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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.

The continental part of west-central Mexico is characterized by the active extensional tectonic regimes of the Trans-Mexican volcanic belt and the adjacent southern Basin and Range Province. The deformation of the latter is distributed over several topographically very pronounced grabens and half-grabens (width 10–20 km, length ≤200 km; throw 1–2 km), including the Aguascalientes, Juchipila, Tlaltenango, and Bolaños grabens. Here, an A.D. 1774–1775 earthquake series in that area is documented based on numerous contemporary sources. The 6 November 1774 mainshock caused moderate-to-severe damage in several communities of the Bolaños graben, including the silver mining town of Bolaños, and moderate damage to communities in the Tlaltenango graben, such as the administrative center of Colotlán. Based on the macroseismic intensity distribution, the epicenter was in the Bolaños graben. The preferred magnitude of the mainshock is ∼6.0±0.5. No major historical earthquake had been reported previously from this region. Existing ground-shaking hazard models may, therefore, give a false sense of security.In the Bolaños graben, motion along the graben-bounding faults and the observed tilting of the graben shoulders has to be mostly younger than the 19.9 Ma age of the youngest basalt of the graben-shoulder stratigraphy. Its correlation across the western master fault indicates a 1300 m throw and a vertical long-term slip rate of 0.07 mm/yr. The observations of alluvial fan deposits juxtaposed against the footwall ignimbrites along the western master fault of the Bolaños graben, the displacement of alluvial fan deposits along secondary faults within the graben, and the existence of hot springs along the western boundary fault all are indicative of active deformation, and so is evidently the A.D. 1774 earthquake.

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 accretion of the Avalon and Meguma terranes to the Laurentian margin was a major event in the development of the Appalachian orogen. The Minas Fault Zone delineates the boundary between these terranes. A strongly lineated and foliated granite intrusion (Kelly Brook pluton) exposed along the West River St. Mary's Fault intruded into Meguma Supergroup metasedimentary rocks. Well-developed C-S fabrics characterize the pluton with muscovite aligned in the S fabric, and a shallow (~10°) westerly plunging quartz stretching lineation. New U-Pb (zircon, LA-ICP-MS) geochronological data yield a crystallization age of 375.0 ± 4.6 Ma for the Kelly Brook pluton that is indistinguishable from other Late-Devonian intrusive rocks in the Meguma terrane. Petrographic data for muscovite indicate that it grew prior to deformation. A 100% plateau 40Ar/39Ar age of 369.0 ± 1.2 Ma on a single muscovite grain constrains the time of cooling of the granite to approximately 450 to 420 °C. Apatite grains also demonstrate pre- to syn-deformational fabrics and yield a U-Pb (LA-ICP-MS) age of 361.2 ± 5.6 Ma indicating the temperature of the granite was still above 350 °C at this time. Earliest Tournaisian fossils in the unconformably overlying Horton Group strata indicate that the granite was exposed by ca. 359 Ma. Exhumation rates of the Kelly Brook pluton and the Meguma terrane from approximately 9.5–13.3 km depth from ca. 375 Ma to surface exposure at ca. 359 Ma are 0.06 to 0.08 cm yr−1. Estimates for the Upper Devonian regional geothermal gradient in the northern Meguma terrane are high between 39.5 °C km−1 and 67.8 °C km−1, gradients that are common in extensional tectonic environments such as the Basin and Range province. An apatite fission-track age of 215 ± 14 Ma indicates Mesozoic reburial and reheating of the granite prior to opening of the Atlantic Ocean.

International audience; Breaking the lithosphere in extension without exceeding the driving far-field forces available on Earth is a tough quantitative modeling problem. One can tear it apart by propagation of an existing oceanic basin or weakness zone or one must assist rifting with magmatic processes, which drop the effective stress and weakens locally the lithosphere. While previous 3D models have demonstrated that non-cylindrical plumes produce almost cylindrical rift structures in a lithosphere under slight far-field loading, our contribution goes one step further by producing models of complete continental break-up. We investigate in details how the rheological stratification of the continental lithosphere interacting with active mantle plume influences the geometry and dynamics of rifting to continental break-up in 3D. We find that, irrespective of the rheological stratification, a plume-induced rifting process always occurs in two stages: an early crustal rifting stage and a late lithospheric necking (breakup) stage. In case of a rheologically decoupled lithosphere, initial brittle deformation is concentrated in the upper crust and strongly localized due to compensating ductile flow of lower-crustal material (core complex extension mode). On the contrary, rheological coupling between upper crust and lithospheric mantle results in highly distributed brittle deformation in the crust above mantle plume head (wide rift mode). Both core complex-like and wide rifting are followed by an abrupt transition to narrow rift stage when a localized ascent of mantle plume material focuses high strain along faults zones breaking through the entire lithosphere. The Main Ethiopian Rift, the Basin and Range province, and the East Shetland Basin may be natural examples of regions that have passed through these two stages of extension. Across-strike and along-strike asymmetry of break-up patterns arising spontaneously within initially symmetrical and laterally homogenous environment seems to be an intrinsic characteristic of plume-induced rifting.

The Gulf of California has a long tectonic history. Before the subduction of the Guadalupe and Magdalena plates ceased, extension of the Gulf began to the east, at the Basin and Range province. Later, it was focused west of the Sierra Madre Occidental and the opening of the Gulf started. Currently, the Gulf rifting has different characteristics to the north than to the south. In this study, we analyze the lithosphere thickness in the Gulf of California region by means of P -wave and S -wave receiver functions. We grouped our lithosphere-thickness estimates into five froups: 1) North of the Gulf, with a thin lithosphere (~ 50 km) related to the extension observed in the Salton Through region; 2) the northwestern part of Baja California, with a thicker lithosphere (~ 80 km), thinning towards the Gulf due to the extension and opening processes (~ 65 km); 3) central Baja California, with no converted phase corresponding to the lithosphere-asthenosphere boundary but evidence of the presence of a slab remnant; 4) the southern Baja California peninsula, showing a shallow lithosphere-astenosphere boundary (LAB) (

We derive surface velocities from GPS sites in the interior Northwest U.S. relative to a fixed North American reference frame to investigate surface tectonic kinematics from the Snake River Plain (SRP) to the Canadian border. The Centennial Tectonic Belt (CTB) on the northern margin of the SRP exhibits west-directed extensional velocity gradients and strain distributions similar to the main Basin and Range Province (BRP) suggesting that the CTB is part of the BRP. North of the CTB, however, the vergence of velocities relative to North America switches from westward to eastward along with a concomitant rotation of the principal stress axes based on available seismic focal mechanisms, revealing paired extension in the northern Rockies and shortening across the Rocky Mountain Front. This change in orientation of surface velocities suggests that the change in the boundary conditions on the western margin of North America influences the direction of gravitational collapse of Laramide thickened crust. Throughout the study region, fault slip rate estimates calculated from the new geodetic velocity field are consistently larger than previously reported fault slip rates determined from limited geomorphic and paleoseismic studies.

Evidence of geologic activity still occurring in the Rio Grande rift (RGR) includes quaternary faulting, seismicity, and widening at a small rate. We map the crustal thickness and seismic velocity ratio to generate constrained crustal model cross sections that highlight the regional extension of the southern RGR (SRGR). Specifically, we computed receiver functions and receiver function stacks for 147 stations from EarthScope USArray Transportable Array and previously collected data in the southwestern United States, and interpolated the crustal and velocity results using a kriging interpolation scheme. We include a new optimized gravity inversion approach using the receiver function results as a constraint for inverted density profiles. We produce constrained crustal models that characterize the SRGR as showing a shallower Moho (30 km) in the region of the SRGR, which is thicker than previously suggested. The crust appears to be delaminated west of the RGR in the Basin and Range Province and thicker east of the RGR toward the Great Plains with a denser lower crustal layer. We also find that the Delaware basin shows a significant geophysical anomaly, likely due to thick saturated sediments. Given that there is no deep mantle anomaly determined from other studies in this region, we suggest that rifting could be the result of small‐scale convection of the uppermost mantle, and we conclude that the RGR is at a minimum the boundary between the Basin and Range Province and the Great Plains, perhaps reflecting the terminus of flat slab subduction.

High-strain mylonitic rocks in Cordilleran metamorphic core complexes reflect ductile deformation in the middle crust, but in many examples it is unclear how these mylonites relate to the brittle detachments that overlie them. Field observations, microstructural analyses, and thermobarometric data from the footwalls of three metamorphic core complexes in the Basin and Range Province, USA (the Whipple Mountains, California; the northern Snake Range, Nevada; and Ruby Mountains–East Humboldt Range, Nevada), suggest the presence of two distinct rheological transitions in the middle crust: (1) the brittle–ductile transition (BDT), which depends on thermal gradient and tectonic regime, and marks the switch from discrete brittle faulting and cataclasis to continuous, but still localized, ductile shear, and (2) the localized–distributed transition, or LDT, a deeper, dominantly temperature-dependent transition, which marks the switch from localized ductile shear to distributed ductile flow. In this model, brittle normal faults in the upper crust persist as ductile shear zones below the BDT in the middle crust, and sole into the subhorizontal LDT at greater depths.In metamorphic core complexes, the presence of these two distinct rheological transitions results in the development of two zones of ductile deformation: a relatively narrow zone of high-stress mylonite that is spatially and genetically related to the brittle detachment, underlain by a broader zone of high-strain, relatively low-stress rock that formed in the middle crust below the LDT, and in some cases before the detachment was initiated. The two zones show distinct microstructural assemblages, reflecting different conditions of temperature and stress during deformation, and contain superposed sequences of microstructures reflecting progressive exhumation, cooling, and strain localization. The LDT is not always exhumed, or it may be obscured by later deformation, but in the Whipple Mountains, it can be directly observed where high-strain mylonites captured from the middle crust depart from the brittle detachment along a mylonitic front.

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.

Joint seismic and gravity analyses of the San Emidio geothermal field in the northwest Basin and Range province of Nevada demonstrate that joint optimization changes interpretation outcomes. The prior 0.3–0.5 km deep basin interpretation gives way to a deeper than 1.3 km basin model. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts, flattening antiformal reflectors that could have been interpreted as folds. Furthermore, joint optimization provides a clearer picture of the rangefront fault by increasing the depth of constrained velocities, which improves reflector coherency at depth. This technique provides new insight when applied to existing data sets and could replace the existing strategy of forward modeling to match gravity data. We have achieved stable joint optimization through simulated annealing, a global optimization algorithm that does not require an accurate initial model. Balancing the combined seismic-gravity objective function is accomplished by a new approach based on analysis of Pareto charts. Gravity modeling uses an efficient convolution model, and the basis of seismic modeling is the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests found that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Restricted offset-range migration analysis provides insights into precritical and gradient reflections in the data set.

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.

We present 264 new interseismic GPS velocities from the Mobile Array of GPS for Nevada Transtension (MAGNET) and continuous GPS networks that measure Pacific–North American plate boundary deformation in the Central Walker Lane. Relative to a North America-fixed reference frame, northwestward velocities increase smoothly from ∼4 mm/yr in the Basin and Range province to 12.2 mm/yr in the central Sierra Nevada resulting in a Central Walker Lane deformation budget of ∼8 mm/yr. We use an elastic block model to estimate fault slip and block rotation rates and patterns of deformation from the GPS velocities. Right-lateral shear is distributed throughout the Central Walker Lane with strike-slip rates generally

To better constrain the temperature structure in the upper mantle, we jointly invert seismic surface wave velocities and basalt thermobarometry. New measurements of the water concentration (1.0–3.5 wt %) and oxygen fugacity (FMQ + 0.5 to + 1.5) of basalts from seven recently active volcanic fields in the Basin and Range province (Cima, Pisgah, Amboy, Big Pine, Black Rock, Snow Canyon, W. Grand Canyon) enable more accurate equilibration pressure (P) and temperature (T) estimates of the mantle melts. We developed a revised thermobarometer that more precisely predicts the results of laboratory experiments on melts equilibrated with olivine and orthopyroxene and accounts for the effects of water and CO2. Applying these methods to basalts from the Basin and Range we find that most equilibrated near the dry solidus in P-T space and at depths in the vicinity of the lithosphere-asthenosphere boundary (LAB) inferred from receiver function analysis and Rayleigh surface wave tomography. The wet basalts should have begun melting well below the dry solidus, so the depths of equilibration probably reflect ponding of rising melts beneath the nominally dry lithosphere. A two-parameter thermal model is sufficient to simultaneously satisfy both the seismological and petrological constraints. In the model, the depth to the dry solidus defines the bottom boundary of the conductive lid, while the potential temperature (Tp) controls the asthenosphere and LAB thermal structure. The optimum estimates of Tp range from 1500°C, and depths to the LAB range from ∼55 to 75 km, with uncertainties on the order of ±50°C and ±10 km. In contrast to standard tomographic images or basalt thermobarometry, the output of the joint inversion is a geotherm that can be tested quantitatively against other observations.

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.

Vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways. Sparse but robust geodetic, seismic, and geologic observations in the Basin and Range province of the western United States indicate that immediately after an earthquake, vertical change primarily occurs as subsidence of the normal fault hanging wall. A few decades later, a ±100 km wide zone is symmetrically uplifted. The preserved topography of long-term rifting shows bent and tilted footwall flanks rising high above deep basins. We develop finite element models subjected to extensional and gravitational forces to study time-varying deformation associated with normal faulting. We replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust. A 60° dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone. Stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation. Focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall; the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width (

The question of whether structural segment boundaries along multisegment normal faults such as the Wasatch fault zone (WFZ) act as persistent barriers to rupture is critical to seismic hazard analyses. We synthesized late Holocene paleoseismic data from 20 trench sites along the central WFZ to evaluate earthquake rupture length and fault segmentation. For the youngest (

We used intensity information from five calibration earthquakes to estimate an intensity attenuation model for the Rio Grande rift region (encompassing west Texas, New Mexico, and southern Colorado). The attenuation model lies between similar models developed for the Basin and Range Province and central and eastern North America. Analysis of two test earthquakes occurring in 1931 and 2014 validated that the intensity attenuation relation adequately predicted the events’ magnitudes and epicenters. We then analyzed intensity information for nine historical (1906–1960) earthquakes to determine their magnitudes and epicenters. Our results indicate that the largest earthquakes of the 1906 Socorro, New Mexico, sequence had intensity magnitudes ( M I ) 5.7–5.9 and may represent north‐to‐south migration of seismicity associated with the Socorro magma body. Moderate earthquakes in 1935 and 1960 also are associated with the magma body. The 1938 Arizona–New Mexico border earthquake sequence occurred about 50 km northeast of the ongoing 2014 Arizona–New Mexico border sequence. The 17 September earthquake of the 1938 sequence had an M I (4.1) that was about 1.0 units less than that of the 29 June 2014 Arizona–New Mexico event ( M I 4.9).

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. …

During the 3 May 1887 Mw 7.5 Sonora earthquake (surface rupture end-to-end length: 101.8 km), an array of three north-south striking Basin-and-Range Province faults (from north to south Pitaycachi, Teras, and Otates) slipped sequentially along the western margin of the Sierra Madre Occidental Plateau. This detailed field survey of the 1887 earthquake rupture zone along the Pitaycachi fault includes mapping the rupture scarp and measurements of surface deformation. The surface rupture has an endpoint-to-endpoint length of ≥41.0 km, dips ~70°W, and is characterized by normal left-lateral extension. The maximum surface offset is 487 cm and the mean offset 260 cm. The rupture trace shows a complex pattern of second-order segmentation. However, this segmentation is not expressed in the 1887 along-rupture surface offset profile, which indicates that the secondary segments are linked at depth into a single coherent fault surface. The Pitaycachi surface rupture shows a well-developed bipolar branching pattern suggesting that the rupture originated in its central part, where the polarity of the rupture bifurcations changes. Most likely the rupture first propagated bilaterally along the Pitaycachi fault. The southern rupture front likely jumped across a step over to the Teras fault and from there across a major relay zone to the Otates fault. Branching probably resulted from the lateral propagation of the rupture after breaching the seismogenic part of the crust, given that the much shorter ruptures of the Otates and Teras segments did not develop branches.

Diffuse degassing processes provide valuable information on geothermal reservoir characteristics not only in the context of monitoring, but also for exploration purposes. Areas with increased gas emissions can be indicative of major upflow zones from the reservoir through deep-reaching, permeable fault zones. These fault zones may act as preferential target areas for geothermal production drillings. In this study it is successfully demonstrated that diffuse degassing measurements can be used for the detection and characterization of permeable structural elements. The combination of following techniques has been applied at the Brady's geothermal system in the Basin-and-Range Province (Nevada, USA): accumulation chamber method for carbon dioxide and hydrogen sulfide measurements, alpha-spectroscopic measurements of radon and thoron activity concentrations, and gamma-spectroscopic measurements of selected nuclides.

© 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.

The seismic effective quality factor (QC) and its frequently dependences or the frequency parameter (n) and attenuation coefficient (δ) for the Earth’s crust and upper mantle of the North Tanzanian divergence zone (East African rift system) were estimated from an analysis of the earthquake coda waves recorded in the SEISMO-TANZ’07 French-Tanzanian seismic experiment. The QC values increase and the n and δ values decrease with increasing frequency and length of the lapse time window. This behavior of the attenuation parameters may be evidence that the degree of heterogeneity of the lithosphere decreases with depth. Comparison of the depth variations in the attenuation coefficient δ and the frequency parameter n with the velocity structure of the region shows that there is a distinct change in the behavior of seismic wave attenuation at velocity discontinuities. The obtained attenuation parameters were compared with the same parameters obtained in our previous studies for other continental rift systems—the Baikal rift system (Eurasia) and the Basin and Range Province (North America).

The Southern terminus of the Rio Grande Rift region has been poorly defined in the geologic record, with few seismic studies that provide information on the deeper Rift structure. In consequence, important questions related to tectonic and lithospheric activity of the Rio Grande Rift remain unresolved. To address some of these geological questions, we collect and analyze seismic data from 147 EarthScope Transportable Array (USArray) and other seismic stations in the region, to develop a 3-D crust and upper mantle velocity model. We apply a constrained optimization approach for joint inversion of surface wave and receiver functions using seismic S wave velocities as a model parameter. In particular, we compute receiver functions stacks based on ray parameter, and invert them jointly with collected surface wave group velocity dispersion observations. The inversions estimate 1-D seismic S-wave velocity profiles to 300 km depth, which are then interpolated to a 3-D velocity model using a Bayesian kriging scheme. Our 3-D models show a thin lower velocity crust anomaly along the southeastern Rio Grande Rift, a persistent low velocity anomaly underneath the Colorado Plateau and Basin and Range province, and another one at depth beneath the Jemez lineament, and the southern RGR.

Tectonic activity generates topography, and the variability of tectonic forcing is responsible for topographic patterns and variability of relief in fluvial landscapes. Despite this basic relation, the inverse problem, by which features of the topography are used for inferring tectonic uplift rates, has proven challenging. Here we develop formal linear inversion schemes to infer a record of the rate of relative uplift as a function of space and time from the long profiles of rivers. The relative uplift rate is the difference between the rates of rock uplift and of the base level change. The inversion schemes are based on a closed-form analytic solution to the transient linear stream power model, and to increase model resolution they make use of the multiplicity of information made available by multiple rivers and their tributaries. The distribution of the fluvial response time to tectonic perturbations is a key component of the inversion scheme, as this determines which tectonic events are preserved in the topography. We develop two inversion parameterizations that differ in their assumptions about the tectonic forcing: space-invariant and time-space variability with an assumed spatial distribution. The inversion schemes are applied to the Inyo Mountains, an uplifted block along the western boundary of the Basin and Range Province in California. Inversion results indicate that the range has been experiencing an acceleration of the relative uplift in the past ∼2-3 Ma. We use the inversion results to constrain the paleotopography and paleo-erosion rate along the range and to recover the throw rate history along the fault that bounds the Inyo range.

We use data from western U.S. GPS networks to estimate the rate, pattern, and style of tectonic deformation of the central Basin and Range Province (BRP). Previous geodetic investigations have found the crust of eastern Nevada and western Utah to act as a rigid microplate, with zero deformation rates to within measurement uncertainty. Observed transients in GPS time series have led others to propose a megadetachment model, predicting that the central BRP behaves as a microplate, but with time-varying translation. Here we reassess these hypotheses, benefiting from a significant increase in GPS stations and time span, and innovations in analysis techniques. Our results show that the BRP crust deforms everywhere and all the time. In a group of 24 stations between longitude −113.5° and −116.8°, we find strain rates of 1.9 ± 0.2 × 10−9 yr−1 extension directed N55°W and 2.2 ± 0.2 × 10−9 yr−1 contraction directed N35°E, inconsistent with microplate behavior. The linearity of time series of strain from GPS station triplets is inconsistent with episodic translation of quasi-rigid domains. One exception is station EGAN that exhibits nonlinear motion not found in adjacent stations. The dominant signal in Nevada is distributed shear consistent with Pacific/North America relative plate motion, suggesting that stresses are transmitted through the lithosphere at least 800 km from the plate boundary. The observed active extension is consistent with earthquake focal mechanisms and is in agreement with integrated rates estimated from earthquake geology. Our results do not support the proposed megadetachment in the BRP.

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.

In this article, we demonstrate the use of the 2D directional continuous wavelet transform (DCWT) for structural boundary delimitation. We include an example of Bouguer gravity anomaly data analysis from the Basin and Range Province of the United States. Our approach is based on mapping maxima in the modulus of the directional continuous wavelet transform for various scales. We initially validate our concept using synthetic gravity anomaly fields generated from cylindrical and prismatic model bodies (source geometries). Subsequent application of our concept to real gravity anomaly data shows that the method is versatile and robust.

Recent national programs in Canada (Lithoprobe) and the U.S. (EarthScope) are providing vast quantities of data and many new scientific insights concerning crustal and lithospheric mantle structure and evolution. More modest but significant results are also being produced in and about Mexico. This paper primarily focuses on results published since 2005 and presents an updated Moho map of North America. This overview of crustal structure does reveal a number of interesting observations. For example, two buried distinct crustal blocks have been discovered in the past 20 years. One was caught in a Precambrian suture zone in Canada, and the other is buried under the Gulf Coast region and is still of unknown origin. The Precambrian assembly of the continent has been documented by the mapping of numerous suture zones, and shallow portions of subducted slabs have been preserved in several cases. Not surprisingly, the internal structure of these suture zones is complex and highly variable. Isostatic adjustment has been shown to be a complex process involving the lithospheric mantle not just crustal structure variations. Specifically, the correlation of crustal thickness with elevation is only approximate at best. Several crustal blocks that have been stable over very long periods of time possess unusually thick crust whose lower portion is usually fast (Vp > 7.0 km/s). Rifting has been shown to affect the crust in a variety of ways ranging from the massive magmatic modification that produced the Mid-continent rift system to the broad region of extension in the Basin and Range province. Crustal structure along the active modern western margin of North America is highly complex as would be expected as a result of transitions between subduction and transform faulting and variations in volcanism and intraplate magmatism. We clearly still have a lot to learn about the structure and evolution of this continent.

To evaluate whether anatectic and/or highly fractionated lithophile element-enriched rhyolite tuffs deposited in arid lacustrine basins lose enough lithium during eruption, lithification, and weathering to generate significant Li brine resources, pre-eruptive melt compositions, preserved in inclusions, and the magnitude of post-eruptive Li depletions, evident in host rhyolites, were documented at six sites in the western United States. Each rhyolite is a member of the bimodal basalt-rhyolite assemblage associated with extensional tectonics that produced the Basin and Range province and Rio Grande rift, an evolving pattern of closed drainage basins, and geothermal energy or mineral resources. Results from the 0.8 Ma Bishop tuff (geothermal) in California, 1.3 to 1.6 Ma Cerro Toledo and Upper Bandelier tephra (geothermal) and 27.9 Ma Taylor Creek rhyolite (Sn) in New Mexico, 21.7 Ma Spor Mountain tuff (Be, U, F) and 24.6 Ma Pine Grove tuff (Mo) in Utah, and 27.6 Ma Hideaway Park tuff (Mo) in Colorado support the following conclusions. Melt inclusions in quartz phenocrysts from rhyolite tuffs associated with hydrothermal deposits of Sn, Mo, and Be are extremely enriched in Li (1,000s of ppm); those from Spor Mountain have the highest Li abundance yet recorded (max 5,200 ppm, median 3,750 ppm). Forty-five to 98% of the Li present in pre-eruptive magma was lost to the environment from these rhyolite tuffs. The amount of Li lost from the small volumes (1–10 km3) of Li-enriched rhyolite deposited in closed basins is sufficient to produce world-class Li brine resources. After each eruption, meteoric water leaches Li from tuff, which drains into playas, where it is concentrated by evaporation. The localized occurrence of Li-enriched rhyolites may explain why brines in arid lacustrine basins seldom have economic concentrations of Li. Considering that hydrothermal deposits of Sn, Mo, Be, U, and F may indicate potential for Li brines in nearby basins, we surmise that the world’s largest Li brine resource in the Salar de Uyuni (10 Mt) received Li from nearby rhyolite tuffs in the Bolivian tin belt.

[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.

The depths of mantle melting zones can be constrained by forward (in terms of physicochemical thermodynamics) or inverse (in terms of equilibrium thermodynamics) modeling. However, there is discrepancy in this respect between fluid-dynamic models of decompression melting in convecting upper mantle and thermodynamic models of basaltic magma sources beneath mid-ocean ridges. We investigate the causes of the mismatch in melting depth predictions with reference to the magmatic systems of the Basin and Range Province in the western margin of North America. The inverse solutions turn out to represent melts from different substrates (depth facies) in the lithospheric mantle, while modeling decompression melting in convecting fertile upper mantle refers to the depths the faults in spreading zones never reach. The discrepancy between forward and inverse solutions may be due to the fact that the respective depth estimates correspond to different levels of the same mantle–crust magmatic systems.

We welcome you to the 2013 Annual Meeting of the Seismological Society of America in Salt Lake City. On 24 July 1847, when Mormon pioneers first viewed the Salt Lake Valley, Brigham Young famously pronounced, "This is the right place" - the place of destiny and refuge they had been seeking. By the time of Young's death in 1877, Mormon pioneers had extensively colonized most of what we now recognize as Utah's main seismic belt, notably along the Wasatch Front, the western escarpment of the Wasatch Range that forms the eastern topographic boundary of the Basin and Range Province (Fig. 1). This contrast in geology and geography signals active tectonic forces inexorably at work.

[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.

This paper presents results of the study of attenuation of seismic waves in the lithosphere and upper mantle of the northern part of the Basin and Range Province (BRP) (Fig. 1). In this study, the coda-wave method [Aki, Chouet, 1975] is applied to process data collected in the seismic experiment conducted in 1988–1989, PASSCAL Basin and Range Passive Seismic Experiment [Owens, Randall, 1989], including records of 66 earthquakes and explosions (Mb=1.1–5.0) which occurred in BRP (Fig. 2). The effective seismic quality factor by the coda is calculated using the single-backscattering model [Aki, Chouet, 1975]. The QC values are calculated for 18 values of the lapse time window W from 10 to 95 sec with the step of 5 sec at six (6) central frequencies (0.3, 0.75, 1.5, 3.0, 6.0, and 12.0 Hz). In total, 7776 individual measurements of QC were done. It is observed that the quality factor QC is strongly dependent on the frequency and the lapse time window W: QC increases from 12±6 to 359±17 for the central frequencies of 0.3 and 12.0 Hz when the lapse time window is W=10 sec and from 87±6 to 1177±87 for the same frequencies when W=95 sec (Fig. 6). On the basis of the QС values obtained for all the lapse time windows W empirical relationships of quality factors and frequencies are calculated according to [Mitchell, 1981], and values of quality factor Q0 at reference frequency f0 (f0=1 Hz) and frequency parameter n (which is close to 1 and varies depending on the heterogeneity of the medium [Aki, 1981]) are obtained. In this study, Q0 varies from 60±8 to 222±17, the frequency parameter ranges from 0.57±0.04 to 0.84±0.05, and the attenuation coefficient δ varies from 0.015 to 0.004 km–1, depending on W (Fig. 8); similar values of attenuation parameters are typical of regions with high tectonic activity [Mak et al., 2004]. In the single-backscattering model, the dependence of the attenuation parameters from the lapse time window can be explained in terms of the depth of formation of the coda [Pulli, 1984]: a larger value of W corresponds to a greater depth through which the coda-waves go. As shown by the analysis of variations of attenuation coefficient δ and frequency parameter n for the Basin and Range Province, both parameters decrease irregularly with depth – the slope of the curve showing variations of δ is considerably changed at the depth of 150 km. At the top of the graph (to the depth of 150 km), an abrupt change of δ with depth is observed; it is clearly seen in the graph of gradient δ (Fig. 9 and Fig. 10); such behaviour is also characteristic of n. At the depth of 140 km, parameter n is increased. In the middle section (at depths of 150–200 km), the slope of the δ curve increases, and gradients of δ and the frequency parameter are significantly reduced. At the bottom of the profile (> 200 km), the value of δ is almost constant, and an abrupt increase of n is observed (Fig. 9 and Fig. 10). Figure 10 shows the high-speed profile of the area under study, which is published in [Wagner et al., 2012]. The profile shows the low velocity mantle under the Basin and Range Province, actually starting underneath the Moho (at the depth of 50–60 km). The lower boundary of the low-velocity mantle is located at the depth of 130–160 km. Thus, there are grounds to conclude that the change in the slope of the curve showing dependence of δ from the depth is related to the deep structure of the medium. The abrupt changes of δ and n are associated with the velocity discontinuities of the medium. The high values of δ and n, which are characteristic of the upper part of the profile, indicate the high degree of heterogeneity of the medium, which is also confirmed by the low velocities of seismic waves in the area under study [Wagner et al., 2012]. The reduction of parameters δ and n in the middle and lower parts of the profile suggests a more homogeneous structure of the medium at larger depths. As a result of the study of the characteristics of seismic wave’s attenuation in the lithosphere and the upper mantle of the northern part of the Basin and Range Province, it is established that the effective seismic quality factor QC is highly dependent on the frequency in the range of 0.5–16.0 Hz. The empirical relationships of Q(f) for various lapse time windows are obtained; it is shown that increasing the lapse time window causes the values of the effective seismic quality factor to increase, which may be interpreted as reduction of attenuation with depth. By comparing the depth variations of the attenuation coefficient and the frequency parameter against the velocity structure, it is shown that there is a distinct change in attenuation of seismic waves at the velocity discontinuities in the northern part of the Basin and Range Province.

Asthenosphere beneath the relatively thin lithosphere of the Basin and Range province appears to be juxtaposed in step-like fashion against the Colorado Plateau's thick lithospheric keel. Primary to near-primary basalts are found above this edge, in the San Francisco-Morman Mountain volcanic fields, north central Arizona, western USA. We show that at least two distinct peridotite-dominated mantle end-members contributed to the origin of the basalts. One has paired Nd and Hf isotopic characteristics that cluster near the mantle array and trace element patterns as expected for melts generated in the asthenosphere, possibly in the presence of garnet. The second has isotopic compositions displaced above the eHf - eNd mantle array which, together with its particular trace element characteristics, indicate contributions from hydrogenous sediments and/or melt (carbonatite or silicate)-related metasomatism. Melt equilibration temperatures obtained from Si- and Mg-thermobarometry are mostly 1340–1425°C and account for the effects of water (assumed to be 2 wt.%) and estimated CO2 (variable). Melt equilibration depths cluster at the inferred location of the lithosphere-asthenosphere boundary at ∼70–75 km beneath the southwestern margin of the Colorado Plateau but scatter to somewhat greater values (∼100 km). Melt generation may have initiated in or below the garnet-spinel facies transition zone by edge-driven convection and continued as mantle and/or melts upwelled, assimilating and sometimes equilibrating with shallower contaminated mantle, until melts were finally extracted.

Stable isotope paleoaltimetry data from the Snake Range metamorphic core complex (MCC) and Sacramento Pass Basin (NV, USA) document that extensional mylonite zones and kinematically linked syntectonic basins reliably record paleotopography in the continental interior of western North America when compared to a sea-level reference. Here we show that this basin–MCC pair tracks meteoric fluid flow at different levels of actively extending crust in a high-topography region during Oligo-Miocene extension of the Basin and Range Province. For paleoaltimetry purposes we compare multi-proxy oxygen (δ 18 O) and hydrogen (δD) isotope data as well as geochronological information from the Snake Range MCC to a time-equivalent (ca. 20 Ma) stable isotopic proxy record from the Buckskin Mountains MCC (AZ, USA), which developed next to the Pacific Coast near Miocene sea level. We complement this paleoaltimetry study by comparing the Buckskin Mountains MCC data with older (∼35 Ma) lacustrine stable isotope and paleofloral records from the nearby House Range (UT, USA), whose paleoelevation has been determined independently through paleobotanical analysis. Each of the investigated compartments of the paleohydrologic system within the Snake Range MCC depicts a coherent scenario of low Oligo-Miocene δ 18 O and δD values of meteoric water that reflect precipitation sourced at high elevation. A 77‰ difference in δD water between the Snake Range (δD water ∼−113‰) and the Buckskin Mountains (δD water ∼−36‰) is consistent with minimum mean paleoelevation of the Snake Range of about 3850±650 m above Miocene sea level. Additional support for such elevations comes from a comparison between the Buckskin Mountains MCC and the Eocene House Range basin (UT, USA) where differences in δ 18 O water values are consistent with 2300±500 m minimum paleoelevation of the House Range. Based on the presence of brecciated rock-avalanche deposits within the Sacramento Pass Basin, we conclude that the Snake Range was a topographic high and locus of significant relief during regional scale extension within the Cordilleran hinterland.

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.

Smith Valley is bounded on its western edge by an active normal fault and the Pine Nut mountains. Displacement on the fault is responsible for development of one of the westernmost basins of the Basin and Range province of the western United States. Interpretation of an exposure afforded by excavation of a trench across the range-bounding fault places the most recent surface-rupture earthquake after 5176±130 cal yr B.P. and suggests it was close in time to 3530±82 cal yr B.P. Utilization of tephrochonologic and cosmogenic analyses and mapping of fault scarps across the Artesia Road fan are the basis for putting forth an initial estimate of the late Pleistocene vertical slip rate of the fault at between 0.125 mm/yr and 0.33 mm/yr.

SUMMARY Many extension zones have been subjected to folding and shortening in a direction perpendicular to the stretching. Such deformation can be accounted for by the extension of a thin superficial elastic layer overlying a substrate that has small elastic moduli or that deforms in a viscous regime. Laboratory experiments are used to document the wavelength and amplitude of the folds for a range of geometrical configurations. Folding is observed even for very small amounts of extension (less than 1 per cent) with characteristics that are consistent with finite-amplitude scaling laws. Because of the intrinsically 3-D nature of the deformation field, the size of the region affected by folding and the direction of the fold axes depend on the orientation of the extension with respect to the rigid blocks that bound the deforming region. For regions of extension where the elastic thickness is about 10 km, as in the Basin and Range province for example, it is predicted that folding occurs with wavelengths in a 20–40 km range, such that it induces little deformation in the lower crust and maintains a flat Moho discontinuity. These predictions are consistent with the observations. The characteristics of faulting that is associated with such deformation are discussed.

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.

Seismic reflection profiling demonstrates that the active, significant-offset Surprise Valley Fault that marks the western boundary of the Basin-and-Range Province in northernmost California dips at a moderate angle, only ~ 30° to ~ 2 km depth. A nearby seismic refraction/wide-angle reflection profile, albeit of lower-resolution, shows the fault-plane remains approximately planar to at least 7 km depth. Variably-tilted volcanic strata of known ages within the Surprise Valley basin demonstrate that ≥ 7 km of normal slip occurred along the Surprise Valley Fault within the past 8–4 Myr at a time-averaged slip rate of ~ 1–2 mm/yr, and that the fault rotated from an initial dip of as much as 60° to its present dip of 30°. The rotation of this isolated fault was not accomplished by domino-style rotation as seen elsewhere in the Basin-and-Range province, but rather by flexural rift-shoulder uplift aided by mid-crustal flow.

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.

We calculated the spectral decay parameter (κ) in the southern Basin and Range province, using records from earthquakes located near the Pitaycachi fault. We found that for a given distance and recording site the values of κ vary considerably, possibly as a result of the lateral heterogeneity of the crust. Individual values of κ do not show a clear trend with magnitude, nor with the average values of κ. The average values of κ tend to increase with distance up to about 70-80 km and then to decrease between 80 and 100 km, suggesting higher S-wave attenuation at shallow depths and lower attenuation for deeper paths. We analyzed the possible dependence of κ on earthquake size by determining empirical curves that describe the behavior of κ with distance and magnitude. Our results indicate that κ is independent of earthquake size within the magnitude range ( M< 3:5) of the events analyzed. The nonparametric curves also provided site-specific estimates of κ near the surface (κ0) for the stations and groups of stations analyzed. We found that the average κ0 value of 0.04 sec in northeastern Sonora is similar to values of κ0 reported in other regions. We conclude that κ0 depends not only on the rock type but also on the degree of fracturing and erosion of the rocks near the recording site.

High-grade epithermal gold deposits in the Northern Great Basin have long been associated with regional Miocene basaltic to rhyolitic volcanism. Previous models for the low-sulfidation epithermal gold ores in this region have generally portrayed the bimodal magmas as a source of heat to drive large-scale convection of meteoritic water that leached gold from crustal sources and deposited it in hydrothermal vein systems, or required that the gold evolve from fractionated silicic magmas. New data of the present study indicate a more direct genetic link to the plume-related basaltic magmas of the region. Laser 40Ar/39Ar incremental heating plateau ages for single crystals of adularia from several of these low-sulfidation epithermal gold deposits range from 16.6 Ma to 15.5 Ma. Adularia from the Jumbo deposit yields three concordant plateau ages with a combined statistical result of 16.54 ± 0.04 Ma (95% confidence level, MSWD = 0.23). Plateau ages for adularia from other deposits in the region, and from gold-bearing veins in the Owyhee Mountains of southwestern Idaho, yield similar ages up to ~16.5 Ma, however some veins are as young as ca. 15.5 Ma and the grain-to-grain ages for a given sample can vary by up to ca. 0.5 Ma. Observed variations in age among the adularia crystals of a given rock sample indicate varying amounts of extraneous argon, and also loss of radiogenic 40Ar, among the population of grains for a particular sample. The single-crystal results are interpreted to indicate a 16.5–15.5 Ma interval for formation of gold-bearing adularia veins in the region. The initiation and duration of this gold-forming event appears contemporaneous (within uncertainties) with the basaltic volcanism at the Steens Mountain section and an ensuing one-million-year episode of basaltic volcanism from multiple centers in the region ( Brueseke et al., 2007 ). Trace amounts of lead are alloyed with gold in the deposits studied. The isotopic compositions of this lead are not compatible with regional crustal units that host the gold ores, or the silicic igneous lithologies of the region, but have the same lead isotopic composition as basalts of the earliest Yellowstone plume (represented by the earliest lavas of the Columbia River basalt province, the Steens basalts, and Stonyford Volcanic Complex; Hanan et al., 2008 ). We propose that the gold studied and its traces of alloyed lead were derived together from the mantle, released from basaltic magma chambers of the province, and carried by low-density fluids into shallow geothermal systems during the earliest stages of Yellowstone hotspot magmatism.

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.

A high degree of correlation between present-day relative rock uplift measured using continuous GPS geodesy and spatially averaged surface elevations suggests that long-wavelength topographic relief is presently increasing along the southeastern flank of the Sierra Nevada range and within an adjacent portion of the northern Basin and Range province. Current estimates for erosion rate are an order of magnitude smaller than the relative rates determined by geodesy. Thus, although the uplift serves to enhance long-wavelength relief, it cannot be explained entirely as an isostatic response to erosion. If uplift rates have been constant through time, the duration over which the uplift could have been active (