Papers by Gregory Lyzenga
Toppling of a Trona Pinnacles Spire following the Mw 5.5 Ridgecrest Aftershock of June 2020
Seismological Research Letters, 2022
The 2019 Mw 7.1 Ridgecrest California earthquake rupture passed within 4 km of the Trona Pinnacle... more The 2019 Mw 7.1 Ridgecrest California earthquake rupture passed within 4 km of the Trona Pinnacles, a large group of tufa rock pillars. Reconnaissance following the Ridgecrest mainshock documented fresh damage to several of the Pinnacles. Repeated aerial photogrammetric surveys also documented damage during subsequent aftershocks. Here, we describe the photogrammetric data with emphasis on a specific rock spire that toppled during an Mw 5.5 aftershock. We calculate the volumes of the intact spire and of its subsequent debris. To explore the utility of the pinnacles as fragile geologic features for constraining past earthquake shaking intensity, we calculate the quasi static, horizontal acceleration required to break the spire at its base. We also examine the response of this feature to observed shaking using a dynamic model of the spire. In this case, we find that the quasi-static estimate provides a conservative maximum constraint on fragility. The dynamic model of the spire sugges...
Earth and Space Science, 2021
We present a data-driven approach to clustering or grouping Global Navigation Satellite System (G... more We present a data-driven approach to clustering or grouping Global Navigation Satellite System (GNSS) stations according to observed velocities, displacements or other selected characteristics. Clustering GNSS stations provides useful scientific information, and is a necessary initial step in other analysis, such as detecting aseismic transient signals (Granat et al., 2013,
Earth and Space Science, 2020
Positions, velocities, breaks, and seasonal terms for thousands of GNSS stations are updated ever... more Positions, velocities, breaks, and seasonal terms for thousands of GNSS stations are updated every week. 2. These results can be used for scientific studies of interseismic plate motion, coseismic deformation, postseismic deformation, and seasonal variations. 3. Use of these tools shows highly variable nonlinear motion of GPS stations in southern California.
Parallel finite elements applied to 3D electromagnetic scattering problems
International Symposium on Antennas and Propagation Society, Merging Technologies for the 90's, 1990
A two-dimensional electromagnetic (EM) finite element analysis code which runs on the JPL/Caltech... more A two-dimensional electromagnetic (EM) finite element analysis code which runs on the JPL/Caltech Mark IIIfp Hypercube is being upgraded to handle fully three-dimensional scattering problems. The EM code uses finite elements to model a finite problem domain which may include regions of anisotropic or nonuniform dielectric properties. It solves the single-frequency source driven vector wave equation for electric or magnetic fields in this domain. The code is being implemented as a testbed for finite elements as applied to EM problems, with several types of elements, radiation boundary condition strategies, and parallel solvers
Walker: solving problems on concurrent processors
Parallel Finite Elements Applied to the Electromagnetic Scattering Problem
Proceedings of the Fifth Distributed Memory Computing Conference, 1990.
A two-dimensional electromagnetic (EM) finite element analysis code which runs on the JPL/Caltech... more A two-dimensional electromagnetic (EM) finite element analysis code which runs on the JPL/Caltech Mark IIIfp Hypercube is being upgraded to handle fully three-dimensional scattering problems. The EM code uses finite elements to model a finite problem domain which may include regions of anisotropic or nonuniform dielectric properties. It solves the single-frequency source driven vector wave equation for electric or magnetic
The QuakeSim GeoFEST modeling system - new features inspired by San Andreas Fault motion
The NASA QuakeSim project modeling environment GeoFEST (Geophysical Finite Element Simulation Too... more The NASA QuakeSim project modeling environment GeoFEST (Geophysical Finite Element Simulation Tool) has demonstrated features for rapidly scaling up to very large problems (of order 1e8 linear tetrahedral finite elements) by incorporating load-balanced parallel partitioning of the mesh, low-communication iterative solution of the sparse linear systems, and solution-driven strain energy based automatic parallel mesh refinement. Inspired by several San Andreas Fault modeling problems, new features have been added and are incorporated into a new public release. These include support for tectonic velocities at the boundaries within the adaptive mesh framework (giving support for repeat-event spinup), independent specified periodic motions on specified sets of fault nodes (supporting steady motion of faults at depth in same model with periodic crust events), buoyancy counterforces that arise from vertical deformation across density contrast surfaces. Support has been added for nonuniform...
Computational Electromagnetics on the Hypercube Parallel Computer
Numerical Modeling of Deformation in the Los Angeles Basin, Southern California
ABSTRACT Deformation in the Los Angeles Basin is characterized by a narrow band of shortening bet... more ABSTRACT Deformation in the Los Angeles Basin is characterized by a narrow band of shortening between downtown Los Angeles and the San Gabriel Mountains. Geodetic measurements indicate that there is ˜4.5 mm/yr shortening across this band; however, the mechanism by which this shortening is accommodated is poorly characterized and understood. It is unclear whether shortening is accommodated by elastic strain accumulation and release along a series of sub-parallel thrust faults, including the Sierra Madre fault (the frontal fault of the San Gabriel Mountains) or whether it is accommodated by anelastic processes taking place in the low rigidity sediments within the basin. We will present the results of numerical modeling of the region using both 2D and 3D finite element models from the GeoFEST (Geophysical Finite Element Simulation Tool) code and the QuakeSim Computational Portal. These results will be compared with geodetically observed deformation being recorded by the Southern California Integrated GPS Network (SCIGN). Previous modeling indicates that the low rigidity basin sediments play a key role in accommodating the observed shortening, but those models were unable to predict the observed deformation. We have further refined our 2D models by testing model sensitivity to changes in the modeling domain (i.e. creating a box with greater depth) and to the degree of mesh refinement in areas characterized by large material contrasts. The results of these model sensitivity tests indicate that a modeling domain that is 400 km x 600 km with a mesh refinement of ˜1.25 km node spacing near the transition between basin sediments and bedrock (and 5 km node spacing elsewhere) produce velocities that do not reflect errors caused by numerical artifacts within the model. We will compare the newly refined 2D results with kinematic models constructed by other workers. We will also construct a simple D model of the Los Angeles Basin in order to characterize the problem and to see if we are better able to predict observed deformation with a more realistic geometric and mechanical model.
Application of GeoFEST with PYRAMID mesh refinement to Southern California crustal deformation
ABSTRACT Modeling of southern California tectonics with its wide range of length scales, complex ... more ABSTRACT Modeling of southern California tectonics with its wide range of length scales, complex faulting pattern and variety of relevant material properties demands high-performance techniques with unprecedented flexibility. The finite element method is a natural choice, but requires special techniques to treat all these features within the bounds of affordable high performance computing. We have demonstrated the parallel scalability of a faulted crust finite element system, GeoFEST. But in three dimensions, element size must be automatically scaled to the local physics. Otherwise extra elements are used, leading to extravagant waste on the order of an inverse-length cubed in memory (and I/O) and at least fourth-power in flops. We apply the PYRAMID parallel adaptive mesh refinement library to generate the needed elements based on an initial coarse mesh, solution, and a strain energy metric. Application to models of the Landers earthquake and the interseismic Los Angeles basin compression highlight the utility and long-range potential of this method for interpreting space geodetic measurements.
Design and Performance Optimization of GeoFEST for Adaptive Geophysical Modeling on High Performance Computers
The Geophysical Finite Element Simulation Tool (GeoFEST) and the PYRAMID parallel adaptive mesh r... more The Geophysical Finite Element Simulation Tool (GeoFEST) and the PYRAMID parallel adaptive mesh refinement library have been integrated to provide high performance and high resolution modeling of 3D Earth crustal deformation under tectonic loading associated with the Earthquake cycle. This includes co-seismic and post-seismic modeling capabilities as well as other problems of geophysical interest. The use of the PYRAMID AMR
Modeling of Natural Hazards Related to the Los Angeles Basin, Southern California
ABSTRACT Geodetic observations in the Los Angeles Basin show 4.5 mm/yr of convergence between dow... more ABSTRACT Geodetic observations in the Los Angeles Basin show 4.5 mm/yr of convergence between downtown Los Angeles and the San Gabriel Mountains. This high rate of convergence is being accommodated either along faults in the Basin or within basin sediments. Modeling results using elastic backslip models and the GeoFEST viscoelastic modeling code indicate several mm/yr of deformation at the surface resulting from motion along thrust faults in the basin. These models can be used to study the strain partitioning between faults within the region in order to determine which faults accommodate the convergence across the Basin. While there is a relatively high GPS station density in the LA Basin, vertical velocities are not well-constrained. In a deformation regime characterized by convergence and thrust faulting, vertical velocities are important to understanding how the region is deforming. The frequent observations provided by a mission such as DESDynI would improve our understanding of deformation signals, especially in the vertical direction. A study of time dependent postseismic surface deformation with 1 cm error from an ensemble of synthetic earthquakes to understand the impact of InSAR sampling interval on the discrimination of post seismic processes indicates that an 8-day repeat pass is the maximum interval in order to resolve these processes following events. Both a linear combination of a logarithmic afterslip function and an exponential decay relaxation function are considered as post seismic processes. Any greater interval for a half-year or two-year observation period following an event shows significant degradation in ability to resolve these processes. Deformation within the LA Basin is further complicated by anthropogenic contributions to the overall velocity signal. Distinguishing between geologic and anthropogenic processes is critical to correctly modeling the ongoing deformation within the Basin, characterizing the tectonic processes, and evaluating earthquake hazard. For example, extraction processes that lead to local subsidence mask deeper tectonic activity. These effects may be minimized by a combination of GPS (which has a continuous time series) and InSAR (which has high spatial sampling). Residual postseismic signals from models are on the order of a few (1-2) mm/yr, which requires measurement accuracy in the same scale in order to verify models, distinguish between different processes and material properties, and to determine which faults are contributing to the deformation within a region. With a combination of numerical modeling codes such as GeoFEST and further studies into the optimal design for a proposed InSAR mission will help better elucidate the deformation processes at play, as well as the hazards they may pose.
UAVSAR and GPS Observations of Crustal Deformation in Southern California and Implications for Earthquake Risk
The 2010 El-Mayor Cucapah earthquake was the first earthquake to be observed with UAVSAR. UAVSAR ... more The 2010 El-Mayor Cucapah earthquake was the first earthquake to be observed with UAVSAR. UAVSAR observations, GPS time series analysis, and simulations suggest that the fault that ruptured in the earthquake is coupled to the Elsinore, San Jacinto, and San Andreas faults to the north. GPS and UAVSAR observations indicate a zone of shear that extends southward from the Big
Concurrent electromagnetic scattering analysis
7th Computers in Aerospace Conference, 1989
ABSTRACT The computational power of the hypercube parallel computing architecture is applied to t... more ABSTRACT The computational power of the hypercube parallel computing architecture is applied to the solution of large-scale electromagnetic scattering and radiation problems. Three analysis codes have been implemented. A Hypercube Electromagnetic Interactive Analysis Workstation was developed to aid in the design and analysis of metallic structures such as antennas and to facilitate the use of these analysis codes. The workstation provides a general user environment for specification of the structure to be analyzed and graphical representations of the results.
Pure and Applied Geophysics, 2008
GeoFEST (Geophysical Finite Element Simulation Tool) is a two-and three-dimensional finite elemen... more GeoFEST (Geophysical Finite Element Simulation Tool) is a two-and three-dimensional finite element software package for the modeling of solid stress and strain in geophysical and other continuum domain applications. It is one of the featured high-performance applications of the NASA QuakeSim project. The program is targeted to be compiled and run on UNIX systems, and is running on diverse systems including sequential and message-passing parallel systems. Solution to the elliptical partial differential equations is obtained by finite element basis sampling, resulting in a sparse linear system primarily solved by conjugate gradient iteration to a tolerance level; on sequential systems a Crout factorization for the direct inversion of the linear system is also supported. The physics models supported include isotropic linear elasticity and both Newtonian and power-law viscoelasticity, via implicit quasi-static time stepping. In addition to triangular, quadrilateral, tetrahedral and hexahedral continuum elements, GeoFEST supports split-node faulting, body forces, and surface tractions. This software and related mesh refinement strategies have been validated on a variety of test cases with rigorous comparison to analytical solutions. These include a box-shaped domain with imposed motion on one surface, a pair of strike slip faults in stepover arrangement, and two community-agreed benchmark cases: a strike slip fault in an enclosing box, and a quarter-domain circular fault problem. Scientific applications of the code include the modeling of static and transient co-and post-seismic earth deformation, Earth response to glacial, atmospheric and hydrological loading, and other scenarios involving the bulk deformation of geologic media.
IEEE Transactions on Magnetics, 1989
The Hypercube is a general purpose computing tool for scientific applications. Investigators use ... more The Hypercube is a general purpose computing tool for scientific applications. Investigators use the Mark I11 Hypercube for numerical simulations in a variety of disciplines. To the list of analysis codes running on the Hypercube, we add two electromagnetic codes, the Numerical Electromagnetic Code (NEC) and the Finite Difference "ime Domain Code (FDTD). We want to evaluate the execution times for these codes. For both the NEC and FDTD codes, we found large speedup factors when we compared runs on 32 nodes to runs on 1 node and to runs on a VAX 11/750. We verified the accuracy of these codes by comparisons with versions running on sequential machines and with published results'.
Geophysical Research Letters, 1993
We use space geodetic data from very long baseline interferometry to estimate the velocity relati... more We use space geodetic data from very long baseline interferometry to estimate the velocity relative to the plates of two sites near Tokyo. We use these results and elastic models of interseismic deformation to put constraints on the slip rate along the main thrust at the Japan subduction zone. The sites at Kashima and Tsukuba lie 150 and 200 km, respectively, west of the axis of the Japan trench, where the Pacific plate subducts at-97 mm/yr. The two sites also lie 160 km from the Sagami trough, where the Philippine plate subducts obliquely at-32 nun/yr. Relative to the North American plate .Kashima moves at 13+2 mm/yr toward N46+4øW and Tsukuba moves at 9- !-_3 mrn/yr toward N42+19øW. These observed velocities are intermediate between the velocities of the Pacific and Eurasian plates, consistent with the overriding plate being the Eurasian plate. In this case the observed velocities reflect the sum of (a) permanent west-northwest shortening in northern Honshu and (b) elastic deformation due to locking the main thrust fault at Japan trench. But the observed velocities are also part way between the velocities of the Philippine and North American plates, and they may result from Philippine-North American deformation. Nevertheless, the observed velocities limit the locked segment of the main thrust at Japan trench to no more than 27 km vertically or 100 km along dip. Thus, the main Pacific plate thrust fault is not strongly coupled, part of it must creep, and it probably does not generate great earthquakes.
Geophysical Research Letters, 2000
The M-7.1 Hector Mine earthquake ruptured the Lavic Lake fault near Twentynine Palms, CA at 09:46... more The M-7.1 Hector Mine earthquake ruptured the Lavic Lake fault near Twentynine Palms, CA at 09:46 UTC October 16, 1999. Because it occurred near the eastern edge of the Southern California Integrated GPS Network (SCIGN), a network of permanent, continuously recording GPS receivers for measuring the crustal deformation field around Los Angeles, CA, it was possible to determine the deformation associated with the earthquake with unprecedented speed and reliability. Thirty-four stations recorded displacements over the 3-sigma level. The displacements measured with GPS can be modeled by a fault 46.2-+-2.6 km long, 8.2 q-1.0 km wide, striking 330 ø , dipping 84 ø east, with 301 q-36 cm right lateral strike-slip, and 145 q-36 cm of east-up dip-slip, yielding a potency of 1.3 km a and geodetic moment of 3.8 x 1026 dyne-cm. The trace and dip of the model fault is consistent with the observed ground rupture and seismic focal mechanisms.
Hypercube matrix computation task. Report, 1986-1988
The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
Earth Science Computational Architecture for Multi-disciplinary Investigations
AGU Fall Meeting Abstracts, Dec 1, 2005
Understanding the processes underlying Earth's deformation and mass transport requires a non... more Understanding the processes underlying Earth's deformation and mass transport requires a non-traditional, integrated, interdisciplinary, approach dependent on multiple space and ground based data sets, modeling, and computational tools. Currently, details of geophysical data acquisition, analysis, and modeling largely limit research to discipline domain experts. Interdisciplinary research requires a new computational architecture that is optimized to perform complex data processing of multiple solid Earth science data types in ...
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Papers by Gregory Lyzenga