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Faults & earthquakes

Explore USGS earthquake and fault publications. Search fault names, locations and seismic hazards; follow the original report for maps, methods and publication context.

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At least 397 records · Page 22Linked to original sources

USGS1977

Application of linear statistical models of earthquake magnitude versus fault length in estimating maximum expectable earthquakes

Correlation or linear regression estimates of earthquake magnitude from data on historical magnitude and length of surface rupture should be based upon the correct regression. For example, the regression of magnitude on the logarithm of the length of surface rupture L can be used to estimate magnitude, but the regression of log L on magnitude cannot. Regression estimates are most probable values, and estimates of maximum values require consideration of one-sided confidence limits.

Geology↗

USGS1978

Earthquake swarms and local crustal spreading along major strike-slip faults in California

Earthquake swarms in California are often localized to areas within dextral offsets in the linear trend in active fault strands, suggesting a relation between earthquake swarms and local crustal spreading. Local crustal spereading is required by the geometry of dextral offsets when, as in the San Andreas system, faults have dominantly strike-slip motion with right-lateral displacement. Three clear examples of this relation occur in the Imperial Valley, Coso Hot Springs, and the Danville region, all in California. The first two of these areas are known for their Holocene volcanism and geothermal potential, which is consistent with crustal spreading and magmatic intrusion. The third example, however, shows no evidence for volcanism or geothermal activity at the surface. ?? 1978 Birkha??user Verlag.

Pure and Applied Geophysics PAGEOPH↗

USGS2000

Intra-basinal water movements induced by faulting: The August 17, 1999, Golcuk (Izmit Bay) earthquake (M(W) = 7.4)

A strong earthquake (M(w) = 7.4) occurred near the town of Golcuk, Izmit Bay, Western Turkey, at 00:01 GMT on August 17, 1999. Izmit Bay is a E-W trending pull-apart basin with a surface area of about 300 km2 along the North Anatolian Fault Zone (NAF), in the eastern extension of the Sea of Marmara. The earthquake was caused by a westerly movement of the Anatolian plate along NAF and was accompanied by isolated, chaotic water movements along the northern and southern shores of the bay. At localities along the shoreline a sudden drop in sea level, and a subsequent rise was prominent. The mode of observed sea-level movements rules out the occurrence of a basin-wide tsunami, sensu stricto. Instead, the water movements are attributed to localized sudden dip-slip movements of fault blocks in this pull-apart basin. (C) 2000 Elsevier Science B.V.

Marine Geology↗

USGS2002

Strong interseismic coupling, fault afterslip, and viscoelastic flow before and after the Oct. 9, 1995 Colima-Jalisco earthquake: continuous GPS measurements from Colima, Mexico

Continuous GPS measurements from Colima, Mexico during 4/93-6/01, bracketing the Oct. 9, 1995 M = 8.0 Colima-Jalisco earthquake, provide new constraints on Rivera plate subduction mechanics. Modeling of margin-normal strain accumulation before the earthquake suggests the Rivera-North America subduction interface was fully locked. Transient postseismic motion from 10/ 95-6/97 is well fit by a model that includes logarithmically-decaying fault afterslip, elastic strain from shallow fault relocking, and possibly a minor viscoelastic response, but is fit poorly by models that assume a dominant Maxwell viscoelastic response of the lower crust and upper mantle, independent of the assumed viscosities. Landward, margin-normal motion since mid-1997 is parallel to but ??? 75% slower than the pre-seismic velocity. Afterslip alone fails to account for this slowdown. The viscoelastic response predicted by a FEM correctly resolves the remaining velocity difference within the uncertainties. Both processes thus offset elastic strain accumulating from the relocked subduction interface.

Colima↗

USGS2019

On the utilization of synthetic and measured earthquake ground motions for designing building monitoring systems in the near-field of major faults

Agencies and research groups engaged in studying measures for enhancing the resiliency of communities have recently placed emphasis on the need for extensive implementation of monitoring systems for rapid post-event assessment of structural integrity. Designing a monitoring system for a building requires a thorough knowledge of its potential nonlinear dynamic behavior with an associated localization of interstory drift. Extending this task across a regional scale becomes even more challenging because of the heterogeneity of the buildings inventory and the limited knowledge of the characteristics of the demand especially for sites located in the near-field of a major fault. The existing observational database of near-field ground motion records is in fact too limited to constitute a comprehensive basis for full understanding of the potential range of structural response variability at different locations near a major fault. In addition, current insight into monitoring system design typically relies on linear structural models and sensors deployed on a limited number of floors. In this context, this paper presents first results of a study that combines synthetic earthquake ground motions generated from a massively parallel regional-scale geophysics wave propagation model at frequencies of engineering interest (0-5 Hz) with nonlinear tall building models. The objective is to gain new insight into the potential impact of localization of nonlinearities in structures subjected to realistic near-field earthquakes and develop a methodology that optimizes the deployment of sensors at the building and site level. In addition to the large database of synthetic motions, available real records are also employed to compare and contrast with the trends observed using synthetic ground motions. Preliminary results confirm a tendency of the demand to localize in specific portions of the structure, especially when nonlinearities occur. The building analyses provide guidance for various sensor deployment configurations associated with different probability of error in measuring structural drifts.

Conference Paper↗

USGS2000

A Double-difference Earthquake location algorithm: Method and application to the Northern Hayward Fault, California

We have developed an efficient method to determine high-resolution hypocenter locations over large distances. The location method incorporates ordinary absolute travel-time measurements and/or cross-correlation P-and S-wave differential travel-time measurements. Residuals between observed and theoretical travel-time differences (or double-differences) are minimized for pairs of earthquakes at each station while linking together all observed event-station pairs. A least-squares solution is found by iteratively adjusting the vector difference between hypocentral pairs. The double-difference algorithm minimizes errors due to unmodeled velocity structure without the use of station corrections. Because catalog and cross-correlation data are combined into one system of equations, interevent distances within multiplets are determined to the accuracy of the cross-correlation data, while the relative locations between multiplets and uncorrelated events are simultaneously determined to the accuracy of the absolute travel-time data. Statistical resampling methods are used to estimate data accuracy and location errors. Uncertainties in double-difference locations are improved by more than an order of magnitude compared to catalog locations. The algorithm is tested, and its performance is demonstrated on two clusters of earthquakes located on the northern Hayward fault, California. There it colapses the diffuse catalog locations into sharp images of seismicity and reveals horizontal lineations of hypocenter that define the narrow regions on the fault where stress is released by brittle failure.

Bulletin of the Seismological Society of America↗

USGS2002

The surface rupture and slip distribution of the 17 August 1999 Izmit earthquake (M 7.4), North Anatolian fault

The 17 August 1999 İzmit earthquake occurred on the northern strand of the North Anatolian fault zone. The earthquake is associated with a 145-km-long surface rupture that extends from southwest of Düzce in the east to west of Hersek delta in the west. Detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step-overs; herein named the Hersek, Karamürsel-Gölcük, İzmit-Sapanca Lake, Sapanca-Akyazi, and Karadere segments from west to east, respectively. The Hersek segment, which cuts the tip of a large delta plain in the western end of the rupture zone, has an orientation of N80°. The N70°-80°E-trending Karamürsel-Gölcük segment extends along the linear southern coasts of the İzmit Gulf between Karamürsel and Gölcük and produced the 470-cm maximum displacement in Gölcük. The northwest-southeast-striking Gölcük normal fault between the Karamürsel-Gölcük and İzmit-Sapanca segments has 2.3-m maximum vertical displacement. The maximum dextral offset along the İzmit-Sapanca Lake segment was measured to be about 3.5 m, and its trend varies between N80°E and east-west. The Sapanca-Akyazi segment trends N75°-85°W and expresses a maximum displacement of 5.2 m. The Karadere segment trends N65°E and produced up to 1.5-m maximum displacement. The Karadere and Sapanca-Akyazi segments form fan-shape or splaying ruptures near their eastern ends where the displacement also diminished.

Bulletin of the Seismological Society of America↗

USGS2002

Simulation of broadband ground motion including nonlinear soil effects for a magnitude 6.5 earthquake on the Seattle fault, Seattle, Washington

The Seattle fault poses a significant seismic hazard to the city of Seattle, Washington. A hybrid, low-frequency, high-frequency method is used to calculate broadband (0-20 Hz) ground-motion time histories for a M 6.5 earthquake on the Seattle fault. Low frequencies (1 Hz) are calculated by a stochastic method that uses a fractal subevent size distribution to give an ω -2 displacement spectrum. Time histories are calculated for a grid of stations and then corrected for the local site response using a classification scheme based on the surficial geology. Average shear-wave velocity profiles are developed for six surficial geologic units: artificial fill, modified land, Esperance sand, Lawton clay, till, and Tertiary sandstone. These profiles together with other soil parameters are used to compare linear, equivalent-linear, and nonlinear predictions of ground motion in the frequency band 0-15 Hz. Linear site-response corrections are found to yield unreasonably large ground motions. Equivalent-linear and nonlinear calculations give peak values similar to the 1994 Northridge, California, earthquake and those predicted by regression relationships. Ground-motion variance is estimated for (1) randomization of the velocity profiles, (2) variation in source parameters, and (3) choice of nonlinear model. Within the limits of the models tested, the results are found to be most sensitive to the nonlinear model and soil parameters, notably the over consolidation ratio.

Washington↗

USGS2026

Simulation-based scenario ShakeMaps for large magnitude (MW6.5+) crustal earthquakes on the Seattle, Tacoma, and southern Whidbey Island faults, Washington, USA

Scenario ground‐motion maps based on empirical ground‐motion models (GMMs) provide a rapid and generally reliable means of estimating the amplitude and distribution of earthquake shaking. However, because GMMs are designed for broad applicability, they often rely on simplified representations of Earth structure, which can limit their accuracy in regions with complex source, path, and site effects. This can substantially impact the accuracy of predicted shaking in areas like western Washington State, where deep, interconnected basin structure exerts a strong influence on seismic‐wave propagation. In this study, we present a new suite of simulation‐based scenario ShakeMaps that characterize ground shaking from large‐magnitude ( ⁠ M W 6.5–7.5) earthquakes on the Seattle, Tacoma, and southern Whidbey Island faults. These maps are developed using results from recent 3D wave propagation simulations ( Stone et al. , 2022 , 2023 , 2025 ) that incorporate realistic rupture geometries, variable slip distributions, and a regional 3D seismic velocity model with shallow soils. Broadband ground motions are estimated by combining the low‐frequency (<1 Hz) deterministic seismograms from these studies with high‐frequency (1–10 Hz) stochastic seismograms. Simulated ground motions are corrected to account for the enforced minimum shear‐wave velocity and nonlinear site response. The resulting ShakeMaps represent median ground‐shaking estimates derived from multiple rupture scenarios with varying slip distributions and hypocenter locations for each fault. To extend ShakeMap coverage beyond the simulation domain (i.e., into eastern Washington, northern Oregon, and southwestern British Columbia), we scale GMM‐based ground‐motion estimates using amplification patterns observed in the simulations. These new ShakeMaps reveal the substantial influence of deep basin structure on shaking intensity, underscoring the importance of considering crustal structure complexity in regional hazard assessments for the Pacific Northwest.

Washington↗

USGS2017

Geodetic slip model of the 3 September 2016 Mw 5.8 Pawnee, Oklahoma, earthquake: Evidence for fault‐zone collapse

The 3 September 2016 M w 5.8 Pawnee earthquake in northern Oklahoma is the largest earthquake ever recorded in Oklahoma. The coseismic deformation was measured with both Interferometric Synthetic Aperture Radar and Global Positioning System (GPS), with measureable signals of order 1 cm and 1 mm, respectively. We derive a coseismic slip model from Sentinel‐1A and Radarsat 2 interferograms and GPS static offsets, dominated by distributed left‐lateral strike slip on a primary west‐northwest–east‐southeast‐trending subvertical plane, whereas strike slip is concentrated near the hypocenter (5.6 km depth), with maximum slip of ∼1 m located slightly east and down‐dip of the hypocenter. Based on systematic misfits of observed interferogram line‐of‐sight (LoS) displacements, with LoS based on shear‐dislocation models, a few decimeters of fault‐zone collapse are inferred in the hypocentral region where coseismic slip was the largest. This may represent the postseismic migration of large volumes of fluid away from the high‐slip areas, made possible by the creation of a temporary high‐permeability damage zone around the fault.

Oklahoma↗

USGS2021

Coseismic fault slip and afterslip associated with the M5.7 March 18, 2020 Magna, Utah, earthquake

The 2020 Magna, Utah, earthquake produced observable crustal deformation over a ∼ 100 km 2 area around the southeast margin of Great Salt Lake, but it did not produce any surface rupture. To obtain a detailed picture of the fault slip, we combine strong motion seismic waveforms with GPS static oﬀsets and Interferometric Synthetic Aperture Radar (InSAR) observations to obtain kinematic and static slip models of the event. We sample the regional seismic waveﬁeld with 3-component records from 68 stations of the University of Utah Seismograph Stations network. We ﬁnd that coseismic slip and afterslip, with predominantly normal slip, distributed on a shallowly west-dipping plane, possibly augmented by afterslip on a steeply northeast-dipping plane, best ﬁts the joint dataset. The west-dipping plane locates near previously inferred sources of interseismic creep at depth. Hence the earthquake may have occurred on the downdip ex-tension of the Wasatch fault and activated further slip (afterslip) at shallow depth east of the hypocenter. This inferred afterslip may have driven the vigorous aftershock activity that was concentrated east of the hypocenter.

Utah↗

USGS2004

Cross-sections and maps showing double-difference relocated earthquakes from 1984-2000 along the Hayward and Calaveras faults, California

We present cross-section and map views of earthquakes that occurred from 1984 to 2000 in the vicinity of the Hayward and Calaveras faults in the San Francisco Bay region, California. These earthquakes came from a catalog of events relocated using the double-difference technique, which provides superior relative locations of nearby events. As a result, structures such as fault surfaces and alignments of events along these surfaces are more sharply defined than in previous catalogs.

California↗

USGS2008

Development of final a-fault rupture models for WGCEP/ NSHMP Earthquake Rate Model 2

This appendix discusses how we compute the magnitude and rate of earthquake ruptures for the seven Type-A faults (Elsinore, Garlock, San Jacinto, S. San Andreas, N. San Andreas, Hayward-Rodgers Creek, and Calaveras) in the WGCEP/NSHMP Earthquake Rate Model 2 (referred to as ERM 2. hereafter). By definition, Type-A faults are those that have relatively abundant paleoseismic information (e.g., mean recurrence-interval estimates). The first section below discusses segmentation-based models, where ruptures are assumed be confined to one or more identifiable segments. The second section discusses an un-segmented-model option, the third section discusses results and implications, and we end with a discussion of possible future improvements. General background information can be found in the main report.

Open-File Report↗

USGS2011

Using the 2011 M w 9.0 Tohoku earthquake to test the Coulomb stress triggering hypothesis and to calculate faults brought closer to failure

The 11 March 2011 Tohoku Earthquake provides an unprecedented test of the extent to which Coulomb stress transfer governs the triggering of aftershocks. During 11-31 March, there were 177 aftershocks with focal mechanisms, and so the Coulomb stress change imparted by the rupture can be resolved on the aftershock nodal planes to learn whether they were brought closer to failure. Numerous source models for the mainshock have been inverted from seismic, geodetic, and tsunami observations. Here, we show that, among six tested source models, there is a mean 47% gain in positively-stressed aftershock mechanisms over that for the background (1997-10 March 2011) earthquakes, which serve as the control group. An aftershock fault friction of 0.4 is found to fit the data better than 0.0 or 0.8, and among all the tested models, Wei and Sladen (2011) produced the largest gain, 63%. We also calculate that at least 5 of the seven large, exotic, or remote aftershocks were brought ≥0.3 bars closer to failure. With these tests as confirmation, we calculate that large sections of the Japan trench megathrust, the outer trench slope normal faults, the Kanto fragment beneath Tokyo, and the Itoigawa-Shizuoka Tectonic Line, were also brought ≥0.3 bars closer to failure.

Earth, Planets and Space↗

USGS2014

Low-frequency earthquakes reveal punctuated slow slip on the deep extent of the Alpine Fault, New Zealand

We present the first evidence of low-frequency earthquakes (LFEs) associated with the deep extension of the transpressional Alpine Fault beneath the central Southern Alps of New Zealand. Our database comprises a temporally continuous 36 month-long catalog of 8760 LFEs within 14 families. To generate this catalog, we first identify 14 primary template LFEs within known periods of seismic tremor and use these templates to detect similar events in an iterative stacking and cross-correlation routine. The hypocentres of 12 of the 14 LFE families lie within 10 km of the inferred location of the Alpine Fault at depths of approximately 20–30 km, in a zone of high P-wave attenuation, low P-wave speeds, and high seismic reflectivity. The LFE catalog consists of persistent, discrete events punctuated by swarm-like bursts of activity associated with previously and newly identified tremor periods. The magnitudes of the LFEs range between M L – 0.8 and M L 1.8, with an average of M L 0.5. We find that the frequency-magnitude distribution of the LFE catalog both as a whole and within individual families is not consistent with a power law, but that individual families' frequency-amplitude distributions approximate an exponential relationship, suggestive of a characteristic length-scale of failure. We interpret this LFE activity to represent quasi-continuous slip on the deep extent of the Alpine Fault, with LFEs highlighting asperities within an otherwise steadily creeping region of the fault.

Alpine Fault↗

USGS1991

The Wasatch fault zone, utah-segmentation and history of Holocene earthquakes

The Wasatch fault zone (WFZ) forms the eastern boundary of the Basin and Range province and is the longest continuous, active normal fault (343 km) in the United States. It underlies an urban corridor of 1.6 million people (80% of Utah's population) representing the largest earthquake risk in the interior of the western United States. We have used paleoseismological data to identify 10 discrete segments of the WFZ. Five are active, medial segments with Holocene slip rates of 1–2 mm a −1 , recurrence intervals of 2000–4000 years and average lengths of about 50 km. Five are less active, distal segments with mostly pre-Holocene surface ruptures, late Quaternary slip rates of <0.5 mm a −1 recurrence intervals of ≥10,000 years and average lengths of about 20 km. Surface-faulting events on each of the medial segments of the WFZ formed 2–4-m-high scarps repeatedly during the Holocene; latest Pleistocene (14–15 ka) deposits commonly have scarps as much as 15–20 m in height. Segments identified from paleoseismological studies of other major late Quaternary normal faults in the northern Basin and Range province are 20–25 km long, or about half of that proposed for the medial segments of the WFZ.

Journal of Structural Geology↗

USGS2000

A method for mapping apparent stress and energy radiation applied to the 1994 Northridge earthquake fault zone

Using the Northridge earthquake as an example, we demonstrate a new technique able to resolve apparent stress within subfaults of a larger fault plane. From the model of Wald et al. (1996), we estimated apparent stress for each subfault using τ a = (G/β)<Ḋ>/2 where G is the modulus of rigidity, β is the shear wave speed, and <Ḋ> is the average slip rate. The image of apparent stress mapped over the Northridge fault plane supports the idea that the stresses causing fault slip are inhomogeneous, but limited by the strength of the crust. Indeed, over the depth range 5 to 17 km, maximum values of apparent stress for a given depth interval agree with τ a (max)=0.06S(z), where S is the laboratory estimate of crustal strength as a function of depth z. The seismic energy from each subfault was estimated from the product τ a DA, where A is subfault area and D its slip. Over the fault zone, we found that the radiated energy is quite variable spatially, with more than 50% of the total coming from just 15% of the subfaults.

Geophysical Research Letters↗

USGS2021

Identification of low-frequency earthquakes on the San Andreas fault with deep learning

Low-frequency earthquakes are a seismic manifestation of slow fault slip. Their emergent onsets, low amplitudes, and unique frequency characteristics make these events difficult to detect in continuous seismic data. Here, we train a convolutional neural network to detect low-frequency earthquakes near Parkfield, CA using the catalog of Shelly (2017), https://doi.org/10.1002/2017jb014047 as training data. We explore how varying model size and targets influence the performance of the resulting network. Our preferred network has a peak accuracy of 85% and can reliably pick low-frequency earthquake (LFE) S-wave arrival times on single station records. We demonstrate the abilities of the network using data from permanent and temporary stations near Parkfield, and show that it detects new LFEs that are not part of the Shelly (2017), https://doi.org/10.1002/2017jb014047 catalog. Overall, machine-learning approaches show great promise for identifying additional low-frequency earthquake sources. The technique is fast, generalizable, and does not require sources to repeat.

Geophysical Research Letters↗