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ABSTRACT 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. 

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. 

Pese a ser reconocida como una de las más significativas transformaciones culturales en Norteamérica, la reintroducción del caballo en continente luego del año 1492 raramente ha sido abordada por la arqueología. Una razón de la escasez de tales trabajos es la aparente ausencia de restos esqueletarios de equinos en contextos arqueológicos históricos tempranos. Presentamos un análisis multidisciplinario de los restos de caballo recuperados en Lehi, Utah, los que fueron originalmente identificados como de la “Edad del Hielo” basados sobre el contexto geológico. El reanálisis del contexto estratigráfico junto con la datación radiocarbónica indica una edad histórica para este caballo (1681–1939 años calibrados de la era), relacionándolo con grupos indígenas Ute u otros. A pesar de que parte del caballo fue destruido antes de su recuperación, la columna vertebral revela fisuras y osteofitos que indican que había sido montado y el uso de sillas sin marco, mientras que una artritis severa en la parte inferior de las extremidades habría reducido drásticamente su movilidad. El análisis de ADN demostró que el animal era una hembra doméstica, posiblemente cuidada como parte de una tropilla de cría. Finalmente, los valores de isótopos estables de carbono, oxígeno, y estroncio (δ 13 C, δ 18 O, y 87 Sr/ 86 Sr) muestreados secuencialmente del esmalte dental sugieren que fue criada localmente en la región de Lehi. Estos resultados demuestran la utilidad de la aplicación del conocimiento arqueológico a los restos de caballo para entender el pastoralismo de esta especie por parte de las poblaciones indígenas. Por su parte, una consideración más amplia del registro arqueológico sugiere un patrón de identificación errónea de huesos de caballo en contextos históricos tempranos.