Continental rupture and the creation of new crust in the Salton Trough rift, Southern California and northern Mexico: Results from the Salton Seismic Imaging Project

A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, California and Mexico, was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting. From the northern Salton Sea to the southern Imperial Valley, the crust is 17–18 km thick and approximately one-dimensional. The transition at depth from Colorado River sediment to underlying crystalline rock is gradual and is not a depositional surface. The crystalline rock from ~3 to ~8 km depth is interpreted as sediment metamorphosed by high heat flow. Deeper felsic crystalline rock could be stretched preexisting crust or higher-grade metamorphosed sediment. The lower crust below ~12 km depth is interpreted to be gabbro emplaced by rift-related magmatic intrusion by underplating. Low upper mantle velocity indicates high temperature and partial melting. Under the Coachella Valley, sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement. Mafic rock does not exist at 12–18 km depth as it does to the south, and a weak reflection suggests Moho at ~28 km depth. Structure in adjacent Mexico has slower midcrustal velocity, and rocks with mantle velocity must be much deeper than in the Imperial Valley. Slower velocity and thicker crust in the Coachella and Mexicali valleys define the rift zone between them to be >100 km wide in the direction of plate motion. North American lithosphere in the central Salton Trough has been rifted apart and is being replaced by new crust created by magmatism, sedimentation, and metamorphism

Symptom-based stratification of patients with primary Sjögren's syndrome: multi-dimensional characterisation of international observational cohorts and reanalyses of randomised clinical trials

Background Heterogeneity is a major obstacle to developing effective treatments for patients with primary Sjögren's syndrome. We aimed to develop a robust method for stratification, exploiting heterogeneity in patient-reported symptoms, and to relate these differences to pathobiology and therapeutic response. Methods We did hierarchical cluster analysis using five common symptoms associated with primary Sjögren's syndrome (pain, fatigue, dryness, anxiety, and depression), followed by multinomial logistic regression to identify subgroups in the UK Primary Sjögren's Syndrome Registry (UKPSSR). We assessed clinical and biological differences between these subgroups, including transcriptional differences in peripheral blood. Patients from two independent validation cohorts in Norway and France were used to confirm patient stratification. Data from two phase 3 clinical trials were similarly stratified to assess the differences between subgroups in treatment response to hydroxychloroquine and rituximab. Findings In the UKPSSR cohort (n=608), we identified four subgroups: Low symptom burden (LSB), high symptom burden (HSB), dryness dominant with fatigue (DDF), and pain dominant with fatigue (PDF). Significant differences in peripheral blood lymphocyte counts, anti-SSA and anti-SSB antibody positivity, as well as serum IgG, κ-free light chain, β2-microglobulin, and CXCL13 concentrations were observed between these subgroups, along with differentially expressed transcriptomic modules in peripheral blood. Similar findings were observed in the independent validation cohorts (n=396). Reanalysis of trial data stratifying patients into these subgroups suggested a treatment effect with hydroxychloroquine in the HSB subgroup and with rituximab in the DDF subgroup compared with placebo. Interpretation Stratification on the basis of patient-reported symptoms of patients with primary Sjögren's syndrome revealed distinct pathobiological endotypes with distinct responses to immunomodulatory treatments. Our data have important implications for clinical management, trial design, and therapeutic development. Similar stratification approaches might be useful for patients with other chronic immune-mediated diseases. Funding UK Medical Research Council, British Sjogren's Syndrome Association, French Ministry of Health, Arthritis Research UK, Foundation for Research in Rheumatology

Alien Registration- Kell, Annie J. (Augusta, Kennebec County)

https://digitalmaine.com/alien_docs/18334/thumbnail.jp

Interpretations of a 3D Seismic Volume, Hawthorne Geothermal Field, Nevada

Hawthorne, Nevada is located in the Walker Lake Domain of the Great Basin, a region in the western United States known for extensional tectonics and the high temperature gradients necessary for geothermal power production. Geothermal heat sources include magmatic types and extensional. The extensional type is more common for Nevada, where near-surface thermal gradients come from a thinned crust instead of from volcanism. Extensional systems often do not exhibit surface indicators such as springs or fumaroles; rather, the thermal fluids remain capped below the surface in “blind” systems requiring the need for geophysical exploration. Heterogeneous compositions and seismic velocities common to geothermal systems create particular seismic imaging difficulties because simplifying assumptions about velocity gradients cannot be made. A 3d seismic volume collected by the Navy Geothermal Programs Office on the Hawthorne Ammunitions Depot represents a rare opportunity to examine the range of geologic interpretations that can exist on seismic data in the Great Basin. Strong reflection events within the volume project to a ~20 degree dip, allowing the possibility of a low angle normal fault; while bedding offsets could be interpreted as a series of steep basinward step faults. Synclines in vertical sections correspond to concentric circles in horizontal sections, not only raising questions about the possibility of migration processing artifacts, but also present similarities to sill intrusions as seen in marine 3d data. This paper explores the seismic evidence for a range of structural interpretations

The application of active-source seismic imaging techniques to transtensional problems the Walker Lane and Salton Trough

The plate margin in the western United States is an active tectonic region that contains the integrated deformation between the North American and Pacific plates. Nearly focused plate motion between the North American and Pacific plates within the northern Gulf of California gives way north of the Salton Trough to more diffuse deformation. In particular a large fraction of the slip along the southernmost San Andreas fault ultimately bleeds eastward, including about 20% of the total plate motion budget that finds its way through the transtensional Walker Lane Deformation Belt just east of the Sierra Nevada mountain range. Fault-bounded ranges combined with intervening low-lying basins characterize this region; the down-dropped features are often filled with water, which present opportunities for seismic imaging at unprecedented scales. Here I present active-source seismic imaging from the Salton Sea and Walker Lane Deformation Belt, including both marine applications in lakes and shallow seas, and more conventional land-based techniques along the Carson range front. The complex fault network beneath the Salton Trough in eastern California is the on-land continuation of the Gulf of California rift system, where North American-Pacific plate motion is accommodated by a series of long transform faults, separated by small pull-apart, transtensional basins; the right-lateral San Andreas fault bounds this system to the north where it carries, on average, about 50% of total plate motion. The Salton Sea resides within the most youthful and northerly "spreading center" in this several thousand-kilometer-long rift system. The Sea provides an ideal environment for the use of high-data-density marine seismic techniques. Two active-source seismic campaigns in 2010 and 2011 show progression of the development of the Salton pull-apart sub-basin and the northerly propagation of the Imperial-San Andreas system through time at varying resolutions. High fidelity seismic imagery documents the timing of strain transfer from the Imperial fault onto the San Andreas fault through the application of sequence stratigraphy. Evidence shows that the formation of the Salton and Mesquite sub-basins and the associated change of strain partitioning occurred within the last 20-40 k.y., essentially modifying a broader zone of transtension bounding the Imperial and San Andreas faults into two smaller zones of focused extension. The sedimentary infill within the Salton sub-basin has been modified through hydrothermal alteration and magmatism providing new insight into the formation of crust within a basin characterized by thick sediments and high heat flow. Modern earthquakes beneath the Salton Sea proper appear to nucleate at times within this altered sedimentary pile, providing constraints on the degree of metamorphism of lake sediments that now comprise "basement." Stratigraphic relationships within the northern Salton Sea also provide evidence that the southern San Andreas fault locally dips to the southwest and this geometry has persisted for at least the past 200-300 k.y. The north-central Walker Lane contains a diffuse network of both strike-slip and normal faults, with some degree of strain partitioning characterized by normal faulting to the west along the eastern edge of the Sierra Nevada mountain range, and strike-slip faults to the east that define a diffuse boundary against the Basin and Range proper. A seismic study across the Mount Rose fault zone, bounding the Carson Range near Reno, Nevada, was carried out to investigate slip across a potential low-angle normal fault. A hammer seismic reflection and refraction profile combined with airborne LiDAR (light detection and ranging) imagery highlights fault scarp modification through minor slumping/landslides, providing a better understanding of the nature of slip on this fault. The seismic data were processed using both a linear and a non-linear velocity inversion scheme; both techniques indicate a shallow low velocity zone suggestive of a landslide section. The combination prestack depth migration (PSDM) reflectivity and LiDAR imagery suggests that a high-angle normal fault scarp could have been modified at the surface by at least one landslide event, allowing doubt that slip was isolated at the top of the Sandstone of Hunter Lake (an ~33° dipping plane). The northeastern margin of the Walker Lane is a region where both "Basin and Range" style normal faults and dextral strike-slip faults contribute to the northward propagation of the Walker Lane (essentially parallel to an equivalent northward propagation of the Mendocino triple junction). Near this intersection lies Pyramid Lake, bounded to the southwest by the dextral Pyramid Lake fault and to the northeast by the normal Lake Range fault. A high-resolution (sub-meter) seismic CHIRP survey collected in 2010 shows intriguing relationships into fault architecture beneath Pyramid Lake. Over 500 line-km of seismic data reveal a polarity flip in basin structure as down-to-the-east motion at the northern end of the Pyramid Lake fault rapidly gives way to down-to-the-west normal motion along the Lake Range fault. Alternating patterns of asymmetric and symmetric stratal patterns west of the Lake Range fault provides some evidence for segmentation of total slip along this large normal fault. Using dated sediment cores, slip rate for the Lake Range fault was found to be approximately 1 mm/yr during the Holocene. A complex zone of transtenstion was also observed in seismic CHIRP data in the northwest quadrant of the lake, where short, discontinuous faults hint at the development of a nascent shear zone trending to the northwest.The complex fault network beneath the Salton Trough in eastern California is the on-land continuation of the Gulf of California rift system, where North American-Pacific plate motion is accommodated by a series of long transform faults, separated by small pull-apart, transtensional basins; the right-lateral San Andreas fault bounds this system to the north where it carries, on average, about 50% of total plate motion. The Salton Sea resides within the most youthful and northerly "spreading center" in this several thousand-kilometer-long rift system. The Sea provides an ideal environment for the use of high-data-density marine seismic techniques. Two active-source seismic campaigns in 2010 and 2011 show progression of the development of the Salton pull-apart sub-basin and the northerly propagation of the Imperial-San Andreas system through time at varying resolutions. High fidelity seismic imagery documents the timing of strain transfer from the Imperial fault onto the San Andreas fault through the application of sequence stratigraphy. Evidence shows that the formation of the Salton and Mesquite sub-basins and the associated change of strain partitioning occurred within the last 20-40 k.y., essentially modifying a broader zone of transtension bounding the Imperial and San Andreas faults into two smaller zones of focused extension. The sedimentary infill within the Salton sub-basin has been modified through hydrothermal alteration and magmatism providing new insight into the formation of crust within a basin characterized by thick sediments and high heat flow. Modern earthquakes beneath the Salton Sea proper appear to nucleate at times within this altered sedimentary pile, providing constraints on the degree of metamorphism of lake sediments that now comprise "basement." Stratigraphic relationships within the northern Salton Sea also provide evidence that the southern San Andreas fault locally dips to the southwest and this geometry has persisted for at least the past 200-300 k.y. The north-central Walker Lane contains a diffuse network of both strike-slip and normal faults, with some degree of strain partitioning characterized by normal faulting to the west along the eastern edge of the Sierra Nevada mountain range, and strike-slip faults to the east that define a diffuse boundary against the Basin and Range proper. A seismic study across the Mount Rose fault zone, bounding the Carson Range near Reno, Nevada, was carried out to investigate slip across a potential low-angle normal fault. A hammer seismic reflection and refraction profile combined with airborne LiDAR (light detection and ranging) imagery highlights fault scarp modification through minor slumping/landslides, providing a better understanding of the nature of slip on this fault. The seismic data were processed using both a linear and a non-linear velocity inversion scheme; both techniques indicate a shallow low velocity zone suggestive of a landslide section. The combination prestack depth migration (PSDM) reflectivity and LiDAR imagery suggests that a high-angle normal fault scarp could have been modified at the surface by at least one landslide event, allowing doubt that slip was isolated at the top of the Sandstone of Hunter Lake (an ~33° dipping plane). The northeastern margin of the Walker Lane is a region where both "Basin and Range" style normal faults and dextral strike-slip faults contribute to the northward propagation of the Walker Lane (essentially parallel to an equivalent northward propagation of the Mendocino triple junction). Near this intersection lies Pyramid Lake, bounded to the southwest by the dextral Pyramid Lake fault and to the northeast by the normal Lake Range fault. A high-resolution (sub-meter) seismic CHIRP survey collected in 2010 shows intriguing relationships into fault architecture beneath Pyramid Lake. Over 500 line-km of seismic data reveal a polarity flip in basin structure as down-to-the-east motion at the northern end of the Pyramid Lake fault rapidly gives way to down-to-the-west normal motion along the Lake Range fault. Alternating patterns of asymmetric and symmetric stratal patterns west of the Lake Range fault provides some evidence for segmentation of total slip along this large normal fault. Using dated sediment cores, slip rate for the Lake Range fault was found to be approximately 1 mm/yr during the Holocene. A complex zone of transtenstion was also observed in seismic CHIRP data in the northwest quadrant of the lake, where short, discontinuous faults hint at the development of a nascent shear zone trending to the northwest

Interpretations of a 3D Seismic Volume, Hawthorne Geothermal Field, Nevada

Hawthorne, Nevada is located in the Walker Lake Domain of the Great Basin, aregion in the western United States known for extensional tectonics and the hightemperature gradients necessary for geothermal power production. Geothermal heatsources include magmatic types and extensional. The extensional type is more commonfor Nevada, where near-surface thermal gradients come from a thinned crust instead offrom volcanism. Extensional systems often do not exhibit surface indicators such assprings or fumaroles; rather, the thermal fluids remain capped below the surface in"blind" systems requiring the need for geophysical exploration. Heterogeneouscompositions and seismic velocities common to geothermal systems create particularseismic imaging difficulties because simplifying assumptions about velocity gradientscannot be made. A 3d seismic volume collected by the Navy Geothermal ProgramsOffice on the Hawthorne Ammunitions Depot represents a rare opportunity to examinethe range of geologic interpretations that can exist on seismic data in the Great Basin.Strong reflection events within the volume project to a ~20 degree dip, allowing thepossibility of a low angle normal fault; while bedding offsets could be interpreted as aseries of steep basinward step faults. Synclines in vertical sections correspond toconcentric circles in horizontal sections, not only raising questions about the possibilityof migration processing artifacts, but also present similarities to sill intrusions as seen inmarine 3d data. This paper explores the seismic evidence for a range of structuralinterpretations

Alien Registration- Kell, Annie J. (Augusta, Kennebec County)

https://digitalmaine.com/alien_docs/18334/thumbnail.jp

Station Delays, Their Standard Deviations, and Event Relocations in the Reno-Area Basin from a Dense Deployment During the 2008 West Reno Earthquake Swarm

The Nevada Seismological Laboratory (NSL) conducted a citizen volunteer multiple-instrument temporary deployment using 90 USArray Flexible Array single-channel RefTek RT-125A (Texan) recorders. Stations were deployed at 106 locations in the Reno area basin during the May-July 2008 period of the 2008 west urban Reno-Mogul earthquake swarm (mainshock Mw 5.0). This was a very dense deployment as the basin only occupies about 150 square kilometers. The Flexible Array deployment supplemented recordings from 46 NSL/ANSS regional network and Reno-area strong-motion stations, plus 10 IRIS RAMP stations. ANSS strong-motion stations are distributed throughout the Reno basin, and IRIS RAMP instruments (broadband and accelerometer) were deployed in the near-source area. We have relocated 97 events in the West Reno/Mogul sequence from May-July 2008, using phase arrivals on all network and volunteer Texan stations. Hypoinverse runs showed that the dense station dataset improves event locations, leaving very small residuals, generally less than 0.5 sec. Event magnitudes varied from M0.19 to M3.05. Histograms of delays at each station show that the delays are relatively insensitive to the details of the Hypoinverse relocation process. HYPODD relocations show the detail of the local aftershock sequence of the largest event recorded during the Texan deployment, a M 3.05. We prepared an average station delay map, a mode-of-station-delay map, and a map of the standard deviations of the average station delays. We expect these delay maps will help in understanding the geometry of the Reno Basin

Plant population monitoring methodologies for the in situ genetic conservation of CWR

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New constraints on fault architecture, slip rates, and strain partitioning beneath Pyramid Lake, Nevada

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