The 2018 update of the US National Seismic Hazard Model: Overview of model and implications

Petersen, Mark D.; Shumway, Allison M.; Powers, Peter M.; Mueller, Charles S.; Moschetti, Morgan P.; Frankel, Arthur; Rezaeian, Sanaz; McNamara, Daniel E.; Luco, N.; Boyd, Oliver S.; Rukstales, Kenneth S.; Jaiswal, Kishor; Thompson, Eric M.; Hoover, Susan M.; Clayton, Brandon S.; Field, Edward H.; Zeng, Yuehua

doi:10.1177/8755293019878199

Cited by 194 publications

(221 citation statements)

References 71 publications

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“…Chang et al (2006) show that a steeply dipping (55–70°) planar structure is also consistent with geodetic data collected along the Wasatch front. Seismic hazard modeling for northern Utah has largely adopted this structure for the WFZ, employing a dip of 50° ± 15° (Petersen et al, 2019; Wong et al, 2016). Ground motion modeling (Moschetti et al, 2017; Roten et al, 2011) and ShakeMap scenarios (Pankow et al, 2015) of hypothetical M7 earthquakes on the SLCS also use a dip of ~50°.…”

Section: Introductionmentioning

confidence: 99%

Seismic Analysis of the 2020 Magna, Utah, Earthquake Sequence: Evidence for a Listric Wasatch Fault

Pang

Koper

Mesimeri

et al. 2020

Geophysical Research Letters

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The 18 March 2020 M w 5.7 Magna earthquake near Salt Lake City, Utah, offers a rare glimpse into the subsurface geometry of the Wasatch fault system-one of the world's longest active normal faults and a major source of seismic hazard in northern Utah. We analyze the Magna earthquake sequence and resolve oblique-normal slip on a shallow (30-35°) west-dipping fault at~9-to 12-km depth. Combined with near-surface geological observations of steep dip (~70°), our results support a curved, or listric, fault shape. High-precision aftershock locations show the activation of multiple, low-angle (<30-35°) structures, indicating the existence of a complicated fault system. Our observations constrain the deep structure of the Wasatch fault system and suggest that ground shaking in the Salt Lake City region in future Wasatch fault earthquakes may be higher than previously estimated. Plain Language Summary On 18 March 2020, a moment magnitude (M w) 5.7 earthquake occurred beneath Magna, Utah, a suburb of Salt Lake City. It was the largest earthquake in the Wasatch fault system in historical times, and shaking was felt throughout northern Utah. The mainshock and its aftershocks were located in the middle of a dense seismic network, generating a rare and valuable data set of strong ground accelerations from normal-faulting earthquakes. We analyzed the first~6 weeks of seismic data following the mainshock and found that the aftershocks formed a shallow-dipping planar structure at depths of 9-12 km, implying that this segment of the Wasatch fault zone has a curved shape. At the surface, it dips steeply to the west at~70°, but as the depth increases, the dip becomes progressively more shallow. Simulations of ground shaking from large earthquakes previously assumed that this fault segment was planar and steeply dipping (~50°) throughout the upper crust. Our observations suggest that the rupture area of future large earthquakes will be closer to the surface than previously thought, which would cause increased ground shaking in the Salt Lake City metropolitan area with its~1.2 million residents. Geological mapping and modeling of the WFZ finds near-surface dips of 45-90°on the SLCS (Bruhn et al., 1992); however, there are competing models for its subsurface structure under the Salt Lake ©2020. American Geophysical Union. All Rights Reserved.

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Section: Introductionmentioning

confidence: 99%

Seismic Analysis of the 2020 Magna, Utah, Earthquake Sequence: Evidence for a Listric Wasatch Fault

Pang

Koper

Mesimeri

et al. 2020

Geophysical Research Letters

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“…Probabilistic seismic hazard analysis (PSHA) depends on the distribution, size, and rate of earthquakes near a given site. For example, the Uniform California Earthquake Rupture Forecast (UCERF) estimates earthquake magnitude rates on California faults for use in PSHA, such as for the National Seismic Hazard Model (e.g., Petersen et al, 2020). A major addition to the third version of the forecast, UCERF3 (Field et al, 2014), is the inclusion of multifault ruptures throughout the state.…”

Section: Introductionmentioning

confidence: 99%

Distribution of Earthquakes on a Branching Fault System Using Integer Programming and Greedy‐Sequential Methods

Geist

Parsons

2020

Geochem Geophys Geosyst

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A new global optimization method is used to determine the distribution of earthquakes on a complex, connected fault system. The method, integer programming, has been advanced in the field of operations research but has not been widely applied to geophysical problems until recently. In this application, we determine the optimal distribution of earthquakes on mapped faults to minimize the global misfit in slip rates for multifault ruptures. Integer programming solves for a decision vector composed of every possible location that a sample of earthquakes can occur on every fault, subject to slip rate uncertainty constraints. Step over connections are straightforward to include, whereas branching fault connections are not. To include branching ruptures, we distinguish between individual multifault rupture paths, as opposed to formulating the integer programming problem based on individual faults as in previous studies. The new method is applied to the complex fault system in the San Francisco Bay Area as a case study. Results from the integer programming method are compared to those from a local optimization method, termed the greedy‐sequential method. Several experiments using these two methods indicate that shape of the on‐fault magnitude distributions and which branching faults are involved in multifault ruptures depend on how much emphasis is placed on fitting the target slip rate. In cases where the underlying data are not strong enough to warrant chasing the target slip rate, it is better to focus on the distribution of feasible results that better represents the uncertainty in the solutions imposed by the data.

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“…[90,91]. This approach is also being adopted by the US IBC [85]. Thus, it is suggested that, for future editions of the AS1170.4, seismic hazard be calculated directly for a given site class using amplification models provided by the developers of each of the GMMs used in the ground-motion logic tree.…”

Section: Site Class Factorsmentioning

confidence: 99%

Seismic Hazard Estimation in Stable Continental Regions: Does Psha Meet the Needs for Modern Engineering Design in Australia?

Allen

2020

BNZSEE

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Damaging earthquakes in Australia and other regions characterised by low seismicity are considered low probability but high consequence events. Uncertainties in modelling earthquake occurrence rates and ground motions for damaging earthquakes in these regions pose unique challenges to forecasting seismic hazard, including the use of this information as a reliable benchmark to improve seismic safety within our communities. Key challenges for assessing seismic hazards in these regions are explored, including: the completeness and continuity of earthquake catalogues; the identification and characterisation of neotectonic faults; the difficulties in characterising earthquake ground motions; the uncertainties in earthquake source modelling, and; the use of modern earthquake hazard information to support the development of future building provisions. Geoscience Australia recently released its 2018 National Seismic Hazard Assessment (NSHA18). Results from the NSHA18 indicate significantly lower seismic hazard across almost all Australian localities at the 1/500 annual exceedance probability level relative to the factors adopted for the current Australian Standard AS1170.4–2007 (R2018). These new hazard estimates have challenged notions of seismic hazard in Australia in terms of the recurrence of damaging ground motions. This raises the question of whether current practices in probabilistic seismic hazard analysis (PSHA) deliver the outcomes required to protect communities and infrastructure assets in low-seismicity regions, such as Australia. This manuscript explores a range of measures that could be undertaken to update and modernise the Australian earthquake loading standard, in the context of these modern seismic hazard estimates, including the use of alternate ground-motion exceedance probabilities for assigning seismic demands for ordinary-use structures. The estimation of seismic hazard at any location is an uncertain science, particularly in low-seismicity regions. However, as our knowledge of the physical characteristics of earthquakes improve, our estimates of the hazard will converge more closely to the actual – but unknowable – (time independent) hazard. Understanding the uncertainties in the estimation of seismic hazard is also of key importance, and new software and approaches allow hazard modellers to better understand and quantify this uncertainty. It is therefore prudent to regularly update the estimates of the seismic demands in our building codes using the best available evidence-based methods and models.

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The 2018 update of the US National Seismic Hazard Model: Overview of model and implications

Cited by 194 publications

References 71 publications

Seismic Analysis of the 2020 Magna, Utah, Earthquake Sequence: Evidence for a Listric Wasatch Fault

Seismic Analysis of the 2020 Magna, Utah, Earthquake Sequence: Evidence for a Listric Wasatch Fault

Distribution of Earthquakes on a Branching Fault System Using Integer Programming and Greedy‐Sequential Methods

Seismic Hazard Estimation in Stable Continental Regions: Does Psha Meet the Needs for Modern Engineering Design in Australia?

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