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USGS2008

Geospatial Information is the Cornerstone of Effective Hazards Response

Every day there are hundreds of natural disasters world-wide. Some are dramatic, whereas others are barely noticeable. A natural disaster is commonly defined as a natural event with catastrophic consequences for living things in the vicinity. Those events include earthquakes, floods, hurricanes, landslides, tsunami, volcanoes, and wildfires. Man-made disasters are events that are caused by man either intentionally or by accident, and that directly or indirectly threaten public health and well-being. These occurrences span the spectrum from terrorist attacks to accidental oil spills. To assist in responding to natural and potential man-made disasters, the U.S. Geological Survey (USGS) has established the Geospatial Information Response Team (GIRT) (http://www.usgs.gov/emergency/). The primary purpose of the GIRT is to ensure rapid coordination and availability of geospatial information for effective response by emergency responders, and land and resource managers, and for scientific analysis. The GIRT is responsible for establishing monitoring procedures for geospatial data acquisition, processing, and archiving; discovery, access, and delivery of data; anticipating geospatial needs; and providing relevant geospatial products and services. The GIRT is focused on supporting programs, offices, other agencies, and the public in mission response to hazards. The GIRT will leverage the USGS Geospatial Liaison Network and partnerships with the Department of Homeland Security (DHS), National Geospatial-Intelligence Agency (NGA), and Northern Command (NORTHCOM) to coordinate the provisioning and deployment of USGS geospatial data, products, services, and equipment. The USGS geospatial liaisons will coordinate geospatial information sharing with State, local, and tribal governments, and ensure geospatial liaison back-up support procedures are in place. The GIRT will coordinate disposition of USGS staff in support of DHS response center activities as requested by DHS. The GIRT is a standing team that is available during all hazard events and is on high alert during the hurricane season from June through November each year. To track all of the requirements and data acquisitions processed through the team, the GIRT will use the new Emergency Request Track (ER Track) tool. Currently, the ER Track is only available to USGS personnel.

Fact Sheet↗

USGS2017

3-D simulations of M9 earthquakes on the Cascadia Megathrust: Key parameters and uncertainty

Geologic and historical records indicate that the Cascadia subduction zone is capable of generating large, megathrust earthquakes up to magnitude 9. The last great Cascadia earthquake occurred in 1700, and thus there is no direct measure on the intensity of ground shaking or specific rupture parameters from seismic recordings. We use 3-D numerical simulations to generate broadband (0-10 Hz) synthetic seismograms for 50 M9 rupture scenarios on the Cascadia megathrust. Slip consists of multiple high-stress drop subevents (~M8) with short rise times on the deeper portion of the fault, superimposed on a background slip distribution with longer rise times. We find a >4x variation in the intensity of ground shaking depending upon several key parameters, including the down-dip limit of rupture, the slip distribution and location of strong-motion-generating subevents, and the hypocenter location. We find that extending the down-dip limit of rupture to the top of the non-volcanic tremor zone results in a ~2-3x increase in peak ground acceleration for the inland city of Seattle, Washington, compared to a completely offshore rupture. However, our simulations show that allowing the rupture to extend to the up-dip limit of tremor (i.e., the deepest rupture extent in the National Seismic Hazard Maps), even when tapering the slip to zero at the down-dip edge, results in multiple areas of coseismic coastal uplift. This is inconsistent with coastal geologic evidence (e.g., buried soils, submerged forests), which suggests predominantly coastal subsidence for the 1700 earthquake and previous events. Defining the down-dip limit of rupture as the 1 cm/yr locking contour (i.e., mostly offshore) results in primarily coseismic subsidence at coastal sites. We also find that the presence of deep subevents can produce along-strike variations in subsidence and ground shaking along the coast. Our results demonstrate the wide range of possible ground motions from an M9 megathrust earthquake in Cascadia, and the potential to further constrain key rupture parameters using geologic and geophysical observations, ultimately improving our estimation of seismic hazard associated with the Cascadia megathrust.

Conference Paper↗

USGS1977

Assessment of increased thermal activity at Mount Baker, Washington, March 1975-March 1976

In March 1975 Mount Baker showed a large increase in thermal emission, which has persisted for more than 1 year. Fumarole ejecta accompanied the thermal activity from March to September, but the ejecta had no constituents that suggest a magmatic source. Estimates of that part of the total heat flux that would account for the observed snow and ice loss show that the heat-flow increase was roughly one order of magnitude, from about 2 megawatts at 10 watts per square meter, averaged over Sherman Crater before 1975, to about 30 megawatts at 180 watts per square meter, during 1975. Almost half of the glacier that occupied the basin of Sherman Crater was melted in 1975. The new activity generated great concern among the public and the government agencies responsible for geological evaluation of potential hazards and for protection of life and property. The past geologic history, current topography, rock alteration, and location of major fumarolic activity indicate that large rock avalanches and mudflows on the east slope in Boulder Creek valley are the potential hazards of most significance related to present conditions. The most probable types of large mass movements would be mudflows, having speeds of as much as 50 kilometers per hour, that would originate from mixtures of snow, ice, and melt water and avalanches of structurally weak clay-rich rocks that make up the rim of Sherman Crater. Similar mudflows from the volcano have traveled at least 12 kilometers 8 times during the past 10,000 years. A possible worst case event, however, might be a larger, air-cushioned avalanche of as much as 20 to 30 million cubic meters that could hit Baker Lake at speeds of more than 300 kilometers per hour and generate a wave of water large enough to overtop Upper Baker Dam. At least 30 million cubic meters of potentially unstable material occurs as hydrothermally altered remnants of the rim of Sherman Crater and could provide the required volume for the estimated worst case event or for smaller avalanches and mudflows. An earthquake, steam explosion, or eruption could provide a suitable trigger to initiate movement. Although such triggering events were possible before 1975, the probability might have been as much as 10 times greater in 1975 because of the increased thermal activity. The threat of avalanches and mudflows on Boulder Creek valley and Baker Lake prompted the closure by management agencies of the Boulder Creek drainage and of Baker Lake and its shoreline in the summer of 1975. Additionally, Baker Lake was kept below full pool at a level calculated to prevent overtopping of Upper Baker Dam by waves which could result from a worst-case avalanche. In 1975 an interdisciplinary program of seismic, tilt, gravity, gas, hydrologic, petrologic, thermal infrared, and photographic studies by Federal and university scientists was initiated to evaluate the impact of the current thermal activity and to monitor changes that might indicate an impending eruption. By March 1976 only one small earth- quake had been identified beneath Mount Baker. Tilt and gravity changes have been observed but cannot be attributed solely to volcanic causes. The data available thus far provide no evidence of an impending eruption, but they cannot be fully interpreted without many additional geophysical and geochemical measurements, as it is not yet possible to clearly distinguish volcanic effects from non- volcanic background effects. Inasmuch as current activity continues unchanged - without steam explosions, eruptions, or frequent or large earthquakes - the probability of a suitable trigger for large avalanches and mudflows should decrease and should approach that of a more average year. Such an average year would have a hazard probability at least as great as that which existed before 1975, although that level of hazard was not recognized at the time by the public or by administrative agencies. The potential hazard and the uncertainties of future activ

Professional Paper↗

USGS2019

When the earth doesn’t stop shaking: How experiences over time influenced information needs, communication, and interpretation of aftershock information during the Canterbury Earthquake Sequence, New Zealand

The Canterbury Earthquake Sequence (CES) began with the Darfield earthquake on 4 September 2010. Continual large and small aftershocks since that time have meant communities have cycled through repeated periods of impact, response and recovery. Scientific communication about aftershocks during such a prolonged sequence has faced distinct challenges. We conducted research to better understand aftershock information needs for agencies and the public, and how people interpreted and responded to such information. We found that a wide range of information was needed from basic facts about aftershocks through to more technical information, and in different formats (e.g. maps, tables, graphs, text, analogies). Information needs also evolved throughout the sequence, and differed depending on people’s roles and experiences, and the phase of impact, response and recovery communities were in. Interpretation of aftershock information was influenced by a variety of factors including how understandable and relevant the information was, whether people had prior knowledge or experience of aftershocks, whether the information was personalised or contextualised, emotions and feelings, credibility and trust, and external influences. Given that such a diversity of evolving information is required, it is imperative that geoscientists strategize how to provide such information before a significant earthquake occurs.

Natural Hazards↗

USGS2021

Commentary: The role of geodetic algorithms for earthquake early warning in Cascadia

The ShakeAlert earthquake early warning (EEW) system issues public alerts in California and will soon extend to Oregon and Washington. The Cascadia subduction zone presents significant new challenges and opportunities for EEW. Initial publications suggested that EEW algorithms based on Global Navigation Satellite System (GNSS) data could provide improved warning for intraslab events and dramatically improved warning for offshore megathrust events, both of which contribute significantly to hazard in Cascadia. We find that some expectations in these publications were unrealistic, and we demonstrate that in general geodetic algorithms would not produce timely warnings for intraslab events nor warning times of two minutes or more for severe shaking from megathrust earthquakes. Nonetheless, lessons from recent earthquakes in Japan and California, for which alerts from seismic algorithms suffered from magnitude saturation and high data latencies, demonstrate the urgent need for rigorous testing of geodetic EEW as a potential complement to seismic EEW.

California, Oregon, Washington↗

USGS2018

Broadband synthetic seismograms for magnitude 9 earthquakes on the Cascadia Megathrust based on 3D simulations and stochastic synthetics, Part 2: Rupture parameters and variability

We used a combination of 3D finite‐difference simulations ( < 1    Hz "> < 1 Hz ) and 1D stochastic synthetics ( > 1    Hz "> > 1 Hz ) to generate broadband (0–10 Hz) synthetic seismograms for numerous M w "> Mw 9 earthquake rupture scenarios on the Cascadia megathrust. Slip consists of multiple high‐stress‐drop subevents ( M w "> Mw 8) with short rise times on the deeper portions of the fault, superimposed on a background slip distribution with longer rise times. We identify key rupture parameters that control the intensity of ground shaking and resulting seismic hazard; these include the hypocenter location, the down‐dip limit of slip, the average rupture velocity, and the character (i.e., location, magnitude, and stress drop) of subevents. Extending the down‐dip limit of rupture to the top of the nonvolcanic tremor zone results in localized regions with a factor of 5–10 increase in spectral acceleration (SA) for periods < 5    s "> <5 s , compared to a rupture that is completely offshore. This is primarily due to the closer proximity of high‐stress‐drop subevents to inland locations when the rupture is allowed to extend deeper. Similarly, we find that the hypocenter location can result in a variation in the intensity of ground motions of a factor of > 10 "> >10 , due to the effects of rupture directivity (i.e., SA at periods > 1    s "> >1 s ). We also observe a coupling between rupture directivity and basin amplification. The intensity of ground motions is also strongly affected by the magnitude, stress drop, and location of high‐stress‐drop subevents, which are poorly constrained. Overall, our results quantify the effect of kinematic rupture parameters on ground motions for an M w "> Mw 9 earthquake in Cascadia and emphasize the need for further constraints on these parameters to improve seismic hazard estimates in the Pacific Northwest.

Bulletin of the Seismological Society of America↗

USGS2005

Development of ground-motion prediction equations relevant to shallow-mining-induced seismicity in the Trial Mountain area, Emery County, Utah

To provide a basis for assessing the seismic hazard to the Joes Valley Dam due to future coal mining in the nearby Cottonwood Tract, central Utah, we developed ground-motion prediction relations using data recorded by a seismic network, established and operated by the University of Utah Seismograph Stations. The network was centered on the Trail Mountain coal mine, located adjacent to the Cottonwood Tract. From late 2000 until early 2001, this network recorded numerous mining-induced events with magnitudes as large as 2.17. The ground motion from these events, recorded at hypocentral distances ranging from about 500 m to approximately 10 km, were well suited to developing new ground-motion prediction relations, especially when augmented by data from a M 4.2 earthquake in the Willow Creek mine, about 50 km north of Trail Mountain. Using a two-stage regression analysis, we determined prediction relations for peak acceleration, peak velocity, and pseudovelocity response spectra, at 5% damping, for periods of 0.1, 0.2, 0.5, 1.0, and 2.0 s. To illustrate the potential seismic hazard at the Joes Valley dam, we used these ground-motion relations to predict a peak velocity of 6.8 cm/s due to an earthquake with the probable maximum magnitude of 3.9, at a hypocentral distance of 1 km, recorded at a rock site typical for this region. This result does not take into account the site response at the dam.

Bulletin of the Seismological Society of America↗

USGS1997

Geologic studies in Alaska by the U.S. Geological Survey, 1995

This collection of 20 papers continues the annual series of U.S. Geological Survey (USGS) reports on geologic investigations in Alaska1 . Contributions cover a broad spectrum of earth science topics and report results from all parts of the State (fig. 1). USGS activities in Alaska include studies of environment and climate, hazards, resources, and geologic framework. Five papers in this volume discuss aspects of environment and climate. Environmental geochemistry of parts of southwestern and south-central Alaska is the focus of four articles; a fifth study, of emergent postglacial lake shorelines in southwestern Alaska, contributes to ongoing investigations of paleoclimate. Two papers address geologic hazards. The first assesses ground deformation in Katmai National Park at Novarupta dome, site of the largest volcanic eruption in this century, and the second evaluates earthquake risks related to the "Twin Peak fault" near Anchorage. Resources, including metallic minerals in northern, southwestern, and southeastern Alaska and coal in south-central Alaska, are discussed in four articles. Nine geologic framework studies apply a variety of techniques to a wide range of subjects throughout Alaska, including tectonics, geophysics, geochronology, bio stratigraphy, sedimentology, paleogeography, and paleomagnetism. Two bibliographies at the end of the volume list reports about Alaska in USGS publications released in 1995 and reports about Alaska by USGS authors in non-USGS publications in 1995.

Alaska↗

USGS2000

Gravitational stability of three-dimensional stratovolcano edifices

Catastrophic flank collapses have occurred at many stratovolcanoes worldwide. We present a three-dimensional (3-D) slope stability analysis for assessing and quantifying both the locations of minimum edifice stability and the expected volumes of potential failure. Our approach can search the materials underlying a topographic surface, represented as a digital elevation model (DEM), and determine the relative stability of all parts of the edifice. Our 3-D extension of Bishop's [1955] simplified limit-equilibrium analysis incorporates spherical failure surfaces, variable material properties, pore fluid pressures, and earthquake shaking. Although a variety of processes can trigger collapse, we focus here on gravitationally induced instability. Even homogeneous rock properties strongly influence the depth and volume of the least stable potential failure. For large failures in complex topography, patterns of potential instability do not mimic local ground surface slope alone. The May 18, 1980, catastrophic failure of the north flank of Mount St. Helens provides the best documented case history to test our method. Using the undeformed edifice topography of Mount St. Helens in an analysis of dry, static slope stability with homogeneous materials, as might be conducted in a precollapse hazard analysis, our method identified the northwest flank as the least stable region, although the north flank stability was within 5% of the minimum. Using estimates of the conditions that existed 2 days prior to collapse, including deformed topography with a north flank bulge and combined pore pressure and earthquake shaking effects, we obtained good estimates of the actual failure location and volume. Our method can provide estimates of initial failure volume and location to aid in assessing downslope or downstream hazards.

Washington↗

USGS2009

Use of airborne and terrestrial lidar to detect ground displacement hazards to water systems

We investigate the use of multiepoch airborne and terrestrial lidar to detect and measure ground displacements of sufficient magnitude to damage buried pipelines and other water system facilities that might result, for example, from earthquake or rainfall-induced landslides. Lidar scans are performed at three sites with coincident measurements by total station surveying. Relative horizontal accuracy is evaluated by measurements of lateral dimensions of well defined objects such as buildings and tanks; we find misfits ranging from approximately 5 to 12 cm, which is consistent with previous work. The bias and dispersion of lidar elevation measurements, relative to total station surveying, is assessed at two sites: (1) a power plant site (PP2) with vegetated steeply sloping terrain; and (2) a relatively flat and unvegetated site before and after trenching operations were performed. At PP2, airborne lidar showed minimal elevation bias and a standard deviation of approximately 70 cm, whereas terrestrial lidar did not produce useful results due to beam divergence issues and inadequate sampling of the study region. At the trench site, airborne lidar showed minimal elevation bias and reduced standard deviation relative to PP2 (6-20 cm), whereas terrestrial lidar was nearly unbiased with very low dispersion (4-6 cm). Pre- and posttrench bias-adjusted normalized residuals showed minimal to negligible correlation, but elevation change was affected by relative bias between epochs. The mean of elevation change bias essentially matches the difference in means of pre- and posttrench elevation bias, whereas elevation change standard deviation is sensitive to the dispersion of individual epoch elevations and their correlation coefficient. The observed lidar bias and standard deviations enable reliable detection of damaging ground displacements for some pipelines types (e.g., welded steel) but not all (e.g., concrete with unwelded, mortared joints). ?? ASCE 2009.

Journal of Surveying Engineering↗

USGS2022

Selected crater and small caldera lakes in Alaska: Characteristics and hazards

This study addresses the characteristics, potential hazards, and both eruptive and non-eruptive role of water at selected volcanic crater lakes in Alaska. Crater lakes are an important feature of some stratovolcanoes in Alaska. Of the volcanoes in the state with known Holocene eruptive activity, about one third have summit crater lakes. Also included are two volcanoes with small caldera lakes (Katmai, Kaguyak). The lakes play an important but not well studied role in influencing eruptive behavior and pose some significant hydrologic hazards. Floods from crater lakes in Alaska are evaluated by estimating maximum potential crater lake water volumes and peak outflow discharge with a dam-break model. Some recent eruptions and hydrologic events that involved crater lakes also are reviewed. The large volumes of water potentially hosted by crater lakes in Alaska indicate that significant flowage hazards resulting from catastrophic breaching of crater rims are possible. Estimates of maximum peak flood discharge associated with breaching of lake-filled craters derived from dam-break modeling indicate that flood magnitudes could be as large as 10 3 –10 6 m 3 /s if summit crater lakes drain rapidly when at maximum volume. Many of the Alaska crater lakes discussed are situated in hydrothermally altered craters characterized by complex assemblages of stratified unconsolidated volcaniclastic deposits, in a region known for large magnitude (>M7) earthquakes. Although there are only a few historical examples of eruptions involving crater lakes in Alaska, these provide noteworthy examples of the role of external water in cooling pyroclastic deposits, acidic crater-lake drainage, and water-related hazards such as lahars and base surge.

Alaska↗

USGS2015

Update of the Graizer-Kalkan ground-motion prediction equations for shallow crustal continental earthquakes

A ground-motion prediction equation (GMPE) for computing medians and standard deviations of peak ground acceleration and 5-percent damped pseudo spectral acceleration response ordinates of maximum horizontal component of randomly oriented ground motions was developed by Graizer and Kalkan (2007, 2009) to be used for seismic hazard analyses and engineering applications. This GMPE was derived from the greatly expanded Next Generation of Attenuation (NGA)-West1 database. In this study, Graizer and Kalkan’s GMPE is revised to include (1) an anelastic attenuation term as a function of quality factor (Q0) in order to capture regional differences in large-distance attenuation and (2) a new frequency-dependent sedimentary-basin scaling term as a function of depth to the 1.5-km/s shear-wave velocity isosurface to improve ground-motion predictions for sites on deep sedimentary basins. The new model (GK15), developed to be simple, is applicable to the western United States and other regions with shallow continental crust in active tectonic environments and may be used for earthquakes with moment magnitudes 5.0–8.0, distances 0–250 km, average shear-wave velocities 200–1,300 m/s, and spectral periods 0.01–5 s. Directivity effects are not explicitly modeled but are included through the variability of the data. Our aleatory variability model captures inter-event variability, which decreases with magnitude and increases with distance. The mixed-effects residuals analysis shows that the GK15 reveals no trend with respect to the independent parameters. The GK15 is a significant improvement over Graizer and Kalkan (2007, 2009), and provides a demonstrable, reliable description of ground-motion amplitudes recorded from shallow crustal earthquakes in active tectonic regions over a wide range of magnitudes, distances, and site conditions.

Open-File Report↗

USGS1990

International decade for natural disaster reduction

Throughout history, humanity has found itself in conflict with naturally occurring events of geologic, hydrologic, and atmospheric origin. this conflict has been demonstrated repeatedly when people build urban centers at the water's edge, in or near active fault systems capable of generating earthquakes, on steep slopes, near active volcanoes, or at the urban-wilderness interface prone to wildfires. Naturally occurring, recurrent events such as floods, windstorms, tsunamis, earthquakes, landslides, volcanic eruptions, and wildfires have tested human-engineered works many times and have often found them unable to withstand the forces generated by the event. In the past 20 years, for example, events like these throughout the world have claimed more than 2.8 million lives and adversely affected 820 million people; single disasters have caused economic losses of billions of dollars. Industrialized countries like the United States and Japan have been able to absorb the socioeconomic losses of past natural disasters, but the economics of many developing countries have been devastated by losses equal to a large percentage of their gross national product. Furthermore, the magnitude of the losses is increasing at a rapid rate as the building wealth of nations is expanded to meet the needs of rapidly increasing population, often without adequate consideration of the potential threat posed by the recurrent natural hazards and without implementing effective loss-reduction measures because of lack of knowledge or lack of technical capability.

Earthquakes & Volcanoes (USGS)↗

USGS2010

New seismic hazard maps for Puerto Rico and the U.S. Virgin Islands

The probabilistic methodology developed by the U.S. Geological Survey is applied to a new seismic hazard assessment for Puerto Rico and the U.S. Virgin Islands. Modeled seismic sources include gridded historical seismicity, subduction-interface and strike-slip faults with known slip rates, and two broad zones of crustal extension with seismicity rates constrained by GPS geodesy. We use attenuation relations from western North American and worldwide data, as well as a Caribbean-specific relation. Results are presented as maps of peak ground acceleration and 0.2- and 1.0-second spectral response acceleration for 2% and 10% probabilities of exceedance in 50 years (return periods of about 2,500 and 500 years, respectively). This paper describes the hazard model and maps that were balloted by the Building Seismic Safety Council and recommended for the 2003 NEHRP Provisions and the 2006 International Building Code. ?? 2010, Earthquake Engineering Research Institute.

Earthquake Spectra↗

USGS2015

Seismic hazard in the Intermountain West

The 2014 national seismic-hazard model for the conterminous United States incorporates new scientific results and important model adjustments. The current model includes updates to the historical catalog, which is spatially smoothed using both fixed-length and adaptive-length smoothing kernels. Fault-source characterization improved by adding faults, revising rates of activity, and incorporating new results from combined inversions of geologic and geodetic data. The update also includes a new suite of published ground motion models. Changes in probabilistic ground motion are generally less than 10% in most of the Intermountain West compared to the prior assessment, and ground-motion hazard in four Intermountain West cities illustrates the range and magnitude of change in the region. Seismic hazard at reference sites in Boise and Reno increased as much as 10%, whereas hazard in Salt Lake City decreased 5–6%. The largest change was in Las Vegas, where hazard increased 32–35%.

Earthquake Spectra↗

USGS2019

#EarthquakeAdvisory: Exploring discourse between government officials, news media and social media during the Bombay Beach 2016 Swarm

Communicating probabilities of natural hazards to varied audiences is a notoriously difficult task. Many of these challenges were encountered during the 2016 Bombay Beach, California, swarm of ~100 2≤M≤4.3 earthquakes, which began on 26 September 2016 and lasted for several days. The swarm’s proximity to the southern end of the San Andreas fault caused concern that a larger earthquake could be triggered. Within 1–2 days, different forecast models were used to evaluate the likelihood of a larger event with two agencies (the U.S. Geological Survey [USGS] and the California Governor’s Office of Emergency Services) releasing probabilities and forecasts for larger earthquakes. Our research explores communication and news media efforts, as well as how people on a microblogging social media site (Twitter) responded to these forecasts. Our findings suggest that news media used a combination of information sources, basing their articles on what they learned from social media, as well as using information provided by government agencies. As the swarm slowed down, there is evidence of the continued interplay between news media and social media, with the USGS issuing revised probability reports and scientists from the USGS and other institutions participating in media interviews. In reporting on the swarm, news media often used language more generally than the scientists; terms such as probability, likelihood, chance, and possibility were used interchangeably. Knowledge of how news media used scientific information from the 2016 Bombay Beach forecasts can assist local, state, and federal agencies in developing effective communication strategies to respond to future earthquakes.

California↗

USGS2001

Earthquakes and tsunamis in Puerto Rico and the U.S. Virgin Islands

Many earthquakes and tsunamis have occurred in the northeastern Caribbean, where the movements of the Earth's surface plates are rapid and complicated. Future such events pose serious hazards to the 3.7 million people who live in Puerto Rico and the U.S. Virgin Islands.

Puerto Rico, U.S. Virgin Islands↗

USGS2024

The 2023 U.S. 50-state National Seismic Hazard Model: Changes in 2023 compared to 2018 ground motions

We present the 2023 U.S. National Seismic Hazard Model (NSHM) for all 50 states that applies new smoothed seismicity, fault rupture, and ground motion models. New data and methods are introduced in the 2023 earthquake rupture forecast that include: new earthquake catalogs - excluding induced earthquakes, alternative declustering methods, spatially smoothed seismicity distributions, full-catalog scaled rates to account for aftershocks, updated CEUS-WUS attenuation boundary, new magnitude-scaling equations, new geodetic and geologic deformation models, and alternative fault system solutions accounting for a more complete representation of epistemic uncertainty potential for earthquake generation in Alaska, Hawaii, and the conterminous U.S. Improved ground motion models consider new Next Generation Attenuation NGASubduction, modified NGA-East, and adjustments to account for regional biases in ground shaking observations. Semi-empirical and 3D simulations of ground motion are applied to account for shaking at 21 oscillator periods, 2 peak motions, and 8 site conditions. Site effects models are constructed for western U.S. basins (Seattle, Portland/Tualatin, San Francisco, Central Valley of California, Los Angeles, and Salt Lake City) and for sites with deep sedimentary wedges found across the central and eastern U.S. Gulf Coast and Atlantic coastal plain regions. These models result in substantial changes compared to the older NSHMs and are differentiated for the earthquake rupture forecast and ground motion model changes to display sensitivities and impacts.

Conference Paper↗