Faults In California Research Articles

Present‐day stress orientations adjacent to active strike‐slip faults: California and Sumatra

Present‐day stress directions interpreted from well bore breakouts adjacent to two crastal‐scale, active, strike‐slip faults (the San Andreas fault in California and the Great Sumatran fault in Sumatra) indicate that the maximum horizontal stress direction (SH) is oriented at a high angle (70°–90°) to both faults. The regionally defined stress fields spanning these faults show that adjacent young or actively growing folds have formed orthogonal to SH and are therefore in the thrust‐fault orientation. These observations indicate a decoupling of the strike‐slip and compressional components of the deformation within these broadly transpressive zones. Borehole breakouts in 118 wells in western California indicate a regionally consistent stress pattern with SH generally oriented NE‐SW, nearly perpendicular (80°–90°) to the strike of the San Andreas fault. The orientation of SH nearly perpendicular to the San Andreas fault implies low shear stress on the fault and is consistent with geological interpretations of the Coast and Transverse Ranges indicating active compressional deformation, fault plane solutions for recent dip‐slip‐style earthquakes, principal stress directions determined from inversion of earthquake focal mechanisms, and induced hydraulic fracture orientations. A stress trajectory map for western California is computed using an iterative statistical algorithm in which observed directional data, such as breakout directions, are used to obtain a model regional stress field. Analysis of well bore breakouts in 25 wells within the central and southern oil districts of Sumatra indicates that the regionally defined SH adjacent to the active Great Sumatran strike‐slip fault is oriented at a high angle (70°–80°) to the fault This orientation of SH is consistent regionally with geologic stress indicators and focal mechanisms of dip‐slip earthquakes. Preliminary analysis of the stress field in the vicinity of the Philippine and Alpine faults suggests SH is also oriented at a high angle to these active strike‐slip faults. Similarly, the minimum horizontal stress Sh is oriented at a high angle to the the Kane and Dead Sea transforms. The observation of SH and Sh in the vicinity of active strike‐slip faults being oriented nearly perpendicular and parallel to the faults suggests that large, crustal‐scale strike‐slip faults may, in general, be inherently weak surfaces.

Thermal and barometric constraints on the intrusive and unroofing history of the Black Mountains: Implications for timing, initial dip, and kinematics of detachment faulting in the Death Valley Region, California

Unroofing of the Black Mountains, Death Valley, California, has resulted in the exposure of 1.7 Ga crystalline basement, late Precambrian amphibolite facies metasedimentary rocks, and a Tertiary magmatic complex. The 40Ar/39Ar cooling ages, obtained from samples collected across the entire length of the range (>55 km), combined with geobarometric results from synextensional intrusions, provide time‐depth constraints on the Miocene intrusive history and extensional unroofing of the Black Mountains. Data from the southeastern Black Mountains and adjacent Greenwater Range suggest unroofing from shallow depths between 9 and 10 Ma. To the northwest in the crystalline core of the range, biotite plateau ages from ∼13 to 6.8 Ma from rocks making up the Death Valley turtlebacks indicate a midcrustal residence (with temperatures >300°C) prior to extensional unroofing. Biotite 40Ar/39Ar ages from both Precambrian basement and Tertiary plutons reveal a diachronous cooling pattern of decreasing ages toward the northwest, subparallel to the regional extension direction. Diachronous cooling was accompanied by dike intrusion which also decreases in age toward the northwest. The cooling age pattern and geobarometric constraints in crystalline rocks of the Black Mountains suggest denudation of 10–15 km along a northwest directed detachment system, consistent with regional reconstructions of Tertiary extension and with unroofing of a northwest deepening crustal section. Mica cooling ages that deviate from the northwest younging trend are consistent with northwestward transport of rocks initially at shallower crustal levels onto deeper levels along splays of the detachment. The well‐known Amargosa chaos and perhaps the Badwater turtleback are examples of this “splaying” process.Considering the current distance of the structurally deepest samples away from moderately to steeply east tilted Tertiary strata in the southeastern Black Mountains, these data indicate an average initial dip of the detachment system of the order of 20°, similar to that determined for detachment faults in west central Arizona and southeastern California. Beginning with an initially listric geometry, a pattern of footwall unroofing accompanied by dike intrusion progresses northwestward. This pattern may be explained by a model where migration of footwall flexures occur below a scoop‐shaped hanging wall block. One consequence of this model is that gently dipping ductile fabrics developed in the middle crust steepen in the upper crust during unloading. This process resolves the low initial dips obtained here with mapping which suggests transport of the upper plate on moderately to steeply dipping surfaces in the middle and upper crust.

California Faults Unleash Week of Turmoil

California Faults Unleash Week of Turmoil

Stress orientation profile to 3.5 km depth near the San Andreas Fault at Cajon Pass, California

A detailed profile of the orientation of the apparent maximum horizontal compressive stress was constructed over the depth interval 1.75–3.46 km in the Cajon Pass drill hole, located 4.2 km from the San Andreas fault in southern California. The profile is based on the analysis of stress‐induced well bore breakouts and consists of 32,616 orientation determinations at a basic sampling interval of ∼4 cm. The azimuth of the apparent maximum horizontal compressive stress around the borehole is 057° (s.d. = 19°). Depth‐dependent variations in breakout azimuths, from a few degrees to as much as 100°, occur over depth intervals of several centimeters to hundreds of meters in the borehole, with wavelengths showing a self‐similar distribution over a range of depth intervals. The variations in breakout orientation at depth seem to reflect stress fluctuations associated with active faults penetrated by the drill hole. Assuming linear elastic behavior, perturbations in stress magnitude and orientation were computed for predrilling slip on these faults. Fault stress drops limited to the ambient shear stress (i.e., up to total stress drop), along with occasional, local extreme stress drops and geometrical complications, can explain the variations in breakout orientations in the drill hole. The penetrative stress inhomogeneity may suggest that the average orientation of borehole breakouts in Cajon Pass, which indicates left‐lateral shear on planes parallel to the San Andreas fault, may not be representative of the state of stress near the fault at depth in this region. Rather, the stress orientation profile indicates the superposition of numerous local stress perturbations on an average stress field which is characterized by an absence of appreciable right‐lateral shear on planes parallel to the San Andreas. Combining these observations with the highly variable stress state in shallow boreholes in the western Mojave Desert, it is suggested that the heterogeneous stress field in this region, representing a spectrum of seismic events, may extend over substantial distances across and along the San Andreas fault zone. If the average measured breakout orientation in Cajon Pass is representative of the state of stress near the San Andreas in this region, then substantial left‐lateral shear stress is resolved on planes parallel to the fault, in contradiction to the sense of its long‐term motion. We use an elastic dislocation model to compute the net stress change near the Cajon Pass drill site since just prior to the large 1812 earthquake, taking into account coseismic slip in major earthquakes and aseismic accumulation of slip on the San Andreas and San Jacinto faults. The model suggests that the net change in fault‐parallel shear stress during the current earthquake cycle in the Cajon Pass area is nearly negligible. The difference between the measured and computed results requires that additional left‐lateral shear stress be superimposed on a generally fault‐normal maximum horizontal compressive stress. The results suggest that during the great Fort Tejon earthquake of 1857, left‐lateral shear stress parallel to the San Andreas fault in the region of Cajon Pass may have played a role in terminating the southeastward extent of the rupture propagation.

The Effectiveness of Fault Zone Regulations in California

In 1990 a study was completed for the California Division of Mines and Geology on the effectiveness of California's fault zone regulations (the Alquist-Priolo Special Studies Zones Act and associated policies and activities). The Act, passed in 1972, instituted the following elements of a statewide mandatory approach to dealing with the hazard of surface fault rupture: state mapping of fault zones (Special Study Zones) where active faults are suspected; local government imposition of the requirement of a geologic study on new building projects within these Zones (with some single family dwellings and low-occupancy structures exempt); review procedures for the studies submitted by an applicant's geologist; prohibition of the siting of projects on active faults; notification of real estate purchasers that a property is located within a Zone. This paper presents the results of that evaluation and comments more broadly on applying the Alquist-Priolo model to other regions and to other geologic hazards.

How wide is the Calaveras fault zone—Evidence for distributed shear along a major fault in central California

Research Article| January 01, 1992 How wide is the Calaveras fault zone—Evidence for distributed shear along a major fault in central California David R. Montgomery; David R. Montgomery 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar David L. Jones David L. Jones 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar Author and Article Information David R. Montgomery 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 David L. Jones 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1992) 20 (1): 55–58. https://doi.org/10.1130/0091-7613(1992)020<0055:HWITCF>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David R. Montgomery, David L. Jones; How wide is the Calaveras fault zone—Evidence for distributed shear along a major fault in central California. Geology 1992;; 20 (1): 55–58. doi: https://doi.org/10.1130/0091-7613(1992)020<0055:HWITCF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract High-angle and reverse faults offset Pleistocene and Holocene deposits across a zone several kilometres wide east of the Calaveras fault near Sunol, California. Alignment of recent epicenters with these and other fault traces suggests that a band of contemporary deformation roughly parallels the Calaveras fault. These exposures provide evidence that active deformation associated with this major transverse fault is distributed over a broad zone. This complex pattern of faulting suggests that other faults throughout central California may be more active than is recognized in seismic hazard assessments. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Comparative geometry of the San Andreas fault, California, and laboratory fault zones

Comparative geometry of the San Andreas fault, California, and laboratory fault zones

Changes in static stress on southern California faults after the 1992 Landers earthquake

THE magnitude 7.5 Landers earthquake of 28 June 1992 was the largest earthquake to strike California in 40 years. The slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults; these changes in stress should in turn affect the likelihood of future earthquakes. Stress changes that load faults towards failure have been cited as the cause of small1–5, moderate6 and large7 earthquakes; conversely, those that relax neighbouring faults have been related to a decrease in seismicity5. Here we use an elastic half-space model8 to estimate the stress changes produced by the Landers earthquake on selected southern California faults, including the San Andreas. We find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4.5, and that the largest changes (1–10 bar), occurring on part of the San Bernardino segment of the San Andreas fault, may have decreased the time to the next magnitude 8 earthquake by about 14 years.

A rheologically layered three‐dimensional model of the San Andreas Fault in central and southern California

Three‐dimensional kinematic finite element models of the San Andreas fault in central and southern California have been used to estimate the effects of rheological parameters and fault slip distribution on the horizontal and vertical deformation in the vicinity of the fault. The models include the effects of vertically layered power law viscoelastic rheology, and isostatic forces are considered in calculations of vertical uplift. Several different rheological layering schemes are used, using laboratory results on rock rheology to define the properties of the various layers. The depth to which the fault remains locked between earthquakes (D) is held constant at 20 km for the entire locked portion of the fault between Cholame and the Salton Sea. Between Hollister and Cholame the entire fault is assumed to slip at a rate consistent with a relative plate velocity of 35 mm/yr along a direction striking N41°W. Steady aseismic slip corresponding to plate velocity is imposed below the fault locking depth to a depth H on the locked section of the fault. The depth to which aseismic slip occurs (H) is assigned a value of either 20 km or 40 km, resulting in two versions of each rheological model. Variations in the model parameters are found to produce distinctive deformation patterns, providing a means for differentiating between models. Specifically, lower effective viscosities near the surface result in increased strain rates and uplift rates at all times during the earthquake cycle. Lower effective viscosities also produce subsidence near the creeping portion of the fault. Models that do not include aseismic slip below the fault locking depth (H = 20 km) display greater time dependence in both horizontal and vertical deformation than those including aseismic slip below the locking depth (H = 40 km). These differences are due, in part, to the time‐invariant nature of the imposed slip condition. The differences are more pronounced as the effective viscosity close to the surface is increased. The vertical uplift rate is particularly sensitive to the depth of aseismic slip (H) at the two bends in the fault, especially for models with high effective viscosities below the surface. For models in which the effective viscosity near the surface is relatively low, measurements of total uplift at the two bends in the fault could provide sufficient resolution to distinguish between models with and without aseismic slip over time periods of 10 to 20 years or more with current abilities to measure vertical uplift. Among our San Andreas fault models, the one most consistent with current strain rate data includes aseismic slip between 20 and 40 km (H = 40 km) and uses assumed rheological properties from the surface to 100 km depth consistent with laboratory results for wet rock samples. The rheological parameters for this model are based on laboratory results for the following rock types wet granite in the upper crust (0 to 20 km), wet diabase in the lower crust (20 to 40 km), wet dunite in the upper mantle (40 to 100 km), and dry olivine below 100 km. These modeling results are preliminary, however, and several additional factors should be considered prior to constructing a comprehensive model. Furthermore, it should be emphasized that the present models represent a small subset of possible rheological models, and numerous other models may provide similar or better fits to the data. The field of possible models will continue to narrow with further knowledge of the variations in Earth composition and temperature with depth, with more information on rock rheology, and with further observations of the earthquake cycle.

The Duparquet Formation: sedimentation in a late Archean successor basin, Abitibi greenstone belt, Quebec, Canada

In the south-central part of the Abitibi greenstone belt, a succession of Archean epiclastic sediments at least 2 km thick was deposited in the Duparquet Basin. The Destor–Porcupine fault and a secondary fault that splays off the major fault define the margins of this basin, which is at least 15 km long and up to 2.5 km wide. Sedimentary evidence of tectonic influence includes (i) rapid vertical and lateral facies changes over tens of metres; (ii) cyclic repetition of facies associations; (iii) mixed fining-upward – coarsening-upward – fining-upward sequences in conglomerate units; (iv) local derivation of most clasts; and (v) asymmetric distribution of fan deltas and braid deltas along the strike of the fault-bounded basin. Three basic facies associations are recognized: (i) conglomerate–sandstone facies association (CSFA); (ii) sandstone–argillite facies association (SAFA); and (iii) argillite–sandstone facies association (ASFA). The CSFA, which predominates at the faulted basin margins, constitutes 60–70% of the basin sediments. It exhibits salient features of streamflow-dominated fans or fan deltas, proximal braid deltas, and (or) coarse clastic braidplains. Large angular clasts of local derivation near the basin margins reflect limited distances of transport, supporting the alluvial fan – fan delta interpretation. The SAFA is assigned to a subaerial to subaqueous fan delta – braid delta setting, in part deposited during episodic storms and floods. The ASFA for the most part records sedimentation in a calm aqueous environment in which suspension deposition prevailed; a lacustrine setting is inferred, but incised conglomerates and channel-fill sandstones attest to sporadic floods and (or) storms. The CSFA in places occupies channels in the ASFA, suggesting progradation of alluvial fans into shallow water in response to source-area uplift. Modern analogues of the Duparquet Basin occur at convergent plate margins. Because it developed during a late orogenic stage, the Duparquet Basin may be classified as a successor basin. Sedimentary facies organization and basin configuration are similar to successor basins of the Cordillera of western Canada, as well as pull-apart basins adjacent to the San Andreas fault in California and the East Anatolian fault in Turkey.

Introduction to Special Section on the California‐Arizona Crustal Transect: CACTIS, Part 3

The CACTIS (California‐Arizona Crustal Transect Interim Synthesis) workshop in May 1988 brought researchers together in Flagstaff, Arizona, to discuss the geologic evolution and crustal structure of the southern Cordillera between the San Andreas fault in southeastern California and the Colorado Plateau in Arizona [Sass et al., 1988]. The first set of papers resulting from the workshop appeared in the Journal of Geophysical Research (JGR) as the special CACTIS 1 section in January 1990 [Howard et al., 1990], and a second as CACTIS 2 in November 1990 [Haxel et al., 1990]. Twelve papers in this issue form part 3 of the CACTIS series. A final collection of papers will appear in the future as a joint special section with the California Consortium for Crustal Studies (CALCRUST).

Pipeline Response to Loma Prieta Earthquake

A field experiment to investigate the response of buried pipelines to lateral offsets and to traveling wave effects is currently being operated at a test site on a trace of the San Andreas Fault in central California. The experiment is located near Parkfield, California, where the U.S. Geological Survey has predicted the recurrence of a moderate earthquake within the next few years. The goal of the experiment is to develop data that can be used to qualify design and analysis methods for pipelines in seismically active areas. Welded steel and ductile iron pipeline segments are buried and instrumented adjacent to an array of survey monuments and strong motion seismographs. Although the predicted moderate earthquake on the Parkfield‐Cholame segment of the San Andreas Fault has not yet occurred, data obtained during low‐intensity shaking from the surface wave phase of the October 1989 Loma Prieta earthquake yields valuable insight into pipeline response. Close correlation is found between ground strains induc...

Slip line model for southern California crustal kinematics

We propose a simple slip line model to explain the faulting and seismicity patterns of southern California. We assume the Sierra Nevada–Great Valley (SNGV) block to be rigid, in view of its low seismicity, and other regions to undergo plastic deformation. From this point of view, the complex deformation patterns observed in southern California, including the Borderland region, result from the “plowing” of the eastern margin of the Pacific plate by the nondeforming SNGV block. A simple analogy can then be made between regional tectonics in southern California and two‐dimensional flow solutions obtained in metallurgy for the extrusion of rigid‐plastic metals. We use a simplified geometry based on the geology and seismicity of southern California to calculate a two‐dimensional slip line field which predicts the shape of the San Andreas fault near the “big bend” surprisingly well. The largely aseismic, high‐topography western Mojave can then be interpreted as an analogue to the nondeforming “dead metal” zone which arises for certain metal extrusion geometries. The slip field agrees quite well with the strikes and slip orientation of major dextral faults in southern California, including the San Jacinto, Elsinore, and Newport‐Inglewood faults. It also predicts correctly the strikes and slip orientation of sinistral “cross faults” found in some areas of the region. In the Transverse Ranges, where thrust faulting dominates, the slip lines are no longer potential fault planes, but a simple argument predicts that they should lie at 45° on the strikes of thrust faults, in fair agreement with the observations.

The velocity field along the San Andreas Fault in central and southern California

The velocity field within a 100‐km‐broad zone centered on the San Andreas fault between the Mexican border and San Francisco Bay has been inferred from repeated surveys of trilateration networks in the 1973–1989 interval. The velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the San Andreas fault in the Transverse Ranges of southern California. Across‐strike profiles of the fault‐parallel component of velocity exhibit the expected sigmoidal shape, whereas across‐strike profiles of the fault‐normal component of velocity are flat and featureless. No significant convergence upon the fault is observed even along the big bend sector of the fault. Simple dislocation models can explain most of the features of the observed velocity field, but those explanations are not unique. About 35 mm/yr of relative plate motion is accounted for within the span of the trilateration networks. Geologic studies indicate that the secular slip rate on the San Andreas fault is about 35 mm/yr. The agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes. The relative motion observed across the San Andreas fault (35 mm/yr) plus that observed across the Eastern California shear zone (8 mm/yr) accounts for most (43 mm/yr) of the observed North America‐Pacific relative plate motion (47 mm/yr).

Kinematics of compressional fold development in convergent wrench terranes

Kinematic models are presented for compressional fold development in wrench and convergent wrench terranes that relate fold shortening, axial rotation, and axial extension. Fold shortening may be derived from final fold geometry. Existing fold geometry and axial orientation, two readily measurable quantities, provide the data needed to determine the relative components of shearing and convergence within the fold system. Analyses utilizing these kinematic models indicate that folds developed in sedimentary rocks in the wrench borderlands of both the Rineonada and San Andreas wrench faults in central California are the product of strongly convergent wrenching. The axes of these folds have been rotated no more than a few degrees during the course of their development. In contrast, folds developed in the Alpine Schists along the Alpine fault in New Zealand and in Pleistocene sediments along the southern limit of the San Andreas fault suggest an almost pure wrench setting and large (>25 °) axial rotations. Significant axial extension is inherent in wrench-related compressional folds. This axial extension is commonly manifest in the form of normal and strike-slip faults that are internal to the folds and trend at high angles to the fold axes. The relative amount of axial extension diminishes as the degree of convergence increases. This axial extension, and the associated extensional features, can be a diagnostic indication of the influence of wrenching.

Earthquake depths and the relation to strain accumulation and stress near strike-slip faults in southern California : Sanders, C O J Geophys ResV95, NB4, April 1990, P4751–4762

Earthquake depths and the relation to strain accumulation and stress near strike-slip faults in southern California : Sanders, C O J Geophys ResV95, NB4, April 1990, P4751–4762

Fault orientations in extensional and conjugate strike-slip environments and their implications

Seismically active conjugate strike-slip faults in California and Japan typically have mutually orthogonal right- and left-lateral fault planes. Normal- fault dips at earthquake nucleation depths are concentrated between 40° and 50°. The observed orientations and their strong clustering are surprising, because conventional faulting theory suggests fault initiation with conjugate 60° and 120° intersecting planes and 60° normal-fault dip or fault reactivation with a broad range of permitted orientations. The observations place new constraints on the mechanics of fault initiation, rotation, and evolutionary development. We speculate that the data could be explained by fault rotation into the observed orientations and deactivation for greater rotation or by formation of localized shear zones beneath the brittle-ductile transition in Earth9s crust. Initiation as weak frictional faults seems unlikely.

Observations and implications of water well and creepmeter anomalies in the Mojave segment of the San Andreas fault zone

Four years of continuous water level data from a 1,900 m deep well near the San Andreas fault in southern California show a 21-month period of unusual rapid fluctuations. The anomalous water level activity ceases with the occurrence of the 8 July 1986, ML = 5.6 North Palm Springs earthquake on the San Andreas fault, approximately 120 km southeast of the well site. The water level data correlate with signals from two San Andreas fault zone strain sensors. The long-term water level variations are similar in shape to those recorded by a borehole dilatometer 30 km from the well site, while the rapid water level fluctuations correlate in time with anomalies in the record of a fault zone creepmeter located 35 km from the water level monitor. The observations are interpreted in terms of strain occurring in a horizontally and vertically heterogeneous crust. Tectonic deformation is concentrated along weak block-bounding fault zones. The blocks are sufficiently rigid to generate correlated displacement phenomena along their weak boundaries. As a consequence, fault zone strain events can be related over large distances as in the case of the North Palm Springs earthquake and the coincident creep and water level anomalies. The observed creep and water level events occur in a weak aseismic shallow (<3 km) material overlying stronger asperities along which the fault is locked and regional strain loading occurs. Local failure of the fault within the weak shallow material has no far-field effects and is not important in the crustal stress budget, but may signal accelerated strain accumulation at depth. In this context, the reported observations demonstrate the possibility of joint detection of fault zone anomalies that relate to, and possibly anticipate, major tectonic strain events on large faults.

Evidence for chaotic fault interactions in the seismicity of the San Andreas fault and Nankai trough

INTERACTIONS between fault segments are one of the main sources of complexity in the seismicity of active tectonic regions. Such interactions are likely to influence the spatial and temporal patterns of earthquakes. Here we examine the dynamical behaviour introduced by fault interactions using a simple spring-loaded, slider-block model with velocity-weakening friction. The model consists of two slider blocks coupled to each other and to a constant-velocity driver by elastic springs. For an asymmetric system in which the frictional forces on the two blocks are not equal, the solutions exhibit chaotic behaviour. The system's behaviour over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault. We see similarities between our model simulations and observed patterns of seismicity on the south central San Andreas fault in California and in the Nankai trough along the coast of southwestern Japan.

Pacific–North American Plate Motion from very long baseline interferometry compared with motion inferred from magnetic anomalies, transform faults, and earthquake slip vectors

We use geodetic measurements from very long baseline interferometry (VLBI) to test whether the Pacific‐North American plate velocity averaged over several years (1984–1987) of direct observation equals that averaged over millions of years as inferred from other data. We furthermore test whether the Pacific‐North America velocity estimated from VLBI parallels the San Andreas fault, transform faults and earthquake slip vectors in the Gulf of California, and earthquake slip vectors along the Queen Charlotte fault, along the Alaskan peninsula, and along the Kamchatkan peninsula. We assume that VLBI sites at Fairbanks (Alaska), Fort Davis (Texas), Richmond (Florida), Westford (Massachusetts), and Platteville (Colorado) lie on the North American plate and that VLBI sites on the Hawaiian island of Kauai, on the Marshall island of Kwajalein, and at Vandenberg Air Force Base (California) lie on the Pacific plate. The Euler vector (0.806°/m.y. about 47.5°N, 79.9°W) that we estimate from VLBI is well constrained; its three‐dimensional 95% confidence ellipsoid axes are only 5–15% as long as the Euler vector itself. The VLBI Euler vector is nearly identical to the Pacific‐North America Euler vector of plate motion model NUVEL‐1, which is determined from transform fault azimuths, earthquake slip vectors, and spreading rates from marine magnetic anomalies that integrate motions since 3 Ma. The VLBI Euler vector has a rotation rate only 0.023°/m.y. faster than that of NUVEL‐1, and the VLBI Euler pole lies only 2° from that of NUVEL‐1. The VLBI Euler vector predicts that Pacific‐North America motion is on average 10°±4° clockwise of earthquake slip vectors along the Queen Charlotte fault, suggesting that these slip vectors are biased measures of the direction of relative plate motion. The VLBI Euler vector predicts that Pacific‐North America motion is 6°±4° clockwise of the San Andreas fault in central California, reinforcing the conclusion from plate motion models that the San Andreas fault does not parallel Pacific‐North American plate motion. The VLBI Euler vector predicts that Pacific‐North America motion is parallel to most transform faults and earthquake slip vectors in the Gulf of California and to most earthquake slip vectors along the Alaskan and Kamchatkan peninsulas. The Pacific‐North America velocity averaged over several years equals its velocity averaged over millions of years with the difference along the mutual boundary nowhere exceeding 4±7 mm/yr. Therefore the motions between the Pacific and North American plates appear to be steady. Moreover, our results imply that one can combine rates averaged over intervals as long as millions of years with rates averaged over intervals as short as a few years when constructing models of lithosphere kinematics.