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At least 1,261 records · Page 70Linked to original sources
USGS2014

Three-dimensional ground-motion simulations of earthquakes for the Hanford area, Washington

This report describes the results of ground-motion simulations of earthquakes using three-dimensional (3D) and one-dimensional (1D) crustal models conducted for the probabilistic seismic hazard assessment (PSHA) of the Hanford facility, Washington, under the Senior Seismic Hazard Analysis Committee (SSHAC) guidelines. The first portion of this report demonstrates that the 3D seismic velocity model for the area produces synthetic seismograms with characteristics (spectral response values, duration) that better match those of the observed recordings of local earthquakes, compared to a 1D model with horizontal layers. The second part of the report compares the response spectra of synthetics from 3D and 1D models for moment magnitude (M) 6.6–6.8 earthquakes on three nearby faults and for a dipping plane wave source meant to approximate regional S-waves from a Cascadia great earthquake. The 1D models are specific to each site used for the PSHA. The use of the 3D model produces spectral response accelerations at periods of 0.5–2.0 seconds as much as a factor of 4.5 greater than those from the 1D models for the crustal fault sources. The spectral accelerations of the 3D synthetics for the Cascadia plane-wave source are as much as a factor of 9 greater than those from the 1D models. The differences between the spectral accelerations for the 3D and 1D models are most pronounced for sites with thicker supra-basalt sediments and for stations with earthquakes on the Rattlesnake Hills fault and for the Cascadia plane-wave source.

Washington↗
USGS2025

Paleoseismology and paleogeodesy using coral microatolls

Establishing the rupture extent and slip distribution of individual paleo-earthquakes is vital for assessing fault behavior including the persistence of rupture segmentation, recurrence patterns, and similarity of successive events, key issues in both fault mechanics and hazard assessment. Techniques with high temporal and geodetic precision as well as a wide distribution of study sites are necessary to investigate past earthquakes in such detail. Coral microatoll growth is one of the best types of geologic record for paleoseismology and paleogeodesy given these needs, as it provides long, continuous, widely distributed records of centimeter-scale vertical tectonic motion with potentially annual-level temporal precision. This chapter describes the process of interpreting microatoll growth records to obtain time series of relative sea level, tectonic vertical deformation fields, and finally slip and coupling parameters on an underlying fault interface.

Book chapter↗
USGS2020

Improving paleoseismic earthquake magnitude estimates with rupture length information: Application to the Puget Lowland, Washington State, U.S.A.

Both earthquake displacement and rupture length correlate with magnitude, and therefore observations of each from past earthquakes can be used to estimate the magnitude of those earthquakes in the absence of instrumental records. We extend the Bayesian inversion method of Biasi and Weldon (2006), which estimates paleoearthquake magnitude from displacement observations, to incorporate both rupture length and surface displacement measurements into the magnitude inversion. We then use this method on 27 late Pleistocene to Holocene paleoearthquakes in the Puget Lowland region of Washington. Observations of (typically vertical) fault separation per event range from 0.6 to 7 m, implying net displacement per event of up to 10 ± 4 m for the largest event. Rupture lengths are estimated to vary between the smallest contiguous mapped scarps to the full extent of the faults mapped from geology and geophysical observations. Although a few of the ruptures may be longer than 150 km, the ruptures have a median of 53 km, indicating that earthquakes in the Puget Lowland have relatively high displacement to length ratios. By considering both datasets, we find that all events were between M 6.3 and 7.5, generally consistent with the expected seismicity from the USGS National Seismic Hazard Map for the region. The simultaneous use of both length and displacement data in the magnitude inversion decreases both the estimated earthquake magnitudes and the uncertainty. The magnitude reduction in particular is due to the relatively short rupture lengths possible for Puget Lowland faults. This implies a decrease in the seismic hazard (relative to a displacement-only assessment) to a highly populated and rapidly urbanizing region.

Washington↗
USGS2013

Comment on “Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region” by U. ten Brink et al.

The analysis of historical earthquakes in the northeastern Caribbean by ten Brink et al. [2011, hereafter TB11] addresses the occurrence of large and destructive historical earthquakes associated with the North American-Caribbean plate boundary. One conclusion presented in TB11 is that the recurrence interval for large earthquakes on the left-lateral, strike-slip Septentrional Fault (SF) (Figure 1a) is approximately 300 years. Their Figure 7 shows rupture of the SF across the entire island of Hispaniola in CE 1200, 1542, and 1842. Our comment challenges this model for SF earthquake recurrence because it is inconsistent with our published paleoseismic data that show no large historical earthquake is associated with surface rupture along the SF east of Santiago (Figure 1a)[Prentice et al., 1993; Mann et al., 1998; Prentice et al., 2003].

Hispaniola↗
USGS2023

“Aftershock Faults” and what they could mean for seismic hazard assessment

We study stress‐loading mechanisms for the California faults used in rupture forecasts. Stress accumulation drives earthquakes, and that accumulation mechanism governs recurrence. Most moment release in California occurs because of relative motion between the Pacific plate and the Sierra Nevada block; we calculate relative motion directions at fault centers and compare with fault displacement directions. Dot products between these vectors reveal that some displacement directions are poorly aligned with plate motions. We displace a 3D finite‐element model according to relative motions and resolve stress tensors onto defined fault surfaces, which reveal that poorly aligned faults receive no tectonic loading. Because these faults are known to be active, we search for other loading mechanisms. We find that nearly all faults with no tectonic loading show increase in stress caused by slip on the San Andreas fault, according to an elastic dislocation model. Globally, faults that receive a sudden stress change respond with triggered earthquakes that obey an Omori law rate decay with time. We therefore term this class of faults as “aftershock faults.” These faults release ∼4% of the moment release in California, have ∼0.1%–5% probability of M 6.7 earthquakes in 30 yr, and have a 0.001%–1% 30 yr M 7.7 probability range.

California↗
USGS2007

Holocene slip rate and revised characteristic earthquake parameters for the western segment of the Castle Mountain fault, Alaska

The western segment of the Castle Mountain fault poses a significant seismic hazard to the most populated region of south-central Alaska. We identify a previously unrecognized margin of a postglacial outwash channel that is offset right laterally 36 ± 4 m across the western segment of the Castle Mountain fault. This offset occurred after glaciers withdrew from the lowland 11,300–15,380 cal yr b.p. and after outwash channel margins were cut and stabilized 11,210–13,470 cal yr b.p. Using these ages and the measured separation, we obtain a maximum slip rate of 3.0 ± 0.6 mm yr −1 and a minimum slip rate of 2.8 ± 0.7 mm yr −1 . These are the first lateral slip rates for the Castle Mountain fault established by a field measurement. Based on timing of the most recent earthquake, 670 ± 60 yr b.p. , the Castle Mountain fault could have accumulated an average single-event slip of about 1.9 m (extremes range from 1.3 to 2.6 m). The fault consists of two segments; a surface-rupturing earthquake likely will be limited to the 62-km-long western segment. Area-magnitude regression calculations suggest that such an earthquake on the western Castle Mountain fault would have a moment magnitude of 6.9 to 7.3.

Alaska↗
USGS2000

Development of Maximum Considered Earthquake Ground Motion Maps

The 1997 NEHRP Recommended Provisions for Seismic Regulations for New Buildings use a design procedure that is based on spectral response acceleration rather than the traditional peak ground acceleration, peak ground velocity, or zone factors. The spectral response accelerations are obtained from maps prepared following the recommendations of the Building Seismic Safety Council's (BSSC) Seismic Design Procedures Group (SDPG). The SDPG-recommended maps, the Maximum Considered Earthquake (MCE) Ground Motion Maps, are based on the U.S. Geological Survey (USGS) probabilistic hazard maps with additional modifications incorporating deterministic ground motions in selected areas and the application of engineering judgement. The MCE ground motion maps included with the 1997 NEHRP Provisions also serve as the basis for the ground motion maps used in the seismic design portions of the 2000 International Building Code and the 2000 International Residential Code . Additionally the design maps prepared for the 1997 NEHRP Provisions , combined with selected USGS probabilistic maps, are used with the 1997 NEHRP Guidelines for the Seismic Rehabilitation of Buildings .

Earthquake Spectra↗
USGS2022

Development of a companion questionnaire for “Did You Feel It?”: Assessing response in earthquakes where an earthquake early warning may have been received

Earthquake early warning (EEW) systems are relatively new technologies having first emerged as regional systems in the 1990s. Japan was the first nation to develop and implement a nationwide system in October 2007, and in the United States, ShakeAlert ® became available on the entire length of the US West Coast in May 2021. Assessing how EEW is perceived and utilized by alert recipients is considered essential. Such assessments are necessary to evaluate whether alert recipients are taking advantage of alert messages to initiate protective actions upon receipt of an alert, how they regard the usefulness of alerts, desirable thresholds for issuing alerts, and other aspects of these systems. Having information from users will also facilitate assessments of the success of earthquake preparedness educational programs such as the ShakeOut and whether annual drills which include information on EEW systems are resulting in behavioral response consistent with the content of these programs. Finally, information on EEW utilization will provide data useful to social scientists who study hazards to advance our understanding of behavioral response to warnings. Survey research in the aftermath of a significant earthquake in which an EEW has been issued is one obvious method of achieving these objectives and there already exist a number of survey instruments for this purpose. A related strategy and the goal of the present research is to develop a brief questionnaire, consistent with those already developed, as a supplement to the United States Geological Survey’s “Did You Feel It?” questionnaire that has provided earthquake intensities and information on behavioral response in earthquakes, both domestic and international, since 2004. Having the intensity level at each respondent’s location is essential for relating their perspectives and actions to the shaking they experienced.

Earthquake Spectra↗
USGS2006

Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2005

The Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, the Geophysical Institute of the University of Alaska Fairbanks, and the Alaska Division of Geological and Geophysical Surveys, has maintained seismic monitoring networks at historically active volcanoes in Alaska since 1988 (Figure 1). The primary objectives of the seismic program are the real-time seismic monitoring of active, potentially hazardous, Alaskan volcanoes and the investigation of seismic processes associated with active volcanism. This catalog presents calculated earthquake hypocenters and seismic phase arrival data, and details changes in the seismic monitoring program for the period January 1 through December 31, 2005. The AVO seismograph network was used to monitor the seismic activity at thirty-two volcanoes within Alaska in 2005 (Figure 1). The network was augmented by two new subnetworks to monitor the Semisopochnoi Island volcanoes and Little Sitkin Volcano. Seismicity at these volcanoes was still being studied at the end of 2005 and has not yet been added to the list of permanently monitored volcanoes in the AVO weekly update. Following an extended period of monitoring to determine the background seismicity at the Mount Peulik, Ukinrek Maars, and Korovin Volcano, formal monitoring of these volcanoes began in 2005. AVO located 9,012 earthquakes in 2005. Monitoring highlights in 2005 include: (1) seismicity at Mount Spurr remaining above background, starting in February 2004, through the end of the year and into 2006; (2) an increase in seismicity at Augustine Volcano starting in May 2005, and continuing through the end of the year into 2006; (3) volcanic tremor and seismicity related to low-level strombolian activity at Mount Veniaminof in January to March and September; and (4) a seismic swarm at Tanaga Volcano in October and November. This catalog includes: (1) descriptions and locations of seismic instrumentation deployed in the field in 2005; (2) a description of earthquake detection, recording, analysis, and data archival systems; (3) a description of seismic velocity models used for earthquake locations; (4) a summary of earthquakes located in 2005; and (5) an accompanying UNIX tar-file with a summary of earthquake origin times, hypocenters, magnitudes, phase arrival times, and location quality statistics; daily station usage statistics; and all HYPOELLIPSE files used to determine the earthquake locations in 2005.

Alaska↗
USGS2026

Opportunities for the U.S. Geological Survey’s National Seismic Hazard Model to improve seismic risk assessment of critical infrastructure.

As fragility and risk modeling techniques and computational capabilities evolve, complemented by moving toward more routine and systematic seismic risk assessment of all buildings and critical infrastructure, the authors pose a few critical questions to investigate how the U.S. Geological Survey (USGS) National Seismic Hazard Models (NSHMs) can be used and enhanced further to serve such issues. In this paper, we use three examples from multiple sectors to (1) identify the role of USGS NSHMs in evaluating seismic risks to critical infrastructure, (2) quantify potential impacts from NSHM enhancements (i.e., [i] hazard curves for the vertical component of ground motion, [ii] stochastic event sets, and [iii] maps of probabilistic ground failure hazards), and (3) clarify the feasibility of relevant NSHM improvements. We illuminate that NSHMs are commonly used in location-specific performance assessments, whereas earthquake effects on critical infrastructure can be widespread across large geospatial regions. Further, we found that without the NSHM extensions considered here, risk can be severely underestimated, e.g., neglecting ground failure hazards can underestimate regional loss by a factor of two or more. Although many challenges remain, we developed example prototypes to clarify the feasibility of the NSHM extensions, which can facilitate improved management of risks to critical infrastructure.

Earthquake Spectra Journal↗
USGS2018

Characterizing the Los Angeles Aqueduct crossing of the San Andreas Fault for improved earthquake resilience

The five-mile-long Elizabeth Tunnel, which crosses the San Andreas fault (SAF) zone near Lake Hughes, California, is part of the Los Angeles Aqueduct (LAA) that delivers water from Owens Valley to the City of Los Angeles. Geologic characterization of the Elizabeth Tunnel alignment is focused on developing a better understanding of fault displacement hazards at the SAF crossing to support design of both short- and long-term strategies to increase the earthquake resilience of the City’s water supply system. The results of this study define a fault zone that is wider and more complex at the surface than at tunnel depth. A 750-ft transect of deep, angled core borings, located ~ 100 ft west of, and parallel to the tunnel alignment, penetrated a wide zone (>550 ft) of fault-damaged granitic and gneissic rocks containing a few thick fault zones that can be correlated confidently between borings as well as a multitude of very thin faults and shears throughout the rock mass. Fault rocks are predominantly defined as coherent cataclasites and ultracataclasites, as opposed to incoherent clay gouge, even at this relatively shallow sampling depth. Integrating geomorphic, geologic, petrographic, and geophysical data defines a steeply south-dipping SAF that splays upward and increases in complexity toward the surface, and provides the basis for engineering design considerations at this critical SAF crossing.

California↗
USGS2020

Late Quaternary slip rates on the Sierra Madre fault zone and paleoseismic evidence on the size and frequency of past ruptures

The Sierra Madre fault zone is a south-vergent, active reverse fault that accommodates shortening between basins on the northern margin of the Los Angeles region and the San Gabriel Mountains. The preservation of late Quaternary alluvial fill and fan surfaces in the hanging wall of the fault provides evidence of long-term uplift. Surface rupture from the 1971 Mw 6.6 San Fernando earthquake and evidence of large prehistoric displacements from trenching investigations emphasize the ongoing hazard posed by the fault system to the region. This one-day field trip visits some of the key locations near Pasadena and San Fernando, California, where slip rates have been determined from cosmogenic and luminescence dating of abandoned surfaces dating to 50–70, ca. 30, and ca. 12 ka and surface offsets measured from lidar and pre-development topographic maps. Another stop is the site of a paleoseismic trench, which provided key evidence on the timing and displacement of past ruptures on the fault. In combination, results from these field investigations converge on a slip rate for the eastern ~100 km of the fault zone of 1–2 mm/yr, which matches or exceeds the rates for other reverse faults in southern California. This rate, in combination with trenching data that show no evidence of post–mid Holocene ruptures along the central and eastern portions of the fault, indicate the fault zone poses a significant seismic hazard to the region.

California↗
USGS2013

A scenario study of seismically induced landsliding in Seattle using broadband synthetic seismograms

We demonstrate the value of utilizing broadband synthetic seismograms to assess regional seismically induced landslide hazard. Focusing on a case study of an M w 7.0 Seattle fault earthquake in Seattle, Washington, we computed broadband synthetic seismograms that account for rupture directivity and 3D basin amplification. We then adjusted the computed motions on a fine grid for 1D amplifications based on the site response of typical geologic profiles in Seattle and used these time‐series ground motions to trigger shallow landsliding using the Newmark method. The inclusion of these effects was critical in determining the extent of landsliding triggered. We found that for inertially triggered slope failures modeled by the Newmark method, the ground motions used to simulate landsliding must have broadband frequency content in order to capture the full slope displacement. We applied commonly used simpler methods based on ground‐motion prediction equations for the same scenario and found that they predicted far fewer landslides if only the mean values were used, but far more at the maximum range of the uncertainties, highlighting the danger of using just the mean values for such methods. Our results indicate that landsliding triggered by a large Seattle fault earthquake will be extensive and potentially devastating, causing direct losses and impeding recovery. The high impact of landsliding predicted by this simulation shows that this secondary effect of earthquakes should be studied with as much vigor as other earthquake effects.

Washington↗
USGS2026

The U.S. Geological Survey 2025 Puerto Rico and U.S. Virgin Islands time-independent earthquake rupture forecast

We present the 2025 U.S. Geological Survey Puerto Rico and U.S. Virgin Islands (PRVI) time‐independent earthquake rupture forecast (ERF), developed for the 2025 update to the National Seismic Hazard Model (NSHM) for PRVI. The updated ERF improves upon a prior model from 2003, including an expanded fault inventory with slip‐rate estimates, updated seismicity catalogs, and refined subduction zone geometries and deformation models. It applies the fault‐system inversion methodology to solve for rates of ruptures on modeled faults, adapted from the 2023 NSHM (NSHM23) for the western United States, including the first application of the inversion to model rates on a U.S. subduction interface. Off‐fault and intraslab seismicity are constrained by observed seismicity and use updated methods developed for NSHM23. Uncertainties in model components are substantial, and the ERF represents epistemic uncertainties through a comprehensive logic tree consisting of 1.7 billion logic‐tree branches combined across all sources.

Puerto Rico, U.S. Virgin Islands↗
USGS1978

Pillar Mountain Landslide, Kodiak, Alaska

Pillar Mountain landslide on the southeast face of Pillar Mountain is about 915 m (3,000 ft) southwest of the city of Kodiak, Alaska. The landslide is about 520 m (1,700 ft) wide at its base and extends approximately from sea level to an altitude of about 343 m (1,125 ft). The slide developed on an ancient and apparently inactive landslide. Renewed movement was first detected on December 5, 1971, following removal of about 230,000 m3 (300,000 yd3) of material from the base of the slope. Although movement of the landslide has decreased since December, 1971, movement continues and the possibility exists that it could increase as a result of an earthquake, water saturation of the landslide mass, or other causes. In the most extreme case, as much as 3.8 to 7.6 million m (5-10 million ) of debris could fall into the sea at Inner Anchorage. If this took place suddenly, it could generate a wave comparable in height to the tsunami that damaged Kodiak during the Alaskan Earthquake of 1964. Therefore, we believe that the Pillar landslide is a potential hazard to the city of Kodiak and its environs that merits a thorough investigation and evaluation.

Open-File Report↗
USGS2014

Global assessment of human losses due to earthquakes

Current studies have demonstrated a sharp increase in human losses due to earthquakes. These alarming levels of casualties suggest the need for large-scale investment in seismic risk mitigation, which, in turn, requires an adequate understanding of the extent of the losses, and location of the most affected regions. Recent developments in global and uniform datasets such as instrumental and historical earthquake catalogues, population spatial distribution and country-based vulnerability functions, have opened an unprecedented possibility for a reliable assessment of earthquake consequences at a global scale. In this study, a uniform probabilistic seismic hazard assessment (PSHA) model was employed to derive a set of global seismic hazard curves, using the open-source software OpenQuake for seismic hazard and risk analysis. These results were combined with a collection of empirical fatality vulnerability functions and a population dataset to calculate average annual human losses at the country level. The results from this study highlight the regions/countries in the world with a higher seismic risk, and thus where risk reduction measures should be prioritized.

Conference Paper↗
USGS2022

Implementation of basin models and sediment depth terms in the 2023 update of the U.S. National Seismic Hazard Model: Example from Reno, Nevada

We present a framework to evaluate the inclusion of candidate basin depth models in the U.S. Geological Survey National Seismic Hazard Model. We compute intensity measures (peak and spectral amplitudes) from uniformly processed earthquake ground motions in and around the basin of interest and compare these to ground-motion model (GMM) estimates over a range of oscillator periods. The GMMs use depth to specific shear-wave velocity isosurfaces (Z x ) as a proxy for basin depth. We quantify whether the GMM estimates using Z x from the candidate basin depth model outperform the default estimates based on V S30 (the time-averaged shear wave velocity in the upper 30 m). We partition GMM residuals into event and site terms and compare site terms for stations within the basin to non-basin sites. We apply this framework to the greater Reno, Nevada, region, which has shallow basin depths (less than 450 m) and empirical amplifications of up to a factor of 2.2 at 1.0 s. There are no strong trends in site terms with basin depth, and the use of Z x values from the new candidate basin model shows marginal improvement of GMM total residuals compared to the default V S30 -based model (the condition of no relative basin amplification).

Nevada↗
USGS2002

A bilinear source-scaling model for M-log a observations of continental earthquakes

The Wells and Coppersmith (1994) M-log A data set for continental earthquakes (where M is moment magnitude and A is fault area) and the regression lines derived from it are widely used in seismic hazard analysis for estimating M, given A. Their relations are well determined, whether for the full data set of all mechanism types or for the subset of strike-slip earthquakes. Because the coefficient of the log A term is essentially 1 in both their relations, they are equivalent to constant stress-drop scaling, at least for M ??? 7, where most of the data lie. For M > 7, however, both relations increasingly underestimate the observations with increasing M. This feature, at least for strike-slip earthquakes, is strongly suggestive of L-model scaling at large M. Using constant stress-drop scaling (???? = 26.7 bars) for M ??? 6.63 and L-model scaling (average fault slip u?? = ??L, where L is fault length and ?? = 2.19 &times 10-5) at larger M, we obtain the relations M = log A + 3.98 ?? 0.03, A ??? 537 km2 and M = 4/3 log A + 3.07 ?? 0.04, A > 537 km2. These prediction equations of our bilinear model fit the Wells and Coppersmith (1994) data set well in their respective ranges of validity, the transition magnitude corresponding to A = 537 km2 being M = 6.71.

Bulletin of the Seismological Society of America↗