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We estimated the S-wave quality factor Q(f) of the upper crust in northeastern Sonora, Mexico, using a two-layer model. The first layer of the model has a thickness of 1 km, and the frequency dependence of Q can be represented by the relation Q(f) = 127f 0.7 in the frequency range of 0.5 ≤ f ≤ 20 Hz. The second layer varies in depth between 1 and 21 km, and Q(f) = 181f 0.7 in the same frequency range. The average Q of the model, weighted with the thickness of the layers, gives the relation Q(f) = 179.1f 0.7. We used nonparametric attenuation functions, determined in a previous study, to correct the observed spectral amplitudes, and then we retrieved source and site effects using a spectral inversion scheme. We used the resulting functions to separate source and site effects from the original spectral records and modeled Q for the 1-D model’s depths. We analyzed 38 local earthquakes recorded by 12 stations of the regional network RESNES (Red Sismica del Noreste de Sonora). We found that the S-wave Q of the superficial layer is a factor of only 1.4 smaller than the more profound layer. This result validates the use of an average Q to correct spectral amplitudes by the effect of anelastic attenuation from waves traveling within the upper crust.

In this study, we compiled reports from different catalogs and newspapers about the greatest earthquake documented in Northeastern Mexico. From these descriptions, we located the 28 April 1841 earthquake using the Bakun and Wentworth (1997) attenuation model for the Basin and Range region. From 13 observations with an intensity range of III–VII, we calculated a Mw 6.2 and the central intensity SW from Punta Santa Elena, Coahuila (24.65° N, 101.60° W). This earthquake could represent the fourth biggest event in the Mexican Basin and Range province after the events of Bavispe, Sonora, of 1887 (Mw 7.5), Parral, Chihuahua, of 1928 (Mw 6.5), and Valentine, Texas in the Texas-Chihuahua border, of 1931 (Mw 6.4). Finally, this study provides new insights on earthquake potential in the region to be considered for enhanced hazard quantification and shows that the region is seismically active and prone to events up to M > 6.

We estimated the seismic energy radiated by 47 earthquakes located near the faults that rupture during the 3 May 1887 Mw 7.5 Sonora earthquake in the Mexican Basin and Range Province. We retrieve source parameters from seismograms recorded by the local network RESNES (Red Sismica del Noreste de Sonora) that operated from 2003 to 2011, using a spectral inversion technique. We calculated the seismic energy by integrating the square velocity source spectrum of the earthquakes analyzed. We found that events with high-scaled seismic energy (Es/Mo) are located at the southern end of the fault that rupture in 1887, between the stepovers of the fault segments Teras and Otates. It is likely that tectonic stress accumulated in that zone after the fault ruptured. We estimate an average log(Es/Mo) = − 5.76 and found that most earthquakes analyzed have low apparent stress, varying between 0.5 × 10−3 and 1.85 MPa, with an average value of 0.0521 MPa. The apparent stress is heterogeneous not showing a clear correlation with seismic moment or focal depth.

Extension orientation is a key parameter in rift tectonics. While a clockwise rotation of the extension orientation is widely accepted for the southern Rio Grande rift and the Basin and Range province in the western U.S., in which direction(s) the northern Rio Grande rift opened has been controversial. Moreover, slip re-orientation, a phenomenon caused by local stress rotation on weak faults under a uni-directional regional extension, imposes a serious impact on kinematic interpretations. We investigate the presently oblique Tusas-Abiquiu segment of the Rio Grande rift in north-central New Mexico to assess the rifting kinematics with the presence of pre-existing crustal weaknesses. Fault-slip data show an overall NE-SW extension on the NW-trending Tusas border faults, and WNW-ESE extension on the NNE-trending Abiquiu border and internal faults. The slip vectors on the border faults show a wide variety of oblique-slip component, whereas those on the internal faults are predominantly pure dip-slip. The majority of our field measurements can be reproduced by the slip re-orientation model, although this model's setting does not satisfy regional geological records. Clockwise rotation of the extension axes from NE-SW to WNW-ESE can also explain our fault-slip data, as well as other structures in the rift. Tectonic reactivation during the extension also influenced the landscape evolution of the early rift. The Rio Grande rift shared similar extension orientation with the southern Basin and Range during the late Oligocene. The extensional strain field of the southwestern North American plate shows a progressive, time-transgressive rotational pattern, implying that plate boundary processes, instead of asthenospheric upwelling, governed the initiation and early evolution of this intracontinental rift.

The Salt River and Verde River watersheds provide downstream metropolitan Phoenix, Arizona, USA with much of its water supply, and this paper explains how these rivers integrated in an extensional tectonic setting. Near the end of the Pliocene, segments of the proto-Salt and proto-Verde watersheds of central Arizona consisted of local drainage networks supplying water and sediment into internally drained basins, including depressions occupied by late Pliocene natural lakes occupying the Verde Valley and Tonto basins. A key location, the lower Verde River valley (LVRV), is where the modern-day drainages of the Salt and Verde now meet downstream of these Pliocene lakes. At the time of the Nomlaki tuff deposition ~3.3 Ma, a condition of sediment overfill existed in the LVRV, although there was no exoreic drainage and a playa was still maintained. A fanglomerate unit, named here the Rolls formation, spilled over a bedrock sill and an alluvial-fan ramp transported sediment into the Higley Basin that underlies the eastern part of metropolitan Phoenix. Lithologies of preserved remnants of this Pliocene alluvial-fan system match well cuttings of buried sediment in the Higley Basin with a cosmogenic burial isochron age of 3.90 ± 0.70 Ma. Based on cosmogenic burial isochron ages, ancestral Salt River gravels started depositing on top of this fan ramp between 2.8 and 2.2 Ma. Deposition of Salt and Verde river gravels in the Higley Basin continued for ~2 million years and eventually led to an aggradational piracy event that overtopped a bedrock ridge immediately east of Phoenix's Sky Harbor Airport. A cosmogenic burial age of 460 ± 23 ka is a rough maximum age for this river avulsion that relocated the Salt River into the Luke Basin that underlies western metropolitan Phoenix. Available chronometric data are not precise enough to determine whether the Salt River or Gila River integrated first. All of the exoreic rivers of western North America's Basin and Range Province — the lower Colorado, Gila, Rio Grande, Salt, and Verde rivers — employed lake overflow to integrate across half-graben, graben, rift and supradetachment tectonic settings.

The Arizona-Sonora porphyry copper cluster is one of the most productive provinces of this type on Earth. There, upper-crustal deposits emplaced between Late Cretaceous and Early Eocene, subsequently exhumed and developed supergene enrichment profiles. Despite the Basin and Range regional extension, these shallow intrusions and associated mineralization were preserved in eastern Sonora in the exhumed footwalls of normal faults. In order to better constrain their exhumation history, we performed a thermobarometrical (Al-in-hornblende) and thermochronological (apatite U–Pb and fission-track) study on the La Caridad and Suaqui Verde porphyry copper deposits. On the one hand, thermobarometry allows us to determine that the Suaqui Verde porphyry copper emplaced at 4.8 ± 0.9 km-depth, which implies that Cu–Mo mineralization may occur deeper than the ~2–4 km depth classically proposed for porphyry copper. On the other hand, using thermobarometry and inverse modeling of thermochronologic data obtained for individual and drill core samples, we reconstruct the thermal history of these porphyry copper. After a very fast post-emplacement cooling, numerical models suggest that cooling of rocks was slow and mainly monotonous during exhumation. Indeed, our data do not record an acceleration of the exhumation in eastern Sonora during the Basin and Range regional extension (between ~25 and 12 Ma). However, inverse modeling of fission-track data obtained along a drill core in La Caridad allows us to reconstruct the evolution of the geothermal gradient through time, which is in agreement with the regional geodynamics. Overall, it cannot be excluded that Oligocene volcanic rocks protected the ore deposits from erosion, even if they remained relatively thin (

An earthquake swarm took place from 27 August 2013 to December 2013 in the southern Basin and Range province of Chihuahua, Mexico. During this period, the Seismological Service of Mexico located approximately 60 earthquakes in the region. The largest earthquake took place on 21 September 2013 ( M w 5.3). A temporary seismic network was installed in the area for a period of two weeks. The hypocenters were relocated using the double‐difference algorithm. The results show a cluster of seismicity along the Vallecillo fault, where most of the seismicity took place, and on the Penasco fault. These two faults lie within the foothills of the sierras of the same name that bound the El Caballo desert basin. The seismicity suggests that both faults bounding the El Caballo basin slipped during the swarm. The main event of 27 August 2013 apparently took place on the Vallecillo fault. A third cluster of seismicity was located on Sierra La Mezcalera, about 20 km to the south of the Vallecillo fault, at the western end of the La Boquilla dam. Focal mechanisms of the larger events indicate right‐lateral slip with extensional deformation on the Vallecillo fault, with T axes oriented in a northeast–southwest direction. These source mechanisms reflect a regime of extensional tectonics in the southern Basin and Range province. The Vallecillo and Penasco fault system is exposed for approximately 12 km along strike. Scaling relations suggest that earthquakes as large as M w 6.4 may take place on them. This magnitude is similar to that of the 1928 Parral earthquake that occurred about 125 km to the south of the swarm. However, segmented faults may rupture sequentially and generate a larger earthquake than the one predicted on the basis of the length of individual mapped faults.

The South Tharsis Ridge Belt (STRB) is located along the northeastern edge of Terra Sirenum and partially surrounds the southwestern part of Tharsis in an arc. It consists of 29 large ridges separated by distances 130 to 260 km, with average relief of 1.5 km above the surrounding plains. Because the STRB is among the oldest tectonic features associated both spatially and developmentally with Tharsis, it may provide key information on the early evolution of Tharsis and possibly pre-Tharsis processes. Earlier studies concluded that the ridges formed through compressional tectonism. However, the shape, size, and separation of the ridges support the interpretation that the STRB resembles the extensional Basin and Range Province on Earth. Both regions are characterized by series of parallel mountain ranges separated by broad valleys. In this study, we evaluate both extensional and compressional hypotheses for the origin of the ridges using evidence from topography, deformed craters, crustal thickness models, and strain modeling. Though neither interpretation explains all aspects of the ridges, the topography of the ridges and crustal thinning associated with the western part of the ridge belt support an extensional origin. Strain models predict that Basin and Range-style wide rifting would be expected for early Martian conditions. This extension may have been initiated by plume-induced uplift in the early stages of Tharsis formation, but the large amount of extensional strain inferred in the western STRB must have been accommodated by compression elsewhere, possibly in the heavily deformed craters of western Terra Sirenum.

Garnet–pyroxenite xenoliths from a 25 Ma volcano on the southern edge of the Colorado Plateau in central Arizona (USA) are shown here to have crystallized as deep-seated cumulates from hydrous arc magmas, requiring the generation of a large complement of felsic magmas. U–Pb dating of primary titanite grains indicates that crystallization probably occurred around 60 Ma. These observations suggest that voluminous arc magmatism reached as far inland as the edge of the Colorado Plateau during the Laramide orogeny. Here, we employ a combination of petrology, petrophysics, and seismic imaging to show that the formation and subsequent removal of a thick, dense, cumulate root beneath the ancient North American Nevadaplano modified the buoyancy of the orogenic plateau, possibly resulting in two uplift events. A late Cretaceous–early Tertiary uplift event should have occurred in conjunction with thickening of the crust by felsic magmatism. Additional uplift is predicted if the pyroxenite root later foundered, but such uplift must have occurred after ∼25 Ma, the age of the xenolith host. We show that seismic velocity anomalies and seismic structures in the central part of the Colorado Plateau could represent pyroxenitic layers that still reside there. However, under the southern and western margins of the Colorado Plateau, the seismic signatures of a pyroxenite root are missing, despite xenolith records and geochemical evidence for their existence prior to 25 Ma. We suggest that these particular regions have undergone recent removal of the pyroxenite root, leading to late uplift of the plateau. In summary, our observations suggest that the Nevadaplano, west of the Colorado Plateau and now represented by the Basin and Range province, was underlain by high elevations in the late Cretaceous through early Tertiary due to magmatic thickening. This may have facilitated an east-directed drainage pattern at this time. Subsequent collapse of the Nevadaplano, culminating in Basin and Range extension and coupled with delamination-induced uplift of the margins of the Colorado Plateau in the late Cenozoic, may have reversed this drainage pattern, allowing rivers to flow west, as they do today.

The dynamics of river systems are most easily studied by observing their present geomorphology exposed at Earth's surface. However, the bulk of these often long-lived transportation and depositional systems is mostly buried at depth and hidden from view. Accessing these subsurface archives is often not possible. The Phoenix ‘basin’ of Arizona, USA, with its rich collection of water well drilling information, offers a unique opportunity. Clast assemblages of sand and gravel deposits contained in subsurface drill cuttings enable estimates of sediment provenance and, importantly, reveal changes of provenance over time. This study represents more than a decade of drill cuttings analysis and presents a method for evaluating the depositional history of how the Phoenix basin developed a large external river system that crossed a long-lived internally drained basin. This configuration developed after Basin and Range faulting and extension had ceased, allowing the basin to fill to capacity with sediment. When placed in the context of a series of new isopach maps of the subsurface ancestral Salt River deposits, our clast assemblage analysis supports the conclusion that the Salt and Verde rivers appeared suddenly in the geologic record. The ancestral Salt River deposits and other nearby streams crossing the basin each possess a unique clast assemblage that can be used to ‘fingerprint’ sediments with similar sources. We use these observations to draw conclusions about the age and origin of these streams. Used in conjunction with other types of analyses such as cosmogenic burial dating and detrital zircon analyses, determining clast assemblages of drill cuttings in the context of mapping these assemblages is a powerful new method for estimating the source of sediment and for understanding how the Phoenix basin, and basins in general, fill with sediment. This information is of value in modeling both basin development and groundwater resources in similar contexts in Arizona and elsewhere.

The relative contributions of tectonic and magmatic processes to continental rifting are highly variable. Magnetic, gravity, and seismic reflection data from Surprise Valley, California, in the northwest Basin and Range, reveal an intrabasin, fault-controlled, ∼10-m-thick dike at a depth of ∼150 m, providing an excellent example of the interplay between faulting and dike intrusion. The dike, likely a composite structure representing multiple successive intrusions, is inferred from modeling a positive magnetic anomaly that extends ∼35 km and parallels the basin-bounding Surprise Valley normal fault on the west side of the valley. A two-dimensional high-resolution seismic reflection profile acquired across the magnetic high images a normal fault dipping 56°E with ∼275 m of throw buried ∼60 m below the surface. Densely spaced gravity measurements reveal a

Widespread extension began across the northern and central Basin and Range Province at 17–16 Ma, contemporaneous with magmatism along the Nevada–Columbia Basin magmatic belt, a linear zone of dikes and volcanic centers that extends for >1000 km, from southern Nevada to the Columbia Basin of eastern Washington. This belt was generated above an elongated sublithospheric melt zone associated with arrival of the Yellowstone mantle plume, with a north-south tabular shape attributed to plume ascent through a propagating fracture in the Juan de Fuca slab. Dike orientation along the magmatic belt suggests an extension direction of 245°–250°, but this trend lies oblique to the regional extension direction of 280°–300° during coeval and younger Basin and Range faulting, an ∼45° difference. Field relationships suggest that this magmatic trend was not controlled by regional stress in the upper crust, but rather by magma overpressure from below and forceful dike injection with an orientation inherited from a deeper process in the sublithospheric mantle. The southern half of the elongated zone of mantle upwelling was emplaced beneath a cratonic lithosphere with an elevated surface derived from Late Cretaceous to mid-Tertiary crustal thickening. This high Nevadaplano was primed for collapse with high gravitational potential energy under the influence of regional stress, partly derived from boundary forces due to Pacific–North American plate interaction. Plume arrival at 17–16 Ma resulted in advective thermal weakening of the lithosphere, mantle traction, delamination, and added buoyancy to the northern and central Basin and Range. It was not the sole cause of Basin and Range extension, but rather the catalyst for extension of the Nevadaplano, which was already on the verge of regional collapse.

The Rio Grande rift in central New Mexico provides an excellent location to study the interaction between high-angle and low-angle (15°–35°) normal faults during crustal extension. Here we evaluate the relative importance of low-angle normal faults (LANFs) in the Albuquerque basin of central New Mexico with goals of testing two conflicting models of rift geometry and producing evolutionary models for the northern and southern parts of the basin. Using physiographic relationships, field observations, structural data analysis, and thermal history modeling, we document two brittle LANF systems on salients in adjacent opposite-polarity half-grabens. These fault systems were both active ca. 20–10 Ma and are locations of maximum fault slip as indicated by thickness of sedimentary fill in adjacent sub-basins and highest elevation rift flanks. Average fault dip increases basinward, and outbound faults were abandoned while intrabasinal faults cut Quaternary units, supporting an evolutionary model where master normal faults initiated at a higher dip, were shallowed by isostatic footwall uplift in regions of highest slip, and became inactive while younger normal faults emerged basinward. These geometrical and kinematic observations are predicted by the rolling-hinge model for the formation of LANFs. This mechanism has been widely applied to core complexes in highly extended terranes (e.g., Basin and Range), regions of orogenic collapse, and mid-ocean ridges, and it is shown here to also be applicable to narrow continental rifts of modest (∼35%) extension. Similarities to core complexes include a physiographic expression of domal uplifts, evolution of a master detachment horizon that initiated as a breakaway, and isostatically rotated low-angle normal faults. Although the degree of extension was too low to juxtapose ductile footwall rocks against brittle hanging-wall rocks, if extension had progressed in the Albuquerque basin, eventually a mature metamorphic core complex would have formed, similar to those preserved in the adjacent Basin and Range Province. The Rio Grande rift, therefore, provides a snapshot of the embryonic stages of core complex formation, bridging the gap between mature core complexes and incipient extensional environments.

Online Material: Tables of earthquake and station parameters. Most of northern Mexico is tectonically and morphologically situated in the southern Basin and Range Province (Suter and Contreras, 2002). The region of Sonora is particularly interesting, because the largest historical earthquake (3 May 1887, M w 7.5) occurred in this province. The town of Bavispe was destroyed during this earthquake (Aguilera, 1888), and the seismic source generated the longest recorded normal‐fault surface rupture (101.8 km) in historic time (Suter, 2006). The major fault zone of this earthquake includes (from south to north) three neighboring segments: Otates (length l =18.9 km), Teras ( l =20.7 km), and Pitaycachi ( l =43.8 km) (Fig. 1). These segments are separated by ∼30 km in between, and the basins are about 10 km wide (Suter and Contreras, 2002). Figure 1. Tectonic map showing locations of stations (white triangles) and earthquakes (black circles) used in this study (modified from Castro et al. , 2010). The black stars represent centers of population. Pitaycachi, Teras, and Otates are the faults that ruptured in the 1887 earthquake. The white star is the epicenter location of the 3 May 1887 ( M w 7.5) earthquake reported by Suter and Contreras (2002). A seismic network, Red Sismica del Noreste de Sonora (RESNES), was installed in this region to study the seismicity related to the Basin and Range faults of northeastern Sonora (Castro et al. , 2002; Romero et al. , 2004) and to monitor the major normal faults that generated the 3 May 1887 event (Castro et al. , 2009). The stations of this seismic network consist of Kinemetrics digital recorders (model K2) with internal Episensors that record three components of ground acceleration with a sample rate of 200 samples per second. …

Mountains in the U.S. Basin and Range Province are similar in form, yet they have different histories of deformation and uplift. Unfortunately, chronicling fault slip with techniques like thermochronology and geodetics can still leave sizable, yet potentially important gaps at Pliocene–Quaternary (∼105–106 yr) time scales. Here, we combine existing geochronology with new geomorphic observations and approaches to investigate the Miocene to Quaternary slip history of active normal faults that are exhuming three footwall ranges in northwestern Nevada: the Pine Forest Range, the Jackson Mountains, and the Santa Rosa Range. We use the National Elevation Dataset (10 m) digital elevation model (DEM) to measure bedrock river profiles and hillslope gradients from these ranges. We observe a prominent suite of channel convexities (knickpoints) that segment the channels into upper reaches with low steepness (mean k sn = ∼182; θref = 0.51) and lower, fault-proximal reaches with high steepness (mean k sn = ∼361), with a concomitant increase in hillslope angles of ∼6°–9°. Geologic maps and field-based proxies for rock strength allow us to rule out static causes for the knickpoints and interpret them as transient features triggered by a drop in base level that created ∼20% of the existing relief (∼220 m of ∼1050 m total). We then constrain the timing of base-level change using paleochannel profile reconstructions, catchment-scale volumetric erosion fluxes, and a stream-power–based knickpoint celerity (migration) model. Low-temperature thermochronology data show that faulting began at ca. 11–12 Ma, yet our results estimate knickpoint initiation began in the last 5 Ma and possibly as recently as 0.1 Ma with reasonable migration rates of 0.5–2 mm/yr. We interpret the collective results to be evidence for enhanced Pliocene–Quaternary fault slip that may be related to tectonic reorganization in the American West, although we cannot rule out climate as a contributing mechanism. We propose that similar studies, which remain remarkably rare across the region, be used to further test how robust this Plio–Quaternary landscape signal may be throughout the Great Basin.

© 2017 Elsevier Ltd The region surrounding the Modoc Plateau, encompassing parts of northeastern California, southern Oregon, and northwestern Nevada, lies at an intersection between two tectonic provinces; the Basin and Range province and the Cascade volcanic arc. Both of these provinces have substantial geothermal resource base and resource potential. Geothermal systems with evidence of magmatic heat, associated with Cascade arc magmatism, typify the western side of the region. Systems on the eastern side of the region appear to be fault controlled with heat derived from high crustal heat flow, both of which are typical of the Basin and Range. As it has the potential to host Cascade arc-type geothermal resources, Basin and Range-type geothermal resources, and/or resources with characteristics of both provinces, and because there is relatively little current development, the Modoc Plateau region represents an intriguing potential for undiscovered geothermal resources. It remains unclear however, what specific set(s) of characteristics are diagnostic of Modoc-type geothermal systems and how or if those characteristics are distinct from Basin and Range-type or Cascade arc-type geothermal systems. In order to evaluate the potential for undiscovered geothermal resources in the Modoc area, we integrate a wide variety of existing data in order to evaluate geothermal resource potential and exploration risk utilizing ‘play-fairway’ analysis. We consider that the requisite parameters for hydrothermal circulation are: 1) heat that is sufficient to drive circulation, and 2) permeability that is sufficient to allow for fluid circulation in the subsurface. We synthesize data that indicate the extent and distribution of these parameters throughout the Modoc region. ‘Fuzzy logic’ is used to incorporate expert opinion into the utility of each dataset as an indicator of either heat or permeability, and thus geothermal favorability. The results identify several geothermal prospects, areas that are highly favorable for the occurrence of both heat and permeability. These are also areas where there is sufficient data coverage, quality, and consistency that the exploration risk is relatively low. These unknown, undeveloped, and under-developed prospects are well-suited for continued exploration efforts. The results also indicate to what degree the two ‘play-types,’ i.e. Cascade arc-type or Basin and Range-type, apply to each of the geothermal prospects, a useful guide in exploration efforts.

Knowledge of the last reactivation age of faults in the western Basin and Range province (western North America) is key to understanding the recent evolution of the province in the context of the Pacific-North America plate boundary region. The Dixie Valley fault system (DVFS;Nevada, USA) is an important active normal fault in this region, but its slip history is not well known. Our goal is to determine the age of faulting initiation and the history of vertical displacement at the million-year time scale. We used well data from the Dixie Valley geothermal field and geologic maps to calculate offsets of geologic units. Tectonic events and their ages were determined from knickpoint analysis in the Stillwater Range. We then matched basin unconformities and knickpoints to obtain a vertical displacement history. The age of inception of the modern DVFS is likely between 13 and 7 Ma. The total vertical displacement of the geologic units is between 3 and 3.5 km, and most of it occurred in the last 2-3 Ma. Assuming an erosion rate between 0.03 and 0.07 m/ka, the maximum vertical displacement rate (similar to 1-2 mm/a) occurred between 3 and 0.5 Ma, and resulted in similar to 2 km of vertical displacement. Finally, the age-versus-distance profile of the Stillwater Range crest is tapered at both ends, as expected for a propagating range-bounding normal fault, but it also has two maxima matching the deepest parts of the Dixie Valley basin. This indicates that the present-day DVFS may have started out as two separate strands that connected within 2-3 Ma of inception. Our work shows that the combination of stratigraphic and structural data from the basin with geomorphological data from the adjacent mountain range is suitable for placing constraints on the displacement history at the million-year time scale of an active range-bounding normal fault. The resulting displacement-time paths for normal faults may not be as uniform as commonly assumed.

Transient deformation events observed in Global Positioning System (GPS) data from the Basin and Range extensional province may illuminate qualitatively similar transient events observed in subduction zones and other tectonic environments. We model GPS time series at 22 sites using a combination of hyperbolic tangent function analysis and elastic load deformation estimated from climatological data. We identify two transient events, ~2000.4 and ~2004.4, with roughly similar timing and displacement to those described previously by other researchers. The first few years of GPS observations, adopted as a reference state in earlier studies, are found to be anomalous. Our results differ from previous studies in two respects. First, a significant component of northward transient motion occurs during both events, despite a reversal of sign in east component motion. Second, sites move coherently in the eastern as well as the western Basin and Range. Surface mass loading, the largest source of transient stress forcing in the region, exhibits no evidence of a simple relationship to the deformation transients. Prior studies inferred slip on a single megadetachment at the Moho, but that hypothesis assumes negligible ductile deformation of the lower crust and a dry olivine rheology for the uppermost mantle. Recent measurements of crustal quartz abundance and effective elastic thickness suggest both assumptions are unlikely. Basin and Range transients can be reconciled with the frictional slip mechanism widely accepted for subduction zone transients provided that slip is occurring on discontiguous detachment surfaces at midcrustal depths.

[1] Quantitative paleoelevation histories can help explain both why and how widespread Cenozoic extension occurred in the Basin and Range Province of western North America. We present new estimates of preextensional paleoelevations for the northern and central Basin and Range using clumped isotope (Δ47) thermometry of lacustrine carbonates collected from each region. Comparison of carbonate Δ47-derived mean annual air temperature (MAAT) estimates (~16°C–20°C) for the Late Cretaceous–Eocene Sheep Pass basin of east central Nevada with published MAAT estimates for the Eocene, coastal northern Sierra Nevada (~20°C–25°C), suggests that the early Paleogene Sheep Pass basin had a paleoelevation of ≤2 km. Such a modest paleoelevation suggests that either (1) the proto–northern Basin and Range did not attain maximum paleoelevations of 3–4 km until the late Eocene–early Oligocene; or (2) the Sheep Pass basin was a local, high-relief (>1 km) setting contained within a >3 km orogenic highland (“Nevadaplano”). Similarity of Δ47-derived MAAT estimates (~17°C–24°C) for carbonates from the central Basin and Range and the near–sea level southern Sierra Nevada Bena basin indicate that middle Miocene paleoelevations in the Death Valley region were ≤1.5 km. These fairly low paleoelevations are incompatible with preextensional crustal thicknesses >52 km and indicate that mean elevation change was minor (≤500 m) and lithospheric mass was not conserved during >100% Neogene extension of the central Basin and Range, but was instead likely compensated by synextensional magmatic additions to the crust.

[1] The Fish Lake Valley–northern Death Valley–Furnace Creek fault zone, a ~250 km long, predominantly right-lateral structure in California and Nevada, is a key element in tectonic reconstructions of the Death Valley area, Eastern California Shear Zone and Walker Lane, and central Basin and Range Province. Total displacement on the fault zone is contested, however, with estimates ranging from ~30 to ~63 km or more. Here we present a new synthesis of available constraints. Preextensional thrust faults, folds, and igneous rocks indicate that offset reaches a maximum of ~50 km. Neogene rocks constrain its partitioning over time. Most offset is interpreted as ≤ ~13–10 Ma, accruing at ~3–5 mm/yr in the middle of the fault zone and more slowly toward the tips. The offset markers imply ~68 ± 14 km of translation between the Cottonwood Mountains and Resting Spring–Nopah Range (~60 ± 14 km since ~15 Ma) through a combination of strike slip and crustal extension. This suggests that a previous interpretation of ~104 ± 7 km, based on the middle Miocene Eagle Mountain Formation, is an overestimate by ~50%. Our results also help to mitigate a discrepancy in the ~12–0 Ma strain budget for the Eastern California Shear Zone. Displacement has previously been estimated at ~100 ± 10 km and ~67 ± 6 km for the Basin and Range and Mojave portions of the shear zone, respectively. Our new estimate of ~74 ± 17 km for the Basin and Range is within the uncertainty of the Mojave estimate.

The northern Nevada rift is a prominent mafic dike swarm and magnetic anomaly in north-central Nevada inferred to record the Middle Miocene (16.5–15.0 Ma) extension direction in the northern Basin and Range province in the western United States. From the 245°–250° rift direction, Basin and Range extension is inferred to have shifted 45° clockwise to a modern direction of 290°–300° during the late Miocene. The region surrounding the northern Nevada rift was actively extending while the rift formed, and these domains are all characterized by extension oriented 280°–300°. This direction is distinctly different from the rift direction and nearly identical to the modern Basin and Range direction. Although the rate, structural style, and distribution of Basin and Range extension appear to have undergone a significant change in the late Miocene (ca. 10 Ma), the overall spreading direction does not. Middle Miocene extension was directed perpendicular to the axis of the thickest crust formed during Mesozoic shortening and this orientation may reflect gravitational collapse of this thick crust. Orientation of northern Nevada rift dikes may reflect a short-lived regional stress field related to the onset of Yellowstone hotspot volcanism.

A vast area of the northeastern Great Basin of the western USA was inundated by a succession of Pleistocene lakes, including Lake Bonneville. Playa-sediment deposition from these lakes onlapped onto alluvial fans that blanketed the slopes of adjacent mountain ranges to create prominent angular unconformities. Understanding these unconformities is useful for constraining the interpretation of the geologically recent tectonic evolution of the Basin and Range Province, as well as the interaction of lake sedimentation and alluvial fan development. The Pilot Valley playa, located just east of the Utah–Nevada border near Wendover, Utah, represents a remnant of these lakes. High-resolution seismic profiles have been acquired near the base of the bounding mountain ranges. The profiles reveal the stratigraphic relationships between Quaternary pluvial sediments as a shoreline depositional facies and the adjacent bounding fan deposits. On the western side of the basin, these profiles image subhorizontal playa sediments prograding over inclined alluvial fans. The boundary between the playa and fan sediments is marked by a prominent angular unconformity. Seismic images from the opposite side of the basin reveal a more heterogeneous structural and stratigraphic style, including down-to-the-basin normal faulting of shallow Paleozoic bedrock overlain by alluvial fan deposits, which are in turn onlapped by a thin veneer of playa sediments. The new geophysical images, when integrated with available geologic mapping, also aid in constraining how deep aquifers are locally recharged from an adjacent range. The results demonstrate the structural asymmetry of the range and playa system, consistent with a classic half-graben structure. Lastly, this study demonstrates the utility of the method of shallow seismic reflection to provide high-resolution subsurface images in the challenging environment of alluvial fan–playa geology.

New data indicate that northeast-directed extensional faulting characterizes slip across the Brothers fault zone (BFZ), which marks the northern limit of the northwestern Basin and Range (NWBR) extensional province in southeastern Oregon. Structural separation across individual north-northeast striking NWBR faults decreases to zero south of the BFZ. Field relationships and cross-sections demonstrate limited kinematic linkage and independent evolution of the two fault systems since ∼7 Ma. West-directed extension accumulated on NWBR faults at 0.01 mm/yr and lengthened northward after 7.05 Ma. BFZ faults accumulated northeast-directed extension at rates of 0.01 mm/yr since 5.68 Ma. Deformation coincides with periods of heightened basaltic magmatism in the High Lava Plains, implying that volcanism weakened the crust and promoted extension in the BFZ. In a new model, we reconcile the observed northward diminishing rate and clockwise motion of the modern NWBR deformation field with regional geology. The BFZ defines a small circle about the pole of rotation and separates a stable block to the NE from the extending region to the south. Faults to the south are growing northward, consistent with the northward decrease in rate and magnitude of extension in the NWBR.

We evaluate horizontal Global Positioning System (GPS) velocities together with geologic, volcanic, and seismic data to interpret extension, shear, and contraction within the Snake River Plain and the Northern Basin and Range Province, U.S.A. We estimate horizontal surface velocities using GPS data collected at 385 sites from 1994 to 2009 and present an updated velocity field within the Stable North American Reference Frame (SNARF). Our results show an ENE-oriented extensional strain rate of 5.9 {+-} 0.7 x 10{sup -9} yr{sup -1} in the Centennial Tectonic belt and an E-oriented extensional strain rate of 6.2 {+-} 0.3 x 10{sup -9} yr{sup -1} in the Intermountain Seismic belt combined with the northern Great Basin. These extensional strain rates contrast with the regional north-south contraction of -2.6 {+-} 1.1 x 10{sup -9} yr{sup -1} calculated in the Snake River Plain and Owyhee-Oregon Plateau over a 125 x 650 km region. Tests that include dike-opening reveal that rapid extension by dike intrusion in volcanic rift zones does not occur in the Snake River Plain at present. This slow internal deformation in the Snake River Plain is in contrast to the rapidly-extending adjacent Basin and Range provinces and implies shear along boundaries of the Snakemore » River Plain. We estimate right-lateral shear with slip rates of 0.5-1.5 mm/yr along the northwestern boundary adjacent to the Centennial Tectonic belt and left-lateral oblique extension with slip rates of 10{sup 6} yrs, the low-strain field in the Snake River Plain and Owyhee-Oregon Plateau would extend through the Quaternary.« less

Stretching of the continental crust can double its surface area, but it is unknown whether similar amounts of extension occur at depth. Seismic results from the central Basin and Range province, western USA, reveal a thick root of lithospheric mantle that has not been extended and indicates that crustal stretching is decoupled from extension at depth. Stretching of the continental crust in the Basin and Range, western USA1, has more than doubled the surface area of the central province2. But it is unknown whether stretching affects the entire column of lithosphere down to the convecting mantle, if deep extension occurs offset to the side, or if deeper layers are entirely decoupled from the upper crust3,4. The central Basin and Range province is unusual, compared with its northern and southern counterparts: extension began later1; volcanism was far less voluminous5; and the unique geochemistry of erupted basalts6,7,8,9,10,11 suggests a long-preserved mantle source. Here we use seismic data and isostatic calculations to map lithospheric thickness in the central Basin and Range. We identify an isolated root of ancient mantle lithosphere that is ∼125 km thick, providing geophysical confirmation of a strong, cold mantle previously inferred from geochemistry6,7,8. We suggest that the root caused the later onset of extension and prevented the eruption of voluminous volcanism at the surface. We infer that the root initially pulled away from the Colorado Plateau along with the crust, but then was left behind intact during extension across Death Valley to the Sierra Nevada. We conclude that the upper crust is now decoupled from and moving relative to the root.

Along the northwestern margin of the Basin and Range province, mid-Miocene to Pliocene volcanic rocks cover and obscure much of the earlier history of the region. In northeastern California, however, slip on the Surprise Valley fault has resulted in the uplift of the Warner Range, exposing >4 km of volcaniclastic and volcanic rocks as old as late Eocene. New geologic mapping, combined with geochemistry and geochronology of rocks in the Warner Range and surrounding region, documents a history of volcanism and extension from the Eocene to the present that provides insight into the evolution of this margin. Our work reveals that subduction-related arc volcanism began ca. 40 Ma and continued into the mid-Miocene, despite the nearby impingement of the Yellowstone hotspot and eruptions of flood basalts. Extensional normal faulting began in the mid- to late Miocene in relative isolation from other Basin and Range normal faults. Later Miocene and Pliocene volcanic rocks flowed into low-lying areas produced by mid-Miocene extension. These younger basalts are cut by normal faults, requiring a second episode of extension that began after 3 Ma. Our cross-section reconstructions indicate that 12%–15% extension has been accommodated across the Warner Range region, primarily along the Surprise Valley fault, which has accommodated 8 km of dip-slip motion. A similarly protracted or two-part history of extension has been observed elsewhere in the western Basin and Range. While relatively little extension has been accommodated in the Warner Range region, it continues to the present day. Thus, the Surprise Valley fault appears to have persisted as the westernmost boundary of Basin and Range extension since the mid-Miocene.

The central Wassuk Range is ideally located to investigate the interplay of Basin and Range extension and Walker Lane dextral deformation along the western Nevada margin of the Basin and Range province. To elucidate the Cenozoic evolution of the range, the author conducted geologic mapping, structural data collection and analysis, geochemical analysis of igneous lithologies, and geochronology. This research delineates a three-stage deformational history for the range. A pulse of ENE–WSW-directed extension at high strain rates (∼8.7 mm/yr) was initiated immediately after the eruption of ∼15 Ma andesite flows; strain was accommodated by high-angle, closely spaced (1–2 km), east-dipping normal faults which rotated and remained active to low angles as extension continued. A post-12 Ma period of extension at low strain rates produced a second generation of normal faults and two prominent dextral strike–slip faults which strike NW, subparallel to the dextral faults of the Walker Lane at this latitude. A new pul...

Active tectonics within the northern Basin and Range province provide a natural laboratory for the study of normal fault growth, linkage, and interaction. Here, we present new geologic mapping and morphologic fault-scarp modeling within the Centennial Valley, Montana to characterize Pleistocene – Holocene ruptures of the young and active Lima Reservoir fault. Geologic relationships and rupture ages indicate Middle Pleistocene activity on the Henry Gulch (>50 ka and 23–10 ka), Trail Creek (>43 ka and ∼13 ka), and reservoir (∼23 ka) segments. Offset Quaternary deposits also record Holocene rupture of the reservoir segment (∼8 ka), but unfaulted modern streams show that no segments of the Lima Reservoir fault have experienced a large earthquake in at least several millennia. The clustered pattern of rupture ages on the Lima Reservoir fault segments suggests a seismogenic linkage though segment length and spacing make a physical connection at depth unlikely. Trail Creek and reservoir segment slip rates were non-steady and appear to be increasing. The fault helps accommodate differential horizontal surface velocity measured by GPS geodesy across the boundary between the northern Basin and Range province and the Snake River Plain.

We provide the first synthesis of seismic reflection data and active present-day crustal deformation for the greater Wasatch fault zone. We analyzed a number of previously unpublished seismic reflection lines, horizontal and vertical crustal velocities from continuous GPS, and surface geology to investigate the relationships between interseismic strain accumulation, subsurface fault geometry, and geologic slip rates on seismogenic faults across the eastern third of the northern Basin and Range Province. The seismic reflection data show recent activity along high-angle normal faults that become listric with depth and appear to sole into preexisting decollements, possibly reactivating them. We interpret these listric normal faults as reactivated Sevier-age structures that are connected at depth with a regionally extensive detachment horizon. These observations of subsurface structure are consistent with the mapped geology in areas that have experienced significant extension. We modeled the crustal deformation data using a buried dislocation source in a homogeneous elastic half space. The estimated model results include a low-angle dislocation (~ 8–20°) at a locking depth of ~ 7–10 km and slipping at 3.2 ± 0.2 mm/yr. Despite the model's relative simplicity, we find that the predicted location of the dislocation is consistent with the interpreted seismic reflection data, and suggests an active regionally extensive sub-horizontal surface in the eastern Basin and Range. This result may imply that this surface represents aseismic creep across a reactivated low-angle fault plane or the onset of ductile flow in the lower crust at or beneath the brittle–ductile transition zone under the present-day Basin and Range extensional regime. This result may also have implications for crustal rheology, and suggests that geodesy might, under some circumstances, serve as an appropriate tool for inferring deeper crustal structure.

Surprise Valley in northeastern California offers an ideal opportunity to examine the structural setting of a developing extensional basin due to its late Miocene to recent activity in isolation from other major normal fault-bound basins. Seismic velocity and potential field modeling help determine the nature of basin fill and identify intra-basin faults. Based on a detailed gravity and magnetic profile, we identify shallow subsurface basalt flows and several faults within the valley that may accommodate hundreds of meters of vertical offset, possibly cutting and offsetting the ~ 30° east-dipping Surprise Valley fault that rotated during footwall tilting of the adjacent Warner Mountains. Some of these intra-basin faults correspond with mapped Quaternary fault scarps, but others have no surface expression. These faults may represent the currently active fault system within the basin. If so, they would indicate that basin development is transitioning away from the main range-front normal fault to a new set of steep intra-basin faults that are more favorable for accommodating regional transtensional strain.

Synthetic Aperture Radar Interferometry (InSAR) has been applied in this study to address crustal deformation in a 10,000-km 2 region located immediately west of the Yellowstone hotspot. InSAR results show that surface movements in the study area were non-linear and episodic during the period of observation (1993–2006). The Island Park region and its adjacent Eastern Snake River Plain (ESRP) were characterized by northeast-trending zones of uplift (+ 1 cm yr − 1 ) and subsidence (− 1 cm yr − 1 ) with various extents through time. The western edge of Yellowstone caldera experienced episodes of subsidence (− 1 cm yr − 1 ) during 1997–2000 and uplift (+ 3 cm yr − 1 ) during 2004–2006. Differential surface movements of varying rates were also detected between 1993 and 2006 in the vicinity of Basin and Range normal faults to the north of Henrys Fork caldera. Throughout the study area, surface displacements across the Island Park region, the ESRP, and the adjacent Basin and Range province generally reversed the movement direction in 2004, in concert with displacement reversal to uplift in the Yellowstone caldera. Crustal deformation in the general vicinity of major Basin and Range faults is interpreted to reflect diffuse extensional strain adjacent to the deeper segments of faults, rather than near-surface slip. The northeast-trending displacement zones in the ESRP and the Island Park region may indicate folding in response to converging zones of extension in the surrounding Basin and Range province. Surface displacements of the Yellowstone caldera are interpreted to reflect migration of magma or hydrothermal fluids. The inverse relation between vertical displacements in Yellowstone and its surrounding regions may reflect an upper crustal flexural response or a large-scale movement of hydrothermal fluids, though neither hypothesis is completely supported by the processed data.

The seismically active eastern and western margins of the northern Basin and Range have been extensively studied, yet the northwestern margin of the province remains incompletely understood. The Black Rock Range of northwestern Nevada straddles the transition from the Basin and Range province to the south and east, and flat-lying volcanic plateaus to the west. This poorly understood range preserves a remarkably complete record of Cenozoic magmatism and provides an important window into the pre-Miocene history of the unextended volcanic plateaus of northeastern California and southern Oregon. Geologic mapping and 40Ar/39Ar geochronology from the northern Black Rock Range document three significant episodes of Eocene to middle Miocene volcanism. Eocene (35 Ma) basalts directly overlie Mesozoic granites and arc-related volcanic and sedimentary rocks. Locally erupted Oligocene to early Miocene (27–21 Ma) bimodal volcanic rocks comprise the bulk of the Cenozoic section and conformably overlie the Eocene basalt flows. These bimodal units include rhyolitic lavas, variably welded rhyolitic ash flows, unwelded ash-fall deposits, and thin basalt flows. In the neighboring Pine Forest Range ∼20 km to the north, similar Oligocene to early Miocene units are overlain by more than 500 m of ca. 16.4 Ma Steens-equivalent basalt flows and are capped by ca. 16 Ma rhyolitic ash-flow tuffs. In the northern Black Rock Range, the ca. 16.4 Ma middle Miocene basalts are absent from the section, and a 16.2 Ma rhyolitic ash-flow tuff directly overlies the early Miocene flows. Basaltic and rhyolitic volcanic products in the northern Black Rock Range span 35–16 Ma, with many of the Oligocene volcanic units derived from local vents and dikes. Despite the map-scale complexities of locally derived lava flows, the Cenozoic section is broadly conformable and dips gently (∼5°–10°) to the northwest. The region experi enced no significant tilting between 35 and 16 Ma, with moderate tilting (∼5°–10°) and concomitant uplift occurring after 16 Ma. This tectonic history is consistent with that of the nearby Pine Forest and Santa Rosa Ranges, where low-temperature thermochronology documents footwall exhumation along the range-bounding normal faults after 12 Ma. The velocity structure of the crust beneath the northern Black Rock Range is constrained by a recent geophysical survey (seismic reflection, refraction, and gravity) and contains gradients that correspond to basin depths predicted by our geologic mapping. Together with recently completed geological and geophysical studies from the surrounding region, our results suggest that the evolution of the northwestern margin of the Basin and Range was characterized by long-lived and voluminous volcanism without significant tectonism, followed by low-magnitude (≤20%) extension along high-angle normal faults.

This work constitutes the first attempt to understand the seismic hazard in northeast Mexico. We present a compilation of regional seismicity in northeast Mexico (24–31°N, 97–106°W), finding 148 earthquakes for the 1787–2006 period. The study area lies within three morphotectonic provinces: Basin, Range, and Rio Grande rift; Sierra Madre Oriental; and Gulf coastal plain. Peak ground acceleration (PGA) maps were computed for three different scenarios: 1928 Parral, Chihuahua ( M W = 6.5); 1931 Valentine, Texas ( M W = 6.4); and a hypothetical earthquake located in central Coahuila. Ground motion values were computed using attenuation relations developed for central and eastern North America and the Basin and Range provinces. The earthquake in central Coahuila is considered a critical scenario for the main cities of northeast Mexico. The damage associated with this hypothetical earthquake could be severe because most buildings were constructed without seismic criteria. The expected PGA values in Monterrey, Saltillo, and Monclova are between 30 and 70 cm/s 2 . This earthquake might also produce or trigger significant landslides and rock falls in the Sierra Madre Oriental, where several cities are located on the mountain range.

New 40Ar-39Ar geochronology, bulk rock geochemical data, and physical characteristics for representative stratigraphic sections of rhyolite ignimbrites and lavas from the west-central Snake River Plain (SRP) are combined to develop a coherent stratigraphic framework for Miocene silicic magmatism in this part of the Yellowstone ‘hotspot track’. The magmatic record differs from that in areas to the west and east with regard to its unusually large extrusive volume, broad lateral scale, and extended duration. We infer that the magmatic systems developed in response to large-scale and repeated injections of basaltic magma into the crust, resulting in significant reconstitution of large volumes of the crust, wide distribution of crustal melt zones, and complex feeder systems for individual eruptive events. Some eruptive episodes or ‘events’ appear to be contemporaneous with major normal faulting, and perhaps catastrophic crustal foundering, that may have triggered concurrent evacuations of separate silicic magma reservoirs. This behavior and cumulative time-composition relations are difficult to relate to simple caldera-style single-source feeder systems and imply complex temporal-spatial development of the silicic magma systems. Inferred volumes and timing of mafic magma inputs, as the driving energy source, require a significant component of lithospheric extension on NNW-trending Basin and Range style faults (i.e., roughly parallel to the SW–NE orientation of the eastern SRP). This is needed to accommodate basaltic inputs at crustal levels, and is likely to play a role in generation of those magmas. Anomalously high magma production in the SRP compared to that in adjacent areas (e.g., northern Basin and Range Province) may require additional sub-lithospheric processes.

Earthquakes in central Nevada (1932-1959) were used to develop a modified Mercalli intensity (MMI) attenuation model for estimating moment mag- nitude M for earthquakes in the Basin and Range province of interior western North America. M is 7.4-7.5 for the 26 March 1872 Owens Valley, California, earthquake, in agreement with Beanland and Clark's (1994) M 7.6 that was estimated from geologic field observations. M is 7.5 for the 3 May 1887 Sonora, Mexico, earthquake, in agreement with Natali and Sbar's (1982) M 7.4 and Suter's (2006) M 7.5, both estimated from geologic field observations. MMI at sites in California for earthquakes in the Nevada Basin and Range appar- ently are not much affected by the Sierra Nevada except at sites near the Sierra Nevada where MMI is reduced. This reduction in MMI is consistent with a shadow zone produced by the root of the Sierra Nevada. In contrast, MMI assignments for earthquakes located in the eastern Sierra Nevada near the west margin of the Basin and Range are greater than predicted at sites in California. These higher MMI values may result from critical reflections due to layering near the base of the Sierra Nevada.

A regional synthesis of new and existing geologic and thermochronologic data document late Cretaceous - early Cenozoic regional erosion, Oligocene - Miocene volcanism, and subsequent late Miocene extension of the Basin and Range Province in northwestern Nevada and northeastern California. Across an ∼220-km-wide region between the Santa Rosa and Warner Ranges, conformable sequences of 35 to 15 Ma volcanic rocks are cut by only a single generation of high-angle normal faults that accommodated ∼23 km of total east-west extension (∼12%). Fission-track, (U-Th)/He, geologic, and structural data from the Pine Forest Range show that faulting there began at 11 to 12 Ma, progressed at a relatively constant rate until at least 3 Ma, and has continued until near the present time. Extension in the Santa Rosa Range to the east took place during the same interval, although the post-6 Ma part of this history is less well constrained. Less complete constraints from adjacent ranges permit a similar timing for faulting, and we infer that extensional faulting in northwestern Nevada began everywhere at 12 Ma and has continued up to the present. Faulting in the Warner Range in northeastern California can only be constrained to have begun between 14 and 3 Ma, but may represent westward migration of Basin and Range extension during the Pliocene. Compared to the many parts of the Basin and Range in central and southern Nevada, extension in northwestern Nevada began more recently, is of lesser total magnitude, and was accommodated entirely by high-angle normal faults. Fission-track data document Late Cretaceous unroofing of Cretaceous (115 –100 Ma) granitic basement rocks in northwestern Nevada, followed by a long period of relative tectonic quiescence that persisted through Oligocene and Miocene volcanism until the onset of Basin and Range extension at ∼12 Ma. The low magnitude of extension (12%) and early Tertiary stability suggest that the modern ∼31 km thick crust in northwestern Nevada was only slightly thicker (∼35 km) prior to extension at 12 Ma, and was no thicker than ∼38 km in the Late Cretaceous. This stands in contrast to other parts of the Basin and Range, where the crust was thickened to at least 45 to 50 km by Cretaceous thrusting and subsequently thinned to ∼30 km by large magnitude (>50%) extension.

Records of lithospheric extension and mountain-range uplift are most continuously contained within syntectonic sedimentary rocks in basins adjacent to large structural culminations. In southeastern Arizona, metamorphic core complexes form mountain ranges with the highest elevations in the region, and supposedly much less extended terranes lie at lower elevations. Adjacent to the Santa Catalina-Rincon metamorphic core complex, within the Tucson Basin, stratigraphic-sequence geometries evident in a large suite of 2-D seismic reflection data suggest a two-phase basin-evolution model controlled by the emplacement and subsequent uplift of the core complex. In its earliest stage, Phase I of basin formation was characterized by extensive faults forming relatively small-scale proto-basins, which coalesced with the larger basin-bounding detachment fault system. Synextensional sedimentation within the enlarging basin is evidenced by sediment-growth packages, derived from adjacent footwall material, fanning into brittle hanging-wall faults. During this phase, volcanism was widespread, and growth packages contain interbedded sediments and volcanic products but, paradoxically, no mylonitic clasts from the adjacent metamorphic core complex. Phase II of basin evolution begins after a significant tectonic hiatus and consists of a symmetric deepening of the central basin with the introduction of mylonitic clasts in the basin fill. This is coupled with the activation of a series of high-angle normal faults ringing the core complex. These observations suggest a two-phase model for metamorphic core complex evolution, with an initial stage of isostatic core complex emplacement during detachment faulting that resulted in little topographic expression. This was followed, after a significant tectonic hiatus, by late-stage exhumation and flexural uplift of the Santa Catalina-Rincon metamorphic core complex through younger high-angle faulting. Moreover, the geometry of upper basin fill units suggests an extremely low effective elastic thickness in the region and that flexural uplift of the core complex induced asymmetric transfer of ductile mid-crustal rocks from beneath the subsiding Tucson Basin to the uplifting mountain range.

The unique low-temperature sensitivity of the apatite (U-Th)/He (AHe) technique provides valuable new information relating to the late-stage thermal evolution of metamorphic core complexes in the southern Basin and Range Province. In all the ranges studied, the data show greater complexity than previously seen from other thermochronometers. In the Chemehuevi and northern Sacramento Mountains, a trend of decreasing ages toward the northeast applies only for the structurally shallowest parts of the footwall. This is followed by essentially age-invariant segments of 15 ± 1 Ma, reflecting an increase in the rate of detachment fault movement. The timing of the change suggested by the data agrees with recently published AHe results from the nearby Harcuvar Mountains, located ∼125 km to the southeast, suggesting that an underlying regional mechanism triggered this change. Plate reconstructions indicate that the Pioneer-Mendocino fracture zone migrated northward through the area at this time, leaving a slab window in its wake. We suggest that the additional heat applied to the base of the lithosphere from the slab window resulted in mechanical weakening of the area and that this, combined with the extensional strain regime present, resulted in an increased rate of slip within the actively extending metamorphic core complexes. This agrees well with timing constraints for extension onset in the central Basin and Range Province of southern Nevada, and suggests that weakening of the southern Basin and Range Province at 15 ± 1 Ma was partially responsible for the onset of extension in the central Basin and Range. These findings demonstrate that improved constraints on changes in extension rate within the Basin and Range Province should be possible through the application of the AHe technique to other metamorphic core complex footwalls.

The purpose of this paper is to highlight the outstanding studies George Emory Goodfellow (1855–1910) and Jose Guadalupe Aguilera Serrano (1857–1941) made of the devastating 3 May 1887 M w 7.5 Sonora earthquake (Figure 1). Goodfellow's observational study, based on his fieldwork in 1887 and partly published in Science in 1887 and 1888 (Goodfellow, 1887a, 1887b, 1888), includes the first surface rupture map of an earthquake in North America and photographs of the rupture scarp by Camillus Sidney Fly (1849–1901). Aguilera's 1888 publication (in Spanish), which is based on his expedition to the epicentral region of this earthquake in the summer of 1887, includes the first geologic map of northeastern Sonora, a detailed surface rupture map, and the earliest isoseismal map, source parameters, and seismic velocities of an earthquake in North America. An abridged translated version of Aguilera's 1888 article was published without figures in the Bulletin of the Seismological Society of America (Aguilera, 1920), and his rupture map was reproduced by Richter (1958, p. 595, Figure 31-2). Nevertheless, Aguilera's and Goodfellow's studies are not widely known today, and they are not given credit for their pioneering achievements in reviews of the history of seismology (for example, Davison, 1927; Agnew, 2002) or earthquake geology (historical vignettes in Yeats et al. , 1997). Here I review the major accomplishments in Goodfellow's and Aguilera's contributions and place them in a historical context. The 3 May 1887 Sonora event is the largest historical earthquake of the southern Basin and Range tectonic-physiographic province and produced worldwide the longest recorded normal-fault surface rupture in historic time. The end-to-end length of the rupture trace (Figure 2) measures 101.8 km. The magnitude of the event is estimated as M w = 7.5±0.3 based on this distance and the surface rupture length versus magnitude …

Eocene–middle Miocene volcanic rocks in the northern Pine Forest Range, Nevada, are ideally situated for reconstructing the timing and style of volcanism and extensional faulting in the northwesternmost part of the Basin and Range province. A conformable sequence of Cenozoic volcanic and sedimentary strata in the northern Pine Forest Range dips ~30°W, and 11 new 40 Ar/ 39 Ar ages from this sequence defi ne 3 major episodes of volcanic activity. Pre-Tertiary basement and older (ca. 38 Ma) Tertiary intrusive rocks are overlain unconformably by Oligocene (ca. 30–23 Ma) basalt fl ows and dacitic to rhyolitic ash-fl ow tuffs interbedded with fi ne-grained tuffaceous sedimentary rocks. Oligocene rocks are overlain by ~550 m of ca. 17–16 Ma basalt fl ows equivalent to the Steens Basalt in southern Oregon, and basalt fl ows are capped by a thin 16.3 Ma ignimbrite that likely is correlative with either the Idaho Canyon Tuff or the Tuff of Oregon Canyon. The northern Pine Forest Range is bounded to the east by a major down-to-the-east normal fault that dips ~40°E with well-developed fault striations indicative of dip-slip motion. This fault initiated at an angle of ~70° and was rotated ~30° during uplift of the range. A suite of 17 apatite fi ssion-track ages from the Pine Forest footwall block demonstrates that exhumation, uplift, and slip on the range-bounding fault began ca. 12–11 Ma and continued until at least 7 Ma, with moderate slip since then. The Pine Forest Range did not undergo signifi cant extension before or during peak Oligocene and Miocene volcanism, and similar geologic relationships in nearby ranges suggest that a larger region of northwestern Nevada was also little extended during this interval. Basin and Range faulting in northwestern Nevada appears to have begun no earlier than 12 Ma, making it distinctly younger than deformation in much of central and southern Nevada, where peak extension occurred in the middle Miocene or earlier.

Holocene acceleration of deformation and postseismic relaxation are two hypotheses to explain the present-day deformation in the Central Nevada Seismic Belt (CNSB). Discriminating between these two mechanisms is critical for understanding the dynamics and seismic potential of the Basin and Range province. Interferometric synthetic aperture radar detected a broad area of uplift (2 to 3 millimeters per year) that can be explained by postseismic mantle relaxation after a sequence of large crustal earthquakes from 1915 to 1954. The results lead to a broad agreement between geologic and geodetic strain indicators and support a model of a rigid Basin and Range between the CNSB and the Wasatch fault.

North-northwest normal faults intersect ENE normal faults in the vicinity of Queretaro City, in central Mexico, affecting the Miocene–Pliocene northern-central sector of the Mexican Volcanic Belt province. This intersection produced an orthogonal arrangement of grabens, half-grabens and horsts that include the Queretaro graben. The NNW faults are part of the Taxco–San Miguel de Allende fault system, which is proposed here as part of the southernmost Basin and Range province in Mexico. The ENE to E–W faults are part of the E–W oriented Chapala–Tula fault zone, which has been interpreted as an active intra-arc fault system of the Mexican Volcanic Belt. Seventy-four normal faults were mapped, of which the NNW faults are the largest and have the best morphological expression in the region. More numerous, although shorter, are the ENE faults. Total length of the ENE faults is greater than the total length of the NNW faults. Both sets are dominantly normal faults, indicating ENE extension for the NNW set and NNW extension for the ENE set. Field data indicate that displacement on the two fault sets has overlapped in time, as some NNW faults are younger than some ENE faults, which are supposed to be the younger ones. Seismicity in 1998 on a NNW fault indicates ENE active extension on the NNW faults. These observations support our interpretation that the northern Mexican Volcanic Belt lies on the boundary between the Basin and Range province, which is undergoing ENE extension, and the central Mexican Volcanic Belt province, which is undergoing northerly extension. The apparent overlap in space and time of displacements on the two fault sets reflects the difference in stress regime between the two provinces. Copyright © 2005 John Wiley & Sons, Ltd.

Analysis of historical accounts of the ∼ M 6.3 1884 earthquake in northern Utah reveals that the earthquake had an epicenter near 42.3° N, 111.4° W, approximately 30 km northwest of the event's original location. We use detailed reports of damage to structures and the consequences of ground shaking to define a felt area of approximately 70,000 km2 and estimate the peak ground accelerations as 100-300 cm/sec2. Analysis of the geologic structure of the area indicates that the epicentral area is a half-graben bounded on the east by the listric Bear Lake fault and on the west by the steeply dipping West Bear Lake fault. The earthquake epicenter was on the west side of the basin, and we interpret the event to have been the result of slip on the West Bear Lake fault zone at a depth of 4-5 km. This zone consists of steeply dipping antithetic faults in the hanging wall of the East Bear Lake fault. These data suggest that moderate-magnitude earthquakes on antithetic or small-displacement faults pose a significant, if local, seismic hazard in the northeastern Basin and Range province. We also demonstrate the utility of combining geological and historigraphic analyses to examine pre-instrument-era earthquakes. Online material : Felt reports and town summaries. Manuscript received 16 July 2002.

The White Mountains represent the westernmost range of the central northern Basin and Range province. They are situated to the east of the unextended Sierra Nevada and represent a crustal block that is bounded along its western flank by the high-angle White Mountains fault zone. The fault zone accommodates up to ∼8 km of total dip-slip displacement. Investigation of the structural and thermal history of the White Mountains indicates a two-stage Cenozoic tectonic evolution. Preextensional Miocene volcanic rocks preserved along the eastern side of the range unconformably overlie Mesozoic granitic basement and currently dip up to 25° to the east, recording the total Cenozoic tilt of the crustal block. Apatite fission-track and (U-Th/He) thermochronological data indicate that the White Mountains underwent rapid exhumation and eastward tilting in the middle Miocene, starting at ca. 12 Ma. Geologic mapping (1:10,000), fault kinematic analysis, and dating of younger volcanic sequences show that following middle Miocene east-west extension, the White Mountains have been dominated by right-lateral transtensional deformation related to the Walker Lane belt. The eruption of late Miocene and Pliocene volcanic sequences in the eastern White Mountains postdates the majority of the uplift of the range, as evidenced by infilling of paleodrainages and the presence of east-directed flow fabrics. Fault kinematic indicators from the White Mountains fault zone are characterized by apparent overprinting of dip-slip fault-motion indicators by right-lateral slickenfibers and fault striations, demonstrating that the range-bounding fault system along the western side of the White Mountains was reactivated as a dextral strike-slip fault system. At the northern and southern ends of the range, Pliocene right-lateral transtension along this northwest–southeast-trending fault systems resulted in the formation of northeast-trending pull-apart basins that truncate the mountain range and transfer strike-slip displacement eastward from the Owens Valley fault zone to the Fish Lake Valley fault zone. The inception of strike-slip faulting in Fish Lake Valley occurred at ca. 6 Ma as constrained by late Miocene volcanic units. Right-lateral faulting on the western side of the White Mountains occurred at ca. 3 Ma and is distinctly younger than the faulting in the Fish Lake Valley area, indicating a westward migration of transcurrent deformation through time.

New mapping, structural analysis, and 40Ar/39Ar dating reveal an unusually well‐constrained history of Late Eocene extension in the Copper Mountains of the northern Basin and Range province. In this area, the northeast‐trending Copper Creek normal fault juxtaposes a distinctive sequence of metacarbonate and granitoid rocks against a footwall of Upper Precambrian to Lower Cambrian quartzite and phyllite. Correlation of the hanging wall with footwall rocks to the northwest provides an approximate piercing point that requires 8–12 km displacement in an ESE direction. This displaced fault slice is itself bounded above by another normal fault (the Meadow Fork Fault), which brings down a hanging wall of dacitic to rhyolitic tuff that grades conformably upward into conglomerate. These relationships record the formation of a fault‐bounded basin between 41.3 and 37.4 Ma. The results are consistent with a regional pattern in which volcanism and extension swept southward from British Columbia to southern Ne...

Extensional deformation in the western United States, particularly in the Basin and Range, has frequently been ascribed to buoyancy forces arising from horizontal density contrasts. The Rio Grande rift is subject to buoyancy forces 2-3 times larger than those in the tectonically active northern Basin and Range, suggesting that it should be extending considerably faster than the northern Basin and Range, yet paradoxically is extending more slowly. Using a thin viscous sheet model, we test the hypothesis that regions surrounding the Rio Grande rift, which have rheologically stronger lithosphere, resist deformation and reduce the rate of extensional deformation in the Rio Grande rift to values consistent with observations. We find that these regions must have lithospheric strength at least twice that of the Rio Grande rift. This modest contrast in lithospheric strength is consistent with independent estimates derived from observations of heat flow, seismicity, and crustal thickness.

In areas with prolonged extensional histories or multiple episodes of extension, temporally distinct extensional fault systems, including dip-slip-normal, oblique-slip, and/or strike-slip faults, may form. These fault systems may be spatially distinct, overlapped, or completely superimposed, and different fault systems may have different fault strikes and extension directions. Although fault strike is not a very sensitive indicator of principal stress directions, changes through time in fault strike of as much as 90° exceed the uncertainty. Overprinted extensional fault systems of different ages with significantly different (to 90°) fault strikes and extension directions provide strong evidence of changes in the regional stress field with time. Tens of millions of years of extension occurred in the Basin and Range Province of the United States and many temporally distinct fault sets formed through that time. We document at least four extensional episodes and the fault kinematics of each, where possible, in the central Hiko Range, eastern Nevada. The four Cenozoic extensional events are prevolcanic, synvolcanic, postvolcanic Miocene–Pliocene (?), and postvolcanic Pliocene (?)–Quaternary. The prevolcanic faults strike north-south and are interpreted as footwall faults to the regional Eocene–Oligocene Snake-Stampede extensional system, which caused approximately east-west extension. The synvolcanic faults are late Oligocene–Miocene age and strike east-west. Although they are rare and have minor offset, they accommodated north-south–directed extension. Postvolcanic faults, part of the Timpahute lineament, are approximately east-west– striking normal and northeast-striking oblique-slip faults. They also accommodated approximately north-south extension during Miocene time. The northeast-striking left-normal oblique-slip fault set formed as new faults and records a change between north-south and east-west extension in Miocene time. Later east-west extension occurred along the Pliocene (?) to Quaternary Hiko fault zone. These four overprinted extensional systems show two separate changes in normal fault strike of ∼90°, from north-south to east- west and from east-west back to north-south. Consequently, the extension direction similarly changed through time. We suggest that causes for the changes in direction of upper crustal extension include a change from stresses created by (1) plate interactions, which generated approximately east-west extension, to (2) mantle motions, which generated approximately north-south extension, and (3) back again. The extension related to mantle motions is associated with a band of volcanism that passed across the northern Basin and Range Province, moving generally from north to south, during the protracted period of extension. Therefore, a change from plate boundary– or interaction-derived stresses to mantle- or volcanism-related stresses and back again is possible.

A wealth of pre-Cenozoic geologic markers across the central Basin and Range province, defined mainly by thrust faults developed within a miogeoclinal wedge, makes it one of the best areas on Earth to reconstruct large-scale continental extension. We use this ~100,000 km^2 region, bounded by the southern Sierra Nevada on the west and the Colorado Plateau on the east, to illustrate the concepts of correlation and misalignment for regional strain markers and of strain compatibility and kinematic viability in palinspastic reconstructions. The results indicate ~250 to 300 km of west-northwest motion of the Sierra away from the Plateau, accommodated by both crustal thinning and north-south shortening. Tertiary intermontane basin deposits and mineral cooling ages of deeply exhumed rocks constrain the overall kinematics of motion. Most of the westward motion occurred between 16 and 5 Ma, at rates near 2 cm/yr, slowing to 1 to 1.5 cm/yr in the last 5 Ma. We have quantified the partitioning of strain between vertical crustal thinning (via normal faults) and map-view plane strain (via conjugate strike-slip faults) by placing a grid of 10 x 10 km elements on a retrodeformed map of the region and measuring the increase in area of grid elements between the undeformed and present-day grids. This analysis yields a maximum finite elongation of the Basin and Range at 36°N to 37°N of 3.4, oriented N73°W. Map-view area balance shows that 20 percent of this elongation is compensated by ~north-south shortening, and 80 percent by crustal thinning. This yields an average thinning factor for the upper crust of 2.7 between the Sierra and Plateau, inconsistent with the hypothesis that Neogene deformation in the central Basin and Range is predominantly dextral-shear plane strain. These results, in concert with the observation that the southern Sierra Nevada has similar crustal thickness to the central Basin and Range, support the hypothesis of large-scale eastward flow of Sierran deep crust during extension.

The South Virgin Mountains and Grand Wash trough comprise a mid-Miocene normal fault system that defines the boundary between the unextended Colorado Plateau to the east and highly extended crust of the central Basin and Range province to the west. In the upper 3 km of the crust, the system developed in subhorizontal cratonic strata in the foreland of the Cordilleran fold and thrust system. The rugged topography and lack of vegetation of the area afford exceptional three-dimensional exposures. Compact stratigraphy and well-defined prefaulting configuration of the rocks permitted a detailed reconstruction of the system. Reconstruction of cross sections based on more than 300 km2 of detailed mapping at a scale of 1:12 000 shows that the fault system accommodated more than 15 km of roughly east-west–directed Miocene extension. Extension was initially accommodated on moderately to steeply dipping listric normal faults. As the early faults and fault blocks tilted, steeply to moderately dipping faults initiated within the fault blocks, soling into the early faults. Some of the early faults were active at dips of