Prieta Earthquake. This study included exploring the potential risk of substantial, typical, and minor aftershock sequences. Using graphical inter...
Significance
Science is rooted in the concept that a model can be tested against observations and rejected when necessary. However, the problem of model testing becomes formidable when we consider the probabilistic forecasting of natural systems. We show that testability is facilitated by the definition of an experimental concept, external to the m...
We have successfully applied full-3D tomography (F3DT) based on a combination of the scattering-integral method (SI-F3DT) and the adjoint-wavefield method (AW-F3DT) to iteratively improve a 3D starting model, the Southern California Earthquake Center (SCEC) Community Velocity Model version 4.0 (CVM-S4). In F3DT, the sensitivity (Fréchet) kernels ar...
Editor’s note: The following is the text of the SSA Presidential Address presented at the Annual Luncheon of the Seismological Society of America (SSA) Annual Meeting on 30 April 2014.
The Seismological Society of America (SSA) has always been dedicated to understanding and reducing the earthquake threat. The Society was founded in 1906 “for the...
We generalize the formulation of probabilistic seismic hazard analysis to accommodate simulation-based hazard models by expressing the joint probability distribution among the parameters of a kinematically complete earthquake rupture forecast in terms of a conditional hypocenter distribution and a conditional slip distribution. The seismological hi...
The 2014 Working Group on California Earthquake Probabilities (WGCEP14) present the time-independent component of the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), which provides authoritative estimates of the magnitude, location, and time-averaged frequency of potentially damaging earthquakes in California. The primary achiev...
This Special Focus Section comprises a collection of eight papers describing recent advances in methods for the broadband simulation of earthquake ground motions and their evaluation against recorded data and empirical models. In the jargon of engineering seismology, “broadband” implies seismograms with periods ranging from less than 0.1 s to great...
Online Material: Figures showing bias of PSA between data and simulations and between GMPEs and simulations for validation events and scenarios.
This article summarizes the evaluation of ground‐motion simulation methods implemented on the Southern California Earthquake Center (SCEC) Broadband Platform (BBP), version 14.3 (as of March 2014). A seve...
Online Material: Text‐based (BBP) input and output files and figures of goodness of fit; seismogram comparisons and source model illustrating the BBP validation of the Loma Prieta earthquake.
The Southern California Earthquake Center (SCEC) Broadband Platform (BBP) is an open‐source software distribution that contains physics‐based ground‐motion m...
We have developed a highly scalable and efficient GPU-based finite-difference code (AWP) for earthquake simulation that implements high throughput, memory locality, communication reduction and communication/computation overlap and achieves linear scalability on Cray XK7 Titan at ORNL and NCSA's Blue Waters system. We simulate realistic 0-10 Hz eart...
We project 3-D variations in shear wave (v(S)) velocity from 21 whole-mantle tomographic models onto global tectonic regionalizations. The v(S) profiles of oceanic and continental regions show strong upper mantle variations, as expected from plate tectonics, and most are consistent with lower mantle heterogeneity uncorrelated with surface tectonics...
CyberShake is a computational platform developed by the Southern California Earthquake Center (SCEC) that explicitly incorporates earthquake rupture time histories and deterministic wave propagation effects into seismic hazard calculations through the use of 3D waveform simulations. Using CyberShake, SCEC has created the first physics-based probabi...
The Regional Earthquake Likelihood Models (RELM) working group designed a 5-year experiment to forecast the number, spatial distribution, and magnitude distribution of subsequent target earthquakes, defined to be those with magnitude ≥4.95 (M 4.95+) in a well-defined California testing region. Included in the experiment specification were the descr...
Earthquakes are different from other common natural hazards because
precursory signals diagnostic of the magnitude, location, and time of
impending seismic events have not yet been found. Consequently, the
short-term, localized prediction of large earthquakes at high
probabilities with low error rates (false alarms and
failures-to-predict) is not y...
Editor’s note: The following is the text of an address given at the Public Policy Luncheon of the Seismological Society of America (SSA) Annual Meeting on 19 April 2012. In light of the manslaughter convictions handed down for six earth scientists and a public safety official in an Italian court on 22 October 2012, SRL is publishing the content of...
The assessment of earthquake forecast models for practical purposes requires more than simply checking model consistency in a statistical framework. One also needs to understand how to construct the best model for specific forecasting applications. We describe a Bayesian approach to evaluating earthquake forecasting models, and we consider related...
Although no deterministic and reliable earthquake precursor is known to date, we are steadily
gaining insight into probabilistic forecasting that draws on space–time characteristics of earthquake
clustering. Clustering-based models aiming to forecast earthquakes within the next
24 hours are under test in the global project ‘Collaboratory for the St...
Major objectives of the Japanese earthquake prediction research program
for the period 2009-2013 are to create earthquake forecasting models and
begin the prospective testing of these models against recorded
seismicity. For this purpose, the Earthquake Research Institute of the
University of Tokyo has joined an international partnership to create a...
In his commentary on the International Commission on Earthquake Forecasting (ICEF) report [Jordan et al. 2011], Crampin [2012] claims that observable changes in shear-wave splitting can predict large earthquakes on short time scales with high reliability and skill, and he challenges a central ICEF finding—that no method has yet demonstrated such a...
This study deals with the effects of the built environment on the earthquake ground motion, and with how individual buildings interact with the surrounding soil and with each other. We conduct a parametric study using Hercules, the parallel octree-based finite element earthquake simulator developed by the Quake Group at Carnegie Mellon University....
To study static stress interactions between faults in southern
California and identify cases where one large earthquake could trigger
another, we select fourteen M>7 events simulated by the SCEC/CME
CyberShake project and calculate the Coulomb stress changes those events
impart to major fault surfaces in the UCERF2 fault model for the region.
Cyber...
Though earthquake forecasting models have often represented seismic
sources as space-time points (usually hypocenters), a more complete
hazard analysis requires the consideration of finite-source effects,
such as rupture extent, orientation, directivity, and stress drop. The
most compact source representation that includes these effects is the
fini...
Accurate and rapid CMT inversion is important for seismic hazard
analysis. We have developed an algorithm for very rapid full-wave CMT
inversions in a 3D Earth structure model and applied it on earthquakes
recorded by the Southern California Seismic Network (SCSN). The
procedure relies on the use of receiver-side Green tensors (RGTs), which
compris...
The Southern California Earthquake Center (SCEC) Broadband Platform is a
collaborative software development project involving SCEC researchers,
graduate students, and the SCEC Community Modeling Environment. The goal
of the SCEC Broadband Simulation Platform is to generate broadband (0-10
Hz) ground motions for earthquakes using deterministic low-f...
There is no merit in prosecuting scientists for failing to predict an earthquake, says Thomas H. Jordan, but seismologists can still learn from this fiasco
Scientific workflows are a common computational model for performing scientific simulations. They may include many jobs, many scientific codes, and many file dependencies. Since scientific workflow applications may include both high-performance computing (HPC) and high-throughput computing (HTC) jobs, meaningful performance metrics are difficult to...
Following the 2009 L'Aquila earthquake, the Dipartimento della Protezione Civile Italiana (DPC), appointed an International Commission on Earthquake Forecasting for Civil Protection (ICEF) to report on the current state of knowledge of short-term prediction and forecasting of tectonic earthquakes and indicate guidelines for utilization of possible...
A central problem of seismology is the inversion of regional waveform data for models of earthquake sources. In regions such as Southern California, preliminary 3-D earth structure models are already available, and efficient numerical methods have been developed for 3-D anelastic wave-propagation simulations. We describe an automated procedure that...
In folklore, a "silver bullet" is an effective weapon against were-wolves and witches. In earthquake prediction, a silver bullet is a diagnostic precursor—a signal observed before an earthquake that indicates with high probability the location, time, and magnitude of the impending event (Jordan 2006). In his comment, Crampin (2010) claims that shea...
The Collaboratory for the Study of Earthquake Predictability (CSEP) is an international partnership to support research on rigorous earthquake prediction in multiple tectonic environments. This paper outlines the first earthquake forecast testing experiment for the Japan area conducted within the CSEP framework. We begin with some background and br...
Earthquake simulations in 3D structures are currently being used for forward prediction of ground motions, imaging of sources, and structure refinement (full-3D tomography). The computational platform for such simulations requires the accurate location of sources and receivers within the computational grid; the flexibility to represent geological c...
Accurate and rapid CMT inversion is important for seismic hazard analysis. We have developed an algorithm for very rapid CMT inversions in a 3D Earth structure model and applied it on small to medium-sized earthquakes recorded by the Southern California Seismic Network (SCSN). Our CMT inversion algorithm is an integral component of the scattering-i...
The goal of operational earthquake forecasting (OEF) is to provide the public with authoritative information about how seismic hazards are changing with time. During periods of high seismic activity, short-term earthquake forecasts based on empirical statistical models can attain nominal probability gains in excess of 100 relative to the long-term...
The goal of operational earthquake forecasting (OEF) is to provide authoritative information about the time dependence of seismic hazard to help communities prepare for earthquakes. Statistical and physical models of earthquake interactions have begun to capture many features of natural seismicity, such as aftershock triggering and the clustering o...
Aftershocks are often used to delineate the mainshock rupture zone retrospectively. In aftershock forecasting on the other hand, the problem is to use mainshock rupture area to determine the aftershock zone prospectively. The procedures for this type of prediction are not as well developed and have been restricted to simple parameterizations such a...
Shallow material properties, S-wave velocity in particular, strongly influence ground motions, so must be accurately characterized for ground-motion simulations. Available near-surface velocity information generally exceeds that which is accommodated by crustal velocity models, such as current versions of the SCEC Community Velocity Model (CVM-S4)...
We are automating our full-3D waveform tomography (F3DT) based on the scatteringintegral (SI) method and applying the automated algorithm to iteratively improve the 3D SCEC Community Velocity Model Version 4.0 (CVM4) in Southern California. In F3DT, the starting model as well as the derived model perturbation is 3D in space and the sensitivity kern...
We calculate the Coulomb stress changes imparted to major Southern California faults by thirteen simulated worst-case-scenario earthquakes for the region, including the ``Big Ten'' scenarios (Ely et al, in progress). The source models for the earthquakes are variable-slip simulations from the SCEC CyberShake project (Graves et al, 2010). We find st...