Arben Pitarka

Verified email at llnl.gov

Seismologist, Atmospheric, Earth, and Energy Division
Lawrence Livermore National Laboratory



                             

https://researchid.co/pitarka1
60

Scopus Publications

4202

Scholar Citations

26

Scholar h-index

50

Scholar i10-index

Scopus Publications

  • Deterministic 3D Ground-Motion Simulations (0–5 Hz) and Surface Topography Effects of the 30 October 2016 M<inf>w</inf> 6.5 Norcia, Italy, Earthquake
    Arben Pitarka, Aybige Akinci, Pasquale De Gori, and Mauro Buttinelli

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 112, Pages: 262-286, Published: February 2022 Seismological Society of America (SSA)
    ABSTRACT The Mw 6.5 Norcia, Italy, earthquake occurred on 30 October 2016 and caused extensive damage to buildings in the epicentral area. The earthquake was recorded by a network of strong-motion stations, including 14 stations located within a 5 km distance from the two causative faults. We used a numerical approach for generating seismic waves from two hybrid deterministic and stochastic kinematic fault rupture models propagating through a 3D Earth model derived from seismic tomography and local geology. The broadband simulations were performed in the 0–5 Hz frequency range using a physics-based deterministic approach modeling the earthquake rupture and elastic wave propagation. We used SW4, a finite-difference code that uses a conforming curvilinear mesh, designed to model surface topography with high numerical accuracy. The simulations reproduce the amplitude and duration of observed near-fault ground motions. Our results also suggest that due to the local fault-slip pattern and upward rupture directivity, the spatial pattern of the horizontal near-fault ground motion generated during the earthquake was complex and characterized by several local minima and maxima. Some of these local ground-motion maxima in the near-fault region were not observed because of the sparse station coverage. The simulated peak ground velocity (PGV) is higher than both the recorded PGV and predicted PGV based on empirical models for several areas located above the fault planes. Ground motions calculated with and without surface topography indicate that, on average, the local topography amplifies the ground-motion velocity by 30%. There is correlation between the PGV and local topography, with the PGV being higher at hilltops. In contrast, spatial variations of simulated PGA do not correlate with the surface topography. Simulated ground motions are important for seismic hazard and engineering assessments for areas that lack seismic station coverage and historical recordings from large damaging earthquakes.

  • Refinements to the Graves–Pitarka Kinematic Rupture Generator, Including a Dynamically Consistent Slip-Rate Function, Applied to the 2019 M<inf>w</inf> 7.1 Ridgecrest Earthquake
    Arben Pitarka, Robert Graves, Kojiro Irikura, Ken Miyakoshi, Changjiang Wu, Hiroshi Kawase, Arthur Rodgers, and David McCallen

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 112, Pages: 287-306, Published: February 2022 Seismological Society of America (SSA)
    ABSTRACT The main objective of this study is to develop physics-based constraints on the spatiotemporal variation of the slip-rate function using a simplified dynamic rupture model. First, we performed dynamic rupture modeling of the 2019 Mw 7.1 Ridgecrest, California, earthquake, to analyze the effects of depth-dependent stress and material friction on slip rate. Then, we used our modeling results to guide refinements to the slip-rate function that were implemented in the Graves–Pitarka kinematic rupture generation technique. The dynamic ruptures were computed on a surface-rupturing, planar strike-slip fault that includes a weak (negative to low-stress-drop) zone in the upper 4 km of the crust. Below the weak zone, we placed high-stress-drop patches designed to mirror the large-slip areas seen in various rupture model inversions of the event. The locations of the high-stress-drop patches and the hypocenter were varied in multiple realizations to investigate how changing the dynamic conditions affected the resulting rupture kinematics, in particular, the slip rate. From these simulations, we observed a systematic change in the shape of the slip-rate function from Kostrov type below the weak zone to a predominantly symmetric shape within the weak zone, along with a depth-dependent reduction of peak slip rate. We generalized these shallow rupture features into a depth-dependent parametric variation of the slip-rate function and implemented it in the Graves–Pitarka kinematic rupture model generator. The performance of the updated kinematic approach was then verified in 0–4 Hz simulations of the Mw 7.1 Ridgecrest earthquake, which showed that incorporating the depth-dependent variation in the shape of the slip-rate function improves the fit to the observed near-fault ground motions in the 0.5–3 s period range.

  • Modeling Subsurface Explosions Recorded on a Distributed Fiber Optic Sensor
    Robert J. Mellors, Robert Abbott, David Steedman, David Podrasky, and Arben Pitarka

    Journal of Geophysical Research: Solid Earth, ISSN: 21699313, eISSN: 21699356, Volume: 126, Published: December 2021 American Geophysical Union (AGU)

  • Engineering evaluation of the EQSIM simulated ground-motion database: The San Francisco Bay Area region
    Floriana Petrone, Norman Abrahamson, David McCallen, Arben Pitarka, and Arthur Rodgers

    Earthquake Engineering and Structural Dynamics, ISSN: 00988847, eISSN: 10969845, Pages: 3939-3961, Published: December 2021 Wiley

  • Using dense array waveform correlations to build a velocity model with stochastic variability
    Arben Pitarka and Robert Mellors

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 111, Pages: 2021-2041, Published: August 2021 Seismological Society of America (SSA)
    ABSTRACT In an ongoing effort to improve 3D seismic-wave propagation modeling for frequencies up to 10 Hz, we used cross correlations between vertical-component waveforms from an underground chemical explosion to estimate the statistical properties of small-scale velocity heterogeneities. The waveforms were recorded by a dense 2D seismic array deployed during the Source Physics Experiments for event number 5 (SPE-5) in a series of six underground chemical explosions, conducted at the Nevada National Security Site. The array consisted of 996 geophones with a 50–100 m grid spacing, deployed at the SPE site at the north end of the Yucca Flat basin. The SPE were conducted to investigate the generation and propagation of seismic and acoustic waves from underground explosions. Comparisons of decay rates of waveform cross correlations as function of interstation distance, computed for observed and synthetic seismograms from the SPE-5 chemical explosion, were used to constrain statistical properties of correlated stochastic velocity perturbations representing small-scale heterogeneities added to a geology-based velocity model of the Yucca Flat basin. Using comparisons between recorded and simulated waveform cross correlations, we were able to recover sets of statistical properties of small-scale velocity perturbations in the velocity model that produce the best-fit between the recorded and simulated ground motion. The stochastic velocity fluctuations in the velocity model that produced the smallest misfits have a horizontal correlation distance of between 400 and 800 m, a vertical correlation distance between 100 and 200 m, and a standard deviation of 10% from the nominal model velocity in the alluvium basin layers. They also have a horizontal correlation distance of 1000 m, a vertical correlation distance of 250 m, and a standard deviation of 6% in the underlying and consolidated sedimentary layers, up to a depth of 4 km. Comparisons between observed and simulated wavefields were used to assess the proposed small-scale heterogeneity enhancements to the Yucca Flat basin model. We found that adding a depth-resolved stochastic variability to the geology-based velocity model improves the overall performance of ground-motion simulations of an SPE-5 explosion in the modeled frequency range up to 10 Hz. The results may be applicable to other similar basins.

  • Preliminary Analysis of Source Physics Experiment Explosion-Triggered Microseismicity Using the Back-Projection Method
    G. A. Ichinose, S. R. Ford, K. Kroll, D. Dodge, M. Pyle, A. Pitarka, and W. R. Walter

    Journal of Geophysical Research: Solid Earth, ISSN: 21699313, eISSN: 21699356, Volume: 126, Published: May 2021 American Geophysical Union (AGU)

  • Variability of near-fault seismic risk to reinforced concrete buildings based on high-resolution physics-based ground motion simulations
    Maha Kenawy, David McCallen, and Arben Pitarka

    Earthquake Engineering and Structural Dynamics, ISSN: 00988847, eISSN: 10969845, Pages: 1713-1733, Published: May 2021 Wiley

  • EQSIM—A multidisciplinary framework for fault-to-structure earthquake simulations on exascale computers, part II: Regional simulations of building response
    David McCallen, Floriana Petrone, Mamun Miah, Arben Pitarka, Arthur Rodgers, and Norman Abrahamson

    Earthquake Spectra, ISSN: 87552930, Pages: 736-761, Published: May 2021 SAGE Publications
    The existing observational database of the regional-scale distribution of strong ground motions and measured building response for major earthquakes continues to be quite sparse. As a result, details of the regional variability and spatial distribution of ground motions, and the corresponding distribution of risk to buildings and other infrastructure, are not comprehensively understood. Utilizing high-performance computing platforms, emerging high-resolution, physics-based ground motion simulations can now resolve frequencies of engineering interest and provide detailed synthetic ground motions at high spatial density. This provides an opportunity for new insight into the distribution of infrastructure seismic demands and risk. In the work presented herein, the EQSIM fault-to-structure computational framework described in a companion paper, McCallen et al., is employed to investigate the regional-scale response of buildings to large earthquakes. A representative M = 7.0 strike-slip event is used to explore the distribution and amplitude of building demand, and comparisons are made between building response computed with fault-to-structure simulations and building response computed with existing measured near-fault earthquake records. New information on the distribution and variability of building response from high-performance parallel simulations is described and analyzed, and favorable first comparisons between building response predicted with both fault-to-structure simulations and real ground motions records are presented.

  • EQSIM—A multidisciplinary framework for fault-to-structure earthquake simulations on exascale computers part I: Computational models and workflow
    David McCallen, Anders Petersson, Arthur Rodgers, Arben Pitarka, Mamun Miah, Floriana Petrone, Bjorn Sjogreen, Norman Abrahamson, and Houjun Tang

    Earthquake Spectra, ISSN: 87552930, Pages: 707-735, Published: May 2021 SAGE Publications
    Computational simulations have become central to the seismic analysis and design of major infrastructure over the past several decades. Most major structures are now “proof tested” virtually through representative simulations of earthquake-induced response. More recently, with the advancement of high-performance computing (HPC) platforms and the associated massively parallel computational ecosystems, simulation is beginning to play a role in increased understanding and prediction of ground motions for earthquake hazard assessments. However, the computational requirements for regional-scale geophysics-based ground motion simulations are extreme, which has restricted the frequency resolution of direct simulations and limited the ability to perform the large number of simulations required to numerically explore the problem parametric space. In this article, recent developments toward an integrated, multidisciplinary earth science-engineering computational framework for the regional-scale simulation of both ground motions and resulting structural response are described with a particular emphasis on advancing simulations to frequencies relevant to engineered systems. This multidisciplinary computational development is being carried out as part of the US Department of Energy (DOE) Exascale Computing Project with the goal of achieving a computational framework poised to exploit emerging DOE exaflop computer platforms scheduled for the 2022–2023 timeframe.

  • Effect of random 3d correlated velocity perturbations on numerical modeling of ground motion from the source physics experiment
    Michelle Scalise, Arben Pitarka, John N. Louie, and Kenneth D. Smith

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 111, Pages: 139-156, Published: February 2021 Seismological Society of America (SSA)
    ABSTRACT Explosions are traditionally discriminated from earthquakes, using the relative amplitude of compressional and shear waves at regional and teleseismic distances known as the P/S discriminant. Pyle and Walter (2019) showed this technique to be less robust at shorter distances, in detecting small-magnitude earthquakes and low-yield explosions. The disparity is largely due to ground motion from small, shallow sources being significantly impacted by near-surface structural complexities. To understand the implications of wave propagation effects in generation of shear motion and P/S ratio during underground chemical explosions, we performed simulations of the Source Physics Experiment (SPE) chemical explosions using 1D and 3D velocity models of the Yucca Flat basin. All simulations used isotropic point sources in the frequency range 0–5 Hz. We isolate the effect of large-scale geological structure and small-scale variability at shallow depth (&amp;lt;5  km), using a regional 3D geologic framework model (GFM) and the GFM-R model derived from the GFM, by adding correlated stochastic velocity perturbations. A parametric study of effects of small-scale velocity variations on wave propagation, computed using a reference 1D velocity model with stochastic perturbations, shows that the correlation length and depth of stochastic perturbations significantly impact wave scattering, near-surface wave conversions, and shear-wave generation. Comparisons of recorded and simulated waveforms for the SPE-5 explosion, using 3D velocity models, demonstrate that the shallow structure of the Yucca Flat basin contributes to generation of observed shear motion. The inclusion of 3D wave scattering, simulated by small-scale velocity perturbations in the 3D model, improves the fit between the simulated and recorded waveforms. In addition, a relatively low intrinsic attenuation, combined with small-scale velocity variations in our models, can confirm the observed wave trapping and its effect on duration of coda waves and the spatial variation of P/S ratio at basin sites.

  • Regional-scale 3d ground-motion simulations of m<inf>w</inf> 7 earthquakes on the hayward fault, northern california resolving frequencies 0–10 hz and including site-response corrections
    Arthur J. Rodgers, Arben Pitarka, Ramesh Pankajakshan, Bjorn Sjögreen, and N. Anders Petersson

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 110, Pages: 2862-2881, Published: December 2020 Seismological Society of America (SSA)
    ABSTRACT Large earthquake ground-motion simulations in 3D Earth models provide constraints on site-specific shaking intensities but have suffered from limited frequency resolution and ignored site response in soft soils. We report new regional-scale 3D simulations for moment magnitude 7.0 scenario earthquakes on the Hayward Fault, northern California with SW4. Simulations resolved significantly broader band frequencies (0–10 Hz) than previous studies and represent the highest resolution simulations for any such earthquake to date. Seismic waves were excited by a kinematic rupture following Graves and Pitarka (2016) and obeyed wave propagation in a 3D Earth model with topography from the U.S. Geological Survey (USGS) assuming a minimum shear wavespeed, VSmin, of 500  m/s. We corrected motions for linear and nonlinear site response for the shear wavespeed, VS, from the USGS 3D model, using a recently developed ground-motion model (GMM) for Fourier amplitude spectra (Bayless and Abrahamson, 2018, 2019a). At soft soil locations subjected to strong shaking, the site-corrected intensities reflect the competing effects of linear amplification by low VS material, reduction of stiffness during nonlinear deformation, and damping of high frequencies. Sites with near-surface VS of 500  m/s or greater require no linear site correction but can experience amplitude reduction due to nonlinear response. Averaged over all sites, we obtained reasonable agreement with empirical ergodic median GMMs currently used for seismic hazard and design ground motions (epsilon less than 1), with marked improvement at soft sedimentary sites. At specific locations, the simulated shaking intensities show systematic differences from the GMMs that reveal path and site effects not captured in these ergodic models. Results suggest how next generation regional-scale earthquake simulations can provide higher spatial and frequency resolution while including effects of soft soils that are commonly ignored in scenario earthquake ground-motion simulations.

  • Kinematic Rupture Modeling of Ground Motion from the M7 Kumamoto, Japan Earthquake
    A. Pitarka, R. Graves, K. Irikura, K. Miyakoshi, and A. Rodgers

    Pure and Applied Geophysics, ISSN: 00334553, eISSN: 14209136, Volume: 177, Pages: 2199-2221, Published: 1 May 2020 Springer Science and Business Media LLC
    We analyzed a kinematic earthquake rupture generator that combines the randomized spatial field approach of Graves and Pitarka (Bull Seismol Soc Am 106:2136–2153, 2016 ) (GP2016) with the multiple asperity characterization approach of Irikura and Miyake (Pure Appl Geophys 168:85–104, 2011 ) (IM2011, also known as Irikura recipe). The rupture generator uses a multi-scale hybrid approach that incorporates distinct features of both original approaches, such as small-scale stochastic rupture variability and depth-dependent scaling of rupture speed and slip rate, inherited from GP2016, and specification of discrete high slip rupture patches, inherited from IM2011. The performance of the proposed method is examined in simulations of broadband ground motion from the 2016 Kumamoto, Japan earthquake, as well as comparisons with ground motion prediction equations (GMPEs). We generated rupture models with multi-scale heterogeneity, including a hybrid one in which the slip is a combination of high- slip patches and stochastic small scale variations. We find that the ground motions simulated with these rupture models match the general characteristics of the recorded near-fault motion equally well, over a broad frequency range (0–10 Hz). Additionally, the simulated ground motion is in good agreement with the predictions from Ground Motion Prediction Equations (GMPEs). Nonetheless, due to sensitivity of the ground motion to the local fault rupture characteristics, the performance among the models at near-fault sites is slightly different, with the hybrid model producing a somewhat better fit to the recorded ground velocity waveforms. Sensitivity tests of simulated near-fault ground motion to variations in the prescribed kinematic rupture parameters show that average rupture speeds higher than the default value in GP2016 (average rupture speed = 80% of local shear wave speed), as well as slip rate durations shorter than the default value in GP2016 (rise time coefficient = 1.6), generate ground motions that are higher than the recorded ones at periods longer than 1 s. We found that these two parameters also affect the along strike and updip rupture directivity effects, as illustrated in comparisons with the Kumamoto observations.

  • The effect of fault geometry and minimum shear wavespeed on 3D ground-motion simulations for an M<inf>w</inf> 6.5 hayward fault scenario earthquake, San Francisco bay area, Northern California
    Arthur J. Rodgers, Arben Pitarka, and David B. McCallen

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 109, Pages: 1265-1281, Published: 1 August 2019 Seismological Society of America (SSA)
    Abstract We investigated the effects of fault geometry and assumed minimum shear wavespeed (VSmin) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (Mw) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming VSmin values of 500 and 250  m/s reveal that PGVs are on average 25% higher west of the HF when using the lower VSmin, with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two VSmin cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower VSmin west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or VSmin of 250  m/s. We conclude that assuming a VSmin of 500  m/s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth &amp;lt;10  km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.

  • Broadband (0-5 Hz) fully deterministic 3D ground-motion simulations of a magnitude 7.0 Hayward fault earthquake: Comparison with empirical ground-motion models and 3D path and site effects from source normalized intensities
    Arthur J. Rodgers, N. Anders Petersson, Arben Pitarka, David B. McCallen, Bjorn Sjogreen, and Norman Abrahamson

    Seismological Research Letters, ISSN: 08950695, eISSN: 19382057, Pages: 1268-1284, Published: 2019 Seismological Society of America (SSA)

  • The Source Physics Experiments large N array
    Robert J. Mellors, Arben Pitarka, Eric Matzel, Steven Magana‐Zook, Douglas Knapp, William R. Walter, Ting Chen, Catherine M. Snelson, and Robert E. Abbott

    Seismological Research Letters, ISSN: 08950695, eISSN: 19382057, Pages: 1618-1628, Published: September 2018 Seismological Society of America (SSA)

  • Broadband (0–4 Hz) Ground Motions for a Magnitude 7.0 Hayward Fault Earthquake With Three-Dimensional Structure and Topography
    Arthur J. Rodgers, Arben Pitarka, N. Anders Petersson, Björn Sjögreen, and David B. McCallen

    Geophysical Research Letters, ISSN: 00948276, eISSN: 19448007, Pages: 739-747, Published: 28 January 2018 American Geophysical Union (AGU)
    Author(s): Rodgers, Arthur J; Pitarka, Arben; Petersson, N Anders; Sjogreen, Bjorn; McCallen, David B

  • Using the SCEC broadband platform for strong ground motion simulation and validation
    11th National Conference on Earthquake Engineering 2018, NCEE 2018: Integrating Science, Engineering, and Policy, Pages: 2340-2343, Published: 2018

  • Earthquake ground motion variability in simulations using Gp2016 method and modified rupture generator following irikura recipe
    11th National Conference on Earthquake Engineering 2018, NCEE 2018: Integrating Science, Engineering, and Policy, Pages: 3354-3363, Published: 2018

  • Validating ground-motion simulations on rough faults in complex 3D media
    11th National Conference on Earthquake Engineering 2018, NCEE 2018: Integrating Science, Engineering, and Policy, Pages: 4120-4129, Published: 2018

  • HPC simulations of broadband near-fault ground motions for engineering applications
    11th National Conference on Earthquake Engineering 2018, NCEE 2018: Integrating Science, Engineering, and Policy, Pages: 3343-3353, Published: 2018

  • Simulation of large scenario and recorded moderate earthquakes in the San Francisco Bay area
    11th National Conference on Earthquake Engineering 2018, NCEE 2018: Integrating Science, Engineering, and Policy, Pages: 4094-4103, Published: 2018

  • Performance of Irikura Recipe Rupture Model Generator in Earthquake Ground Motion Simulations with Graves and Pitarka Hybrid Approach
    Arben Pitarka, Robert Graves, Kojiro Irikura, Hiroe Miyake, and Arthur Rodgers

    Pure and Applied Geophysics, ISSN: 00334553, eISSN: 14209136, Volume: 174, Pages: 3537-3555, Published: 1 September 2017 Springer Science and Business Media LLC
    We analyzed the performance of the Irikura and Miyake (Pure and Applied Geophysics 168(2011):85–104, 2011) (IM2011) asperity-based kinematic rupture model generator, as implemented in the hybrid broadband ground motion simulation methodology of Graves and Pitarka (Bulletin of the Seismological Society of America 100(5A):2095–2123, 2010), for simulating ground motion from crustal earthquakes of intermediate size. The primary objective of our study is to investigate the transportability of IM2011 into the framework used by the Southern California Earthquake Center broadband simulation platform. In our analysis, we performed broadband (0–20 Hz) ground motion simulations for a suite of M6.7 crustal scenario earthquakes in a hard rock seismic velocity structure using rupture models produced with both IM2011 and the rupture generation method of Graves and Pitarka (Bulletin of the Seismological Society of America, 2016) (GP2016). The level of simulated ground motions for the two approaches compare favorably with median estimates obtained from the 2014 Next Generation Attenuation-West2 Project (NGA-West2) ground motion prediction equations (GMPEs) over the frequency band 0.1–10 Hz and for distances out to 22 km from the fault. We also found that, compared to GP2016, IM2011 generates ground motion with larger variability, particularly at near-fault distances (<12 km) and at long periods (>1 s). For this specific scenario, the largest systematic difference in ground motion level for the two approaches occurs in the period band 1–3 s where the IM2011 motions are about 20–30% lower than those for GP2016. We found that increasing the rupture speed by 20% on the asperities in IM2011 produced ground motions in the 1–3 s bandwidth that are in much closer agreement with the GMPE medians and similar to those obtained with GP2016. The potential implications of this modification for other rupture mechanisms and magnitudes are not yet fully understood, and this topic is the subject of ongoing study. We concluded that IM2011 rupture generator performs well in ground motion simulations using Graves and Pitarka hybrid method. Therefore, we recommend it to be considered for inclusion into the framework used by the Southern California Earthquake Center broadband simulation platform.

  • Kinematic ground-motion simulations on rough faults including effects of 3D stochastic velocity perturbations
    Robert Graves and Arben Pitarka

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 106, Pages: 2136-2153, Published: October 2016 Seismological Society of America (SSA)
    Abstract We describe a methodology for generating kinematic earthquake ruptures for use in 3D ground‐motion simulations over the 0–5 Hz frequency band. Our approach begins by specifying a spatially random slip distribution that has a roughly wavenumber‐squared fall‐off. Given a hypocenter, the rupture speed is specified to average about 75%–80% of the local shear wavespeed and the prescribed slip‐rate function has a Kostrov‐like shape with a fault‐averaged rise time that scales self‐similarly with the seismic moment. Both the rupture time and rise time include significant local perturbations across the fault surface specified by spatially random fields that are partially correlated with the underlying slip distribution. We represent velocity‐strengthening fault zones in the shallow ( 15  km) crust by decreasing rupture speed and increasing rise time in these regions. Additional refinements to this approach include the incorporation of geometric perturbations to the fault surface, 3D stochastic correlated perturbations to the P ‐ and S ‐wave velocity structure, and a damage zone surrounding the shallow fault surface characterized by a 30% reduction in seismic velocity. We demonstrate the approach using a suite of simulations for a hypothetical M w  6.45 strike‐slip earthquake embedded in a generalized hard‐rock velocity structure. The simulation results are compared with the median predictions from the 2014 Next Generation Attenuation‐West2 Project ground‐motion prediction equations and show very good agreement over the frequency band 0.1–5 Hz for distances out to 25 km from the fault. Additionally, the newly added features act to reduce the coherency of the radiated higher frequency ( f >1  Hz) ground motions, and homogenize radiation‐pattern effects in this same bandwidth, which move the simulations closer to the statistical characteristics of observed motions as illustrated by comparison with recordings from the 1979 Imperial Valley earthquake.

  • Generation of shear motion from an isotropic explosion source by scattering in heterogeneous media
    Evan Hirakawa, Arben Pitarka, and Robert Mellors

    Bulletin of the Seismological Society of America, ISSN: 00371106, eISSN: 19433573, Volume: 106, Pages: 2313-2319, Published: October 2016 Seismological Society of America (SSA)
    One challenging task in explosion seismology is the development of physical models for explaining the generation of S waves during underground explosions. Recent analysis of ground motion from chemical explosions during the Source Physics Experiment (Pitarka et al. , 2015) suggests that, although a large component of shear motion was generated directly at the source, additional scattering from heterogeneous velocity structure and topography is necessary to better match the recorded data. In our study, we used a stochastic representation of small‐scale velocity variability to produce high‐frequency scattering and to analyze its implication on shear‐motion generation during underground explosions. In our stochastic velocity model, the key parameters that affect scattering are the correlation length and the relative amplitude of velocity perturbations. Based on finite‐difference simulations of elastic wave propagation from an isotropic explosion source, we find that higher velocity perturbations result in larger shear motion, whereas the correlation length, which controls the scatterers size, affects the frequency range at which relative transverse motion is larger.

  • Ground Motion Modeling in the Eastern Caucasus
    Arben Pitarka, Rengin Gok, Gurban Yetirmishli, Saida Ismayilova, and Robert Mellors

    Pure and Applied Geophysics, ISSN: 00334553, eISSN: 14209136, Volume: 173, Pages: 2791-2801, Published: 1 August 2016 Springer Science and Business Media LLC
    In this study, we analyzed the performance of a preliminary three-dimensional (3D) velocity model of the Eastern Caucasus covering most of the Azerbaijan. The model was developed in support to long-period ground motion simulations and seismic hazard assessment from regional earthquakes in Azerbaijan. The model’s performance was investigated by simulating ground motion from the damaging Mw 5.9, 2012 Zaqatala earthquake, which was well recorded throughout the region by broadband seismic instruments. In our simulations, we use a parallelized finite-difference method of fourth-order accuracy. The comparison between the simulated and recorded ground motion velocity in the modeled period range of 3–20 s shows that in general, the 3D velocity model performs well. Areas in which the model needs improvements are located mainly in the central part of the Kura basin and in the Caspian Sea coastal areas. Comparisons of simulated ground motion using our 3D velocity model and corresponding 1D regional velocity model were used to locate areas with strong 3D wave propagation effects. In areas with complex underground structure, the 1D model fails to produce the observed ground motion amplitude and duration, and spatial extend of ground motion amplification caused by wave propagation effects.

RECENT SCHOLAR PUBLICATIONS

  • Dynamic Rupture Modeling of the 1999 Chi-Chi, Taiwan Earthquake Using 3DFinite Element Method. Sensitivity Analysis of Slip Rate Function to ModelParameters of Crustal Weak-Zone
    A Pitarka
    Lawrence Livermore National Lab.(LLNL), Livermore, CA (United States) 2022

  • Refinements to the Graves–Pitarka Kinematic Rupture Generator, Including a Dynamically Consistent Slip‐Rate Function, Applied to the 2019 7.1 Ridgecrest
    A Pitarka, R Graves, K Irikura, K Miyakoshi, C Wu, H Kawase, A Rodgers, ...
    Bulletin of the Seismological Society of America 112 (1), 287-306 2022

  • Deterministic 3D Ground‐Motion Simulations (0–5Hz) and Surface Topography Effects of the 30 October 2016 6.5 Norcia, Italy, Earthquake
    A Pitarka, A Akinci, P De Gori, M Buttinelli
    Bulletin of the Seismological Society of America 112 (1), 262-286 2022

  • Simulated Effects of Seismic Source Depth on Coda Waves at Local Distances (< 150 km) in Realistic 3D Earth Models
    S Hutchings, J Voyles, A Pitarka, KD Koper
    AGU Fall Meeting Abstracts 2021, S15C-0262 2021

  • The Generation of Seismic and Acoustic Waves from Explosions
    W Walter, S Ford, M Pyle, A Pitarka, K Kim, M Pasyanos, G Ichinose, ...
    AGU Fall Meeting Abstracts 2021, S13B-01 2021

  • Modeling subsurface explosions recorded on a distributed fiber optic sensor
    RJ Mellors, R Abbott, D Steedman, D Podrasky, A Pitarka
    Journal of Geophysical Research: Solid Earth 126 (12), e2021JB022690 2021

  • Engineering evaluation of the EQSIM simulated ground‐motion database: The San Francisco Bay Area region
    F Petrone, N Abrahamson, D McCallen, A Pitarka, A Rodgers
    Earthquake Engineering & Structural Dynamics 50 (15), 3939-3961 2021

  • Using dense array waveform correlations to build a velocity model with stochastic variability
    A Pitarka, R Mellors
    Bulletin of the Seismological Society of America 111 (4) 2021

  • Preliminary Analysis of Source Physics Experiment Explosion‐Triggered Microseismicity Using the Back‐Projection Method
    GA Ichinose, SR Ford, K Kroll, D Dodge, M Pyle, A Pitarka, WR Walter
    Journal of Geophysical Research: Solid Earth 126 (5), e2020JB021312 2021

  • EQSIM—A multidisciplinary framework for fault-to-structure earthquake simulations on exascale computers, part II: Regional simulations of building response
    D McCallen, F Petrone, M Miah, A Pitarka, A Rodgers, N Abrahamson
    Earthquake Spectra 37 (2), 736-761 2021

  • Variability of near‐fault seismic risk to reinforced concrete buildings based on high‐resolution physics‐based ground motion simulations
    M Kenawy, D McCallen, A Pitarka
    Earthquake Engineering & Structural Dynamics 50 (6), 1713-1733 2021

  • EQSIM—A multidisciplinary framework for fault-to-structure earthquake simulations on exascale computers part I: Computational models and workflow
    D McCallen, A Petersson, A Rodgers, A Pitarka, M Miah, F Petrone, ...
    Earthquake Spectra 37 (2), 707-735 2021

  • Dynamic Rupture Modeling of the M7. 1, 2019 Ridgecrest, California, Earthquake
    A Pitarka
    Lawrence Livermore National Lab.(LLNL), Livermore, CA (United States) 2021

  • Effect of random 3D correlated velocity perturbations on numerical modeling of ground motion from the Source Physics Experiment
    M Scalise, A Pitarka, JN Louie, KD Smith
    Bulletin of the Seismological Society of America 111 (1), 139-156 2021

  • Developments in Earthquake Ground Motion Modeling and Advancements Toward Fault-to-Structure Simulations I
    A Pitarka, D McCallen, M Celebi
    AGU Fall Meeting 2020 2020

  • Simulation of Near Fault Ground Motions for the 2019 M7. 1 Ridgecrest, CA Earthquake
    RW Graves, A Pitarka
    AGU Fall Meeting Abstracts 2020, S068-02 2020

  • Interfrequency Correlation of Characterized Source Modeling for Broadband Ground Motion Validation
    H Miyake, A Pitarka, A Iwaki, N Morikawa, T Maeda, H Fujiwara
    AGU Fall Meeting Abstracts 2020, S060-0007 2020

  • Simulation of Underground Chemical Explosions in Anisotropic Dry Alluvium Geology using Hydrodynamic Generated Source Coupled to Far-Field Linear Anisotropic Wave propagation
    SM Ezzedine, O Vorobiev, A Pitarka, T Antoun, WR Walter
    AGU Fall Meeting Abstracts 2020, S049-08 2020

  • Construction of a Database of Validated Simulated Ground Motions for the Evaluation of the Seismic Risk Posed to Distributed Infrastructure Systems: The San Francisco Bay Area
    F Petrone, N Abrahamson, D McCallen, A Pitarka, AJ Rodgers
    AGU Fall Meeting Abstracts 2020, S060-0016 2020

  • Regional‐Scale 3D ground‐motion simulations of Mw 7 earthquakes on the Hayward fault, northern California resolving frequencies 0–10 Hz and including site‐response corrections
    AJ Rodgers, A Pitarka, R Pankajakshan, B Sjgreen, NA Petersson
    Bulletin of the Seismological Society of America 110 (6), 2862-2881 2020

MOST CITED SCHOLAR PUBLICATIONS

  • Broadband ground-motion simulation using a hybrid approach
    RW Graves, A Pitarka
    Bulletin of the Seismological Society of America 100 (5A), 2095-2123 2010
    Citations: 510

  • 3D elastic finite-difference modeling of seismic motion using staggered grids with nonuniform spacing
    A Pitarka
    Bulletin of the Seismological Society of America 89 (1), 54-68 1999
    Citations: 462

  • Three-dimensional simulation of the near-fault ground motion for the 1995 Hyogo-ken Nanbu (Kobe), Japan, earthquake
    A Pitarka, K Irikura, T Iwata, H Sekiguchi
    Bulletin of the Seismological Society of America 88 (2), 428-440 1998
    Citations: 354

  • Ground-motion amplification in the Santa Monica area: Effects of shallow basin-edge structure
    RW Graves, A Pitarka, PG Somerville
    Bulletin of the Seismological Society of America 88 (5), 1224-1242 1998
    Citations: 321

  • The SCEC/USGS dynamic earthquake rupture code verification exercise
    RA Harris, M Barall, R Archuleta, E Dunham, B Aagaard, JP Ampuero, ...
    Seismological Research Letters 80 (1), 119-126 2009
    Citations: 257

  • A technique for simulating strong ground motion using hybrid Green's function
    K Kamae, K Irikura, A Pitarka
    Bulletin of the Seismological Society of America 88 (2), 357-367 1998
    Citations: 254

  • Model for basin effects on long-period response spectra in southern California
    SM Day, R Graves, J Bielak, D Dreger, S Larsen, KB Olsen, A Pitarka, ...
    Earthquake Spectra 24 (1), 257-277 2008
    Citations: 165

  • Refinements to the Graves and Pitarka (2010) broadband ground-motion simulation method
    R Graves, A Pitarka
    Seismological Research Letters 86 (LLNL-JRNL-741227) 2014
    Citations: 159

  • Simulation of near-fault strong-ground motion using hybrid Green's functions
    A Pitarka, P Somerville, Y Fukushima, T Uetake, K Irikura
    Bulletin of the Seismological Society of America 90 (3), 566-586 2000
    Citations: 156

  • Broadband time history simulation using a hybrid approach
    RW Graves, A Pitarka
    2004
    Citations: 129

  • Kinematic ground‐motion simulations on rough faults including effects of 3D stochastic velocity perturbations
    R Graves, A Pitarka
    Bulletin of the Seismological Society of America 106 (5), 2136-2153 2016
    Citations: 124

  • Basin structure effects in the Kobe area inferred from the modeling of ground motions from two aftershocks of the January 17, 1995, Hyogo-ken Nanbu earthquake
    A Pitarka, K Irikura, T Iwata, T Kagawa
    Journal of Physics of the Earth 44 (5), 563-576 1996
    Citations: 82

  • Modeling 3D surface topography by finite‐difference method: Kobe‐JMA station site, Japan, case study
    A Pitarka, K Irikura
    Geophysical Research Letters 23 (20), 2729-2732 1996
    Citations: 76

  • Basin structure effects on long-period strong motions in the San Fernando Valley and the Los Angeles basin from the 1994 Northridge earthquake and an aftershock
    A Pitarka, K Irikura
    Bulletin of the Seismological Society of America 86 (1B), S126-S137 1996
    Citations: 72

  • Numerical study of ground-motion differences between buried-rupturing and surface-rupturing earthquakes
    A Pitarka, LA Dalguer, SM Day, PG Somerville, K Dan
    Bulletin of the Seismological Society of America 99 (3), 1521-1537 2009
    Citations: 60

  • Three-dimensional finite-difference waveform modeling of strong motions observed in the Sendai basin, Japan
    T Satoh, H Kawase, T Sato, A Pitarka
    Bulletin of the Seismological Society of America 91 (4), 812-825 2001
    Citations: 58

  • Tests of 3D elastodynamic codes: Final report for Lifelines Project 1A02
    SM Day, J Bielak, D Dreger, R Graves, S Larsen, KB Olsen, A Pitarka
    Pacific Earthquake Engineering Research Center 2003
    Citations: 56

  • Broadband (0–4 Hz) ground motions for a magnitude 7.0 Hayward fault earthquake with three-dimensional structure and topography
    AJ Rodgers, A Pitarka, NA Petersson, B Sjgreen, DB McCallen
    Geophysical Research Letters 45 (2), 739-747 2018
    Citations: 50

  • Validation of a 3D velocity model of the Puget Sound region based on modeling ground motion from the 28 February 2001 Nisqually earthquake
    A Pitarka, R Graves, P Somerville
    Bulletin of the Seismological Society of America 94 (5), 1670-1689 2004
    Citations: 42

  • Lesson from the 1995 Hyogo-ken Nanbu earthquake: Why were such destructive motions generated to buildings
    K Irikura, T Iwata, H Sekiguchi, A Pitarka, K Kamae
    J. Nat. Disaster Sci 17 (2), 99-127 1996
    Citations: 42