Geology topics
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.
Application of linear statistical models of earthquake magnitude versus fault length in estimating maximum expectable earthquakes
No abstract available.
Preliminary assessment of long-term probabilities for large earthquakes along selected fault segments of the San Andreas fault system, California
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Proceedings of Workshop XXVIII on the Borah Peak, Idaho, earthquake: Volume B. Fault scarps, landslides and other features associated with the Borah Peak earthquake of October 28, 1983, central Idaho: A field trip guide, with a section on the Doublespring Pass road trench
No abstract available.
Preliminary assessment of paleoseismicity at White Sands Missile Range, southern New Mexico; evidence for recency of faulting, fault segmentation, and repeat intervals for major earthquakes in the region
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Compilation and analysis of displacement measurements obtained on the Superstition Hills fault zone and nearby faults in Imperial Valley, California, following the earthquakes of November 24, 1987
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Joint analysis of geodetic and earthquake fault-plane solution data to constrain magmatic sources: A case study from Kīlauea Volcano
A joint analysis of geodetic and seismic datasets from Kīlauea Volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex, multi-source system. At the end of 2003, Kīlauea's summit began a four-year-long period of inflation due to a surge in magma supply to the volcano. In 2006, for the first time since 1982, Kīlauea's Southwest Rift Zone (SWRZ) also experienced inflation. To investigate the characteristics of active magma sources and the nature of their interactions with faults in the SWRZ during 2006, we integrate, through Coulomb stress modeling, contemporary geodetic data from InSAR and GPS with a new catalogue of double-couple fault-plane solutions for volcano-tectonic earthquakes. We define two periods of inflation during 2006 based on the rate of deformation measured in daily GPS data, spanning February to 15 March 2006 (Period 1) and 16 March to 30 September 2006 (Period 2). InSAR data for these two periods are inverted to determine the position, change in size, and shape of inflation sources in each period. Our new models are consistent with microseismic activity from each period. They suggest that, during Period 1, deformation in the SWRZ can be explained by pressurization of magma in a spherical reservoir beneath the south caldera, and that, during Period 2, magma was also aseismically intruded farther to the southwest into the SWRZ along a sub-horizontal plane. Our Coulomb stress analysis shows that the microseismicity recorded in the SWRZ is induced by overpressurization of the south caldera reservoir, and not by magma intrusion into the SWRZ. This study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation.
Strong tremor near Parkfield, CA, excited by the 2002 Denali Fault earthquake
We show clear evidence of non-volcanic tremor triggered by 2002 Mw7.8 Denali Fault earthquake near Parkfield. Triggered tremor is identified as bursts of high-frequency (∼2–8 Hz), non-impulsive seismic energy whose envelope is coherent among many stations and has the same periodicity as the passing surface waves. The tremor originates from at least three hypocenters near the San Andreas fault with differing frictional regimes, two in the creeping section and the other where the San Andreas is transitional between creeping and locked. All the sources originate below the seismogenic zone, suggesting that transitional frictional properties are necessary conditions for tremor generation. Tremor is excited by the Love waves when the San Andreas is sheared in a right-lateral sense, encouraging slip, and is absent when the San Andreas is sheared in a left-lateral sense, consistent with a simple frictional response to the driving stress.
Slip rate, earthquake recurrence, and seismogenic potential of the Rodgers Creek Fault Zone, northern California: Initial results
Instrumental seismicity defines a seismic gap along the Rodgers Creek fault zone (RCFZ) between Santa Rosa and San Pablo Bay. Results of a paleoseismicity study within the gap, using offset channels in late Holocene alluvial deposits as piercing points, indicate a minimum slip rate of 2.1 to 5.8 mm/yr for the past 1300 years, a preferred range for the maximum recurrence interval of 248 to 679 years, and a surface offset of 2 +0.3, −0.2 m during the most recent event. The RCFZ has produced past M7 earthquakes, and historical seismicity data indicate a minimum elapsed time of 182 years since the most recent earthquake of this size.
Importance of model parameterization in finite fault inversions: Application to the 1974 Mw 8.0 Peru Earthquake
The spatial and temporal slip distributions for the October 3, 1974 ( M w = 8.0), Peru subduction zone earthquake and its largest aftershock on November 9 ( M s = 7.1) are calculated and analyzed in terms of the inversion parameterization and tectonic significance. Teleseismic, long-period World-Wide Standard Seismograph Network, P and SH waveforms are inverted to obtain the rupture histories. We demonstrate that erroneous results are obtained if a parameterization is used that does not allow for a sufficiently complex source, involving spatial variation in slip amplitude, risetime, and rupture time. The inversion method utilizes a parameterization of the fault that allows for a discretized source risetime and rupture time. Well-located aftershocks recorded on a local network have the same general pattern as teleseismically determined hypocenters and help to constrain the geometry of the subduction zone. For the main shock a hinged fault is preferred having a shallow plane with a dip of 11° and a deeper, landward plane with a dip of 30°. The preferred nucleation depth lies between 11 and 15 km. A bilateral rupture is obtained with two major concentrations of slip, one 60 to 70 km to the northwest of the epicenter and a second 80 to 100 km to the south and southeast of the epicenter. For these source regions, risetimes vary from 6 to 18 s. Our estimates of risetimes are consistent with the time for the rupture to traverse the dominant local asperity. The slip distribution for the November 9 aftershock falls within a conspicuous hole in the main shock rupture pattern, near the hypocenter of the main shock. The November 9 event has a simple risetime function with a duration of 2 s. Aftershocks recorded by the local network are shown to cluster near the hypocenter of the impending November 9 event and downdip from the largest main shock source region. Slip during the main shock is concentrated at shallow depths above 15 km and extends updip from the hypocenter to near the plate boundary at the trench axis. The large amount of slip at shallow depths is attributed to the absence of any significant accretionary wedge of sediments, and the relatively young age and high convergence rate of the subducted plate, which results in good seismic coupling near the trench axis.
Comparison of seismic waveform inversion results for the rupture history of a finite fault: Application to the 1986 North Palm Springs, California, earthquake
The July 8, 1986, North Palm Springs earthquake is used as a basis for comparison of several different approaches to the solution for the rupture history of a finite fault. The inversion of different waveform data is considered; both teleseismic P waveforms and local strong ground motion records. Linear parametrizations for slip amplitude are compared with nonlinear parametrizations for both slip amplitude and rupture time. Inversions using both synthetic and empirical Green's functions are considered. In general, accurate Green's functions are more readily calculable for the teleseismic problem where simple ray theory and flat-layered velocity structures are usually sufficient. However, uncertainties in the variation in t * with frequency most limit the resolution of teleseismic inversions. A set of empirical Green's functions that are well recorded at teleseismic distances could avoid the uncertainties in attenuation. In the inversion of strong motion data, the accurate calculation of propagation path effects other than attenuation effects is the limiting factor in the resolution of source parameters. The assumption of a laterally homogeneous velocity structure is usually not a good one, and the use of empirical Green's functions is desirable. Considering the parametrization of the problem, any degree of fault rupture complexity can be described in terms of a linear parametrization for slip amplitudes. However, a nonlinear parametrization for rupture times and slip amplitudes can have a distinct advantage over a simple linear one by limiting the number of unknown parameters. Regardless of the choice of data or the type of parametrization, the model or solution will be affected by the choice of minimization norm and the type of stabilization used.
3-D joint geodetic and strong-motion finite fault inversion of the 2008 May 12, Wenchuan, China Earthquake
We present a source inversion of the 2008 Wenchuan, China earthquake, using strong-motion waveforms and geodetic offsets together with three-dimensional synthetic ground motions. We applied the linear multiple time window technique considering geodetic and dynamic Green's functions computed with the finite element method and the reciprocity and Strain Green’s Tensor formalism. All ground motion estimates, valid up to 1 Hz, accounted for three-dimensional effects, including the topography and the geometry of the Beichuan and Pengguan faults. Our joint inversion has a higher moment (M0) than a purely geodetic inversion and the slip distribution presents differences when compared to one-dimensional model source inversions. The moment is estimated to be M0=1.2x1021 Nm, slightly larger than other works. Our results show that considering a complex 3D structure reduces the size of large areas of 10 m slip or greater by distributing it in wider zones, with reduced slips, in the central portion of the Beichuan and the Pengguan faults. Finally, we compare our source with a relocated aftershock catalog and conclude that the 4-5 m slip contours approximately bound the absence or presence of aftershocks.
Afterslip, tremor, and the Denali fault earthquake
We tested the hypothesis that afterslip should be accompanied by tremor using observations of seismic and aseismic deformation surrounding the 2002 M 7.9 Denali fault, Alaska, earthquake (DFE). Afterslip happens more frequently than spontaneous slow slip and has been observed in a wider range of tectonic environments, and thus the existence or absence of tremor accompanying afterslip may provide new clues about tremor generation. We also searched for precursory tremor, as a proxy for posited accelerating slip leading to rupture. Our search yielded no tremor during the five days prior to the DFE or in several intervals in the three months after. This negative result and an array of other observations all may be explained by rupture penetrating below the presumed locked zone into the frictional transition zone. While not unique, such an explanation corroborates previous models of megathrust and transform earthquake ruptures that extend well into the transition zone.
Erratum to earthquake recurrence estimates for northern Caribbean faults from combinatorial optimization
In the original article (ten Brink and Geist, 2025), we derived on‐fault magnitude–frequency relationships with uncertainties from a combinatorial optimization method that assigns individual earthquakes from a regional catalog to the different faults. Our model used a magnitude versus area relationship from Shaw (2023). His relationship was published with an error, M=f(1/√A), instead of M=f(1/A) (Shaw, 2025). Here, we recalculate the magnitude–frequency relationship with uncertainties using the Shaw (2025) corrected formula. The remaining parameters of the model, the model itself, and the number of repeated optimization runs have not changed. Figures 1 and 2 show the corrected results and replace figures 3 and 4 in the original article.
Effects of the 1983 Coalinga, California, earthquake on creep along the San Andreas fault
The M//L approximately equals 6. 5 earthquake that occurred near Coalinga, California, on May 2, 1983 induced changes in near-surface fault slip along the San Andreas fault. Coseismic steps were observed by creepmeters along a 200-km section of the San Andreas. some of the larger aftershocks induced additional steps, both right-lateral and left-lateral, and in general the sequence disrupted observed creep at several sites from preseismic long-term patterns. Static dislocation models can approximately explain the magnitudes and distribution of the larger coseismic steps on May 2. The smaller, more distant steps appear to be the abrupt release of accumulated slip, triggered by the coseismic strain changes, but independent of the strain change amplitudes.
Three-dimensional records of surface displacement on the Superstition Hills fault zone associated with the earthquakes of 24 November 1987
Seven quadrilaterals, constructed at broadly distributed points on surface breaks within the Superstition Hills fault zone, were repeatedly remeasured after the pair of 24 November 1987 earthquakes to monitor the growing surface displacement. Changes in the dimensions of the quadrilaterals are recalculated to right-lateral and extensional components at millimeter resolution, and vertical components of change are resolved at 0.2 mm precision. The displacement component data for four of the seven quadrilaterals record the complete fault movement with respect to an October 1986 base. These data fit with remarkable agreement the power law
Accelerations near faults that have moved during moderate-sized earthquakes
Peak ground accelerations recently recorded within 10-15 km of faulting during moderate-sized earthquakes (m = 4 to 6) are significantly underestimated by many, if not most, of the empirical acceleration-distance relations commonly used in seismic engineering. The recent data show a rapid decrease of peak acceleration with increasing distances (at a rate between r -1.4 and r -I.8 ) beyond 5 to 20 km and suggest a less rapid rate of attenuation closer to the causative fault.