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Strain rates assessed from brittle fracture (associated with historic earthquakes) and total brittle-ductile deformation measured from geodetic data have been compared to estimates of paleo-strain from Quaternary geology for the intraplate Great Basin part of the Basin-Range, western United States. These data provide an assessment of the kinematics...
Citations
... Similarly to several thrust belts worldwide affected by active extension (Copley et al., 2009;Eddington et al., 1987;Jackson & White, 1989;Nemcok et al., 2005;Poblet & Lisle, 2011), the origin of the current seismic release in the central Apennines is still matter of debate: it likely results from the interplay of different geodynamic factors (among the others: Chiarabba & Chiodini, 2013;Cowie et al., 2017) that trigger episodic slip on segmented normal faults crosscutting a previously shortened crust. In this complex seismotectonic setting, notwithstanding the wealth of neotectonic studies (see section 2), many aspects related to the detailed shallow structure and geometry of the active normal faults in the chain are still unsolved. ...
The Pian Grande di Castelluccio (PGC) basin is the main Quaternary depocenter of the Mt. Vettore‐Mt. Bove normal fault system (VBFS), responsible for the 30 October 2016 Mw 6.5 Norcia earthquake (central Italy). Coseismic surface faulting through the basin attests the occurrence of active splays of the seismogenic master fault; thus, we explore the subsurface basin structure to infer the long‐term behavior of the VBFS. We integrate electrical resistivity tomography (ERT), time domain electromagnetic soundings (TDEM), and horizontal‐to‐vertical spectral ratios of ambient seismic vibrations (HVSR) along a transect crossing the surface ruptures. The ERT models provide high‐resolution details of three shallow fault zones. One‐dimensional resistivity models from TDEM and HVSR frequency peaks suggest abrupt steps in the top bedrock caused by previously unknown faults and indicate an infill thickness of up to ~300 m. We also analyze shear wave splitting of S phases (fast direction φ and delay time δt) from local earthquakes recorded during our surveys to better constrain the fracture field and the properties of the inferred fault zones. We relate the retrieved pattern of fault‐parallel φ, and the associated larger δt, to the main and secondary faults in the upper crust and to the cracks or shear fabric in the damage zones of the active splays. The PGC basin is due to the interference of an older N30° striking fault system subsequently crosscut by the N150° striking VBFS, which is currently active, seismogenic, and capable of rupturing the surface during M > 6 earthquakes.
... Studies show that most of the deformation in the Walker Lane belt occurs along the eastern and western margins of the belt (Hammond et al., 2011). Furthermore, seismicity is concentrated at the eastern and western boundaries of the Basin and Range, with higher rates of strain localized on the western side within the Central Nevada seismic belt and the Walker Lane (Eddington et al., 1987). ...
A seismic compressed high-intensity radar pulse (CHIRP) survey of Pyramid Lake, Nevada, defines fault architecture and distribution within a key sector of the northern Walker Lane belt. More than 500 line-kilometers of high-resolution (decimeter) subsurface imagery, together with dated piston and gravity cores, were used to produce the first comprehensive fault map and attendant slip rates beneath the lake. A reversal of fault polarity is observed beneath Pyramid Lake, where down-to-the-east slip on the dextral Pyramid Lake fault to the south switches to down-to-the-west displacement on the Lake Range fault to the north. Extensional deformation within the northern two thirds of the basin is bounded by the Lake Range fault, which exhibits varying degrees of asymmetric tilting and stratal divergence due to along-strike segmentation. This structural configuration likely results from a combination of changes in slip rate along strike and the splaying of fault segments onshore. The potential splaying of fault segments onshore tends to shift the focus of extension away from the lake. The combination of normal-and oblique-slip faults in the northern basin gives Pyramid Lake its distinctive " fanning open to the north " geometry. The oblique-slip faults in the northwestern region of the lake are short and discontinuous in nature, possibly representing a nascent shear zone. In contrast, the Lake Range fault is long and well defined. Vertical slip rates measured across the Lake Range and other faults provide new estimates on extension across the Pyramid Lake basin. A minimum vertical slip rate of ~1.0 mm/yr is estimated along the Lake Range fault. When combined with fault length, slip rates yield a potential earthquake magnitude range between M6.4 and M7.0. Little to no offset on the Lake Range fault is observed in the sediment rapidly emplaced at the end of Tioga glaciation (12.5–9.5 ka). In contrast, since 9.5 ka, CHIRP imagery provides evidence for three or four major earthquakes, assuming a characteristic offset of 2.5 m per event. Regionally, our CHIRP investigation helps to reveal how strain is partitioned along the boundary between the northeastern edge of the Walker Lane and the northwest Basin and Range Province proper.
... Studies show that most of the deformation in the Walker Lane belt occurs along the eastern and western margins of the belt (Hammond et al., 2011). Furthermore, seismicity is concentrated at the eastern and western boundaries of the Basin and Range, with higher rates of strain localized on the western side within the Central Nevada seismic belt and the Walker Lane (Eddington et al., 1987). ...
The Pyramid Lake fault zone is located in a critical region of the Northern Walker Lane where transtension is accommodated through a complex pattern of dextral strike-slip and normal faulting. To the north, Sierra Nevada microplate motion is accommodated through a series of mostly dextral strike-slip faults (e.g., Honey Lake fault zone); in contrast to this more straightforward geometry, transtension to the south is expressed through a series of north-south-striking, normal fault bounded basins (e.g., Lake Tahoe basin) with small amounts of opening or fanning to the north that is accommodated through north-east striking sinstral faulting. The Pyramid Lake basin straddles this critical boundary between these different domains within the Northern Walker Lane, and thus, forms an ideal laboratory to study key aspects in the development of incipient rifting within transtensional systems (i.e., early Gulf of California). In June 2010, the University of Nevada, Reno, Scripps institution of Oceanography, and the USGS, Salt Lake City conducted a ten-day-long, high-resolution seismic CHIRP survey of Pyramid Lake. During this expedition, more than 500 line-kilometers of data were collected, spanning all regions of the lake. The Pyramid Lake fault, which enters the basin from the south, extending along the west side of the lake, near the shoreline, changes from a dextral strike-slip fault system south of the basin, to include a down-to-the-east normal component as it approaches and enters the lake. As the Pyramid Lake fault dies near mid-lake, the East Pyramid Lake fault becomes dominant and displays down-to-the-west motion; thereafter, splays into a series of dextral dip-slip faults on the northwest end of the lake. The Pyramid Lake basin shows strong segmentation and distinct polarity flips between the north and south ends of the lake. This region provides a natural laboratory to understand how strain is partitioned and how it evolves through time within a proto-rift that is dominated by dextral shear. We also investigated the on-land seismic structure of the dextral dip-slip faults northwest of Pyramid Lake. Last spring the University of Nevada, Reno carried out a program of 27 km of vibrator seismic acquisition. We used three heavy vibrators, long-offset recording with up to 240 channels live, SeisOpt® @2D™ velocity optimization from first arrivals, and prestack depth migration. The preliminary results showed clear imaging of stratigraphic terminations and intersecting fault planes, which the Pyramid Lake Paiute Tribe will use to locate test bores for geothermal power production. The stratigraphic offsets along the faults will help define the nature of the transtensional system north of Pyramid Lake.
... The Basin and Range province and all the continent to the west began to move in part with the Pacific plate. Even today, approximately 15% of the motion between the North American plate and the Pacific plate is taken up by opening in the Basin and Range province (Eddington et al., 1987). ...
An extensive review of geologic and tectonic features of western North America suggests that the interaction of oceanic plates with the continent follows a broad cycli-cal pattern. In a typical cycle, periods of rapid subduction (7-15 c d y r) , andesitic vol-canism, and trench-normal contraction are followed by a shift to trench-normal extension, the onset of voluminous silicic volcanism, formation of large calderas, and the creation of major batholiths. Extension becomes pervasive in metamorphic core complexes, and there is a shift to fundamentally basaltic volcanism, formation of flood basalts, widespread rifting, rotation of terranes, and extensive circulation of flu-ids throughout the plate margin. Strike-slip faulting becomes widespread with the creation of new tectonostratigraphic terranes. A new subduction zone forms and the cycle repeats. Each cycle is 50-80 m.y. long; cycles since the Triassic have ended and begun at approximately 225, 152, 92, 44, and 15 Ma. The youngest two cycles are diachronous, one from Oregon to Alaska, the other from central Mexico to Califor-nia. The transitions from one cycle to the next cycle are characterized by rapid and pervasive changes termed, in this chapter, "major chaotic tectonic events." These events appear to be related to the necking or breaking apart of the formerly sub-ducted slab at shallow depth, the resulting delamination of the plate margin, and the onset of a new subduction cycle. These are times of the most rapid apparent and true polar wander of the North American plate, when the plate appears most free to move relative to surrounding plates and relative to the mantle below the asthenosphere. In western North America, magmatism and tectonics during the Jurassic period are quite similar to magmatism and tectonics since mid-Cretaceous time except strike-slip faulting shifted in sense from left lateral to right lateral.
... Although much more work must be done to reconcile these conflicting estimates, the evidence for large-magnitude (-100%) extension in certain areas within the BRP is compelling [e.g., Proffett, 1977;Gans, 1987;Smith, 1989]. Seismicity [e.g., Eddington et al., 1987;Dewey et al., 1989] and geodetic data [e.g., Savage, 1983] clearly indicate that the BRP continues to extend today. Eddington et al. [1987] inferred contemporary BRP strain rates from seismicity data and found that extension is occurring principally along the eastern and western margins of the province and along the N-S trending Nevada Seismic Belt [Ryall et al., 1966] in westcentral Nevada. ...
... Seismicity [e.g., Eddington et al., 1987;Dewey et al., 1989] and geodetic data [e.g., Savage, 1983] clearly indicate that the BRP continues to extend today. Eddington et al. [1987] inferred contemporary BRP strain rates from seismicity data and found that extension is occurring principally along the eastern and western margins of the province and along the N-S trending Nevada Seismic Belt [Ryall et al., 1966] in westcentral Nevada. ...
... Savage [1983] noted that the contemporary deformation rate in the Nevada Seismic Belt (>2.5 mm/yr) is significantly greater than the geologically determined rates of Thompson and Burke [1973] (1 mm/yr over the past 12,000 years, and 0.4 mm/yr over the past 15 m.y.), strongly suggesting that this recent burst of extension is ephemeral, as has been inferred from independent evidence by other workers [Wallace and Whitney, 1984]. Eddington et al. [1987] and Zoback [1989] have speculated that the intense seismic activity along the Nevada Seismic Belt may be accompanied by magmatic intrusion at depth. To summarize, it should be emphasized that the location of this study, the Dixie Valley/Carson Sink area, is optimum for attempting to detect magmatic additions at the base of the crust. ...
Near-vertical and wide-angle seismic reflection data provide evidence for the presence of a magma body at the base of the crust beneath Buena Vista Valley in northwestern Nevada. The seismic response of this hypothesized magma body is characterized by high-amplitude, near-vertical P wave reflections and a comparably strong P-to-S converted phase. The magma body, referred to here as the Buena Vista Magma Body, is probably a single sill with thickness no greater than 200 m and length no greater than 1.8 km. The melt fraction in the sill is undoubtedly greater than 20–30%, and probably exceeds 50%. Melt composition is unconstrained. Although the age of the Buena Vista Magma Body is difficult to determine precisely, it is probably no older than 500,000 years. This suggests that magmatism in the Basin and Range Province is an ongoing process, despite the relative paucity of volcanic rocks erupted at the surface during the last 6 m.y.
... Figure 6 is a compilation of minimum principal stress directions for the ESRP and surrounding region. The state of stress in the Basin and Range province northwest of the ESRP appears to be characterized by northeast-southwest extension, as indicated by focal mechanisms primarily for the Borah Peak mainshock and aftershocks Richins et al., 1987;Eddington et al., 1987), and by a fault orientation analysis performed by I I I I I I I I I i I I I I I I I I I I I I I I I I I I I I I I I I I I I l I 100 200 300 400 ...
... The tectonic stress field southeast of the ESRP is characterized by an east-west-oriented extensional stress, as indicated by focal mechanisms with T-axes generally aligned east-west. In the Hebgen Lake-Yellowstone area, the T-axes appear to be oriented northeast-southwest to northwest-southeast (Doser, 1985;Eddington et al., 1987), although a recent inversion of 88 well-constrained focal mechanisms indicates that the direction of extension is most likely oriented NNE-SSW (Peyton et al., 1991). ...
Microearthquake monitoring suggests that infrequent, small-magnitude earthquakes are charactersitic of eastern Snake River Plain (ESRP) seismicity. Although a total of only 19 earthquakes have been observed to date, their relatively shallow occurrence at depths of 8km is consistent with the hypothesis that elevated crustal temperatures in the ESRP confine the brittle portion of the crust to the upper 6 to 10km. A composite focal mechanism of two microearthquakes located near the axis of the ESRP indicates normal faulting with a minor component of strike-slip motion. -from Authors
... This information is not presently available..Tectonic Causes Regional Stress/Strain Reversals. General east to northeast extension of the Intermountain seismic be!t, assessed by summing the moments of recent and historic earthquakes, is less than 1 mrn/yr on normal and oblique normal faults[Eddington, et al., 1987]. This compares to 4.7 mm/yr at the Yellowstone-Hebgen Lake region, 50 km north of the Teton fault, and approximately 1 mm/yr on the northern WasatchFront, 150 km southwest. ...
The valley block (hanging wall) of the central segment of the Teton fault rose 8 {plus minus} 0.7 mm during 1988 and 1989, relative to the mountain block west of the fault, a displacement opposite to that expected on a normal fault. The height change is based on first-order leveling data over a 21.2 km-long fault-crossing line of 42 permanent bench marks established and initially surveyed in 1988 and resurveyed in 1989. The rapid height change took place across a 1,200 m-wide zone coincident with the steep escarpment at the base of the range front including the surface trace of the east-dipping Teton fault, a major, active, range-front normal fault bounding the east side of the Teton Range at the northeastern edge of the Basin and Range province. The total stratigraphic offset across the fault, as much as 9 km, accumulated over the last 7 to 9 million years. Quaternary fault scarps, up to 52 m in height, cut Pinedale (about 14,000 yr) glacial and younger fluvial-alluvial deposits, indicating that the Teton fault has been the locus of several large, scarp-forming earthquakes in the past 14,000 years, and it exhibits up to 25 m of latest Quarternary displacement where crossed by the level line. Although the relative uplift of the hanging wall may be local and unique to the Teton fault, this unexpected observation of aseismic, reverse creep may have a variety of tectonic and non-tectonic causes, including hydrologic effects, aseismic fault creep or tilt, and pre-seismic dilation.
... The rate of extension within the Basin and Range of 1-12 mm/yr was estimated by Minster and Jordan [1984] from geologic strain, heat flow, paleoseismicity and recent seismicity. Eddington et al. [1987] estimated a rate of 8-10 mm/yr from a detailed analysis of historical earthquakes. ...
The Global Positioning System (GPS) has rapidly become one of the most important geodetic tools for studying tectonic deformation. With potential 3-dimensional relative positioning accuracies better than 1 cm, GPS can monitor secular deformation as well as rapid strain fluctuations due to seismic and volcanic activity. A 1970/1971 trilateration survey and 1987/1988 GPS observations suggest uniaxial convergence of 6.4 mm/yr oriented N25.1 °E in the eastern third of the Santa Barbara channel, and a combination of convergence and left-lateral shear to the west. GPS surveys have been conducted in the Imperial Valley during 1986, 1988, 1989, and 1990. About 5 ± 1 cm/yr plate-boundary displacement is observed across the valley, somewhat larger than rates obtained through conventional geodesy. These GPS observations have been influenced by the 1987 Superstition Hills earthquake sequence, the first occurrence of a large earthquake within a preexisting GPS network. The measurements suggest 130 cm right-lateral slip along the northwest trending Superstition Hills fault, and 30 cm left-lateral slip along the conjugate northeast trending Elmore Ranch fault. Imperial Valley leveling surveys conducted in 1931, 1941, 1974, 1978, and 1980, are integrated with seismic, geomorphic, and sub-surfacial structural data, to suggest the northern segment of the Imperial fault formed within the last 80,000 years, and support the hypothesis that the Gulf of California rift system is propagating northwestward into the North American continent.
... The rate of extension within the Basin and Range of 1-12 mm/yr was estimated by Minster and Jordan [1984] from geologic strain, heat flow, paleoseismicity and recent seismicity. Eddington et al. [1987] estimated a rate of 8-10 mm/yr from a detailed analysis of historical earthquakes. ...
The very long baseline interferometry (VLBI) measurements made in the western U.S. since 1979 as part of the NASA Crustal Dynamics Project provide discrete samples of the temporal and spatial deformation field. The interpretation of the VLBI-derived rates of deformation requires an examination of geologic information and more densely sampled ground-based geodetic data. In the first two of three related studies, triangulation and trilateration data measured on two regional networks, one in the central Mojave Desert and one in the Coast Ranges east of the San Andreas fault, have been processed. At the spatial scales spanned by these local geodetic networks, auxiliary geologic and geophysical data have been utilized to examine the relation between measured incremental strain and the accommodation of strain seen in local geological structures, strain release in earthquakes, and principal stress directions inferred from in situ measurements. In a third study, the geocentric position vectors from a set of 77 VLBI experiments beginning in October 1982 have been used to estimate the tangential rate of change of station positions in the western U.S. in a North-America-Fixed reference frame.
Although the last rhyolite eruption occurred around 70 ka ago, the silicic Yellowstone volcanic field is still considered active due to high hydrothermal and seismic activity and possible recent magma intrusions. Geodetic measurements document complex deformation patterns in crustal strain and seismic activity likewise reveal spatial and temporal variations in the stress field. We use earthquake data recorded between 1988 and 2010 to investigate these variations and their possible causes in more detail. Earthquake relocations and a set of 369 well-constrained, double-couple, focal mechanism solutions were computed. Events were grouped according to location and time to investigate trends in faulting. The majority of the events have normal-faulting solutions, subordinate strike-slip kinematics, and very rarely, reverse motions. The dominant direction of extension throughout the 0.64 Ma Yellowstone caldera is nearly ENE, consistent with the perpendicular direction of alignments of volcanic vents within the caldera, but our study also reveals spatial and temporal variations. Stress-field solutions for different areas and time periods were calculated from earthquake focal mechanism inversion. A well-resolved rotation of σ3 was found, from NNE-SSW near the Hebgen Lake fault zone, to ENE-WSW near Norris Junction. In particular, the σ3 direction changed throughout the years around Norris Geyser Basin, from being ENE-WSW, as calculated in the study by Waite and Smith (2004), to NNE-SSW, while the other σ3 directions are mostly unchanged over time. The presence of “chocolate tablet” structures, with two sets of nearly perpendicular normal faults, was identified in many stages of the deformation history both in the Norris Geyser Basin area and inside the caldera.
