Pacific-North America Plate Motion Research Articles

Review of Geodetic and Geologic Deformation Models for 2023 U.S. National Seismic Hazard Model

ABSTRACT We review five deformation models generated for the 2023 update to the U.S. National Seismic Hazard Model (NSHM), which provide input fault-slip rates that drive the rate of earthquake moment release. Four of the deformation models use the Global Positioning System-derived surface velocity field and geologic slip-rate data to derive slip-rate estimates (Evans, Pollitz, Shen-Bird, and Zeng), and one model uses geologic data (the “geologic model”). The correlation between the geologic model preferred slip rates and geodetically derived slip rates is high for the Pollitz, Zeng, and Shen-Bird models, and the median of all slip-rate models has correlation coefficient of 0.88. The median geodetic model slip rates are systematically lower than the preferred geologic model rates for faults with slip rates exceeding 10 mm/yr and systematically higher on faults with slip rates less than 0.1 mm/yr. Geodetically derived slip rates tend to the low end of the geologic model range along sections of the San Andreas fault and the Garlock fault, whereas they tend to be higher across north coast California faults. The total on-fault moment rates agree well across models with all rates within 18% of the median. Estimated off-fault strain rate orientations and styles vary considerably across models and off-fault moment rates vary more than on-fault moment rates. Path integrals across the western U.S. accounting for fault-slip rate and off-fault deformation are generally consistent with Pacific-North America plate motion with the median deformation rates recovering about 98% of the plate motion with about 20% of the total plate motion accommodated by off-fault strain rate. The geologic model, which has no off-fault deformation, accounts for about 82% of plate motion with fault slip. Finally, we make a recommendation for relative weighting of the models for the NSHM as well as several recommendations for future NSHM deformation model development.

Geodynamic evolution of southwestern North America since the Late Eocene

Slab rollback, lithospheric body forces, or evolution of plate boundary conditions are strongly debated as possible lithospheric driving mechanisms for Cenozoic extension in southwestern North America. By incorporating paleo-topography, lithospheric structure, and paleo-boundary conditions, we develop a complete geodynamic model that quantifies lithospheric deviatoric stresses and predicts extension and shear history since Late Eocene. We show that lithospheric body forces together with influence of change-over from subduction to transtensional boundary conditions from Late Eocene to Early Miocene were the primary driving factors controlling direction and magnitude of extensional deviatoric stresses that produced topographic collapse. After paleo-highlands collapsed, influence of Pacific-North America plate motion and associated deformation style along the plate boundary became increasingly important from Middle Miocene to present. Smaller-scale convection stress effects from slab rollback and associated mantle flow played only a minor role. However, slab rollback guided deformation rate through introduction of melts and fluids that impacted rheology.

A kinematic model for the evolution of the Eastern California Shear Zone and Garlock Fault, Mojave Desert, California

The Eastern California shear zone in the Mojave Desert, California, accommodates nearly a quarter of Pacific–North America plate motion. In south-central Mojave, the shear zone consists of six active faults, with the central Calico fault having the fastest slip rate. However, faults to the east of the Calico fault have larger total offsets. We explain this pattern of slip rate and total offset with a model involving a crustal block (the Mojave Block) that migrates eastward relative to a shear zone at depth whose position and orientation is fixed by the Coachella segment of the San Andreas fault (SAF), southwest of the transpressive “big bend” in the SAF. Both the shear zone and the Garlock fault are assumed to be a direct result of this restraining bend, and consequent strain redistribution. The model explains several aspects of local and regional tectonics, may apply to other transpressive continental plate boundary zones, and may improve seismic hazard estimates in these zones.

A bottom-driven mechanism for distributed faulting in the Gulf of California rift

Observations of active faulting in the continent-ocean transition of the Northern Gulf of California show multiple oblique-slip faults distributed in a 200×70km2 area developed some time after a westward relocation of the plate boundary at ~2Ma. In contrast, north and south of this broad pull-apart structure, major transform faults accommodate Pacific-North America plate motion. Here we propose that the mechanism for distributed brittle deformation results from the boundary conditions present in the Northern Gulf, where basal shear is distributed between the Cerro Prieto strike-slip fault (southernmost fault of the San Andreas fault system) and the Ballenas Transform Fault. We hypothesize that in oblique-extensional settings whether deformation is partitioned in a few dip-slip and strike-slip faults, or in numerous oblique-slip faults may depend on (1) bottom-driven, distributed extension and shear deformation of the lower crust or upper mantle, and (2) the rift obliquity. To test this idea, we explore the effects of bottom-driven shear on the deformation of a brittle elastic-plastic layer with the help of pseudo-three dimensional numerical models that include side forces. Strain localization results when the basal shear abruptly increases in a step-function manner while oblique-slip on numerous faults dominates when basal shear is distributed. We further explore how the style of faulting varies with obliquity and demonstrate that the style of delocalized faulting observed in the Northern Gulf of California is reproduced in models with an obliquity of 0.7 and distributed basal shear boundary conditions, consistent with the interpreted obliquity and boundary conditions of the study area.

High-resolution reconstructions of Pacific–North America plate motion: 20 Ma to present

High-resolution reconstructions of Pacific–North America plate motion: 20 Ma to present

Pacific plate deformation from horizontal thermal contraction

The central approximation of plate tectonics is that the plates are rigid, which gives the theory its rigor and predictive power. Space geodetic measurements are consistent with the rigidity of stable plate interiors, but some failures of plate-circuit closure, in particular of oceanic plates, indicate that plates may be measurably non-rigid. We explore the hypothesis that horizontal thermal contraction causes deformation of oceanic plates. Here we show significant expected displacement fields due to thermal contraction for the Pacific plate based on a previously proposed relationship between seafloor age and strain rate and on two end-member assumptions on how strain compatibility is enforced. The predicted maxi- mum 2.2 mm/yr southeastward motion of the northeastern part of the plate relative to the Pacific-Antarctic Rise may contribute to a large part of the non-closure of the Pacific-North America plate motion circuit. Our predicted displacement rates cannot (yet) be confirmed by current space geodetic data and will require seafloor geodesy with 1 mm/yr accuracy. The spatial distribution of predicted moment rate agrees reasonably well with that of intraplate earthquake epicenters, similar to what is observed for plate boundary zones. Our results suggest that plate-scale horizontal thermal contraction is significant, and that it may be partly released seismically.

Initiation of the Southern Elsinore Fault at ∼1.2 Ma: Evidence from the Fish Creek–Vallecito Basin, southern California

Strike‐slip faults west of the San Andreas fault (SAF) accommodate more than half of the modern Pacific–North America plate motion in southern California, yet their age, kinematic evolution and long‐term slip rates are incompletely understood. The southern Elsinore fault is part of this zone and occupies the boundary between Mesozoic crystalline rocks of the Peninsular Ranges and Late Cenozoic sedimentary rocks of the Salton Trough depocenter. The Fish Creek–Vallecito Basin, a recently inverted western sub‐basin of the Salton Trough, contains a thick succession of Plio‐Pleistocene sedimentary rocks that preserve a record of crustal subsidence and uplift in response to evolving tectonic controls. Deposits older than ∼1.2 Ma accumulated during transtension and subsidence in the hanging wall of the low‐angle West Salton detachment fault. A fanning‐dip interval high in the section, dated at 1.2–1.0 Ma, accumulated during tilting caused by earliest motion on the Elsinore and Earthquake Valley faults. Total offset of 1–2 km yields a lifetime slip rate of about 1–2 mm/yr for the southern Elsinore fault, similar to a late Pleistocene rate in the Coyote Mountains but slower than published estimates for the northern Elsinore fault. This difference likely results from long‐term transfer of slip from the northern Elsinore fault to the San Felipe and San Jacinto fault zones farther east. Initiation of the Elsinore fault at 1.2 Ma coincides with a major tectonic reorganization that terminated slip on the detachment fault and formed the modern network of strike‐slip faults west of the SAF.

The 2010 M w 7.2 El Mayor-Cucapah Earthquake Sequence, Baja California, Mexico and Southernmost California, USA: Active Seismotectonics along the Mexican Pacific Margin

The El Mayor-Cucapah earthquake sequence started with a few foreshocks in March 2010, and a second sequence of 15 foreshocks of M > 2 (up to M4.4) that occurred during the 24 h preceding the mainshock. The foreshocks occurred along a north–south trend near the mainshock epicenter. The Mw 7.2 mainshock on April 4 exhibited complex faulting, possibly starting with a ~M6 normal faulting event, followed ~15 s later by the main event, which included simultaneous normal and right-lateral strike-slip faulting. The aftershock zone extends for 120 km from the south end of the Elsinore fault zone north of the US–Mexico border almost to the northern tip of the Gulf of California. The waveform-relocated aftershocks form two abutting clusters, each about 50 km long, as well as a 10 km north–south aftershock zone just north of the epicenter of the mainshock. Even though the Baja California data are included, the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border. The spatial distribution of large aftershocks is asymmetric with five M5+ aftershocks located to the south of the mainshock, and only one M5.7 aftershock, but numerous smaller aftershocks to the north. Further, the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes. Thus, the aftershocks also express a complex pattern of stress release along strike. The overall rate of decay of the aftershocks is similar to the rate of decay of a generic California aftershock sequence. In addition, some triggered seismicity was recorded along the Elsinore and San Jacinto faults to the north, but significant northward migration of aftershocks has not occurred. The synthesis of the El Mayor-Cucapah sequence reveals transtensional regional tectonics, including the westward growth of the Mexicali Valley and the transfer of Pacific–North America plate motion from the Gulf of California in the south into the southernmost San Andreas fault system to the north. We propose that the location of the 2010 El Mayor-Cucapah, as well as the 1992 Landers and 1999 Hector Mine earthquakes, may have been controlled by the bends in the plate boundary.

Geologically current plate motions

We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit—MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6–2.6 mm yr−1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca–Antarctic and Nazca–Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also indicates that motions across the Caribbean–North America and Caribbean–South America plate boundaries are twice as fast as given by NUVEL-1A. Summed, least-squares differences between angular velocities estimated from GPS and those for MORVEL, NUVEL-1 and NUVEL-1A are, respectively, 260 per cent larger for NUVEL-1 and 50 per cent larger for NUVEL-1A than for MORVEL, suggesting that MORVEL more accurately describes historically current plate motions. Significant differences between geological and GPS estimates of Nazca plate motion and Arabia–Eurasia and India–Eurasia motion are reduced but not eliminated when using MORVEL instead of NUVEL-1A, possibly indicating that changes have occurred in those plate motions since 3.16 Ma. The MORVEL and GPS estimates of Pacific–North America plate motion in western North America differ by only 2.6 ± 1.7 mm yr−1, ≈25 per cent smaller than for NUVEL-1A. The remaining difference for this plate pair, assuming there are no unrecognized systematic errors and no measurable change in Pacific–North America motion over the past 1–3 Myr, indicates deformation of one or more plates in the global circuit. Tests for closure of six three-plate circuits indicate that two, Pacific–Cocos–Nazca and Sur–Nubia–Antarctic, fail closure, with respective linear velocities of non-closure of 14 ± 5 and 3 ± 1 mm yr−1 (95 per cent confidence limits) at their triple junctions. We conclude that the rigid plate approximation continues to be tremendously useful, but—absent any unrecognized systematic errors—the plates deform measurably, possibly by thermal contraction and wide plate boundaries with deformation rates near or beneath the level of noise in plate kinematic data.

Quantifying Dextral Shear on the Bristol-Granite Mountains Fault Zone: Successful Geologic Prediction from Kinematic Compatibility of the Eastern California Shear Zone

AbstractFor regional kinematic compatibility to be a valid boundary condition for continental tectonic reconstructions, there must be tests that validate or invalidate kinematic model predictions. In several reconstructions of western North America, the displacement history of the Mojave block continues to be unresolved. The magnitude of displacement along the Bristol-Granite mountains fault zone (BGMFZ), which is the eastern margin of the Eastern California Shear Zone (ECSZ) in the Mojave block, is a key example of a long-standing kinematic prediction that has defied a positive field test until now. The ECSZ is a network of late Neogene and Quaternary right-lateral strike-slip faults that extend from the Gulf of California north through the Mojave Desert, linking Pacific–North America plate motion with Basin and Range extension. This network of faults accounts for ∼15% of post-16-Ma plate transform motion. Geologic estimates of net dextral offset along the Mojave portion of the ECSZ (53 ± 6 km) are appro...

Pacific–North America plate motion and opening of the Upper Delfín basin, northern Gulf of California, Mexico

Correlation of conjugate rifted margins of the Upper Delfin basin constrains the timing and amount of transtensional opening along the Pacific–North America plate boundary in the northern Gulf of California. Lithologic, geochemical, paleomagnetic, and geochronologic data from a set of four ignimbrites, consisting of eight distinctive cooling units, are shown to correlate from northeastern Baja California to Isla Tiburon and adjacent areas of western Sonora. These matching ignimbrites are the ca. 12.6 Ma tuff of San Felipe, the 6.3 ± 0.2 Ma tuffs of Mesa Cuadrada (Tmr3 and Tmr4), the tuffs of Dead Battery Canyon (Tmr5), and the 6.1 ± 0.5 Ma tuffs of Arroyo El Canelo. Offset distributions and facies patterns of these ignimbrites support 255 ± 10 km of opening between conjugate rifted margins of the Upper Delfin basin. Addition of deformation from the continental margins of this basin indicates at least 276 ± 13 km of Pacific–North America plate motion between coastal Sonora and the main gulf escarpment in Baja California since ca. 6 Ma; a further 20 ± 10 km of northwestward displacement of Isla Tiburon relative to coastal Sonora occurred sometime after 12.6 Ma. These reconstructions agree with earlier estimates of slip across the Gulf of California and on the San Andreas fault system of southern California, but require that the Pacific–North America plate boundary became localized in the gulf at ca. 6 Ma. The restored continental margins of the Upper Delfin basin show that only a 20–25 km width of upper continental crust has foundered beneath this part of the northern Gulf of California. This result suggests that most of the crustal area formed by opening of the Upper Delfin basin was either exhumed from lower-crustal levels or is new transitional oceanic crust.

Rapid localization of Pacific–North America plate motion in the Gulf of California

Research Article| May 01, 2001 Rapid localization of Pacific–North America plate motion in the Gulf of California Michael Oskin; Michael Oskin 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Search for other works by this author on: GSW Google Scholar Joann Stock; Joann Stock 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Search for other works by this author on: GSW Google Scholar Arturo Martín-Barajas Arturo Martín-Barajas 2Centro de Investigación Científica y Educación Superior de Ensenada, Km 107 Carretera Tijuana- Ensenada, Baja California, Mexico Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (5): 459–462. https://doi.org/10.1130/0091-7613(2001)029<0459:RLOPNA>2.0.CO;2 Article history received: 17 Aug 2000 rev-recd: 22 Jan 2001 accepted: 29 Jan 2001 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Michael Oskin, Joann Stock, Arturo Martín-Barajas; Rapid localization of Pacific–North America plate motion in the Gulf of California. Geology 2001;; 29 (5): 459–462. doi: https://doi.org/10.1130/0091-7613(2001)029<0459:RLOPNA>2.0.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 Correlation of late Miocene volcaniclastic strata across the northern Gulf of California shows that the Pacific–North America plate boundary localized east of the Baja California peninsula ca. 6 Ma. Dextral offset of the 12.6 Ma Tuff of San Felipe and a pair of overlying ca. 6.3 Ma pyroclastic flows indicate at least 255 ± 10 km of displacement along an azimuth of 310°. Isopach and facies trends of the Tuff of San Felipe support no more than a few tens of kilometers of additional dextral displacement between 12.6 and 6.3 Ma. These constraints indicate that nearly all of the dextral displacement between the Pacific and North American plates prior to 6.3 Ma was accommodated outside of the gulf region, and by 4.7 Ma, the plate boundary motion was localized in the Gulf of California. Although continental extension has accounted for a component of plate boundary motion in northwestern Mexico since cessation of subduction offshore of southern Baja California at 12.5 Ma, transfer of Baja California to the Pacific plate was delayed by at least 6–7 m.y. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleoseismological evidence from lake sediments for recent movement on the Denali and other faults, Yukon Territory, Canada

Most of the Pacific–North America plate motion in northwestern Canada and southeastern Alaska occurs along coastal faults that are the inland extension of the Queen Charlotte dextral transform fault. More ancient faults farther east, such as the Denali and Duke River faults, exhibit moderate earthquake activity and may be accommodating part of the Pacific plate motion. Paleoseismological results based on seismic resuspension of lake sediments, covering a period of up to 3000 years, show that the seismicity on the Denali–Duke River fault system is remarkably recent, spanning just the last three to five centuries. There is a northerly-trending zone of seismicity from the active Fairweather–Contact fault system on the coast, across to the part of the Denali fault that is currently, as well as prehistorically, active. This partial transfer eastward of Pacific plate motion may be analogous to a similar proposed transfer of motion northward to the Denali fault from the same Fairweather–Contact fault system, farther west in Alaska.

Pacific-North America Plate Tectonics of the Neogene Southwestern United States: An Update

We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present (8 Ma to the present). No Pliocene changes in Pacific-North America plate motion are resolvable in these data, suggesting that Pliocene changes in deformation style along the boundary were not driven by changes in plate motion. However, the chron 4 change in Pacific-North America plate motion appears to correlate very closely to a change in direction of extension documented between the Sierra Nevada and the Colorado Plateau. Our best solution for the displacement with respect to stable North America of a point on the Pacific plate that is now near the Mendocino triple junction is that from 30 to 12 Ma the point was displaced along an azimuth of ∼N60°W at rate of ∼33 mm/yr; from 12 Ma to about 8 Ma the azimuth of displacement was about the same as previously, but the rate was faster (∼52 mm/yr); and since 8 Ma the point was displaced along an azimuth of N37°W at a rate of ∼52 mm/yr. We compare plate-circuit reconstructions of the edge of the Pacific plate to continental deformation reconstructions of North American tectonic elements across the Basin and Range province and elsewhere in order to evaluate the relationship of this deformation to the plate motions. The oceanic displacements correspond remarkably well to the continental reconstructions where deformations of the latter have been quantified along a path across the Colorado Plateau and central California. They also supply strong constraints for the deformation budgets of regions to the north and south, in Cascadia and northern Mexico, respectively. We examine slab-window formation and evolution in a detailed re-analysis of the spreading geometry of the post-Farallon microplates, from 28 to 19 Ma. Development of the slab window seems linked to early Miocene volcanism and deformation in the Mojave Desert, although detailed correlations await clarification of early Miocene reconstructions of the Tehachapi Mountains. We then trace the post-20 Ma motion of the Mendocino slab window edge beneath the Sierran-Great Valley block and find that it drifted steadily north, then stalled just north of Sutter Buttes at ∼4 Ma.

Cenozoic Tectonism in the Central Basin and Range: Motion of the Sierran-Great Valley Block

According to geologic reconstructions, the motion of the Sierran-Great Valley block with respect to the Colorado Plateau was mainly westerly at more than 20 mm/yr from 16 to 10 Ma, changing to northwest or NNW since 8 to 10 Ma, at an average rate of 15 mm/yr. These kinematics are consistent with two other independent methods of determining the position of the block since 20 Ma–reconstructions based on paleomagnetic data from range blocks that bound the Basin and Range on the west, and a revised history of Pacific-North America plate motion based on a global plate circuit (Atwater and Stock, 1998, this issue). The plate-tectonic reconstruction shows a change to more northerly motion between the Pacific and North American plates at ∼8 Ma, in concert with the motion of the Sierran-Great Valley block. Moreover, the northeast limit of extant oceanic crust (as indicated by the reconstruction of the continental geology) tracks closely with the southwest limit of extant continental crust (as indicated by the positions of oceanic plates) since 20 Ma. The coordination between plate motions and the intraplate geology suggests that plate-boundary forces strongly influenced deformation within the continent.

Current Sierra Nevada-North America motion from very long baseline interferometry:Implications for the kinematics of the western United States

We use geodetic measurements from very long baseline interferometry to estimate the motion of the Sierra Nevadan microplate, which is composed of the Sierra Nevada and the Great Valley. The motion of the Sierra Nevadan microplate relative to the North American plate is described by a right-handed rotation of 0.61°/m.y. about lat 32°N, long 128°W. This Euler pole lies only 10° southwest of the Sierra Nevadan microplate and predicts a significant counterclockwise rotation about a local vertical axis. It further predicts a velocity of the eastern edge of the Sierra Nevada (at 38.0°N, 119.3°W) relative to stable North America of 11 ±1 mm/yr toward N36° ±3°W (quoted uncertainties are plus or minus one standard error), which accounts for about one-fourth of the velocity between the Pacific and North American plates and is ∼25° clockwise of many prior estimates. The velocity nearly parallels the boundary between the Sierra Nevada and the Great Basin, which implies that current motion within the Great Basin results in a rotational, noncoaxial deformation. We use this velocity to estimate how motion is distributed across the broad deforming zone taking up Pacific-North America plate motion. We find that the vector sum of strike slip along the San Andreas fault and motion of the Sierra Nevada relative to stable North America (taken up by deformation within the Great Basin) differs little from the Pacific-North America plate velocity. The difference can be described at 36°N along the San Andreas fault by a vector of 6 mm/yr directed toward N20°W. This vector resolves into components of 5 mm/yr parallel to the fault and 2 mm/yr perpendicular to the fault with 95% confidence intervals of 0 to 10 mm/yr and -1 to +5 mm/yr, respectively. The component perpendicular to the fault is several times smaller than found in prior studies and places a small upper bound on fault-perpendicular shortening. We conclude that motion previously inferred to be taken up by deformation other than strike slip along the San Andreas fault or deformation within the Great Basin is much smaller than previously thought.