Edward H. Field’s research while affiliated with Geological Survey of Alabama and other places

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Publications (90)


Trimming the UCERF3-TD logic tree: Model order reduction for an earthquake rupture forecast considering loss exceedance
  • Article

November 2024

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5 Reads

Earthquake Spectra

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Edward Field

The Uniform California Earthquake Rupture Forecast version 3-Time Dependent depicts California’s seismic faults and their activity. Its logic tree has 5760 leaves. Considering 30 more model combinations related to ground motion produces 172,800 distinct models representing so-called epistemic uncertainties. To calculate risk to a portfolio of buildings, one also considers millions of earthquakes and spatially correlated ground-motion variability. We offer a tree-trimming technique that retains the probability distribution of portfolio loss and identifies the leading sources of uncertainty for further study. We applied it to a California statewide building portfolio and various levels of nonexceedance probability between one in 100 and one in 2500. We trimmed the logic tree from 172,800 leaves to as few as 15. The result: a supercomputer that would otherwise run 24 h to estimate the distribution of one-in-250-year loss can calculate it in moments with the reduced-order model. Others can use the reduced-order model to calculate risk to different California portfolios, and scientists can prioritize study to reduce the remaining epistemic uncertainty.


The 2023 US 50-State National Seismic Hazard Model: Overview and implications
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  • Full-text available

December 2023

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1,679 Reads

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42 Citations

Earthquake Spectra

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Peter M Powers

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The US National Seismic Hazard Model (NSHM) was updated in 2023 for all 50 states using new science on seismicity, fault ruptures, ground motions, and probabilistic techniques to produce a standard of practice for public policy and other engineering applications (defined for return periods greater than ∼475 or less than ∼10,000 years). Changes in 2023 time-independent seismic hazard (both increases and decreases compared to previous NSHMs) are substantial because the new model considers more data and updated earthquake rupture forecasts and ground-motion components. In developing the 2023 model, we tried to apply best available or applicable science based on advice of co-authors, more than 50 reviewers, and hundreds of hazard scientists and end-users, who attended public workshops and provided technical inputs. The hazard assessment incorporates new catalogs, declustering algorithms, gridded seismicity models, magnitude-scaling equations, fault-based structural and deformation models, multi-fault earthquake rupture forecast models, semi-empirical and simulation-based ground-motion models, and site amplification models conditioned on shear-wave velocities of the upper 30 m of soil and deeper sedimentary basin structures. Seismic hazard calculations yield hazard curves at hundreds of thousands of sites, ground-motion maps, uniform-hazard response spectra, and disaggregations developed for pseudo-spectral accelerations at 21 oscillator periods and two peak parameters, Modified Mercalli Intensity, and 8 site classes required by building codes and other public policy applications. Tests show the new model is consistent with past ShakeMap intensity observations. Sensitivity and uncertainty assessments ensure resulting ground motions are compatible with known hazard information and highlight the range and causes of variability in ground motions. We produce several impact products including building seismic design criteria, intensity maps, planning scenarios, and engineering risk assessments showing the potential physical and social impacts. These applications provide a basis for assessing, planning, and mitigating the effects of future earthquakes.

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The USGS 2023 Conterminous U.S. Time-Independent Earthquake Rupture Forecast

December 2023

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395 Reads

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21 Citations

Bulletin of the Seismological Society of America

We present the 2023 U.S. Geological Survey time-independent earthquake rupture forecast for the conterminous United States, which gives authoritative estimates of the magnitude, location, and time-averaged frequency of potentially damaging earthquakes throughout the region. In addition to updating virtually all model components, a major focus has been to provide a better representation of epistemic uncertainties. For example, we have improved the representation of multifault ruptures, both in terms of allowing more and less fault connectivity than in the previous models, and in sweeping over a broader range of viable models. An unprecedented level of diagnostic information has been provided for assessing the model, and the development was overseen by a 19-member participatory review panel. Although we believe the new model embodies significant improvements and represents the best available science, we also discuss potential model limitations, including the applicability of logic tree branch weights with respect different types of hazard and risk metrics. Future improvements are also discussed, with deformation model enhancements being particularly worthy of pursuit, as well as better representation of sampling errors in the gridded seismicity components. We also plan to add time-dependent components, and assess implications with a wider range of hazard and risk metrics.


A Comprehensive Fault-System Inversion Approach: Methods and Application to NSHM23

December 2023

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45 Reads

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7 Citations

Bulletin of the Seismological Society of America

We present updated inversion-based fault-system solutions for the 2023 update to the National Seismic Hazard Model (NSHM23), standardizing earthquake rate model calculations on crustal faults across the western United States. We build upon the inversion methodology used in the Third Uniform California Earthquake Rupture Forecast (UCERF3) to solve for time-independent rates of earthquakes in an interconnected fault system. The updated model explicitly maps out a wide range of fault recurrence and segmentation behavior (epistemic uncertainty), more completely exploring the solution space of viable models beyond those of UCERF3. We also improve the simulated annealing implementation, greatly increasing computational efficiency (and thus inversion convergence), and introduce an adaptive constraint weight calculation algorithm that helps to mediate between competing constraints. Hazard calculations show that ingredient changes (especially fault and deformation models) are the primary driver of hazard changes between NSHM23 and UCERF3. Updates to the inversion methodology are also consequential near faults in which the slip rate in UCERF3 was poorly fit or was satisfied primarily using large multifault ruptures that are now restricted by explicit b-value and segmentation constraints.


Figure 8. Geologic deformation model rates (Hatem, Reitman, et al., 2022) versus median geodetic slip rates that include the ghost transient correction.
Figure 9. Histograms of dimensionless geodetic slip rate, binned according to their rate, for each of the four geodetic deformation models that include the ghost transient correction.
Figure 10. A priori preferred geologic slip rates (Hatem, Collett, et al., 2022) versus estimated geodetic slip rates (with 1 − σ errors) for the four geodetic deformation models in the highest slip rate bin, shown separately for cases with no ghost transient correction and with ghost transient correction.
Figure 11. (a) Map view of coefficient of variation on parent fault sections derived from the four geodetic deformation models with ghost transient correction. (b) The coefficient of variation (COV) estimates of panel (a) are plotted as a function of the geologic deformation model slip rate. Bestfitting linear regression is superimposed.
Figure 12. Regionalization of probability density functions of slip rate applicable to very low slip rate faults proposed by Hatem, Reitman, et al. (2022).

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Western U.S. Deformation Models for the 2023 Update to the U.S. National Seismic Hazard Model

September 2022

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319 Reads

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20 Citations

Seismological Research Letters

This report describes geodetic and geologic information used to constrain deformation models of the 2023 update to the National Seismic Hazard Model (NSHM), a set of deformation models to interpret these data, and their implications for earthquake rates in the western United States. Recent updates provide a much larger data set of Global Positioning System crustal velocities than used in the 2014 NSHM, as well as hundreds of new faults considered as active sources for the 2023 NSHM. These data are interpreted by four geodetic models of deformation that estimate fault slip rates and their uncertainties together with off-fault moment release rates. Key innovations in the 2023 NSHM relative to past practice include (1) the addition of two new (in addition to two existing) deformation models, (2) the revision and expansion of the geologic slip rate database, (3) accounting for fault creep through development of a creep-rate model that is employed by the four deformation models, and (4) accounting for time-dependent earthquake-cycle effects through development of viscoelastic models of the earthquake cycle along the San Andreas fault and the Cascadia subduction zone. The effort includes development of a geologic deformation model that complements the four geodetic models. The current deformation models provide a new assessment of outstanding discrepancies between geologic and geodetic slip rates, at the same time highlighting the need for both geologic and geodetic slip rates to robustly inform the earthquake rate model.


Fig. 2 Schematic diagram of hypothetical fault in plane and cross-section view. Numbered gray circles represent the ordering of coordinates in list form to uphold right-hand rule convention in the fault sections database. The larger green circle represents the location of an EQGeoDB entry. Fault sections attributes highlighted here are further described in the Database Fields section.
Fig. 3 Updated databases across the western U.S. (a) Overlay of NSHM14/18 fault sections on NSHM23 fault sections to highlight spatial distribution of additions to the database. (b) NSHM23 fault sections. (c) Overlay of EQGeoDB on NSHM23 fault sections. Bright green circles indicate where studies have been completed or where rates have been assessed by the community. Light green circles indicate fault centroids where QFFD slip rate bins are recorded for use in deformation modeling.
Fig. 4 Maps of NHSM23 fault sections database colored by (a) QFFD slip rate bin and (b) style of faulting. RL: right-lateral; LL: left-lateral. Histograms showing distribution of fault length (d), QFFD slip rate bin (e), and rake (f) for all NSHM23 fault sections and NSHM23 fault section additions only.
Fig. 6 Example of QFFD geometry simplification from Canyon Ferry fault (Montana), with QFFD fault geometry prior to smoothing (column a), QFFD after smoothing (column b), NSHM23 FSD (column c), and all three representations plotted together (column d). Panel E shows very small distances between ends of line segments in QFFD. Insets in the bottom row of columns a-c show zoomed in view of Canyon Ferry (Totson) section. Inset in lower right corner of figure shows general location of Canyon Ferry fault system.
Fig. 9 Example of output map page of Slinkard Valley fault (California), created using nshm-faultmaps 58 during technical and scientific validation process. The top left panel shows the QFFD representation in the region in cyan; the top middle panel shows the lack of representation of the Slinkard Valley fault in NSHM14/18 FSD, which did include the nearby Antelope Valley fault (shown in blue); the top right panel shows the newly added representation of the Slinkard Valley fault in NSHM23 in orange. The blue dot at the southern extent of the NSHM23 fault trace shows the first node in the line geometry, indicating that this east-dipping fault abides by right-hand rule. The lower right panel shows a regional overview map, with Slinkard Valley fault highlighted in orange. Fault parameters from NSHM23 FSD are called and printed from the database in the text block at the lower left.
Simplifying complex fault data for systems-level analysis: Earthquake geology inputs for U.S. NSHM 2023

August 2022

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292 Reads

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20 Citations

Scientific Data

As part of the U.S. National Seismic Hazard Model (NSHM) update planned for 2023, two databases were prepared to more completely represent Quaternary-active faulting across the western United States: the NSHM23 fault sections database (FSD) and earthquake geology database (EQGeoDB). In prior iterations of NSHM, fault sections were included only if a field-measurement-derived slip rate was estimated along a given fault. By expanding this inclusion criteria, we were able to assess a larger set of faults for use in NSHM23. The USGS Quaternary Fault and Fold Database served as a guide for assessing possible additions to the NSHM23 FSD. Reevaluating available data from published sources yielded an increase of fault sections from ~650 faults in NSHM18 to ~1,000 faults proposed for use in NSHM23. EQGeoDB, a companion dataset linked to NSHM23 FSD, contains geologic slip rate estimates for fault sections included in FSD. Together, these databases serve as common input data used in deformation modeling, earthquake rupture forecasting, and additional downstream uses in NSHM development. Measurement(s)N/ATechnology Type(s)N/A Measurement(s) N/A Technology Type(s) N/A


Enumerating Plausible Multifault Ruptures in Complex Fault Systems with Physical Constraints

May 2022

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74 Reads

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22 Citations

Bulletin of the Seismological Society of America

We propose a new model for determining the set of plausible multifault ruptures in an interconnected fault system. We improve upon the rules used in the Third Uniform California Earthquake Rupture Forecast (UCERF3) to increase connectivity and the physical consistency of ruptures. We replace UCERF3’s simple azimuth change rules with new Coulomb favorability metrics and increase the maximum jump distance to 15 km. Although the UCERF3 rules were appropriate for faults with similar rakes, the Coulomb calculations used here inherently encode preferred orientations between faults with different rakes. Our new rules are designed to be insensitive to discretization details and are generally more permissive than their UCERF3 counterparts; they allow more than twice the connectivity compared with UCERF3, yet heavily penalize long ruptures that take multiple improbable jumps. The set of all possible multifault ruptures in the California fault system is nearly infinite, but our model produces a tractable set of 326,707 ruptures (a modest 29% increase over UCERF3, despite the greatly increased connectivity). Inclusion in the rupture set does not dictate that a rupture receives a significant rate in the final model; rupture rates are subsequently determined by data constraints used in an inversion. We describe the rupture building algorithm and its components in detail and provide comparisons with ruptures generated by a physics-based multicycle earthquake simulator. We find that greater than twice as many ruptures generated by the simulator violate the UCERF3 rules than violate our proposed model.



STEPS: Slip Time Earthquake Path Simulations Applied to the San Andreas and Toe Jam Hill Faults to Redefine Geologic Slip Rate Uncertainty

October 2021

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79 Reads

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6 Citations

Geologic slip rates are a time-averaged measurement of fault displacement calculated over hundreds to million-year time scales and are a primary input for probabilistic seismic hazard analyses, which forecast expected ground shaking in future earthquakes. Despite their utility for seismic hazard calculations, longer-term geologic slip rates represent a time-averaged measure of the tempo of strain release and do not measure variability across earthquake cycles. We have developed a numerical approach called STEPS (Slip Time Earthquake Path Simulations), which is built upon field-based observations and explicitly incorporates realistic variations in displacement per event and variability in the recurrence interval between earthquakes. The STEPS approach, which simulates strain release through time, relies on representing earthquake cycles as stairsteps, rather than straight-line paths, connecting per earthquake time-displacement coordinates. We simulate earthquake histories based on these input constraints using two examples: the Carrizo section of the San Andreas fault and the Toe Jam Hill fault of the Seattle fault zone. We find that modeled slip rate distributions agree with slip rates reported for the sites of interest by the original investigators, while providing a slip rate distribution that reflects the variability of earthquake frequency and displacement. The STEPS approach provides an estimate of fault slip rate uncertainty based on a synthetic suite of plausible time-displacement paths resulting from individual earthquakes, rather than measurement uncertainties associated with offset features. When considering this simulated earthquake behavior between measurements, the uncertainty associated with earthquake paths is greater than that calculated by the long-term rate. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.


The Seismic Hazard Implications of Declustering and Poisson Assumptions Inferred from a Fully Time-Dependent Model

October 2021

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49 Reads

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18 Citations

Bulletin of the Seismological Society of America

We use the Third Uniform California Earthquake Rupture Forecast (UCERF3) epidemic-type aftershock sequence (ETAS) model (UCERF3-ETAS) to evaluate the effects of declustering and Poisson assumptions on seismic hazard estimates. Although declustering is necessary to infer the long-term spatial distribution of earthquake rates, the question is whether it is also necessary to honor the Poisson assumption in classic probabilistic seismic hazard assessment. We use 500,000 yr, M ≥ 2.5 synthetic catalogs to address this question, for which UCERF3-ETAS exhibits realistic spatiotemporal clustering effects (e.g., aftershocks). We find that Gardner and Knopoff (1974) declustering, used in the U.S. Geological Survey seismic hazard models, lowers 2% in 50 yr and risk-targeted ground-motion hazard metrics by about 4% on average (compared with the full time-dependent [TD] model), with the reduction being 5% at 40% in 50 yr ground motions. Keeping all earthquakes and treating them as a Poisson process increases these same hazard metrics by about 3%–12%, on average, due to the removal of relatively quiet time periods in the full TD model. In the interest of model simplification, bias minimization, and consideration of the probabilities of multiple exceedances, we agree with others (Marzocchi and Taroni, 2014) that we are better off keeping aftershocks and treating them as a Poisson process rather than removing them from hazard consideration via declustering. Honoring the true time dependence, however, will likely be important for other hazard and risk metrics, and this study further exemplifies how this can now be evaluated more extensively.


Citations (72)


... Based on the original approach by M. Baiesi and M. Paczuski [19,20], the nearest-neighbor (NN) declustering method introduced by I. Zaliapin and collaborators [21] is currently employed in statistical seismology of both natural [22][23][24][25] and anthropogenic origin [26][27][28][29], rock mechanics [30,31], as well as in other systems exhibiting Omori-like avalanche behavior, such as structural transi- * romualdo.pastor@upc.edu tions [32], crackling noise [33,34] and turning avalanches in schooling fish [35]. ...

Reference:

Leveraging spurious Omori-Utsu relation in the nearest-neighbor declustering method
Improvements to the Third Uniform California Earthquake Rupture Forecast ETAS Model (UCERF3-ETAS)

The Seismic Record

... The 2023 update to the U.S. National Seismic Hazard Model (NSHM) was based partly on an earthquake rupture forecast (Petersen et al., 2023), and this has substantial contributions from deformation models of fault slip-deficit rates (Field et al., 2024;Pollitz et al., 2022). The NSHM geodetic deformation models in the western U.S. are based on crustal deformation models of the interseismic velocity field, each of which yields estimates of fault slip rates on a set of more than 1,000 continental fault sections (Evans, 2022;Pollitz, 2022;Shen & Bird, 2022;Zeng, 2022a). ...

The 2023 US 50-State National Seismic Hazard Model: Overview and implications

Earthquake Spectra

... The 2023 update to the U.S. National Seismic Hazard Model (NSHM) was based partly on an earthquake rupture forecast (Petersen et al., 2023), and this has substantial contributions from deformation models of fault slip-deficit rates (Field et al., 2024;Pollitz et al., 2022). The NSHM geodetic deformation models in the western U.S. are based on crustal deformation models of the interseismic velocity field, each of which yields estimates of fault slip rates on a set of more than 1,000 continental fault sections (Evans, 2022;Pollitz, 2022;Shen & Bird, 2022;Zeng, 2022a). ...

The USGS 2023 Conterminous U.S. Time-Independent Earthquake Rupture Forecast

Bulletin of the Seismological Society of America

... We have used the OpenSHA implementation of the 2023 US NSHM team for the inversion set up and solution calculations. We have revised the UCERF3 recipe, including revisions from Milner and Field, 2023), as discussed in the following sections. The key steps in developing the IFM are described in the following sections, but can be summarized as follows: (2) cumulative of the absolute values of slip-rake change of ≤360°; ...

A Comprehensive Fault-System Inversion Approach: Methods and Application to NSHM23
  • Citing Article
  • December 2023

Bulletin of the Seismological Society of America

... The 2023 update to the U.S. National Seismic Hazard Model (NSHM) was based partly on an earthquake rupture forecast (Petersen et al., 2023), and this has substantial contributions from deformation models of fault slip-deficit rates (Field et al., 2024;Pollitz et al., 2022). The NSHM geodetic deformation models in the western U.S. are based on crustal deformation models of the interseismic velocity field, each of which yields estimates of fault slip rates on a set of more than 1,000 continental fault sections (Evans, 2022;Pollitz, 2022;Shen & Bird, 2022;Zeng, 2022a). ...

Western U.S. Deformation Models for the 2023 Update to the U.S. National Seismic Hazard Model

Seismological Research Letters

... We created three separate geospatial databases to characterize fault geometries and activities in the region between 62°-70°W and 16°-21°N, including Puerto Rico, the U.S. Virgin Islands, and eastern Hispaniola. These geologic input databases include a fault section (line), fault zone (polygon; terms defined subsequently and in Hatem et al., 2022 andThompson Jobe et al., 2022), and earthquake geology (point) databases (Fig. 3). The fault section database consists of linework depicting simplified surface traces of known Quaternary-active crustal faults. ...

Simplifying complex fault data for systems-level analysis: Earthquake geology inputs for U.S. NSHM 2023

Scientific Data

... Continental surface-faulting earthquakes, which generate strong shaking and permanent surface deformation, are rare globally (Nurminen et al., 2022), complicated to forecast (Field and Page, 2011), and potentially devastating to communities and infrastructure lacking risk-reduction measures (Holzer and Savage, 2013). However, such earthquakes provide critical data for informing and testing scaling relations among fault displacement, rupture dimensions, and magnitude (Wells and Coppersmith, 1994;Wesnousky, 2008;Thingbaijam et al., 2017;Shaw, 2023), understanding rupture processes (e.g., Lozos and Harris, 2020) and how multifault ruptures (e.g., Sieh et al., 1993;Eberhart-Phillips et al., 2003;Fletcher et al., 2014;Litchfield et al., 2018) propagate through distributed fault networks (Field et al., 2021;Milner et al., 2022), recording the surface expression of coseismic (Roberts et al., 2010;Koehler et al., 2021;Ruhl et al., 2021) and postseismic (DeLong et al., 2016) slip, and modeling strain release and fault memory (Salditch et al., 2020;Neely et al., 2022). These observations and models help improve earthquake rupture forecasts (Field et al., 2023), seismic hazard modeling (Petersen et al., 2024), and probabilistic fault displacement hazard analysis (PFDHA; Youngs et al., 2003;Petersen et al., 2011;Nurminen et al., 2022). ...

Enumerating Plausible Multifault Ruptures in Complex Fault Systems with Physical Constraints

Bulletin of the Seismological Society of America

... Using these constraints in a Settlement Fault slip rate calculation is difficult as: (1) it is within the bounds of uncertainty that no displacement was accumulated in the period between these constraints (i.e. between ∼3.7-125 ka), and (2) we have no bounds for the minimum age of the most recent Settlement Fault rupture or a maximum bound for its last event prior to ∼125 ka; these constraints therefore indicate the displacement accumulated over open recurrence intervals, and so their resulting slip rate is a maximum estimate (Styron 2019;DuRoss et al. 2020). To address these challenges, we derive a Settlement Fault slip rate estimate by considering its slip accumulation as a sequence of random incremental steps in vertical displacement-time space, where each step represents a single earthquake cycle, and the overall step sequence must pass through the three available vertical displacement-time constraints (Figure 12; Cowie et al. 2012;DuRoss et al. 2020;Hatem et al. 2021). The vertical displacement within each step is sampled from a distribution that considers end member models for the Settlement Fault's length-width ratio: (1) the area-displacement scaling of Stirling et al. (2024), which is calculated by explicitly assuming that the ∼23 km long Settlement Fault extends to the base of the southeastern South Island's relatively thick seismogenic crust (∼24.1 km; Ellis et al. 2024;Seebeck et al. 2024), and results in a 1.5 +1.7 − 0.8 m single event displacement (SED) estimate (1.1 m throw assuming a 45° dip, Table 4), and (2) the length-displacement scaling of Thingbaijam et al. (2017), which implicitly assumes a rupture width (∼16 km) that is independent of the seismogenic crust's thickness, and provides a SED estimate of 0.7 +2.1 − 0.3 m (0.5 m throw, Table 4). ...

STEPS: Slip Time Earthquake Path Simulations Applied to the San Andreas and Toe Jam Hill Faults to Redefine Geologic Slip Rate Uncertainty

... Studies such as Field et al. (2021), Wang et al. (2021), and Iervolino and Giorgio (2022) noted that for return periods typically relevant in design applications, the differences between ETAS and mainshock-only models are minor. However, our study has a broader scope. ...

The Seismic Hazard Implications of Declustering and Poisson Assumptions Inferred from a Fully Time-Dependent Model
  • Citing Article
  • October 2021

Bulletin of the Seismological Society of America

... The HVSR resulted in a comparator or ground frequency (0.36 Hz) with a predominant period (2.75s) ( Figure 6). It identified that the surface soil condition was soft and the predominant period of the soil was > 1 s [29,30]. The building's average natural frequency is 4.01 Hz, with a predominant period of 0.249 seconds, as illustrated Figures 6-b and 6-c and Tables 2 and 3. ...

The 2018 update of the US National Seismic Hazard Model: Where, why, and how much probabilistic ground motion maps changed
  • Citing Article
  • January 2021

Earthquake Spectra